WO2025151199A1

WO2025151199A1 - Feedforward compensation for fluid management system in fluid distension procedure of uterus

Info

Publication number: WO2025151199A1
Application number: PCT/US2024/057249
Authority: WO
Inventors: Neil Judell; Benjamin PAVLOS
Original assignee: Hologic Inc
Current assignee: Hologic Inc
Priority date: 2024-01-10
Filing date: 2024-11-25
Publication date: 2025-07-17
Anticipated expiration: 2026-07-10

Abstract

A fluid management system (FMS) for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope. The FMS comprises a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity, a sensor configured for measuring a fluid pressure within the fluid inflow path, and control circuitry configured for generating a pressure error value based on the measured fluid pressure and an intrauterine setpoint pressure, for generating a pump speed control signal based at least in part on the pressure error value and an internal integrator value, and for resetting the internal integrator value in response to a change in an activation mode of the TRD between a cutting mode and a non-cutting mode.

Description

FEEDFORWARD COMPENSATION FOR FLUID MANAGEMENT SYSTEM IN FLUID DISTENSION PROCEDURE OF UTERUS

Field

[01] The present disclosure relates generally to a fluid management system (FMS), and more specifically to using an FMS to maintain a desired pressure within the uterine cavity of a patient when using a hysteroscope in conjunction with a tissue resecting device (TRD).

Background

[02] Uterine fibroids are well-defined, non-cancerous tumors that are commonly found in the smooth muscle layer of the uterus. In many instances, uterine fibroids can grow to be several centimeters in diameter and may cause symptoms such as menorrhagia (prolonged or heavy menstrual bleeding), pelvic pressure or pain, and reproductive dysfunction. Current treatments for uterine fibroids include hysteroscopic resection, which involves inserting a hysteroscope (i.e., a long thin tube for examination of the uterus) into the uterus transcervical ly (i.e., through the vagina and cervical canal), and then cutting away (i.e., resecting) the fibroid from the uterus using a tissue resection device (TRD) delivered through the hysteroscope. In one resection technique, a TRD comprising an electromechanical cutter is inserted through a working channel in the hysteroscope. Tissue is then removed by contacting the part of the uterus wall of interest with the electromechanical cutter, which typically comprises a tube within a tube design with a lateral opening or cutting window. Examples of TRDs with such electromechanical cutters are disclosed in U.S. Patent Nos. 8,568,424, 7,226,459, 6,032,673, and 5,730,752, and U.S. Patent Publication Nos. 2009/0270898 and 2006/0047185, which are expressly incorporated herein by reference for all that they teach and disclose.

[03] During hysteroscopic resection, the uterus is typically distended to create a working space within the uterine cavity. Such a working space does not normally exist naturally in the uterine cavity, because the uterus is a flaccid organ with its walls typically in contact with one another when in a relaxed state. The conventional technique for creating such a working space within the uterine cavity is to administer a fluid (e.g., saline or other isotonic media) to the uterus through the hysteroscope under sufficient pressure to cause the uterus to become distended. An inflow pump (e.g. , a peristaltic pump) may be used to deliver the distending fluid from a supply container into the uterus via an inflow channel in the hysteroscope, while an outflow pump (e.g., a peristaltic pump) or wall suction may be used to remove the distending fluid, along with resected fibroid tissue, from the uterine cavity to a waste container via one or more separate pathways (e.g., through a removable outflow channel, the TRD during tissue resection, or cervical leakage).

[04] Another benefit of the fluid distension is the tamponade effect that the distension fluid provides on resected vascular tissue. Since the distension fluid is typically maintained at a pressure that exceeds the mean arterial pressure (MAP), the fluid pressure provided by the distension fluid prevents the leakage of arterial blood flowing or oozing from the uterine wall where tissued was resected. However, if sufficient pressure is not maintained within the uterine cavity, the arterial blood will flow or ooze into the cavity, and mix with the distension fluid, thereby rendering visualization more difficult. If not constrained, the flowing or oozing of the blood into the uterine cavity may force the suspension of the procedure. Thus, maintenance of fluid pressure above the intracavity arterial pressure is highly beneficial for the maintenance of a clear visual field. Thus, it is also customary to use a fluid management system (FMS) to monitor the pressure within the uterine cavity and control the rate of inflow of fluid into the uterine cavity in response to such monitored pressure, so that the pressure in the uterine cavity is consistently maintained above MAP of the patient (such that the fluid inflow rate equals the fluid outflow rate plus any leakage and absorption).

[05] During a hysteroscopic tissue resection procedure, suction is typically applied to the TRD to draw tissue into the cutting window. However, such suction also typically has the effect of removing some of the distending fluid from the uterus along with the resected tissue. While most fluid management systems have a pressure sensor that actuates the inflow pump when the fluid pressure drops, the drop in intrauterine pressure may be precipitous, particularly if a high suction pressure is applied. Depending on the extent and speed of the drop in the intrauterine pressure, there may be a lapse of time before the pressure can be restored to a desired level such that adequate visualization is possible. Such lapse of time between the time that the uterine fluid pressure drops in response to the operation of the TRD and the time that the uterine fluid pressure is restored to the desired level is largely caused by integration functions within the FMS. [06] For example, in one known technique for controlling the uterine fluid pressure, a controller (e.g., a proportional, integral, derivative (FID) controller) may control the speed of the inflow pump (i.e. , the rotational speed in the case of a peristaltic pump), and thus, the uterine fluid pressure, based on a pressure measured by a pressure sensor and an intrauterine pressure setpoint that establishes a desired uterine cavity fluid pressure. Because a peristaltic pump, when operated at a constant rotational speed, does not generate constant fluid pressure, but rather cycles the fluid pressure as a function of the rotational speed of the pump shaft multiplied by the number of rollers inside the pump, a peristalsis low-pass filter (LPF) may be used to reduce the cyclical effect of the inflow pump seen by the control algorithm of the controller.

[07] The fluid pressure at the output of the inflow pump (and measured by the pressure sensor) is offset from the from the uterine fluid pressure due to two effects: 1 ) hydrostatic pressure due to the height difference between the patient and the pressure sensor; and 2) and the pressure drop across the tubing (not shown) connecting the inflow pump to the hysteroscope, as well as across the hysteroscope. [08] To correct the fluid pressure offset (error) between the pressure sensor and the uterine cavity, the FMS may employ a priming compensation function that estimates and subtracts such fluid pressure offset from the output of the pressure sensor to obtain an estimated intrauterine fluid pressure. The fluid pressure offset is dynamic in that, as a general rule, it is quadratic with positive slope when the inflow pump is operated at relatively low rotational speeds, and linear with positive slope when the inflow pump is operated at relatively high rotational speeds. This fluid pressure offset may be estimated via a calibration procedure. For example, the hysteroscope may be held in the air at a typical height at which the hysteroscope would be in the uterine cavity of the patient while measuring the pressure at the inflow peristaltic pump and while the inflow pump is operated at a variety of rotational speeds to obtain the fluid pressure offset (i.e., the calibration pressure) as a function of the rotational speed of the inflow pump. During use of the hysteroscope in the uterus, the priming compensation function may compute the estimated intrauterine fluid pressure as a function of the inflow pump speed. The controller can apply negative feedback gain to the pressure error between the intrauterine pressure setpoint and the estimated intrauterine fluid pressure to generate the desired rotational speed control signal for the inflow pump. However, this priming compensation function produces positive feedback that tends to destabilize the overall pressure control loop. This positive feedback may be mitigated by filtering the input to the priming compensation function with a calibration LPF. The calibration LPF has a bandwidth significantly lower than the closed-loop bandwidth of overall pressure control loop. In typical use, the bandwidth of the overall pressure control loop is around 0.2 Hz (settling time around five seconds), while the bandwidth of the calibration LPF is around 0.05 Hz (settling time around twenty seconds).

[09] When the TRD is not in use, the estimated uterine fluid pressure will equilibrate at the intrauterine pressure setpoint and at relatively constant inflow and outflow rates. However, when the TRD is operated, the relatively long time constant of the calibration LPF can cause an undesirable lag in the control system response. For example, when the TRD begins cutting, fluid distending the uterus is evacuated through the open cutting window on the TRD, resulting in an immediate increase in the fluid outflow rate, and consequently, a drop in uterine fluid pressure, due to the increased fluid outflow rate. Because of the relatively long time constant (lag) of the calibration LPF, a significant period of time (e.g., twenty seconds) elapses before the uterine fluid pressure will equilibrate to the intrauterine pressure setpoint and higher outflow rate. Similarly, when the TRD ceases cutting, the cutting window closes, resulting in an immediate decrease in the fluid outflow rate. Because of the relatively long time constant (lag) of the calibration LPF, a significant period of time (e.g., twenty seconds) elapses before the uterine fluid pressure will equilibrate to the intrauterine pressure setpoint and lower outflow rate. Notably, even in the absence of the calibration LPF, the shorter time constant in the overall pressure control loop caused by the integrator term in the PI D controller will cause equilibrium time lags (albeit shorter time lags that would otherwise be caused by the calibration LPF).

