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WO1999034724A2 - Systeme et procede pour caracteriser des lesions et des parois de vaisseaux sanguins au moyen de mesures de pression en plusieurs points - Google Patents

Systeme et procede pour caracteriser des lesions et des parois de vaisseaux sanguins au moyen de mesures de pression en plusieurs points Download PDF

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Publication number
WO1999034724A2
WO1999034724A2 PCT/IL1999/000019 IL9900019W WO9934724A2 WO 1999034724 A2 WO1999034724 A2 WO 1999034724A2 IL 9900019 W IL9900019 W IL 9900019W WO 9934724 A2 WO9934724 A2 WO 9934724A2
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WIPO (PCT)
Prior art keywords
pressure
blood vessel
blood
vessel wall
tubular conduit
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PCT/IL1999/000019
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English (en)
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WO1999034724A3 (fr
Inventor
Elhanan Dgany
Simon Henri Noskowicz
Gideon Tolkowsky
Evgeny Shalman
Alexander Tyomkin
Chen Barak
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Florence Medical Ltd.
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Application filed by Florence Medical Ltd. filed Critical Florence Medical Ltd.
Priority to AU17816/99A priority Critical patent/AU1781699A/en
Publication of WO1999034724A2 publication Critical patent/WO1999034724A2/fr
Publication of WO1999034724A3 publication Critical patent/WO1999034724A3/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/02007—Evaluating blood vessel condition, e.g. elasticity, compliance
    • A61B5/02014—Determining aneurysm
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/02108—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics
    • A61B5/02125—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics of pulse wave propagation time
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/0215—Measuring pressure in heart or blood vessels by means inserted into the body
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/026—Measuring blood flow
    • A61B5/0285—Measuring or recording phase velocity of blood waves

Definitions

  • the present invention relates to the field of medical diagnostic devices in general and to a system for intravascular characterizing blood vessel walls and lesions in particular.
  • Vascular diseases are often manifested by reduced blood flow due to atherosclerotic occlusion of vessels.
  • occlusion ofthe coronary arteries supplying blood to the heart muscle is a major cause of heart disease.
  • Invasive procedures for relieving arterial blockage such as bypass surgery and balloon dilatation with a catheter are currently performed relying on estimates ofthe occlusion characteristics and the blood flow through the occluded artery. These estimates are based on measurements of occlusion size and / or blood flow.
  • current methods of occlusion size compliance rarely used
  • obstruction to flow and blood flow measurement have low resolution, are time consuming, require expertise in the inte ⁇ retation ofthe results and are expensive.
  • decisions on whether or not to use any ofthe blockage relieving methods and which ofthe methods should be used are often based on partial information.
  • Atherosclerotic lesions may have different characteristics. Some lesions exhibit a variable degree of calcification while others have a fatty or thrombotic nature. Lesion characteristics together with vessel condition proximal and distal to the lesion are the major factors for determining the therapeutic procedure needed. Typically, the physician first selects the appropriate treatment method from among medication therapy, transcatheter cardiovascular therapeutics (TCT), coronary artery bypass grafting (CABG), or non- treatment. Recently, increasing number of patients are directed toward TCT. TCT starts with an interventional diagnosis procedure (mostly angiography ), followed by the treatment ofthe patient with medication therapy, CABG or continuation ofthe TCT procedure with interventional treatment.
  • TCT transcatheter cardiovascular therapeutics
  • CABG coronary artery bypass grafting
  • stents are placed within the lesion so as to prevent re-closure ofthe vessel (also known as recoil). Usually stent is placed after lumen predilatation PTCA.
  • Stenting without predilatation is also performed at increasing rates, saving both costs and time.
  • primary stenting is clinically superior.
  • debris, produced by the dilatation are held in place by the stent, instead of flowing downstream and causing a stroke.
  • Lesion characteristics together with vessel condition proximal and distal to the lesion, are used to determine the medically and economically optimal treatment method or combination of methods of choice.
  • a clinically important lesion characteristic is the lesion calcification level.
  • a non- calcified arterial wall or lesion is usually a non-chronic, fat based plaque that may be treated by medication therapy, or by the softer, less expensive, PTCA method.
  • Heavily calcified lesion wall typically requires harder methods, such as ELCA.
  • the vessel wall calcification level influences the decision whether to use a dilatation balloon prior to stenting.
  • the physician may elect not to use a dilatation balloon prior to stenting.
  • the vessel wall calcification level influences the optimal inflation pressure ofthe dilatation balloon.
  • the available diagnostic methods for assessing vessel wall structure and degree of calcification may be categorized according to their "intervention complexity", as judged by the duration ofthe diagnostic procedure and the complexity of inte ⁇ retation ofthe results, or to the measurement principle: either imaging or physiological measurements. These available diagnostic methods are listed in TABLE 1 hereinbelow. TABLE 1
  • angiography When angiography is used for calcification evaluation, an arc of at least 180 degrees of calcification is required to achieve identification of a mass of calcium and quantification of calcification is difficult. Thus, angiography demonstrates poor sensitivity for detecting mild to moderate lesion calcium, and only moderate sensitivity for extensive lesion calcium.
  • Jeffrey J. Pompa and Martin B. Leon show in an article entitled "A Lesion Specific Approach To New-Device Angioplasty" in "Textbook of Interventional Cardiology” published by W.B. Saunders (1993), that more than 10% ofthe lesions that were angiographically identified as calcified, were found by IVUS to be non-calcified.
  • IVUS is the most informative tool that provides reliable information about wall characteristics. IVUS provides a penetrating ultrasound image ofthe vessel wall. The lesion wall characteristics, including calcification zones can be assessed from this ultrasound image.
  • Late works in IVUS inte ⁇ olation present evaluation of wall elasticity by comparing vascular cross sections at different pressure levels. These methods are still within preliminary research and the combination and pressure measurement increases the complexity ofthe procedure, therefore prevents its wide implementation.
  • the calcification level plays a major role, discriminating between deep and superficial calcification as described by Pompa and Leon.
  • IVUS is still primarily used for research pu ⁇ oses, and is not routinely used in the majority of catheter-labs due to its high cost, lack of expert personnel, and its being a time consuming procedure.
  • the average plaque burden in the normal reference segment may comprise 40% ofthe total vessel cross-sectional area. This happens because with increasing plaque accumulation, there is a remodeling process whereby the vessel expands to accommodate the plaque load.
  • Endothelial cells lining the internal vessel lumen are known to play an important function in lesion formation, plaque rupture, angiogenesis and additional clinical processes.
  • Lesion characteristics are used to determine the medically and economically optimal treatment method or combination of methods of choice.
  • Systems and methods of use thereof have been designed which provide information regarding wall physiology fluid flow and characterization of lumen structure which provide for improved treatment of diseased or injured vascular structures.
  • the system provides information from multiple points of measurement within the blood vessels, which allows assessment of wall structure, physiology and mechanical properties. Specifically, by determining the elastic properties of the blood vessels, one can calculate the distensibility and compliance of lesioned and non- lesioned parts of blood vessels.
  • Comparisons ofthe values with standard values in people of similar age, gender, etc., or to the same patient, same procedure, values but in different vessels or different location within the same vessel, or to the same patient values over a range of time provide a means for assessment of disease and/or treatment over time. This also provides a means for determining the most efficacious treatment, particularly with regard to those individuals which have occlusions of less than 50%.
