WO2024263655A2 - Initialization methods for blood pressure measurement - Google Patents

Abstract

A method for measuring blood pressure includes placing a body part on the biometric monitoring device such it covers a photoemitter, a photoreceptor and a pressure sensor; applying light with the photoemitter at an initial intensity; and outputting a signal from the photoreceptor at an initial gain. Increased pressure is applied to the biometric monitoring device until a target pressure is reached, upon which an initial PPG signal is obtained from the photoreceptor and determined to be inadequate. The intensity of the light emitted by the photoemitter and the gain of the photoreceptor are both adjusted, and an adjusted PPG signal is obtained. After it is determined that the adjusted PPG signal is adequate, the initialization routine is terminated, and the adjusted intensity and adjusted gain are used to obtain a blood pressure measurement with the biometric monitoring device.

Description

INITIALIZATION METHODS FOR BLOOD PRESSURE MEASUREMENT

RELATED APPLICATIONS

[001] This application claims the benefit of United States Provisional Patent

Application Serial No. 63/521,843 filed June 19, 2023 and entitled, “Initialization Methods for Blood Pressure Measurement,” the disclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

[002] This invention generally relates to measuring blood pressure and, more particularly, but not by way of limitation, to methods for improving the quality of the biosignals for a blood pressure measurement.

BACKGROUND OF THE INVENTION

[003] There is a growing recognition of the importance of enabling people to take greater control of their health. Notwithstanding this growth of emphasis on personal health management, there is a shortage of biometric measurement devices that are accurate, affordable, easy to use, and readily available to the public. Integrating the functionality for biometric measurement and monitoring into a portable and widely available product, such as a key fob or cellphone, would greatly enhance the ability of people to manage their health.

[004] Blood pressure, for example, is a fundamental diagnostic parameter that is used throughout the world to assess health. The basic measurements for this vital sign are diastolic blood pressure, the lowest pressure observed during the pulse cycle, and systolic blood pressure, the highest pressure observed during the pulse cycle. At least three methods have been established for measuring absolute arterial blood pressure without inserting a measurement device into the artery: auscultatory, oscillometric and volume clamp methods. There are also relative measurement methods that detect changes or trends in blood pressure, but these methods require calibration for each user.

[005] With reference to traditional oscillometric methods for blood pressure measurement, automatic sphygmomanometers such as an inflatable cuff are often used to occlude blood flow in an artery, usually the brachial or radial (wrist) artery. The cuff is then more slowly deflated to allow blood to begin to flow again. During deflation, the flow is detected by observing small pressure fluctuations introduced into the cuff by the pulse.

[006] To enhance user functionality, alternatives to the traditional cuff have been developed to determine blood pressure by measuring photoplethysmography (PPG) signals from a body part (e.g., a finger) until arterial occlusion is achieved. These alternative devices differ from automatic blood pressure cuffs, which rely on Korotkoff sounds rather than PPG signals to estimate blood pressure. In most PPG-based measuring systems, one or more light emitting diodes (LEDs) or other photoemitters emit light into a vascular structure while one or more photoreceptors (e.g., photodiodes) measure the reflective or transmissive light produced by the photoemitter. To successfully estimate blood pressure using a PPG approach, it is crucial to obtain a high-quality PPG signal from the user. The user’s pulse can be evaluated by measuring the alternating current (AC) signal attributable to the cyclical pulse, while limiting the impact of the less-cyclical direct current (DC) signal attributable to baseline blood flow and tissues within the target vascular structure.

[007] Unfortunately, for people suffering from chronic circulatory diseases or experiencing low perfusion, it is difficult to obtain reliable PPG signals. For example, if the user is experiencing low perfusion due to environmental or psychological factors, such as ambient temperature or stress, each of these limitations may negatively affect the quality of the PPG signals obtained and thereby reduce the accuracy of the blood pressure measurement.