[10] As discussed above, these equilibrium times are undesirable. The increased outflow rate, and consequently the decrease in uterine fluid pressure, in response to initiating cutting with the TRD, causes the uterine cavity to collapse and obscure the view of the physician. As a result, the physician is forced to stop the TRD until the uterine fluid pressure equilibrates to the intrauterine pressure setpoint and reinflates the uterine cavity. In particular, because the uterine fluid pressure will be below the intrauterine pressure setpoint during recovery and prior to equilibrating, intrauterine bleeding may increase, thereby obscuring the view of the physician. Conversely, when the physician ceases cutting with the TRD, the outflow rate decreases, and consequently uterine fluid pressure increases above the intrauterine pressure setpoint. [11] In summary, the lapses in time needed to restore uterine fluid pressure following initiation of the TRD are undesirable as they interrupt the resection procedure.

Summary

[12] In accordance with one aspect of the present inventions, a fluid management system (FMS) for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope is provided.

[13] The FMS comprises a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity, and a sensor configured for measuring a fluid pressure within the fluid inflow path.

[14] The FMS further comprises control circuitry configured for generating a pressure error value based on the measured fluid pressure and an intrauterine setpoint pressure, and for generating a pump speed control signal based at least in part on the pressure error value and an internal integrator value. The control circuitry is further configured for resetting the internal integrator value (e.g., containing in a proportional integral derivative (RID) controller) in response to a change in an activation mode of the TRD between a cutting mode and a non-cutting mode.

[15] In one embodiment, the control circuitry is configured for resetting the internal integrator value to a cutting reset value in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and resetting the internal integrator value to a non-cutting reset value different from the cutting reset value in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode. The cutting reset value may be greater than the non-cutting reset value. In another embodiment, the FMS further comprises a constant speed outflow pump configured for removing fluid from the intrauterine cavity via an outflow fluid path passing through the hysteroscope, in which case, the respective cutting and noncutting reset values may be based, at least in part, on the outflow pump speed.

[16] In still another embodiment, the control circuitry further comprises a calibration LPF configured for filtering the pump speed control signal (e.g., based on a resettable DC value), and a priming compensator configured for generating a pressure compensation value based on the filtered pump speed control signal. In this case, the control circuitry may be configured for subtracting the pressure compensation value from the measured fluid pressure to generate an estimated intrauterine fluid pressure, and for subtracting the intrauterine setpoint pressure from the estimated intrauterine pressure to determine the intrauterine pressure error value. In yet another embodiment, the inflow pump is a peristaltic pump, in which case, the FMS may further comprise a peristalsis low pass filter (LPF) configured for filtering the measured fluid pressure. The control circuitry may be configured for generating the pressure error value by comparing the filtered measured fluid pressure with the intrauterine pressure setpoint. In this embodiment, the control circuitry may further comprise the afore- described calibration LPF and priming compensator, in which case, the control circuitry may be configured for subtracting the pressure compensation value from the filtered measured fluid pressure to generate an estimated intrauterine fluid pressure, and for subtracting the intrauterine setpoint pressure from the estimated intrauterine pressure to determine the intrauterine pressure error value.

[17] In yet another embodiment, the control circuitry further comprises a cutting mode low pass filter (LPF) configured for being initialized at a start of a surgical procedure to a predetermined cutting reset value and for filtering the pump speed control signal. The cutting mode LPF may be further configured for retaining an updated cutting reset value when the TRD activation mode changes to the non-cutting mode. This control circuitry may further comprise a non-cutting mode low pass filter (LPF) configured for being initialized at a start of a surgical procedure to a predetermined non-cutting reset value, and for filtering the pump speed control signal. The non-cutting mode LPF may be further configured for retaining an updated noncutting reset value when the TRD activation mode changes to the cutting mode.

[18] In yet another embodiment, the control circuitry is further configured for decreasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and for increasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode. The intrauterine pressure setpoint may be, e.g., decreased or increased, respectively, by a predetermined offset or by a predetermined percentage.

[19] In accordance with a second aspect of the present inventions, another FMS for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope is provided.

[20] The FMS comprises a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity, and control circuitry configured for controlling a speed of the inflow pump based at least in part on an internal integrator value. The control circuitry is configured for resetting the internal integrator value in response to a change in an activation mode of the TRD between a cutting mode and a non-cutting mode.

[21] In one embodiment, the control circuitry is configured for resetting the internal integrator value to a cutting reset value in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and resetting the internal integrator value to a non-cutting reset value different from the cutting reset value in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode. The cutting reset value may be greater than the non-cutting reset value.

[22] In another embodiment, the inflow pump is a peristaltic pump, the FMS further comprises a sensor configured for measuring a fluid pressure within the fluid inflow path, and the control circuitry further comprises a peristalsis low pass filter (LPF) configured for filtering the measured fluid pressure. In this case, the control circuitry is configured for controlling the speed of the inflow pump based at least in part on a pressure error derived from a comparison of the filtered measured fluid pressure and an intrauterine pressure setpoint.

[23] In still another embodiment, the control circuitry is further configured for decreasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and for increasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode. The intrauterine pressure setpoint may be, e.g., decreased or increased, respectively, by a predetermined offset or by a predetermined percentage.

[24] In accordance with a third aspect of the present inventions, still another FMS for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope is provided.

[25] The FMS comprises a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity, a sensor configured for measuring a parameter indicative of a fluid pressure within the uterine cavity, and control circuitry configured for receiving a cutting trigger signal indicative of an activation of the TRD.

[26] The control circuitry comprises a feedback control module configured for controlling a fluid inflow rate of the inflow pump based on the measured parameter to maintain the intrauterine fluid pressure at or proximate to an intrauterine pressure setpoint.

[27] The control circuitry further comprises a feedforward control module configured for increasing the fluid inflow rate of the inflow pump independently of the measured parameter in response to the cutting trigger signal, while continuing to maintain the fluid pressure in the uterine cavity at or proximate to the intrauterine pressure setpoint. In one embodiment, the control circuitry is configured for increasing the fluid inflow rate in response to a change in the activation mode from a non-cutting mode to a cutting mode, and for decreasing the fluid inflow rate in response to a switch in the activation mode from the cutting mode to the non-cutting mode.

[28] In one embodiment, the feedforward control module is configured for increasing the fluid inflow rate of the inflow pump based on an increased fluid flow rate predicted to maintain the fluid pressure in the uterine cavity at or proximate to the intrauterine pressure setpoint during operation of the TRD. The increased fluid inflow rate predicted to maintain the fluid pressure in the body cavity at the intrauterine pressure setpoint during operation of the TRD may be a fixed pre-programmed value. Or, the control circuitry may be configured for updating the predicted fluid inflow rate, e.g., so that it converges from a nominal value to a new value equal to the controlled fluid inflow rate during operation of the TRD.

[29] In another embodiment, the control circuitry is further configured for decreasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and for increasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode. The intrauterine pressure setpoint may be, e.g., decreased or increased, respectively, by a predetermined offset or by a predetermined percentage.

[30] In still another embodiment, the feedback control module comprises a controller (e.g., a proportional, integral, derivative (PID) controller or a proportional-integral (PI) controller) having an integrator term, in which case, the feedforward control module may be configured for controlling the fluid inflow rate of the inflow pump independently of the measured fluid pressure by resetting the integrator term. In this embodiment, the feedforward control module may be configured for resetting the integrator term to a cutting reset value corresponding to an increased fluid inflow rate predicted to maintain the fluid pressure in the body cavity at or proximate to the intrauterine pressure setpoint during operation of the TRD.

[31] Other and further aspects and features of embodiments of the disclosed inventions will become apparent from the ensuing detailed description in view of the accompanying figures.

Brief Description of the Drawings

[32] The drawings illustrate the design and utility of preferred embodiments of the disclosed inventions, in which similar elements are referred to by common reference numerals. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosed inventions, or as a limitation on the scope of the appended claims and their equivalents. In addition, an illustrated embodiment of the disclosed inventions needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment of the disclosed inventions is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated.