  • Fig. 1 is a schematic isometric view of a system for characterizing lesioned and non- lesioned blood vessel walls, constructed and operative in accordance with a preferred embodiment ofthe present invention
  • Fig. la is a schematic isometric view of a system for characterizing lesioned and non- lesioned blood vessel walls, constructed and operative in accordance with another preferred embodiment ofthe present invention
  • Fig. 2 is a schematic functional block diagram illustrating the details ofthe system 1 of Fig. 1;
  • Fig. 2a is a schematic functional block diagram illustrating the details ofthe system a of Fig. a;
  • Fig. 3 is a schematic cross section illustrating the positioning of a pressure catheter ofthe system of Fig. 1 or la within a blood vessel during the operation ofthe system of Fig. 1 or la;
  • Fig. 3a is a schematic cross section illustrating the another positioning of a pressure catheter of the system of Fig. 1 or la across the stenosis, within a blood vessel during the operation ofthe system of Fig. 1 or la;
  • Fig. 4 is a schematic isometric view of an in- vitro system for characterizing lesioned and non-lesioned blood vessel walls, constructed and operative in accordance with a preferred embodiment ofthe present invention
  • Fig. 5 is a schematic detailed illustration ofthe in-vitro tubing system 51 of Fig.4.
  • Fig. 6 is a detailed schematic illustration ofthe experimental section 44 of Fig.4 and the positioning ofthe pressure sensors within a the latex tube during the operation ofthe system of Fig. 4;
  • Fig. 7 is a schematic cross section illustrating the positioning ofthe three pressure sensors of Procedure 1 and Method 1, within a lesioned or non-lesioned blood vessel;
  • Fig. 8 is a schematic cross section illustrating the positioning ofthe two pressure sensors of procedure 2, within a lesioned or non-lesioned blood vessel;
  • Fig. 9 is a schematic flow chart illustrating the steps ofthe method of determining the pressure wave velocity within a blood vessel from pressure data obtained simultaneously by three separate pressure sensors, in accordance with a preferred embodiment ofthe present invention.
  • Fig. 10 is a schematic flow chart illustrating the steps ofthe method of determining pressure wave velocity within a blood vessel from pressure data obtained simultaneously by two separate pressure sensors, using the level fitting procedure, constructed and operative in accordance with another preferred embodiment ofthe present invention
  • Fig. 11 is a schematic flow chart illustrating the steps ofthe method of determining pressure wave velocity within a blood vessel from pressure data obtained simultaneously by two separate pressure sensors, using the optimal overlap procedure, constructed and operative in accordance with another preferred embodiment ofthe present invention
  • Fig. 12a is a schematic flow chart illustrating the steps ofthe method (first approach) of determining pressure wave velocity within a blood vessel from pressure data obtained simultaneously by a fluid field (FF) pressure transducer system and one moving intravascular pressure sensor, constructed and operative in accordance with another preferred embodiment ofthe present invention;
  • FF fluid field
  • Fig. 12b is a schematic flow chart illustrating the steps ofthe method (second approach) of determining pressure wave velocity within a blood vessel from pressure data obtained simultaneously by a fluid field (FF) pressure transducer system and one moving intravascular pressure sensor, constructed and operative in accordance with another preferred embodiment ofthe present invention;
  • FF fluid field
  • Fig. 13 is a schematic cross section illustrating the positioning of one moving intravascular pressure sensor and an FF pressure transducer system as described in Procedure 3, within a lesioned or non-lesioned blood vessel;
  • Fig. 14 is a schematic cross section illustrating the positioning of two intravascular pressure sensors and an FF pressure transducer system as described in Method 2, within a lesioned or non-lesioned blood vessel;
  • Fig. 15 is a schematic cross section illustrating the positioning ofthe two pressure sensors of Method 3, within a lesioned or non-lesioned blood vessel;
  • Fig. 16 is a schematic cross section illustrating the positioning of three pressure sensors within a pig carotid during an in- vivo experiment
  • Fig. 17a-17d illustrates in- vivo pressure raw data acquired with two intravascular pressure sensors positioned within the pig carotid; b. applying Procedure 2. a to the raw data presented in a. and detecting the PWV based on 10% level fitting; c. applying Procedure 2.b to the raw data presented in a. and detecting the PWV based on optimal overlap between the two signals; d. using data of three pressure signals and applying Procedure 1 to derive PWV. All methods presented similar PWV values.
  • Fig. 18 illustrates the pressure wave velocity derived by Procedure 2.
  • the numbers appearing on the graph indicate PWV in meter per sec as calculated for each stroke;
  • Fig. 19a-19d illustrates in- vitro pressure raw data acquired with three intravascular pressure sensors positioned within the experimental latex section; b. applying Procedure 1 to the raw data presented in a. and detecting the averaged PWV; c. applying Procedure 2. a to the raw data presented in a. and detecting the PWV based on 10% level fitting on a series of strokes, yielding a PWV value for each stroke and the averaged PWV value. Both methods presented similar PWV values.
  • Fig. 20 is a schematic cross section illustrating the positioning of one intravascular pressure sensor and an FF pressure transducer system as described in Method 4, within a lesioned or non-lesioned blood vessel;
  • Fig. 21 is a schematic cross section illustrating the positioning of one moving intravascular pressure sensors and an FF pressure transducer system as described in Method 5, within a lesioned or non-lesioned blood vessel;
  • Fig. 22 is a schematic cross section illustrating the positioning of one moving intravascular pressure sensor and a FF pressure transducer system connected through the standard guiding catheter within a pig carotid during an in- vivo experiment;
  • Fig. 23a-23b illustrate the application of Procedure 3 to in-vivo pressure raw data acquired with a moving intravascular pressure sensor and FF pressure transducer positioned in point A and then B within the pig carotid.
  • the numbers appearing on the graph indicate a procedural interim value as calculated for each stroke;
  • Fig. 24 illustrates the validation ofthe results presented in Figs. 23a-23b by applying Procedure 2.a to two intravascular pressure sensors within the pig carotid.
  • the numbers appearing on the graph indicate PWV in meter per sec as calculated for each stroke;
  • Fig. 25a - 25b present the simultaneous raw data of FF and Radi pressures at proximal position
  • Fig. 26a - 26b present the simultaneous raw data of FF and Radi pressures, at distal position
  • Fig. 27 illustrates one pulse ofthe two FF pressure signals (proximal and distal);
  • Fig. 28 illustrates the application ofthe optimal overlap procedure on the signals of
  • Fig. 29 illustrates one pulse ofthe two Radi pressure signals (proximal and distal);
  • Fig. 30 illustrates the application ofthe optimal overlap procedure on the signals of Fig. 27;
  • Fig. 31 is a schematic cross section illustrating the positioning of one moving intravascular flow probe and an FF pressure transducer system as described in Method 6, within a lesioned or non-lesioned blood vessel;
  • Fig. 32a-32b illustrates flow raw data [ml/min] acquired on the in-vitro system with an ultrasonic flowmeter probe positioned within the experimental latex section; b. illustrates in-vitro pressure [mmHg] raw data acquired with an intravascular pressure sensor probe positioned within the experimental latex section;
  • Figs. 33-34 illustrate the application of Procedure 3 to the flow and pressure raw data, detecting the PWV;
  • Figure 35 is a cross section illustrating the positioning of a single pressure transducer of procedure 5 and method 7, within a stenosed blood vessel;
  • Figure 36 is a cross section illustrating the positioning of a single pressure transducer of procedure 5 and method 7, within a pig carotid during an in-vivo experiment;
  • Figure 37 illustrates in-vivo pressure raw data acquired with a single pressure sensor positioned within the pig carotid
  • Figure 38 illustrates the cepstrum ofthe pressure raw data presented in Fig. 37, calculated using the first step of procedure 5;
  • Figure 39 illustrates the final result of procedure 5, as applied to the raw data of Fig. 37
  • Figure 40 illustrates the reflection coefficient calculation from the raw data presented in Fig. 37;
  • Figure 41 illustrates in-vivo pressure raw data acquired with a single pressure sensor positioned at a second position within the same pig carotid
  • Figure 42 illustrates the cepstrum ofthe pressure raw data presented in Fig. 40, calculated using the first step of procedure 5;
  • Figure 43 illustrates the final result of procedure 5, as applied to the raw data of Fig. 40.
  • Figure 44 illustrates the reflection coefficient calculation from the raw data presented in Fig. 41.
  • the present invention relates to devices and methods determining tubular wall properties for improved clinical diagnosis and treatment.
  • tubular wall characteristics are recorded that correspond to the distensibility .and compliance ofthe tubular walls.
  • the invention provides for a quantitative determination ofthe pressure wave velocity (PWV) of blood vessels, thereby characterizing, inter alia, the Young modulus, the distensibility and the compliance of lesioned and non-lesioned parts of blood vessels.
  • the determined properties may be further used to evaluate the degree of calcification of lesioned and non-lesioned parts of blood vessels. These determined values can be calculated and reported in absolute terms as a ratio ofthe relevant parameter value in the lesion region to the parameter value in a non-lesion region ofthe same patient.
  • the system may calculate and report a ratio ofthe relevant parameter determined in the lesion region ofthe patient to a "standard" average value ofthe relevant parameter as measured in a group of healthy people with similar physiology (age group, gender, vessel type, etc.).
  • the system will include means for storing such standard averaged values of the relevant parameters such as a data-base stored in a suitable storage device included in the system (not shown).
  • PWV provides a PWV ratio. These PWV measurements and the reported PWV ratio disclosed hereinabove may be useful in the detection of otherwise "angiographically occult" diseased vessel regions.
  • the present invention is embodied in a system for determining at least one viscoelastic parameter of a region of a blood vessel.
  • the system comprises a flexible elongated member having a portion insertable into said blood vessel; means for simultaneously measuring the blood pressure in at least two predetermined positions along said longitudinal axis and for producing simultaneous pressure signals; and a processing unit connected to said means for measuring the blood pressure for receiving said pressure signals and for processing said simultaneous pressure signals to determine said at least one viscoelastic parameter.
  • the system comprises a flexible elongated member having a portion insertable into said blood vessel and a longitudinal axis; a plurality of pressure sensors, each of said plurality of pressure sensors being attached to said elongated member at a predetermined position along said longitudinal axis for simultaneously sensing the pressure at said positions and for producing pressure signals; and a processing unit connected to said plurality of sensors for receiving said pressure signals and for processing said pressure signals to determine said at least on viscoelastic parameter.
  • the present invention is embodied in a method for determining at least one viscoelastic parameter of a region of a blood vessel.
  • the method comprises the steps of simultaneously measuring the pressure in at least two measurement points within said blood vessel to obtain data representing the variation of pressure with time at said at least two measurement points; calculating at least one viscoelastic parameter of said region from said data; and reporting said at least one viscoelastic parameter.
  • Yet another embodiment ofthe present invention is disclosed in a system for determining at least the pressure wave velocity and derived characteristics of a region of a blood vessel.
  • the system comprises a flexible elongated member having a portion insertable into said blood vessel and a longitudinal axis; a plurality of pressure sensors, each of said plurality of pressure sensors being attached to said elongated member at a predetermined position along said longitudinal axis for simultaneously sensing the pressure at said positions and for producing pressure signals; and a processing unit connected to said plurality of sensors for receiving said pressure signals and for processing said pressure signals to determine said at least the pressure wave velocity and derived characteristics.
  • a method for determining at least the pressure wave velocity and derived characteristics of a region of a blood vessel comprises the steps of simultaneously measuring the pressure in at least one measurement point within said blood vessel to obtain data representing the variation of pressure with time at said at least two measurement points; calculating said at least the pressure wave velocity of said region from said data; reporting said at least the pressure wave velocity and derived characteristics.
  • a system for determining at least the pressure wave velocity and derived characteristics of a lesioned region of a blood vessel comprises a flexible elongated member having a portion insertable into said blood vessel; means for simultaneously measuring the blood pressure in at least one predetermined position along said longitudinal axis and for assessing simultaneous pressure signals; and a processing unit connected to said means for measuring the blood pressure for receiving said pressure signals and for processing said simultaneous pressure signals to determine said at least the pressure wave velocity and derived characteristics, and thereby recommend the best treatment needed.
  • a system for determining at least the pressure wave velocity and derived characteristics of a region of a blood vessel, where a PTCA procedure has been applied comprises a flexible elongated member having a portion insertable into said blood vessel ; means for simultaneously measuring the blood pressure in at least one predetermined position along said longitudinal axis and for assessing simultaneous pressure signals; and a processing unit connected to said means for measuring the blood pressure for receiving said pressure signals and for processing said simultaneous pressure signals to determine said at least the pressure wave velocity and derived characteristics, and the efficacy ofthe PTCA applied intervention, or any other dilatation procedure.
  • a system for determining at least the pressure wave velocity and derived characteristics of a lesioned region of a blood vessel, where a STENT was deployed comprises a flexible elongated member having a portion insertable into said blood vessel ; means for simultaneously measuring the blood pressure in at least one predetermined position along said longitudinal axis and for assessing simultaneous pressure signals; and a processing unit connected to said means for measuring the blood pressure for receiving said pressure signals and for processing said simultaneous pressure signals to determine said at least the pressure wave velocity and derived characteristics, and the efficacy ofthe STENT deployment.
  • a system for characterizing changes in a tubular conduit system within a living body for transferring fluids comprises a flexible elongated member having a portion insertable into said tubul.ar conduit and a longitudinal axis; at least one pressure sensor being positioned along said elongated member at a predetermined location along said longitudinal axis for sensing the pressure and operative to generate a pressure signal representative of said sensed pressure at a plurality of points within said tubular conduit; a processing unit operatively connected in circuit to said at least one pressure sensor; a program for controlling said processor unit; said processor unit operative with said program to receive said pressure signal and to identify changes in the pressure signal; detect characteristics of said tubular conduit system being derived from changes in said pressure signal; recognize and assign a label to said characteristic.
  • said at least one pressure sensor includes one pressure sensor movable relative to said tubular conduit; said pressure signal is representative of a plurality of pressure measurements taken over time a predetermined locations within said tubular conduit.
  • said at least one pressure sensor includes two pressure sensors located in predetermined spaced-apart positions along said elongated member; said pressure signal is representative of a plurality pressure measurements taken simultaneously by said pressure sensors.
  • said at least one pressure sensor includes three pressure sensors located in predetermined spaced-apart positions along said elongated member; said pressure signal is representative of a plurality pressure measurements taken simultaneously by said pressure sensors.
  • tubular conduit system is a blood vessel system
  • said processor unit is operative to detect characteristics of a blood vessel wall wherein said characteristics of said blood vessel wall detected by said processor include vessel wall compliance and distensibility wherein said processor unit is operative to recognize wall calcification and thickening, thereby permitting occult disease identification wherein said processor unit is operative to recognize a low compliance thereby identifying weak vascular sections of said blood vessels.
  • Another embodiment includes a method for using a flexible elongated member having a portion insertable into said tubular conduit and a longitudinal axis, at least one pressure sensor being positioned along said elongated member at a predetermined location along said longitudinal axis for sensing the pressure and operative to generate a pressure signal representative of said sensed pressure at a plurality of points within said tubular conduit, a processing unit operatively connected in circuit to said at least one pressure sensor, a program for controlling said processor unit, said processor unit operative with said program to receive said pressure signal to characterize changes in a tubular conduit system within a living body for transferring fluids.