[33] Fig. 1 is a plan view of one embodiment of a tissue removal system constructed in accordance with the disclosed inventions.

[34] Fig. 2 is a cross-sectional view of the distal end of a tissue removal device (TRD) employed in the tissue removal system of Fig. 1.

[35] Fig. 3 is a cross-sectional view of a hysteroscope employed in the tissue removal system of Fig. 1.

[36] Fig. 4 is a block diagram of the tissue removal system of Fig. 1 having a pump control unit for maintaining an intrauterine pressure at or near a pressure setpoint.

[37] Fig. 5 is a block diagram of the tissue removal system of Fig. 1 having a pump control unit that employs a pressure setpoint reduction to improve cutting efficiency.

[38] Fig. 6 is a block diagram of the tissue removal system of Fig. 1 having a pump control unit that learns and adjusts the inflow rate during a procedure. Detailed Description of the Illustrated Embodiments

[39] The tissue removal systems described herein utilize a fluid management system (FMS) that maintains pressurized fluid distension of a patient’s uterus during a surgical procedure by estimating a rate of fluid loss when an electromechanical tissue resection device (TRD) is active, and controlling the fluid inflow rate (e.g., by elevating the fluid inflow rate) of an inflow pump that delivers fluid into the uterine cavity based at least in part upon the estimated rate of fluid loss from the body cavity when the TRD is active.

[40] The FMS may also estimate a rate of fluid loss from the uterine cavity when the TRD is inactive, and controlling the fluid inflow rate (e.g., by lowering the fluid inflow rate) of the inflow pump based at least in part upon the estimated rate of fluid loss from the uterus when the TRD is inactive. In this manner, the pressure within the uterine cavity is maintained at a desired level throughout the surgical procedure regardless of whether the TRD is active or inactive.

[41] Referring now to Fig. 1 , a tissue removal system 10 generally comprises a tissue removal assembly 12 configured for removing tissue from a body cavity of patient (and in this case, one or more fibroids or polyps from a uterine cavity 8 (represented in Fig. 4), a surgical scope 14 configured for providing access to the body cavity (and in this case, a hysteroscope for providing access to the uterine cavity 8), and a fluid management system (FMS) 16 configured for maintaining pressurized fluid distension of the body cavity (and in this case, the uterine cavity 8) during a surgical procedure. The tissue removal assembly 12 generally comprises a hysteroscopic tissue removal device (TRD) 18 and a motor drive assembly 20. The motor drive assembly 20 comprises a motor console 38 that can be connected to a source of electricity, such as an alternating current (AC) wall outlet, via a power cord (not shown), a flexible drive cable 40 operably coupling the motor console 38 to a gear assembly (not shown) contained within the handle 24 via a connector 44 located on the motor console 38 and the drive connector 34 located on the handle 24 of the TRD 18, and a manual actuator 46 connected to the motor console 38 via an electrical cable 48 and connector 50 for operation by a physician or hospital personnel.

[42] Referring further to Fig. 2, the TRD 18 comprises an outer sleeve 22, a handle 24 (shown in Fig. 1) affixed to the proximal end of the outer sleeve 22, and inner sleeve 26 configured for rotating and reciprocating within a lumen 28 of the outer sleeve 22 to resect tissue. The outer sleeve 22 includes a distally located cutting window 30 that is alternately opened and closed to resect tissue as the cutting element 26 reciprocates within the lumen 28 of the outer sleeve 22. As the cutting element 26 is translated to its most distal position to close the cutting window 30, the prolapsed tissue is sheared and removed through an evacuation lumen 32 of the cutting element 26. The handle 24 is shaped and sized to be ergonomically held by a physician with one hand. The TRD 18 further comprises a gear assembly (not shown) contained within the handle 24 forfacilitating reciprocating and rotational movement of the cutting element 26 within the lumen 28 of the outer sleeve 22. The TRD 18 further comprises a drive connector 34 located on the handle 24 for connection to the motor console 38 via a drive cable 40, and a vacuum connector 36 located on the handle 24 for connection to the FMS 16 via an outflow tube 108a.

[43] The motor drive assembly 20 may be operated to reciprocate and rotate the cutting element 26 within the lumen 28 of the outer sleeve 22. In the illustrated embodiment, the manual actuator 46 takes the form of a foot pedal that can be depressed by the physician to activate the motor console 38, and thus, operate the gear assembly contained within the handle 24 via the drive cable 40 to reciprocate and rotate the cutting element 26 within the lumen 28 of the outer sleeve 22 to resect tissue (i.e., the TRD 18 is in a “cutting” mode). The foot pedal 46 may be released by the physician to deactivate the motor console 38, and thus, terminate operation of the drive assembly contained within the handle 24 via the drive cable 40 to cease reciprocation and rotation of the cutting element 26 within the lumen 28 of the outer sleeve 22 to cease resection of tissue (i.e., the TRD 18 is in a “non-cutting” mode). In an alternative embodiment, instead of a foot pedal, the manual actuator 46 is located on the handle 24 of the TRD 18 or on the motor console 38. As will be described in further detail below, the FMS 16 monitors the cutting/non-cutting mode of the TRD 18 via an electrical cable 52 and a connector 54 located on the motor console 38.

[44] As will be described in further detail below, the FMS 16 applies a vacuum to the evacuation lumen 32 of the TRD 18, such that during operation of the TRD 18, tissue prolapses into the cutting window 30 of the outer sleeve 22 to facilitate resection of the tissue, while the resected tissue, liquids, or similar matter may be withdrawn through the TRD 18 and evacuated through the evacuation lumen 32 of the cutting element 26. In an alternative embodiment, a vacuum source (not shown) separate from the FMS 16 may be used to apply a vacuum to the evacuation lumen 32 of the TRD 18. [45] Continuing to refer to Fig. 1 , the hysteroscope 14 comprises an elongated shaft 56 and a handle 58 affixed to the proximal end of the shaft 56. The shaft 56 is shaped and sized to reach a surgical site within the uterine cavity 8 (represented in Fig. 4). The handle 58 is shaped and sized to be ergonomically held by a physician with one hand. As best illustrated in Fig. 3, the hysteroscope 14 further comprises a plurality of channels extending distally from the handle 58 and continuing longitudinally through the shaft 56. In particular, the hysteroscope 14 comprises a working channel 60 configured for receiving a removable outflow channel 100 or TRD 18 while the area around the removable outflow channel 100 or TRD 18 can act as a fluid inflow conduit. A wide variety of instruments may be inserted in working channel 60. The hysteroscope 14 further comprises a combined visualization/illumination channel 62 associated with a visualization port 68 and an illumination port 70 located at the proximal end of the shaft 56 (e.g., defined by the handle 58). A rod lens 72 or other suitable light collecting means may be disposed in the visualization/illumination channel 62, with the remainder of the combined visualization/illumination channel 62 being occupied by a light guide 74 or other suitable light transmitting means. A camera (not shown) may be coupled to the visualization port 68 via an optical cable (not shown), such that light transmitted by the rod lens 72 may be converted to electrical signals for visualization at the surgical site in the uterine cavity 8, while a source of light (not shown) may be coupled to the illumination port 70 via an optical cable (not shown), such that light may be transmitted through the light guide 74 to the surgical site in the uterine cavity 8. Further details on the tissue removal assembly 12 and the hysteroscope 14 are discussed in U.S. Patent Publication Nos. 2009/0270898 and 2011/0118544, which are expressly incorporated herein by reference.

[46] Referring back to Fig. 1 , the FMS 16 generally comprises an inflow pump 76, an outflow pump 78, a sensor 80, and a pump control unit 82, the pump control unit including a feedback control module 162 and a feedforward control module 178.

The inflow pump 76 is configured for pumping distending fluid via a fluid inflow path passing through the hysteroscope 14 into the uterine cavity 8 at a fluid inflow rate. To this end, the inflow pump 76 includes an inflow pump inlet 84 fluidly coupled to a supply fluid container 86 (e.g., a saline bag) via a flexible tube 88, and an inflow pump outlet 90 fluidly coupled to the fluid entry port 66 of the hysteroscope 14 via a flexible tube 92, such that operation of the inflow pump 76 causes fluid to flow from the supply fluid container 86, through the flexible tubes 88, 92, and into the uterine cavity 8 via the hysteroscope 14. The inflow pump 76 is operatively coupled to the pump control unit 82, which as will be described in further detail below, controls the speed of the inflow pump 76, and thus, the fluid inflow rate of the fluid introduced from the supply fluid container 86 into the uterine cavity 8 via the hysteroscope 14.