  • the method comprises the steps of sensing a pressure using said pressure sensor; generating a pressure signal representative of said sensed pressure at a plurality of points within said tubular conduit; identifying changes in the pressure signal; detecting characteristics of said tubular conduit system being derived from changes in said pressure signal; and recognizing and assigning a label to said characteristic.
  • the determination ofthe elastic properties of an artery is based on calculating the phase velocity ofthe pressure wave. It is noted that, actually, PWV is a complex number containing information on the phase velocity and the attenuation ofthe pressure wave. For simplicity of derivation the attenuation is initially ignored hereinbelow.
  • Equation 2 is the continuity equation:
  • A is the instantaneous cross-section.
  • A A (P ) ( 3) It is noted that A(0) is the cross-section for zero excess pressure. The latter assumption is equivalent to neglecting at least one viscoelastic and hysteresis behavior.
  • the distensibility D is defined as: D - ⁇ wherein ⁇ is the compliance.
  • the wall is assumed to be purely elastic (that is viscoelasticity is negligible), thin, homogeneous and isotropic with Young modulus, E, and incompressible. Defining the Moens-Korteweg velocity:
  • PWV enables computation of the circumferential strain ofthe vessel wall.
  • the inner side ofthe wall is covered by endothelial cells which are known to play a major role in the wall biology, e.g. plaque formation and rupture.
  • Womersley's blood vessel model can be used. Womersley's model is based on the linearized Navier-Stokes equation assuming incompressible blood and Newtonian behavior. The blood viscosity ⁇ is constant, assuming a laminar blood flow. In Womersley's model, the vessel wall becomes an active component ofthe system. The dynamic behavior ofthe vessel wall is taken into account and has its own Newton equation for longitudinal and radial displacement.
  • the Womersley number is defined as:
  • F 10 is a function of CC and is therefore a function of ⁇ .
  • J Q , J ⁇ are the Bessel functions of order 0 and 1, respectively.
  • C 0 is the frequency-independent pressure wave velocity ofthe Moens-
  • the pressure wave velocity .and the pressure wave attenuation have to be measured as a function of ⁇ , yielding the complex function.
  • the function F 10 (a) has been tabulated and tends to unity in the l.arge a limit .
  • Figs. 1 and La present a schematic isometric view of a system for determining the pressure wave velocity and the compliance and circumferential strain acting on wall cells of blood vessel lesion regions and non-lesioned regions, and other body conduits constructed and operative in accordance with the objects ofthe present invention.
  • Fig. 2 and 2.a are schematic functional block diagrams illustrating the details ofthe system 1 of Fig. 1 and system a of Fig. La...
  • the systems 1 and La include at least one pressure sensor catheter or guide wire 4, inserted into the vessel directly or via a catheter lumen 3 for measuring the pressure inside a blood vessel.
  • the lumen catheter may be a guiding catheter of the type sold as 8F Archer coronary guiding catheter from Medtronic Interventional Vascular, Minneapolis, U.S.A. or a diagnostic catheter of the type sold as Siteseer diagnostic catheter, from Bard Cardiology,
  • the systems of Figures 1 and la may include one, two or three pressure sensor catheters or guide wires 4 for measuring the pressure inside a blood vessel.
  • An exemplary, but not limiting, embodiment of a pressure sensor 4 having one sensor is a 3F one pressure sensor model, model SPC-330A, commercially available from Millar Instruments Inc., TX, U.S.A.; however, any other pressure catheter suitable for diagnostic or combined diagnostic / treatment pu ⁇ oses may be used, such as the 0.014 " guidewire mounted pressure sensor product number 12000 from Radi Medical Systems, Upsala, Sweden, or Cardiometrics Wave Wire pressure guidewire from Cardiometrics Inc. .an Endsonics company of CA, U.S.A.
  • the two and three pressure sensor embodiments may also include combinations ofthe pressure sensors; however, a dual pressure catheter SPC-721 commercially available from Millar Instruments Inc., TX, U.S.A., may also be used.
  • the system 1 and La may also include a fluid filled (FF) pressure transducer 31, i.e. model PX272 disposable pressure transducer by Baxter Healthcare Co ⁇ oration, CA, USA, connected via the end of the guiding catheter 3.
  • the fluid filled pressure transducer 31 is connected to the system 1, when additional pressure readings are needed, or in place of an intravascular pressure transducer, according to the defined study.
  • the system 1 and a also includes a signal conditioner 23, such as a model TCB-500 control unit commercially available from Millar Instruments, or Radi Pressure Wire Interface Type PWI10, Radi Medical Systems, Upsala, Sweden , or other suitable signal conditioner.
  • the signal conditioner 23 is suitably connected to the pressure sensor 4 for amplifying the signals of the pressure sensor.
  • the system 1 further includes an analog to digital (A/D) converter 28 such as the NI E Series Multifunction I/O model PCI-MIO-16XE-10 commercially available by National Instruments, Austin, TX connected to the signal conditioner 23 and to the FF pressure transducer 31 for receiving the analog signals therefrom.
  • A/D analog to digital
  • the signal conditioner 23 may be integrated in the data acquisition card of the computer 20, or may also be omitted altogether, depending on the specific type of pressure sensors used. It will be appreciated by those skilled in the art of Digital Signal Processing that the implementation of a signal conditioner depends on the nature and character of pressure sensor, the signal transmission circuit leads, environmental factors and the nature and character of FF pressure transducer 31. It should be noted that either optical data transmission (e.g. Radi pressure sensor) or wireless communication (e.g. Siemens pressure transducer) may be used.
  • the system 1.a of Fig. 1.a also includes a standard cardiac catheterization system 22, such as Nihon Kohden Model RMC-1100, commercially available from Nihon Kohden Co ⁇ oration, Tokyo, Japan.
  • the signal conditioner 23 and the FF pressure transducer 31 are directly connected to the monitoring system 22.
  • the system 1.a further includes an analog to digital (A D) converter 28 connected to the output ofthe monitoring system 22 through a shielded I/O connector box 27, such as models NI SCB-68 or BNC-2090 commercially available from
  • the systems 1 and 1.a also include a signal analyzer 20 connected to the A/D converter 28 for receiving the digitized conditioned pressure signals from the A/D converter 28.
  • the signal analyzer 20 includes a computer 25 under the control of signal analysis software, and optionally a display 21 connected to the computer 25 for displaying text numbers and graphs representing the results ofthe calculations performed by the computer 25 and a printer 26 suitably connected to the computer 25 for providing hard copy of the results for documentation and archiving.
  • the A/D converter 28 can be a separate unit or can be integrated in a data acquisition computer card installed in the computer 25.
  • the computer 25 processes the pressure data, sensed by the pressure sensors 4 and acquired by the A/D converter 28 or the data acquisition card (not shown) and generates textual, numerical and/or graphic data that is displayed on the display 21.
  • the data displayed on the display 21 is calculated and displayed in real time for providing the operator of the pressure catheter 3 with information assisting him in the manipulation of the pressure catheter 3 within the patient's vascular system.
  • the real time operation is particularly advantageous in cases where aneurysms are diagnosed and treated; e.g., by filling the aneurysm with a filling Material.
  • both locations ofthe aneurysm may be defined by the altered (higher) compliance resulting from both local wall thinning and local dilatation comparing with neighbor segments. Treatment success may be indicated by compliance decrease, due to wall thickening and cross-section area reduction.
  • the real time operation is particularly advantageous in cases where the pressure catheter used also includes a dilation balloon or any other ablation devices such a laser ablation device, a mechanical ablation device or an ultrasound ablation devices for relieving the obstruction.
  • the data provided in real time enables the physician to quantitatively assess the obstruction parameters before, during and after a therapeutic procedure, and to decide whether to proceed to use the dilation balloon or any other therapeutic device based on the data provided in real time.
  • the present apparatus and methods correspond to the diagnosis of various blood vessel characteristics including but not limited to vessel wall compliance and distnesibility, in general, and more particularly to wall calcification and thickening to allow occult disease identification, low compliance characteristics to identify weak vascular wall sections, detecting circumferential strain of vessel walls, and attend higher compliance characteristics relating to aneurysms.
  • Diagnosis provided by the present invention not only provides initial guidance in implementing a treatment, but also allows for cooperative analysis ofthe vessel during treatments such as, but not limited to medication therapy, transcatheter cardiovascular therapeutics (TCT), coronary artery bypass grafting (CABG), or non-treatment. Additionally, numerous methods are currently available for treating various lesion types.
  • stents are placed within the lesion so as to prevent re-closure ofthe vessel (also known as recoil). Usually stent is placed after lumen predilatation PTCA. Stenting without predilatation is also performed at increasing rates, saving both costs and time. In some cases, e.g. carotid stenting, primary stenting is clinically superior.
  • the data acquired and/or calculated by the computer 25 may also be stored in the computer's memory or in a suitable storage device included in the computer 25 (not shown) for later off-line calculations, statistics, patient long time monitoring and/or analysis and presentation. This can be useful for training and educational pu ⁇ oses at a later time.
  • Fig. 3 is a schematic cross section illustrating the positioning of the guiding or diagnostic catheter 3, within the blood vessel of interest 30, during operation ofthe systems 1 and la of Figs. 1 and la, respectively.
  • the guiding catheter (or diagnostic catheter) 3 with three pressure sensors 4a, 4b or 4c, are inserted into the vascular system ofthe patient using a standard connector 8 and standard methods and moved to reach the blood vessel of interest 30.
  • Fig. 3 illustrates a cross section of an artery 30 having an arterial wall 32.
  • the artery 30 may also include a stenotic obstruction 34 obstructing the blood flow through the artery 30.
  • the pressure sensors may be located along the vessel, proximal (Fig. 3), distal, across or within the stenosis (Fig. 3a) in order to characterize the various regions ofthe vessel.
  • Fig. 5 is a schematic diagram representing an in-vitro experimental apparatus constructed and operative for determining flow characteristics in simulated non-lesioned and lesioned blood vessels, in accordance with an embodiment ofthe present invention.
  • Fig. 2 is a schematic functional block diagram illustrating the functional details of a system including the apparatus of Fig. 5 and apparatus for data acquisition, analysis and display.
  • the fluidics system 51 of Fig. 5 is a recirculating system for providing pulsatile flow.
  • the system 51 includes a pulsatile pump 42, model 1421 A pulsatile blood pump, commercially available from Harvard Apparatus, Inc., Ma, U.S.A.
  • the pump 42 allows control over rate, stroke volume and systole/diastole ratio.
  • the pump 42 recirculates distilled water or other liquid solutions, such as glycerin water solution, to stimulate blood viscosity, from an input reservoir 15 to an output reservoir 14, according to the specification ofthe experiment.
  • the system 51 further includes a flexible tube 43 immersed in a water bath 44, to compensate for gravitational effects.
  • the flexible tube 43 is made from Latex® and has a length of 120 cm.
  • the flexible tube 43 simulates an artery.
  • the flexible tube 43 is connected to the pulsatile pump 42 and to other system components by Teflon® tubes. All the tubes in system 51 have 4 mm internal diameter.
  • a bypass tube 45 allows flow control in the system and simulates flow partition between blood vessels.
  • a Windkessel® compliance chamber 46 is located proximal to the flexible tube 43 to control the pressure signal characteristics.
  • a Windkessel® compliance chamber 47 and a flow control valve 48 are located distal to flexible tube 43 to simulate the impedance ofthe vascular bed.
  • Fig. 6 is a schematic cross sectional view illustrating a part ofthe fluidics system 51 in detail. Pressure is measured along the flexible tube 43 using a pressure measurement system including MIKRO-TIP pressure catheters 57,58 and 59, model
  • the catheters 57,58 and 59 are inserted into the flexible tube 43 via the connector 10, connected at the end ofthe flexible tube 43.
  • the catheters 57,58 and 59 include pressure sensors 24A, 24B and 24C, respectively, for pressure measurements. It is noted that the number of pressure transducers used varies according to the experiment specifications.
  • the system further included an artificial stenosis made of a tube section 55, inserted within the flexible tube 43.
  • the tube section 55 is made from a piece of
  • the internal diameter 52 (not shown) ofthe artificial stenosis 55 may be varied by using artificial stenosis sections fabricated separately and having various internal diameter.
  • a fluid filled pressure transducer 31 is connected to the system 51 via the end of the guiding catheter 3, inserted into the flexible tube 43 via the connector 9.
  • the fluid filled pressure transducer 31 is connected to the system 51, when additional pressure readings are needed, or in place of an intravascular pressure transducer, according to the defined experiment.
  • the system 51 of Fig. 5 also includes a flowmeter 11 connected distal to the flexible tube
  • the flowmeters 11 and 12 are suitably connected to the A/D converter 28.
  • the flowmeters 11 and 12 are model 1 11 turbine flow meters, commercially available from McMillan Company, TX, U.S.A.. In certain cases, an ultrasonic flowmeter model T206, commercially available from Transonic Systems Inc., NY, U.S.A. was used.
  • the system 41 includes the system 51.
  • the system 41 also includes a signal conditioner 23, such as a model TCB-500 control unit commercially available from Millar Instruments.
  • the signal conditioner 23 is suitably connected to the pressure sensors 24A, 24B .and/or 24C for .amplifying the pressure signals.
  • the system 41 further includes an analog to digital (A D) converter 28 connected to the signal conditioner 23 for receiving the conditioned analog signals therefrom.
  • the system 41 also includes a signal analyzer 20 connected to the A/D converter 28 for receiving the digitized conditioned pressure signals from the A/D converter 28.
  • the signal analyzer 20 includes a computer 25, a display 21 connected to the computer 25 under the control of signal analysis software for displaying text numbers and graphs representing the results ofthe calculations performed by the computer 25.
  • a printer 26 is suitably connected to the computer 25 for providing hard copy ofthe results for documentation and archiving.
  • the computer 25 processes the pressure data which is sensed by the pressure sensors 24A, 24B and 24C and acquired by the A/D converter 28 or the data acquisition card (not shown) and generates textual, numerical and graphic data that is displayed on the display 21.
  • the pressure sensor of the system ofthe present invention may also be inco ⁇ orated into an IVUS catheter system such as IVUS catheter model 82700 available from Endosonics co ⁇ . U.S.A., and connected to a suitable signal analyzer.
  • IVUS catheter model 82700 available from Endosonics co ⁇ . U.S.A.
  • the PWV, the distensibility and the compliance of blood vessel regions may be derived using IVUS geometrical data and FF pressure readings.
  • the IVUS probe is inserted into the vessel of interest through a standard guiding catheter, serving simultaneously the FF pressure measurement system.
  • an IVUS may replace a pressure sensor in each ofthe methods and embodiments presented. For example, in two pressure sensor, located apart application, IVUS replace each ofthe pressure sensors. It then allows to perform both compliance and reflection diagnostics described in this patent together with conventional IVUS tasks (Intravascular lumen and vascular wall imaging).
  • IVF Intravascular flow
  • a flow wave sensor ofthe type suitable for this pu ⁇ ose are the Flowwire catheters manufactured by Endosonics Co ⁇ oration, U.S.A. in which the system uses doppler ultrasound technology to accurately measure arterial blood flow velocity providing functional lesion assessment.