[47] The outflow pump 78 is configured for pumping the distending fluid from the uterine cavity 8 via one or more outflow fluid paths at a fluid outflow rate. To this end, the outflow pump 78 includes one or more fluid inlets (in this case, three fluid inlets 98a-98c respectively fluidly coupled via flexible tubes 108a-108c to the vacuum connector 36 of the TRD 16, the removable outflow channel 100, and a drape 102 placed on the buttocks of the patient for collecting fluid that leaks from the cervix of the patient during the tissue removal procedure) and a fluid outlet port 104 fluidly coupled to a waste container 106 (e.g., a waste fluid bag) via a flexible tube 108d, such that operation of the outflow pump 78 pumps fluid from the TRD 18 or the removable outflow channel 100, and the drape 102, into the waste container 106. The waste container 106 may be coupled to a scale (not shown) for monitoring the amount of fluid that is removed from the patient. It should be appreciated that the outflow pump 78 may have more or less fluid inlets, depending on the number of devices used to collect fluid from the patient. In other alternative embodiments, instead of employing an outflow pump, a separate vacuum source (not shown) or gravity may be employed to remove fluid, along with the resected tissue, from the uterine cavity 8.

[48] The outflow pump 78 is operatively coupled to the pump control unit 82, which controls the fluid outflow rate of the fluid removed from the uterine cavity 8 into the waste container 106 via the hysteroscope 14 and the drape 102. The speed of the outflow pump 78, and thus, the fluid outflow rate, may be varied under user control, e.g., by manipulating controls (not shown on the pump control unit 82). For example, in some embodiments the user may select between three constant speeds for the outflow pump 78 — low, medium, and high, to correspondingly vary the fluid outflow rate.

[49] The sensor 80 is configured for measuring a parameter indicative of the fluid pressure in the uterine cavity 8 (i.e., the intrauterine fluid pressure). In the illustrated embodiment, the sensor 80 is configured for measuring the fluid back pressure at the inflow pump outlet 90 of the inflow pump 76. Alternatively, the sensor 80 may be located at any location between the inflow pump 76 and the uterus 8. As will be described in further detail below, the pump control unit 82 is configured for estimating the intrauterine fluid pressure based on the back pressure measured and sent by the pressure sensor 80 to the pump control unit 82.

[50] It should be appreciated that, although all functionality of the pump control unit 82 illustrated in Fig. 1 is described herein as being performed by a single device, such functionality of the pump control unit 82 may be distributed amongst several devices. Moreover, it should be appreciated that the pump control unit may be implemented in software, firmware, hardware, or any suitable combination thereof.

[51] The pump control unit 82 is configured for maintaining the intrauterine fluid pressure at a desired intrauterine pressure setpoint. Towards this end, the pump control unit 82 is coupled via an electrical connector 116 to a corresponding electrical connector 54 located on the motor console 38 of the tissue resection assembly 12 via the electrical cable 52, such that the pump control unit 82 may monitor the activation mode (i.e., the cutting/non-cutting mode) of the TRD 18, and control the speed of the inflow pump 76 (and, thus, the inflow rate) based on, in part, the activation mode of the TRD 18.

[52] When the TRD 18 remains in the non-cutting mode or the cutting mode, the pump control unit 82 is configured for maintaining the uterine cavity 8 at the intrauterine pressure setpoint by controlling the fluid inflow rate of the inflow pump 76 (in this case, by controlling the speed of the inflow pump 76) based on the fluid pressure measured by the pressure sensor 80 by comparing a function of the pressure measured by the pressure sensor 80 to the intrauterine pressure setpoint.

[53] When the TRD 18 is in the non-cutting mode, the pump control unit 82 controls the inflow pump 76 to output a non-cutting fluid inflow rate to maintain the uterine cavity 8 at or near the intrauterine pressure setpoint. Similarly, when the TRD 18 is in the cutting mode, the pump control unit 82 controls the inflow pump 76 to output a cutting fluid inflow rate to maintain the uterine cavity 8 at or near the intrauterine pressure setpoint. In one embodiment, the user may select the intrauterine pressure setpoint, e.g., using one or more controls located on the pump control unit 82 (not shown). In another embodiment, the intrauterine pressure setpoint may be pre-defined during manufacture of the FMS 16 or subsequently programmed into the pump control unit 82 without user input. As will be discussed in further detail below, the pump control unit 82 may employ negative feedback control to maintain the intrauterine fluid pressure at the intrauterine pressure setpoint. [54] In alternative embodiments, the pump control unit 82 may define an intrauterine pressure setpoint range, such that when the intrauterine fluid pressure rises to a maximum pressure limit, the pump control unit 82 may reduce the fluid inflow rate of the inflow pump 76 to decrease the intrauterine fluid pressure, and when the intrauterine fluid pressure drops to a minimum pressure limit, the pump control unit 82 may increase the fluid inflow rate of the inflow pump 76 to increase the intrauterine fluid pressure. In this manner, the fluid pressure in the uterine cavity 8 may effectively be maintained at the intrauterine pressure setpoint, albeit within the range defined by the maximum/minimum pressure limits.

[55] In these alternative embodiments, the pump control unit 82 may automatically define the maximum/minimum pressure limits in response to the user defining the intrauterine pressure setpoint. For example, the user may select an intrauterine pressure setpoint (e.g., 60 mm Hg) around which the pump control unit 82 may define maximum/minimum pressure limits as a function of the intrauterine pressure setpoint (e.g., by adding/subtracting an absolute pressure value (e.g., 5 mm Hg to define maximum/minimum pressure limits of 65 mm Hg and 55 mm Hg) or by adding/subtracting a percentage of the intrauterine pressure setpoint (e.g., 10% to define to define maximum/minimum pressure limits of 66 mm Hg and 54 mm Hg). As another example, the user may select the maximum/minimum pressure limits. In either example, the maximum/ minimum pressure limits may be restricted by the pump control unit 82, such that the intrauterine pressure is safe and efficacious. In another embodiment, the maximum/minimum pressure limits may be pre-defined during manufacture of the FMS 16 or subsequently programmed into the pump control unit 82 without user input. Whether user-defined or pre-defined, the maximum/minimum pressure limits are typically set values; however, in alternative embodiments, the maximum/minimum pressure limits may pseudo-randomly or randomly vary around the intrauterine pressure setpoint.

[56] The pump control unit 82 is configured for receiving as input the activation mode of the TRD 18 and, for each mode, a predicted inflow pump speed programmed into the pump control unit 82. In yet another embodiment, the predicted rate of fluid loss from the uterine cavity 8 may be based at least in part on the pre-set or user-selected constant fluid outflow rate of the outflow pump 78 (or alternatively a vacuum source in lieu of an outflow pump). [57] Significantly, the pump control unit 82 is configured for employing feedforward compensation to adjust the fluid inflow rate of the inflow pump 76 in response to a change in the activation mode of the TRD 18 to maintain the uterine cavity 8 at or proximate to the intrauterine pressure setpoint. That is, for each activation mode, the predicted inflow pump speed is fed forward into the pump control unit 82 to improve overall system performance. Thus, feedforward compensation of the FMS 16 lowers the time constant (lag) otherwise present in a pump control unit without feedforward compensation or that solely relies on a negative feedback control loop.

[58] After feedforward compensation has been implemented to control the inflow pump 76 in response to a change in the activation mode of the TRD 18, the pump control unit 82 may then return to employing negative feedback control to minimize a difference between the measured intrauterine fluid pressure and the intrauterine pressure setpoint; that is, while the TRD 18 activation mode remains unchanged, the pump control unit 82 controls the inflow pump 76 based on the estimated intrauterine pressure (as derived from the pressure sensor 80) and the intrauterine pressure setpoint.

[59] The predicted fluid inflow pump speed may be based at least in part upon an estimated rate of fluid loss from the uterine cavity 8 observed in prior procedures or benchtop testing. For example, in one embodiment, such estimated rate of fluid loss from the uterine cavity 8 may be based at least in part upon measured fluid losses through a tissue resection device that is identical or similar to the TRD 18 during one or more prior surgical procedures and in both cutting mode and non-cutting modes.