  • Such device provide for measurements suitable for the procedures ofthe present invention as sold commercially or preferably when modified to allow for frequency increases to 200 Hz may replace a pressure sensor in each ofthe methods and embodiments presented.
  • IVF may replace each ofthe pressure sensors. It then allows to perform both compliance and reflection diagnostics described in this patent together with conventional IVF tasks (Intravascular velocity and flow measurements).
  • IVF Intravascular velocity and flow measurements.
  • obtaining compliance and distensibility information about vessels using measurements ofthe PWV provide valuable diagnostic information in an area of medical practice with an increasing number of treatments available to the physician.
  • One ofthe advantages of providing physicians with compliance values of different vessel regions relates to improving of stenting procedures.
  • stenting is performed after pre-dilatation balloon angioplasty. If the compliance ofthe vessel region to be stented is known prior to stenting by using the devices and methods ofthe present invention as disclosed hereinabove, the physician may decide, based on the compliance values, whether a pre-dilatation procedure is required. In cases where the vessel wall compliance is high, this pre-dilatation procedure may be omitted, saving the time and the additional expense involved with the pre-dilatation procedure and decreasing the patient's risk and discomfort.
  • the physician may utilize the vessel characteristics obtained to avoid PTCA failure by identifying failure risks such as enhanced risk of vessel wall dissection in advance, and applying proper decision procedures prior to PTCA for choosing an adequate treatment a priori. It may serve for identifying occult lesions where vessel wall thickness and/or calcification increases, reducing compliance in specific regions. It may also serve, together with geometrical data (e.g. angiography) for the quantification of wall-cell-strains.
  • geometrical data e.g. angiography
  • the system ofthe present invention can also be used for confirming stent deployment. After stent deployment, the compliance and distensibility of the stented vessel region will significantly decrease and the PWV in that region will significantly increase. Thus, the methods and systems ofthe present invention may be used to confirm stent deployment by determining the PWV, the distensibility and the compliance values in the stented region.
  • the system can be adapted for use for characterizing aneurysms in blood vessels for diagnostic pu ⁇ oses.
  • the system can be adapted for characterizing and localizing the aneurysm before, during and after the therapeutic procedure. It may also serve for in process monitoring ofthe aneurysm filling process.
  • Another potential application ofthe multi-point pressure measurement system ofthe present invention is in the diagnostic evaluation ofthe feasibility of insertion of intra-aortic balloon pumps (heart-assist devices). In situations where the relevant vessel wall has low compliance, the use of such intra-aortic pump may be dangerous.
  • the ability ofthe method and system ofthe present invention to provide a value for the compliance ofthe vessel segment makes it useful as a diagnostic method, which can be performed prior to pump insertion procedures. "Mapping" compliance values and providing the physicians with quantitative compliance data enable a better decision on whether pump insertion should be performed.
  • a further potential application ofthe system is in assisting the physician in selecting an appropriate stent.
  • the compliance values determined for a lesioned vessel region by the devices and methods disclosed hereinabove for multi-point pressure measurements can be used for selecting the most appropriate stent that is desirable for deployment in that lesioned region.
  • the proximal measurement was collected using a fluid filled pressure transducer system 31 such as Baxter Model PX272, pressure monitoring kit from Baxter Healthcare Co ⁇ oration, Ca, U.S.A.), connected to the guiding catheter of system 1 via the connector 8, or an intravascular pressure transducer 4 as described hereinabove.
  • a fluid filled pressure transducer system 31 such as Baxter Model PX272, pressure monitoring kit from Baxter Healthcare Co ⁇ oration, Ca, U.S.A.
  • the system uses various methods to derive the pressure wave velocity in a vessel, or in a stenosis or aneurysm area.
  • the methods are based on five main data analysis procedures, which are described hereinbelow. Other data analysis procedures may be developed based on the principles, hereinbelow presented. The choice between procedures depends on the number of measurements performed and number and kind of transducer used.
  • transducer refers to the pressure sensor either alone or in combination with other components to which it is associated, such as the catheter or other fluid filled system.
  • Fig. 9 is a schematic flow chart illustrating the steps ofthe method of calculating the (complex) propagation coefficient g(w) and the pressure wave velocity from pressure data obtained simultaneously and continuously by three separate pressure sensors in accordance with a preferred embodiment ofthe present invention.
  • the distance between the first pressure sensor and the second pressure sensor is ⁇ and the distance between the second pressure sensor .and the third pressure sensor is ⁇ .
  • the system starts by digitizing the pressure signals received from the pressure sensors 4A, 4B and 4C
  • step 62 and transmitted to the computer to yield the digitized pressure signals p j (t), p 2 (t) and p 3 (t).
  • the system computes the Fourier coefficients P j (w), ⁇ 2 (w) and p 3 (w) from the digitized pressure signals p t (t), p 2 (t) and p 3 (t) (step 64).
  • the computation of step 64 can be performed using any suitable FFT program such as Matlab 5.1, The Math Works, Inc., MA, U.S.A.
  • the system then directly computes ⁇ ( ⁇ ) from the equation:
  • the asymptotic value of c( ⁇ ) is already attained for an equivalent Wormersley number of 5. Referring to the in-vivo example given hereinbelow, where a pig carotid was studied (internal diameter of 6-
  • the asymptotic value of PWV is reached at a frequency of around 4 Hz.
  • the reflection coefficient may be determined by dividing Eq. 19 by Eq. 20, yielding:
  • Level fitting procedure involves estimation ofthe time delay between comparable levels ofthe pressure wave in the foot region.
  • a level of L% is defined as follows. Let two pressure sensors be located at x and x+d, giving pressure readings P,(t) and P 2 (t). Then t, is the time at which P,(t) reaches a level of L% if: L
  • Fig. 10 is a schematic flow chart illustrating the steps ofthe method of calculating the PWN from pressure data obtained simultaneously by two pressure sensors, located within a vessel d cm apart, in accordance with a preferred embodiment ofthe present invention.
  • the system After the guiding catheter 3 and the pressure sensors 4a and 4b are positioned within a blood vessel at the place selected for performing a measurement as disclosed hereinabove and illustrated in Fig. 8, the system starts by digitizing the pressure signals received from the pressure sensors (step 70) to yield the digitized pressure signals p,(t) .and p 2 (t). The system then applies pre-conditioning steps to the digitized signals that include linear inte ⁇ olation of the discrete signals. In addition, since the Fourier components ofthe pressure wave above 15 Hz are negligibly small, the measured signals are filtered out by means of a low-pass filter (FIR) at this frequency (step 72), thereby, partially eliminating measurement noise, as well.
  • FIR low-pass filter
  • the system then computes t, and t 2 , the time at which P,(t) .and P 2 (t) reaches a level of L%, respectively (step 74 and 76). If simultaneous pressure measurements with two pressure transducers are acquired, then the PWV may be derived as d/ ⁇ t (step 78), where d is the distance between the transducers and ⁇ t is the time delay between corresponding points on the pressure-time curves as measured by the two transducers (e.g. 10%).
  • i be the index of N successive samples in the foot ofthe same heart beat (that is from onset of systole to, say 80%, of the maximum of the pressure wave P,(t) ) and t ; the corresponding sample times.
  • the optimal overlap criterion reads:
  • FIG. 11 is a schematic flow chart illustrating the steps ofthe method of calculating the PWV from pressure data obtained simultaneously by two pressure sensors, located within a vessel d cm apart, in accordance with a preferred embodiment ofthe present invention.
  • the system starts by digitizing the pressure signals received from the pressure sensors (step 80) to yield the digitized pressure signals p,(t) and p 2 (t). Since the Fourier components ofthe pressure wave above 15 Hz are negligibly small, the system filters out the measured signals by means of a low-pass filter (FIR) at this frequency (step 82).