[60] In another embodiment, the predicted inflow pump speed may be based at least in part upon data collected during one or more prior activations of the TRD 18 during the particular surgical procedure. Data may include historical intrauterine pressure response or measured fluid losses. In effect, the pump control unit 82 learns and optimizes the inflow pump speed required to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint, and updates the predicted inflow pump speed (or predicted fluid inflow rate). In this manner, the accuracy of the predicted inflow pump speed will improve during the procedure, so that the FMS 16 is more responsive when the activation mode of the TRD 18 is subsequently switched.

[61] Fig. 4 illustrates a pump control unit 82 according to one specific embodiment of the FMS 16. When the TRD 18 is inserted through the hysteroscope 14 and the inflow pump 76 and outflow pump 78 are activated, a fluid inflow path 150 is created from the fluid supply container 86, through the inflow pump 76, through the hysteroscope 14, and into the uterine cavity 8; a first outflow path 152a is created from the uterine cavity 8, through the TRD 18.

[62] The pump control unit 82 receives a cutting trigger signal 154a or a non-cutting trigger signal 154b from the foot pedal 46 (indirectly through the motor console 38 of the tissue removal assembly 12 (shown in Fig. 1) in response to activation/deactivation of the TRD 18, as also shown in Fig. 4. In this case, the tissue removal assembly 12 toggles between sending a cutting trigger signal 154a and sending a non-cutting trigger signal 154b to the pump control unit 82. For example, when the foot pedal 46 is actuated (e.g., the foot pedal is depressed), a logical high representing a cutting trigger signal 154a may be sent to the pump control unit 82, and when the foot pedal 46 is not actuated (e.g., the foot pedal is released), a logical low representing a non-cutting trigger signal 154b may be sent to the pump control unit 82 (or alternatively, the lack of a logical high may represent a non-cutting trigger signal 154b). The pump control unit 82 receives, from the pressure sensor 80 located adjacent the inflow pump 76, a pressure signal 156 indicating the back pressure in the fluid inflow path 150 between the inflow pump 76 and the uterine cavity 8, and thus, the intrauterine fluid pressure. The pump control unit 82 sends a pump speed control signal 158 to the inflow pump 76 to adjust the inflow pump speed in order to regulate the intrauterine pressure at the setpoint, as described above. Although not illustrated in Fig. 4, the pump control unit 82 also sends a pump speed control signal 158 to the outflow pump 78 to set a constant speed of the outflow pump 78.

[63] Referring to Fig. 4, the feedback control module 162 is configured for controlling a fluid inflow rate of the inflow pump 76 based on the fluid pressure measured by the pressure sensor 80, thereby maintaining the intrauterine fluid pressure at near the intrauterine pressure setpoint. The feedback control module 162 comprises a memory element 164 (in this case, an intrauterine pressure setpoint register) configured for storing pressure setpoint information (e.g., user-controlled via a control located on the pump control unit 82 or otherwise in communication with the pump control unit 82) or pre-defined during manufacture of the pump control unit 82 or subsequently programmed into the pump control unit 82. In embodiments in which the inflow pump 76 is a peristaltic pump or any other pump that is not capable of generating constant fluid pressure when operating at a constant speed, the feedback control module 162 further comprises a peristalsis low pass filter (LPF) 166 configured for receiving the pressure signal 156 from the pressure sensor 80 and reducing the cyclical pressure effect characteristic of peristaltic pumps.

[64] The feedback control module 162 further comprises a controller 168. In the illustrated embodiment, the controller 168 comprises a conventional proportional, integral, derivative (PID) controller, although in alternative embodiments, the controller 168 may take the form of any controller having an integrator term, e.g., a PI controller. In the context of a fluid management system, the integrator term is configured for matching inflow to and outflow from the uterine cavity, and the proportional term is configured for correcting the fluid pressure. The controller 168 is configured for controlling the fluid inflow rate of the inflow pump 76 by outputting the pump speed control signal 158 (i.e., the signal that varies the speed of the inflow pump 76) at least partially based on an internal integrator value 169 generated by the integrator term, as well as a comparison between the estimated intrauterine pressure, as derived from the pressure sensor 80, and the nominal intrauterine pressure setpoint stored in the intrauterine pressure setpoint register 164, as will be discussed in further detail below.

[65] The feedback control module 162 further comprises a calibration LPF 170, a priming compensator 172, and a subtractor 174, which operate together to correct the fluid pressure offset between the fluid pressure measured by the pressure sensor 80 and the fluid pressure in the uterine cavity 8 (i.e., the intrauterine fluid pressure). The subtractor 174 receives the fluid pressure offset from the priming compensator 172 and subtracts the fluid pressure offset from the fluid pressure output by the peristalsis low-pass filter 166 in order to obtain an estimated intrauterine fluid pressure.

[66] The calibration LPF 170 is configured for filtering the pump speed control signal 158 to mitigate the positive feedback that may otherwise tend to destabilize the pressure control loop of the controller 168. The calibration LPF 170 is configured for filtering the pump speed control signal 158 at least partially based on an internal DC value 171. The priming compensator 172 is configured for generating an updated estimate of the fluid pressure offset and providing the updated fluid pressure offset to the subtractor 174.

[67] In particular, the priming compensator 172 may be programmed with a fluid pressure offset function that varies in accordance with a speed of the inflow pump 76 (e.g., quadratic with positive slope when the inflow pump 76 is operated at relatively low rotational speeds, and linear with positive slope when the inflow pump 76 is operated at relatively high rotational speeds). The fluid pressure offset function programmed into the priming compensator 172 may be calibrated by, e.g., holding the hysteroscope 14 (or similar hysteroscope) in the air at a typical height at which the hysteroscope 14 would be in the uterine cavity 8, and measuring the pressure at the inflow pump 76 via the pressure sensor 80 while the inflow pump 76 is operated at a variety of speeds to obtain the fluid pressure offset (i.e. , the calibration pressure) as a function of the speed of the inflow pump 76. Once the fluid pressure offset function has been calibrated, the priming compensator 172 continually receives the pump speed control signal 158 (i.e., the controlled speed at which the inflow pump 76 is currently set) output by the controller 168 and filtered by the calibration LPF 170, and computes the estimated fluid pressure offset as a function of the controlled speed of the inflow pump 76.

[68] The feedback control module 162 further comprises a subtractor 176 configured for computing and outputting an intrauterine fluid pressure error based on a difference between the estimated intrauterine fluid pressure computed by the subtractor 174 and the intrauterine pressure setpoint obtained from the intrauterine pressure setpoint register 164, in particular, by subtracting the intrauterine pressure setpoint from the estimated intrauterine fluid pressure. The controller 168 applies a negative feedback gain (which is a function of the internal integrator value 169 output by the integrator term) to the intrauterine fluid pressure error to generate the desired pump speed control signal 158 for the inflow pump 76, thereby achieving desired intrauterine fluid pressure. Thus, when the estimated intrauterine fluid pressure rises above the intrauterine pressure setpoint, thereby generating a positive intrauterine fluid pressure error, the pump control unit 82 may reduce the fluid inflow rate of the inflow pump 76 to decrease the intrauterine fluid pressure, and when the intrauterine fluid pressure drops below the intrauterine pressure setpoint, thereby generating a negative intrauterine pressure error, the pump control unit 82 may increase the fluid inflow rate of the inflow pump 76 to increase the intrauterine fluid pressure.

[69] In embodiments in which a quantized controller with hysteresis is used, the intrauterine fluid pressure may be maintained within a range around the intrauterine pressure setpoint having a maximum pressure limit value and a minimum pressure limit value, such that when the estimated intrauterine fluid pressure rises to the maximum pressure limit, the pump control unit 82 may reduce the fluid inflow rate of the inflow pump 76 to decrease the intrauterine fluid pressure, and when the intrauterine fluid pressure drops to the minimum pressure limit, the pump control unit 82 may increase the fluid inflow rate of the inflow pump 76 to increase the intrauterine fluid pressure. As such, the controller 168, in this case, is configured for varying the speed of the inflow pump 76 only when the intrauterine fluid pressure error exceeds an error threshold. For example, if the intrauterine pressure setpoint is 60 mm Hg, and the maximum and minimum pressure limit values are respectively 58 mm Hg and 62 mm Hg, the controller 168 may output the pump speed control signal 158 to vary the speed of the inflow pump 76 only when the intrauterine fluid pressure error is exceeds ±2 mm Hg.