  • FIR low-pass filter
  • the " .0 low pass filter is preferably embodied in the software, however, an analog hardware version may be useful as well.
  • Procedure 3 Moving pressure measurement- first approach.
  • FF fluid-filled
  • a single, moving, pressure sensor any other device which measures a parameter which is closely correlated with local the pressure at a specific site within the vessel and a single, moving, pressure sensor.
  • the PWV is obtained in two stages: the pressure sensor is first located at a known distance d, from the tip of the FF catheter, denoted point A, and a measurement is taken. The pressure sensor is subsequently moved to a distance d 2 denoted point B, and the measurement is repeated there.
  • both the pressure sensor and the FF catheter curves exhibit a "foot".
  • the foot ofthe fluid-filled catheter curve is, however, in general, different from the one ofthe pressure sensor (function of the FF catheter characteristics: "FF catheter transfer function").
  • the difference is twofold: the shape ofthe foots differ .and, most importantly the foots start at different times, t and t+ ⁇ t.
  • the first and the second measurement yield delays ⁇ t, and ⁇ t 2 , respectively.
  • the PWV is given by the formula:
  • This method uses the FF pressure catheter as a clock, for gating pu ⁇ oses, therefore has the advantage that it eliminates the need of any prior knowledge regarding the catheter characteristics. Also, the distance between the tip ofthe FF catheter and the pressure sensor is irrelevant. The procedure requires the knowledge of one distance - the distance d, between point A .and B.
  • FF catheter instead ofthe FF catheter another type of pressure sensor or flow or a transducer tracking the diameter or crossection changes in time may serve.
  • a transducer tracking the diameter or crossection changes are IVUS catheter available from Endosonics or the guidewire designated "imaging core wire" described in the paper "First experience with imaging core wires"by Di Mario C, Akiyama T, Moussa I, Reimers B, Jang
  • Such an "imaging core wire” may be inco ⁇ orated together with pressure and or doppler flow transducer on the same wire.
  • Fig. 12a is a schematic flow chart illustrating the steps of the method of calculating the PWV from pressure data obtained simultaneously by a FF pressure catheter and one moving pressure sensor, where the FF pressure catheter is in a fixed location and the pressure sensor is measuring in two independent locations (d cm apart), in accordance with a preferred embodiment ofthe present invention.
  • Procedure 4 Moving pressure measurement - second approach.
  • FF fluid-filled
  • PWV Pressure measurement - second approach.
  • the PWV is obtained in two stages: the pressure sensor is first located at a known distance d, from the tip ofthe FF catheter, denoted point A and a measurement is taken. The pressure sensor is subsequently moved to a distance d 2 denoted point B, and the measurement is repeated there.
  • the FF pressure catheter data are used as a clock, therefore avoiding the need of any prior knowledge regarding the catheter characteristics. Also, the distance between the tip ofthe FF catheter and the pressure sensor is irrelevant. The algorithm requires the knowledge of one distance - the distance d, between point A and B.
  • FF catheter instead of the FF catheter, another type of pressure sensor or flow or a transducer tracking the diameter or crossection changes in time may serve, as described hereinabove.
  • the ECG signal is another signal that may serve for gating in this procedure. Indeed its main advantage is that it is a routine and essential measurement in the catheterization lab, independent ofthe presented procedure. This means that a single movable pressure transducer may be used in conjunction with the existing ECG in order to derive the PWV and its derived parameters. This approach is elaborated in Method 5a.
  • Fig. 12b is a schematic flow chart illustrating the steps ofthe method of calculating the PWV from pressure data obtained simultaneously by a FF pressure catheter and one pressure sensor.
  • the FF pressure catheter is in a fixed location and the pressure sensor is measuring in two independent locations (1cm apart), in accordance with a preferred embodiment ofthe present invention.
  • the system After the guiding catheter 3 and the pressure sensor 4a are positioned within a blood vessel at the place selected for performing a measurement as disclosed hereinabove and illustrated in Fig. 13, the system starts by digitizing the pressure signals received from the FF pressure catheter and the sensor (step 100) to yield the digitized pressure signals p,(t) and P (t)- Now the pressure sensor 4a, is moved a distance d, to point B. The system then digitizes the pressure signals received from the FF pressure catheter and the sensor (step 102) to yield the digitized pressure signals p,(t) and p 2 (t). The system then applies the Algorithm
  • the shape ofthe pressure wave changes along the arterial system due to a multiplicity of factors: dispersion ofthe phase velocity, attenuation and reflection at obstacles due to a sudden change of flow impedance such as bifurcations, side branches, reflections from the vascular bed (arterioles and capillars) and occlusions along the path ofthe wave (stenosis).
  • the presence of a stenosis dominates all the other reflecting sites. Even in the absence of stenosis, a pressure wave is always reflected, albeit weakly, because ofthe vascular bed.
  • the present algorithm exploit the reflection ofthe pressure wave and detects the duration ofthe echo using the cepstrum method (Oppenheim and Schafer "Discrete-Time Signal Processing” 1989 Prentice-Hall), a well-established mathematical technique in the field of signal processing.
  • a pressure transducer is inserted at a distance d from a stenosis according to the following experimental setup (the obstacle is a stenosis):
  • ® is the discrete convolution operator; ⁇ is the discrete delta function; g(n) is the response ofthe vessel for a distance of 2-d (to stenosis and back). It is implicitly assumed that g(n) is close to the delta function ⁇ (n); it is also assumed that the energy dissipation along short section of a blood vessel is negligible, that is ⁇ ⁇ g( ⁇ ) ⁇ 1;
  • R is the reflection coefficient
  • m is the integer part of (2-d/C)
  • C is the PWV (pressure wave velocity);
  • Step 2 Separate the regular Reg(n) and the singular Sng(n) component of K(n).
  • PROCEDURE 5a The distance to the obstacle is known.
  • PROCEDURE 5b The distance to the obstacle is not known.
  • the PWV is given by the formula:
  • Three pressure sensors 4a, 4b, 4c are inserted via a standard connector 8 into a standard guiding catheter 3 and located within the blood vessel of interest 30.
  • the distance between pressure sensor 4a and 4b is equal to the distance between pressure sensor 4b and 4c.
  • Simultaneous pressure data is acquired and analyzed. The method is demonstrated in Example 1, an in-vivo study on the carotid of a young pig, described hereinbelow.
  • Two pressure sensors 4a and 4b ,or 4a and 4c or 4b and 4c may be a dual pressure catheter or guidewire, i.e. two pressure sensor model spc-721, catalog no 803509, available from Millar.
  • Three pressure sensors 4a ,4b and 4c may also be inco ⁇ orated on a single catheter or guidewire, i.e. using three pressure transducers adapted in a custom design configuration available from Millar Instruments Inc., Houston TEXAS. Obvious procedure modification may enable unequal distances between the sensors.
  • METHOD NO. 2 FF catheter and two pressure measurements.
  • a FF pressure system 31 connected to a standard guiding catheter 3, and two intravascular pressure sensors 4a and 4b are inserted via a standard connector 8 and located within the vessel of interest 30.
  • the distance between the tip ofthe GC and the sensor 4a is equal to the distance between sensor 4a and sensor 4b.
  • the FF catheter signal is transformed to a signal replacing an actual measurement at the tip ofthe guiding catheter.
  • the pressure wave velocity is derived by using the FF transformed signal as pressure input, one ofthe three expected inputs of Procedure 1 , presented hereinabove.