[70] The feedforward control module 178 is configured for increasing the fluid inflow rate by increasing the speed of the inflow pump 76 independently of the fluid pressure measured by the pressure sensor 80 in response to a change from the non-cutting mode to the cutting mode. Likewise, the feedforward control module 178 is configured for decreasing the fluid inflow rate by decreasing the speed of the inflow pump 76 independently of the fluid pressure measured by the pressure sensor 80 in response to a change from cutting mode to the non-cutting mode. Following a respective upward or downward adjustment in the speed of the inflow pump 176 due to a change in the TRD cutting mode, the feedback control module 162 thereafter controls the intrauterine fluid pressure at the intrauterine pressure setpoint based on the fluid pressure measured by the pressure sensor 80, as discussed above.

[71] In one embodiment, the increased fluid inflow rate (or equivalent increased pump speed) predicted to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint during operation of the TRD 18, and the decreased fluid inflow rate (or equivalent decreased pump speed) predicted to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint during non-operation of the TRD 18 may be based on an estimated rate of fluid loss (or fluid outflow rate) from the uterine cavity 8. As briefly discussed above, the fluid outflow rate will, at least partially, depend on the speed of the outflow pump 78, which may be varied or selected by the user. Thus, increased fluid inflow rate predicted to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint during operation of the TRD 18 will be higher at higher speeds of the outflow pump 78, and lower at lower speeds of the outflow pump 78 decreases, while the decreased fluid inflow rate predicted to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint during non-operation of the TRD 18 will likewise be higher at higher speeds of the outflow pump 78 increases, and lower at lower speeds of the outflow pump 78.

[72] Significantly, the feedforward control module 178 is configured for increasing or decreasing the fluid inflow rate of the inflow pump 76 independently of the fluid pressure measured by the pressure sensor 80 by modifying at least one parameter (e.g., an integrator term) in the feedback control module 162, such that intrauterine fluid pressure does not overshoot or undershoot the desired intrauterine fluid pressure in response to the activation/deactivation of the TRD 18. In the illustrated embodiment, the feedback control module 162 increases or decreases the fluid inflow rate of the inflow pump 76 by resetting the internal integrator value 169 output by the integrator term in the controller 168 and resetting the internal DC value 171 of calibration LPF 170.

[73] In particular, the feedforward control module 178 comprises memory elements 180a, 180b (in this case, a cutting speed register and a non-cutting speed register) configured for respectively storing an increased pump speed value (or cutting reset value) and a decreased pump speed value (or non-cutting reset value) and a multiplexor 182. In the illustrated embodiment, the cutting reset value corresponds to the increased fluid flow rate predicted to maintain the fluid pressure in the uterine cavity at or proximate to the intrauterine pressure setpoint during operation of the TRD, while the cutting reset value corresponds to the decreased fluid flow rate predicted to maintain the fluid pressure in the uterine cavity at or proximate to the intrauterine pressure setpoint during non-operation of the TRD. As discussed above, the increased and decreased pump speed values (and thus the cutting reset value and non-cutting reset value) may depend on the speed of the outflow flow pump 78. In the case where the fluid outflow rate of the output flow pump 78 may be selected by a user, a plurality of memory elements 180a may be provided for respectively storing a plurality of cutting reset values (one for each speed of the outflow pump 78), and multiple memory elements 180b may be provided for storing a plurality of non-cutting reset values (one for each speed of the outflow pump 78).

[74] The multiplexor 182 receives three inputs and outputs a reset value. The three inputs include two data inputs respectively coupled to the cutting speed register 180a and the non-cutting speed register 180b for respectively receiving the cutting reset value and the non-cutting reset value from the cutting speed register 180a and the non-cutting speed register 180b and a control input coupled to the foot pedal 46 to receive the cutting trigger signal 154a/non-cutting trigger signal 154b in response to activation/deactivation of the TRD 18 (i.e. , switching the TRD 18 from the cutting mode to the non-cutting mode or from the non-cutting mode to the cutting mode). The output of the multiplexor 182 is one of the cutting reset value and the non-cutting reset value based on the whether the control input receives the cutting trigger signal 154a or the non-cutting trigger signal 154b. That is, if the cutting trigger signal 154a (e.g., a logical high (“1”)) is received at the control input, the multiplexor 182 selects and outputs the cutting reset value from the cutting speed register 180a, and if the non-cutting trigger signal 154b (e.g., a logical low (“0”)) is received at the control input, the multiplexor 182 selects and outputs the non-cutting reset value from the non-cutting speed register 180b. In the case where the fluid outflow rate of the outflow pump 78 may be selected by a user, the feedforward control module 178 may select the cutting reset value or non-cutting reset value corresponding to the selected speed of the outflow pump 78. For example, the feedforward control module 178 may comprise additional multiplexors (not shown) coupled between outputs of the respective cutting speed registers and non-cutting registers and the inputs to the multiplexor 182), such that the multiplexor 182 outputs the cutting reset value or non-cutting reset value corresponding to the selected speed of the outflow pump 78.

[75] The multiplexor 182 outputs the selected one of the cutting reset value and the non-cutting reset value to both the controller 168 and the calibration LPF 170. Additionally, the foot pedal 46 outputs the cutting trigger signal 154a or the non-cutting trigger signal 154b to both the controller 168 and the calibration LPF 170. The feedback control module 162 then uses these parameters to modify the internal integrator value 169 of the integrator term of the controller 168 and the DC value 171 of calibration LPF 170.

[76] In particular, the controller 168 is configured for receiving the selected one of the cutting reset value and non-cutting reset value from the multiplexor 182, and for receiving the cutting trigger signal 154a/non-cutting trigger signal 154b from the foot pedal 46. Upon receipt of the cutting trigger signal 154a from the foot pedal 46, the internal integrator value 169 output by the integrator term in the controller 168 is reset (or reinitialized) to a cutting reset value corresponding to the increased fluid inflow rate (i.e., the equivalent cutting reset value) received from the multiplexor 182, and upon receipt of the non-cutting trigger signal 154b from the tissue removal assembly 12, the internal integrator value 169 output by the integrator term in the controller 168 is reset (or reinitialized) with non-cutting reset value corresponding to the decreased fluid inflow rate (i.e. , the equivalent non-cutting reset value).

[77] Like the controller 168, the calibration LPF 170 is configured for receiving (i) either the cutting reset value or non-cutting reset value from the multiplexor 182 and (ii) either the cutting trigger signal 154a or non-cutting trigger signal 154b from the foot pedal 46. Upon receipt of the cutting trigger signal 154a, the internal DC value 171 of the calibration LPF 170 is reset (or reinitialized) to the cutting reset value corresponding to the increased fluid inflow rate (i.e., the equivalent cutting reset value) received from the multiplexor 182. Likewise, upon receipt of the non-cutting trigger signal 154b, the internal DC value 171 of the calibration LPF 170 is reset (or reinitialized) to the non-cutting value corresponding to the decreased fluid inflow rate (i.e., the equivalent non-cutting reset value).

[78] It should be appreciated that by increasing or decreasing the fluid inflow rate of the inflow pump 76 independently of the fluid pressure measured by the pressure sensor 80, the feedforward control module 178 reduces the settling time of the feedback control module 162 from a nominal settling time (e.g., greater than five seconds, or even greater than twenty seconds) to a new settling time (e.g., less than one second). In this manner, the intrauterine fluid pressure will not significantly overshoot or undershoot the intrauterine pressure setpoint in response to the activation/deactivation of the TRD 18.

[79] Once the internal integrator value 169 in the controller 168 and the internal DC value 171 of the calibration LPF 170 are reset (or reinitialized) in response to the cutting trigger signal 154a or non-cutting trigger signal 154b, the feedforward control module 178 relinquishes control over to the feedback control module 162. The feedback control module 176 continues to control the fluid inflow rate (i.e., the speed) of the inflow pump 76 based on the pressure measured by the pressure sensor 80 until another cutting trigger signal 154a or non-cutting trigger signal 154b is received from the foot pedal 46 when the feedback control module 176 again relinquishes control to feedforward control module 178.

[80] Fig. 5 illustrates a pump control unit 82’ similar to pump control unit 82 (shown in Fig. 4) except that pump control unit 82’ comprises a feedback control module 162’ configured for maintaining the intrauterine fluid pressure lower than the intrauterine pressure setpoint (e.g., by 10 mm Hg or a predetermined percentage) when the TRD 18 is in cutting mode. Applicants have observed that targeting a lower setpoint in cutting mode slightly reduces the degree of distention (as compared to when the TRD 18 was in non-cutting mode) and therefore allows better prolapse of tissue into the cutting window.