  • METHOD NO. 3 Two pressure measurements
  • Detection ofthe onset of systole is automatically carried out on a set of data containing multiple beats, yielding the PWV per beat, and its statistical properties (average, standard deviation, etc.). See Example 2 and 3, hereinbelow.
  • the same data set was analyzed using the three pressure procedure, Procedure 1, presented hereinabove, referring to all three pressure measurements within the vessel.
  • Fig. 17d. presents the pressure wave velocity as a function of frequency. The monotonically increasing profile is consistent with the Wormesley theory. Since we are interested in the asymptotic value of this function, the average velocity is computed as an average ofthe data while neglecting the first and last two harmonics.
  • Example 2 In-vivo experiment With reference Fig. 16, in-vivo experiment was performed within the coronaries of a different pig, on the left circumflex of a young (3 months old) pig using two pressure sensors 35 and 36 inserted into the vessel via a standard 8F guiding catheter 38, and positioned 6cm apart.
  • Example 4 In-vitro experiment
  • a FF pressure system 31 a standard guiding catheter 3 and a pressure sensor 4a are inserted into the blood vessel of interest 30.
  • the FF pressure signal is transformed.
  • PWV is derived using Procedure 2 (either 2a or 2b) with the transformed FF signal and the pressure sensor signal.
  • METHOD NO. 5 FF pressure catheter and a single moving pressure sensor
  • a FF pressure system 31 a standard guiding catheter 3 and a single pressure sensor 4a are inserted into the blood vessel of interest 30 and positioned at point A. Data of pressure at point A are obtained. Than, the pressure sensor 4a is moved to B. Data of pressure at point B are obtained
  • Figs. 23a and 23b present the results of Procedure 2.
  • a The level fitting procedure was applied twice, using as input the FF pressure signal and the Radi pressure signal: with Radi pressure sensor located 5 cm and 15 cm from the catheter tip.
  • the pressure curves were filtered by a standard zero-phase 15Hz low-pass filter.
  • FIG. 27 presents the two FF measurements.
  • the optimal coincidence graph is shown in figure 28 for that case.
  • METHOD NO.5 a Single pressure sensor and an electrocardiogram. The method is based on a single pressure sensor .and simultaneous ECG signal, measured at point A and point B, d cm apart within the vessel.
  • the ECG signals e.g. the R wave of a standard lead ECG
  • the time shift is applied to the pressure data.
  • procedure 2 (2a or 2b) is applied to derive PWV and its parameters.
  • PWV ⁇ l ( ⁇ t ⁇ - ⁇ t,).
  • the single pressure may be a FF pressure catheter, a catheter pressure transducer or any type of pressure sensor, flow sensor, diameter or crossection ch.anges sensor, .as described in procedure 3 hereinabove.
  • a FF pressure system 31 a standard guiding catheter 3 and a single velocity(or flow ) sensor 5a , i.e Flo Wire doppler flow guidewire , catalog number 1400 available from Cardiometrics, an Endosonics co ⁇ oration, are inserted into the blood vessel of interest 30 and positioned at point A. Data of FF pressure simultaneously is measured with flow at point A are acquired. Then, the flow sensor 5a is moved to point B. Data of FF pressure .are simultaneously acquired with flow at point B. The PWV is derived by applying the principle of Procedure 3 to flow data acquired by a moving flow sensor, gated to the FF pressure catheter data.
  • Another type of pressure transer may replace FF pressure measurement, i.e. wavewire pressure guidewire catalog number 8400 available from Radi Medical systems, Upsala, Sweden or pressure sensor catheter model SPC-320 (catalog number 800-0509) available from Millar, Texas
  • any other device which measures a parameter which is closely correlated with pressure at a specific site within the vessel may take the gating role ⁇ lacing the FF pressure catheter.
  • it may be an Intravascular flow sensor or an IVUS.
  • the ECG signal is another signal that may serve for gating. Not only it is a convenient signal, but it is also a standard and essential clinically significant measurement.
  • Flow and pressure transducers may also be inco ⁇ orated within the same catheter or guidewire, i.e. model SPVC-663A catalog number 810-1029 available also from Millar.
  • Figs. 32a illustrates a typical ultrasonic flowmeter raw data of one stroke.
  • Fig. 32b illustrates a simultaneous pressure data.
  • Pressure sensor 4 is inserted via a standard connector 8 into a standard guiding catheter 3 and located within the blood vessel of interest 30, proximal to a stenosis 31.
  • the PWV is calculated using a single pressure sensor and a single measurement as described in procedure 5a. The method is demonstrated in Example 7.
  • FIG. 36 in-vivo experiment was performed on a pig carotid using a single pressure sensor 36, inserted into the vessel via a standard 8F guiding catheter 38.
  • the pressure sensor 36 was located 5 cm proximal to an externally induced occlusion 37.
  • the pressure raw data, presented in Fig. 37, was analyzed using procedure 5a. The results are presented in Figs. 38 and 39.
  • Fig. 36 in-vivo experiment was performed on a pig carotid using a single pressure sensor 36, inserted into a vessel via a standard 8F guiding catheter 38.
  • the pressure sensor 36 was first located 7.5 cm (point a) and then 5 cm (point b, not shown) proximal to an externally induced occlusion 37.
  • the relevant pressure raw data are presented in Fig. 37 and 41.
  • the data was analyzed using procedure 5b.
  • this value relates to a stenosis of about 85%, in accordance to the level of stenosis applied in the study.
  • the small decrease in the reflection coefficient value probably relates to the wave attenuation, as the distance to the stenosis is higher.

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Abstract

L'invention concerne des dispositifs et des procédés pour déterminer les propriétés de parois tubulaires en vue d'effectuer un diagnostic clinique et un traitement améliorés. De façon avantageuse, on enregistre les caractéristiques de parois tubulaires qui correspondent à la capacité de dilatation et à l'élasticité des parois tubulaires. De manière plus spécifique, l'invention concerne un procédé de détermination quantitative de la vitesse de propagation d'une onde de pression dans des vaisseaux sanguins, caractérisant ainsi, entre autres, le module de Young, la capacité de dilatation, l'élasticité et le facteur de réflexion d'anévrismes, de parties de vaisseaux sanguins avec et sans lésion. Les propriétés déterminées peuvent en outre être utilisées pour évaluer le degré de calcification de parties de vaisseaux sanguins avec et sans lésion. Les valeurs déterminées peuvent être calculées et rapportées en chiffres absolus sous forme de rapport entre la valeur de paramètre approprié dans la région avec lésion et la valeur de paramètre dans une région sans lésion, du même patient. En variante, le système permet de calculer et d'établir un rapport entre le paramètre approprié déterminé dans la région avec lésion, du patient, et une valeur moyenne standard du paramètre approprié, mesurée dans un groupe de personnes saines présentent une physiologie similaire (groupe d'âges, sexe, type de vaisseau, etc.). Ces valeurs servent à déterminer la méthode de traitement optimale sur le plan médical et économique, ou la combinaison optimale de ces méthodes, et à évaluer l'efficacité et le succès du traitement choisi, pendant la procédure et au fil du temps. Ces méthodes permettent de mesurer les modifications physiologiques, par ex. fonctionnelles, dans la paroi artérielle, et d'atteindre un niveau de traitement inconnu jusqu'à présent en médecine clinique.
PCT/IL1999/000019 1998-01-12 1999-01-12 Systeme et procede pour caracteriser des lesions et des parois de vaisseaux sanguins au moyen de mesures de pression en plusieurs points WO1999034724A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU17816/99A AU1781699A (en) 1998-01-12 1999-01-12 A system and method for characterizing lesions and blood vessel walls using multi-point pressure measurements

Applications Claiming Priority (4)

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US7125598P 1998-01-12 1998-01-12
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