[81] The feedback control module 162’ is configured for decreasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD 18 from the non-cutting mode to the cutting mode, and for increasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD 18 from the cutting mode and the non-cutting mode. In the illustrated embodiment, the feedback control module 162’ comprises memory elements 184a, 184b (in this case, an offset register and a zero register) configured for respectively storing an offset value (e.g., 10) and a zero value, and a multiplexor 186 having two data inputs respectively coupled to the offset register 184a and the zero register 184b for respectively receiving the offset value and the zero value from the offset register 184a and the zero register 184b, a control input coupled to the foot pedal 46 to receive the cutting trigger signal 154a/non- cutting trigger signal 154b in response to activation/deactivation of the TRD 18 (i.e., switching the TRD 18 from the cutting mode to the non-cutting mode or from the noncutting mode to the cutting mode), and a control output for outputting a selected one of the offset value and zero value based on the whether the control input receives the cutting trigger signal 154a or the non-cutting trigger signal 154b. That is, if the cutting trigger signal 154a (e.g., a logical high (“1”)) is received at the control input, the multiplexor 186 selects and outputs the offset value, and if the non-cutting trigger signal 154b (e.g., a logical low (“0”)) is received at the control input, the multiplexor 186 selects and outputs the zero value.

[82] The feedback control module 162’ further comprises a subtractor 188 configured for computing and outputting a function of the intrauterine pressure setpoint to the subtractor 176, in particular, either an identify function (i.e., the nominal pressure setpoint) by subtracting the zero value output by the multiplexor 182 from the intrauterine pressure setpoint output by the intrauterine pressure setpoint register 164 or a difference function (i.e., a decreased pressure setpoint) by subtracting the offset value output by the multiplexor 182 from the intrauterine pressure setpoint output by the intrauterine pressure setpoint register 164. Thus, in response to the non-cutting trigger signal 154b, the subtractor 188 outputs the nominal pressure setpoint to the subtractor 176, and in response to the cutting trigger signal 106, the subtractor 188 outputs the decreased pressure setpoint to the subtractor 176. As a result, the controller 168 will control the fluid inflow rate of the inflow pump 76 based on the fluid pressure measured by the pressure sensor 80, such that the intrauterine fluid pressure is maintained at a nominal intrauterine pressure setpoint when the TRD 18 is in the non-cutting mode, or such that the intrauterine fluid pressure is maintained at the reduced intrauterine pressure setpoint when the TRD 18 is in the cutting mode.

[83] Referring now to Fig. 6, another embodiment of a pump control unit 82” is similar in many respects to pump control units 82 and 82” except that pump control unit 82” controls the inflow rate of the inflow pump 76 based on variable (or dynamic) cutting and non-cutting reset values. The previously described embodiments of the pump control units 82, 82’ control the inflow rate of the inflow pump 76 based on a fixed (or non-dynamic) cutting reset value or non-cutting reset value based on a calibration procedure from the operation of identical or similar tissue resection devices during prior surgical procedures or stimulations of the surgical procedure.

[84] The pump control unit 82” is configured for learning the optimal level of the elevated inflow rate of the inflow pump 76 required to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint in response to switching the TRD 18 from the non-cutting mode to the cutting mode, and learning the optimal level of the reduced inflow rate of the inflow pump 76 required to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint in response to switching the TRD 18 from the cutting mode to the non-cutting mode.

[85] In particular, the pump control unit 82” comprises a feedforward control module 178’ that is similar to the feedforward control module 178 illustrated in Fig. 5, with the exception that the feedforward control module 178’ dynamically learns and predicts the increased pump speed needed to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint during operation of the TRD 18 and, likewise, the decreased pump speed predicted to maintain the intrauterine fluid pressure at or proximate to the intrauterine pressure setpoint during non-operation of the TRD 18. Applicants have observed that this learning function accounts for differences between the tissue resection device (actual or simulated) used to generate the calibrated increased cutting speed value and the TRD 18 used during the current surgical operation, as well procedure-specific amounts of cervical leakage.

[86] The pump control unit 82’ accomplishes this by, after the pump control unit 82’ has increased or decreased the fluid inflow rate of the inflow pump 76 independently of the fluid pressure measured by the pressure sensor 80), changing (or updating) a variable (or dynamic) cutting reset value, such that it converges from a nominal cutting reset value to a new cutting reset value equal to the controlled fluid inflow rate of the inflow pump 76 during operation of the TRD 18, and for changing a variable (or dynamic) non-cutting reset value, such that it converges from a nominal non-cutting reset value to a new non-cutting reset value equal to the controlled fluid inflow rate of the inflow pump 76 during non-operation of the TRD 18.

[87] In the illustrated embodiment, the feedforward control module 178’ comprises a cutting mode LPF 190a and a non-cutting mode LPF 190b. The cutting mode LPF 190a has two data inputs respectively coupled to the cutting speed register 180a and the output of the controller 168, a control input coupled to the foot pedal 46, and a control output coupled to the first data input of the multiplexor 182. The non-cutting mode LPF 190b has two data inputs respectively coupled to the non-cutting speed register 180b and the output of the controller 168, a control input coupled to the foot pedal 46 via an inverter 192, and a control output coupled to the second data input of the multiplexor 182.

[88] The cutting speed register 180a and non-cutting speed register 180b function in the same manner described above with respect to the pump control unit 82 illustrated in Fig. 4; however, in this case, the increased cutting and non-cutting reset values respectively stored in the cutting speed and non-cutting speed registers 180a, 180b serve as nominal (or predetermined) increased cutting and non-cutting reset values for initializing the respective cutting and non-cutting mode LPFs 190a, 190b at the beginning of the surgical procedure. Such nominal increased cutting and noncutting reset values may be determined using a calibration procedure in the same manner discussed above. Thus, the cutting mode LPF 190a is configured for receiving the nominal cutting reset value from the cutting speed register 180a, such that the cutting mode LPF 190a is initialized with a nominal (or predetermined) cutting reset value, while the non-cutting mode LPF 190b is configured for receiving the nominal non-cutting reset value from the non-cutting speed register 180b, such that the noncutting mode LPF 190b is initialized with a nominal (or predetermined) non-cutting reset value.

[89] Both of the cutting mode LPF 190a and the non-cutting mode LPF 190b are configured for receiving the controlled pump speed from the controller 168 (corresponding to the pump speed control signal 158 output by the controller 168), changing the respective variable cutting reset value and non-cutting reset value, such that they converge from the nominal increased cutting and non-cutting reset values to new increased cutting and non-cutting reset values, and storing the new values.

[90] In particular, the cutting mode LPF 190a is configured for filtering the pump speed control signal 158 when the TRD 18 is in the cutting mode, and holding that value when the TRD 18 is in the non-cutting mode. The non-cutting mode LPF 190b is configured for filtering the pump speed control signal 158 when the TRD 18 is in the non-cutting mode, and holding that value to a current value when the TRD 18 is in the cutting mode. For example, if a cutting trigger signal 154a (e.g., a logical high (“1”)) is output by the foot pedal 46, the cutting mode LPF 190a receives the cutting trigger signal 154a, and is thus enabled to low pass filter the pump speed control signal 158 received from the controller 168 and output this low pass filtered value to the multiplexor 182. The non-cutting mode LPF 190b receives an inversion of the cutting trigger signal 154a from the inverter 192, and is held off- retaining the last (or updated) low pass value it held upon the transition of the cutting trigger signal 154a. In contrast, if a non-cutting trigger signal 154b (e.g., a logical low (“0”) is output by the foot pedal 46, the non-cutting mode LPF 190b receives the non-cutting trigger signal 154b, and is thus enabled to low pass filter the pump speed control signal 158 received from the controller 168 and output this low pass filtered value to the multiplexor 182. The cutting mode LPF 190a receives an inversion of the non-cutting trigger signal 154b from the inverter 192, and is held off - retaining the last (or updated) low pass value it held upon the transition of the non-cutting trigger signal 154b.

[91] The multiplexor 182 functions in the same manner described above with respect to the pump control unit 82 illustrated in Fig. 4; however, in this case, instead of directly receiving the cutting reset value and the non-cutting reset value respectively from the cutting speed register 180a and the non-cutting speed register 180b, the multiplexor 182 directly receives the cutting reset value and the non-cutting reset value respectively from the cutting mode LPF 190a and non-cutting mode LPF 190b, and outputs the selected one of the cutting reset value and the non-cutting reset value to the controller 168 and the calibration LPF 170.

[92] Although Fig. 6 illustrates the pump control unit 82” as including the feedback control module 162’, the feedback control module 162 of Fig. 4 could be substituted.

[93] Although particular embodiments of the disclosed inventions have been shown and described herein, it will be obvious to those skilled in the art that various changes and modifications may be made (e.g., the dimensions of various parts) without departing from the scope of the disclosed inventions, which is to be defined only by the following claims and their equivalents. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

Claims

CLAIMS What is claimed is:

1 . A fluid management system (FMS) for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope, the FMS comprising: a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity; a sensor configured for measuring a fluid pressure within the fluid inflow path; and control circuitry configured for (i) generating a pressure error value based on the measured fluid pressure and an intrauterine setpoint pressure, (ii) generating a pump speed control signal based at least in part on the pressure error value and an internal integrator value, and (iii) resetting the internal integrator value in response to a change in an activation mode of the TRD between a cutting mode and a non-cutting mode.

2. The FMS of claim 1 , wherein the control circuitry is configured for resetting the internal integrator value to a cutting reset value in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and resetting the internal integrator value to a non-cutting reset value different from the cutting reset value in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode.

3. The FMS of claim 2, wherein the cutting reset value is greater than the noncutting reset value.

4. The FMS of claim 2 or 3, further comprising a constant speed outflow pump configured for removing fluid from the intrauterine cavity via an outflow fluid path passing through the hysteroscope, wherein the respective cutting and non-cutting reset values are based, at least in part, on the outflow pump speed.

5. The FMS of any of claims 1-4, wherein the control circuitry further comprises a calibration LPF configured for filtering the pump speed control signal; and a priming compensator configured for generating a pressure compensation value based on the filtered pump speed control signal, wherein the control circuitry is configured for subtracting the pressure compensation value from the measured fluid pressure to generate an estimated intrauterine fluid pressure, and for subtracting the intrauterine setpoint pressure from the estimated intrauterine pressure to determine the intrauterine pressure error value.

6. The FMS of any of claims 1-4, wherein the inflow pump is a peristaltic pump, the FMS further comprising a peristalsis low pass filter (LPF) configured for filtering the measured fluid pressure, and wherein the control circuitry is configured for generating the pressure error value by comparing the filtered measured fluid pressure with the intrauterine pressure setpoint.

7. The FMS of claim 6, wherein the control circuitry further comprises: a calibration LPF configured for filtering the pump speed control signal; and a priming compensator configured for generating a pressure compensation value based on the filtered pump speed control signal, wherein the control circuitry is configured for subtracting the pressure compensation value from the filtered measured fluid pressure to generate an estimated intrauterine fluid pressure, and for subtracting the intrauterine setpoint pressure from the estimated intrauterine pressure to determine the intrauterine pressure error value.

8. The FMS of claim 5 or 7, wherein the calibration LPF is configured for filtering the pump speed control signal based at least in part on a resettable DC value.

9. The FMS of any of claims 1-8, wherein the control circuitry further comprises a cutting mode low pass filter (LPF) configured for being initialized at a start of a surgical procedure to a predetermined cutting reset value and for filtering the pump speed control signal.

10. The FMS of claim 9, wherein the cutting mode LPF is further configured for retaining an updated cutting reset value when the TRD activation mode changes to the non-cutting mode.

11. The FMS of any of claims 1-10, wherein the control circuitry further comprises a non-cutting mode low pass filter (LPF) configured for being initialized at a start of a surgical procedure to a predetermined non-cutting reset value, and for filtering the pump speed control signal.

12. The FMS of claim 11 , wherein the non-cutting mode LPF is further configured for retaining an updated non-cutting reset value when the TRD activation mode changes to the cutting mode.

13. The FMS of any of claims 1-12, wherein the control circuitry is further configured for decreasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and for increasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode.

14. The FMS of claim 13, wherein the intrauterine pressure setpoint is decreased or increased, respectively, by a predetermined offset.

15. The FMS of claim 13, wherein the intrauterine pressure setpoint is decreased or increased, respectively, by a predetermined percentage.

16. The FMS of any of claims 1-15, wherein the control circuitry comprises a proportional integral derivative (PID) controller or a proportional-integral (PI) controller comprising the internal integrator value.

17. A fluid management system (FMS) for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope, the FMS comprising: a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity; and control circuitry configured for controlling a speed of the inflow pump based at least in part on an internal integrator value, and for resetting the internal integrator value in response to a change in an activation mode of the TRD between a cutting mode and a non-cutting mode.

18. The FMS of claim 17, wherein the control circuitry is configured for resetting the internal integrator value to a cutting reset value in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and resetting the internal integrator value to a non-cutting reset value different from the cutting reset value in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode.

19. The FMS of claim 18, wherein the cutting reset value is greater than the non-cutting reset value.

20. The FMS of any of claims 17-19, wherein the inflow pump is a peristaltic pump, the FMS further comprising a sensor configured for measuring a fluid pressure within the fluid inflow path, the control circuitry further comprising a peristalsis low pass filter (LPF) configured for filtering the measured fluid pressure, wherein the control circuitry is configured for controlling the speed of the inflow pump based at least in part on a pressure error derived from a comparison of the filtered measured fluid pressure and an intrauterine pressure setpoint.

21. The FMS of any of claims 17-19, wherein the control circuitry is further configured for decreasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the non-cutting mode to the cutting mode, and for increasing the intrauterine pressure setpoint in response to a change in the activation mode of the TRD from the cutting mode to the non-cutting mode.

22. The FMS of claim 21 , wherein the intrauterine pressure setpoint is decreased or increased, respectively, by a predetermined offset.

23. The FMS of claim 21 , wherein the intrauterine pressure setpoint is decreased or increased, respectively, by a predetermined percentage.

24. A fluid management system (FMS) for use with a hysteroscope and a tissue resection device (TRD) positioned in the hysteroscope, the FMS comprising: a variable speed inflow pump configured for pumping fluid via a fluid inflow path passing through the hysteroscope and into a uterine cavity; a sensor configured for measuring a parameter indicative of a fluid pressure within the uterine cavity; and control circuitry configured for maintaining fluid pressure in the uterine cavity at or near an intrauterine pressure setpoint and for receiving a cutting trigger signal indicative of an activation of the TRD, the control circuitry comprising: a feedback control module configured for controlling a fluid inflow rate of the inflow pump based on the measured parameter to maintain the intrauterine fluid pressure at or proximate to an intrauterine pressure setpoint, and a feedforward control module configured for adjusting the fluid inflow rate of the inflow pump independently of the measured parameter in response to a first cutting trigger signal followed by adjusting the fluid inflow rate based on the measured parameter in response to a second cutting trigger signal.

25. The FMS of claim 24, wherein the control circuitry is configured for increasing the fluid inflow rate in response to a change in the activation mode from a non-cutting mode to a cutting mode, and for decreasing the fluid inflow rate in response to a switch in the activation mode from the cutting mode to the non-cutting mode.

26. The FMS of claim 24 or 25, wherein the control circuitry is further configured for adjusting the intrauterine pressure setpoint in response to a change in the activation mode of the TRD.

27. The FMS of claim 26, wherein the intrauterine pressure setpoint is decreased or increased, respectively, by a predetermined offset.

28. The FMS of claim 26, wherein the intrauterine pressure setpoint is decreased or increased, respectively, by a predetermined percentage.

29. The FMS of any of claims 24-28, wherein the feedforward control module is configured for adjusting the fluid inflow rate of the inflow pump based on a predicted fluid inflow rate to maintain the fluid pressure in the uterine cavity at or near the intrauterine pressure setpoint.

30. The FMS of claim 29, wherein the predicted fluid inflow rate is a fixed preprogrammed value.

31 . The FMS of claim 29, wherein the control circuitry is configured for updating the predicted fluid inflow rate.

32. The FMS of claim 31 , wherein the feedforward control module updates the predicted fluid inflow rate so that it converges from a nominal value to a new value equal to the controlled fluid inflow rate during operation of the TRD.

33. The FMS of any of claims 24-32, wherein the feedback control module comprises a controller having an integrator term, and wherein the feedforward control module is configured for controlling the fluid inflow rate of the inflow pump by resetting the integrator term.

34. The FMS of claim 33, wherein the feedforward control module is configured for resetting the integrator term to a cutting reset value corresponding to a fluid inflow rate predicted to maintain the fluid pressure in the body cavity at or proximate to the intrauterine pressure setpoint during operation of the TRD.

35. The FMS of claim 33 or 34, wherein the controller is a proportional, integral, derivative (PID) controller or a proportional-integral (PI) controller.