[008] Some devices attempt to maintain a high-quality PPG signal by actively monitoring and adjusting the measurement conditions. For example, some devices actively adjust the brightness of LEDs during a PPG measurement in response to the signal levels obtained. Within the context of blood pressure measurement, these active adjustments have several drawbacks that make the methods not suitable. For example, changing LED brightness in the middle of a blood pressure measurement introduces unwanted variables into the data that is ultimately used to calculate blood pressure. Although calculations may be made to account for these adjustments, non-idealities will be inherent in the circuit, and it may not be possible to accurately recapture the features of the original PPG signal.

[009] A need exists, therefore, for systems and methods for improving the quality of the biosignals, such as PPG signals, obtained from a user to more accurately estimate blood pressure.

SUMMARY OF THE INVENTION

[0010] In some embodiments, a method for measuring blood pressure is disclosed. The method may include the steps of obtaining a biometric monitoring device with a photoemitter, a photoreceptor and a pressure sensor; placing a body part on the biometric monitoring device, such that the body part covers the photoemitter, the photoreceptor, and the pressure sensor; and outputting a signal from the photoreceptor at an initial gain. Increased pressure is applied by the body part to the biometric monitoring device until a target pressure is reached, upon which an initial PPG signal is obtained from the photoreceptor and determined to be inadequate. The intensity of the light emitted by the photoemitter and the gain of the photoreceptor are both adjusted, and an adjusted PPG signal is obtained from the photoreceptor. After it is determined that the adjusted PPG signal is adequate, the initialization routine is terminated, and the adjusted intensity and adjusted gain are used to obtain a blood pressure measurement with the biometric monitoring device.

BRIEF DESCRIPTION OF THE DRAWINGS

[OOH] FIG. 1 depicts a PPG-based biometric monitoring device configured for engagement by a finger.

[0012] FIG. 2 is a process flow diagram for an optimized method for initializing the

PPG-based biometric monitoring device of FIG. 1. DETAILED DESCRIPTION

[0013] It has been discovered that adjusting brightness and gain prior to a blood pressure measurement can significantly improve the quality of an optical signal, such as a PPG signal, across a broad pressure range. Ideally, brightness and gain are adjusted so that a high- quality PPG signal may be obtained without saturating the photoreceptor electronics involved in obtaining the blood pressure measurement based on the optical signal. More specifically, it is desirable to maximize the cardiac (pulsative) component of the PPG signal (AC) while avoiding saturating electronics due to a high baseline PPG signal (DC). Sufficiently high AC PPG signal may be obtained, for example, by adjusting LED brightness and electronic circuit gain together to optimize both prior to a blood pressure measurement.

[0014] Turning to FIG. 1, shown therein is a biometric monitoring device 100, which is well-suited for measuring blood pressure, pulse, blood oxygenation, or other biometrics. The biometric monitoring device 100 includes a body 102 and a finger trough 104 configured to locate the user’s fingertip onto the biometric monitoring device 100. The biometric monitoring device 100 further includes one or more photoemitters 106, one or more photoreceptors 108 and one or more control circuits 110 which is electrically connected to the photoemitters 106 and photoreceptors 108. The photoemitters 106, photoreceptors 108 and control circuits 110 together present a PPG module 112. The biometric monitoring device 100 may also include a pressure sensor 114 configured to measure the force applied by the fingertip to the biometric monitoring device 100. The pressure sensor 112 is also connected to the control circuits 110. Although the biometric monitoring device 100 in FIG. 1 is designed for use with the user’s fingertip, it will be appreciated that the biometric monitoring device 100 can also be configured for use with other vascular body parts, including toes, wrists, ears, arm, and neck.

[0015] In exemplary embodiments, the photoemitters 106 are light emitting diodes (LEDs) configured to output light (e.g., green, red, infrared) at a selected and controllable intensity (amplitude) based on a command signal from the control circuits 110. In the same exemplary embodiments, the photoreceptors 108 are photodiodes configured to output a voltage signal to the control circuits 110 in response to the detection of light. The strength of the signal produced by the photoreceptors 108 can be tuned or adjusted to increase or decrease the sensitivity and output of the photoreceptors 108. Although the control circuits 110, photoemitters 106 and photoreceptors 108 are depicted as separate, interconnected components in FIG. 1, it will be appreciated that these components can also be presented on a common circuit board with integrated connectivity.

[0016] Turning to FIG. 2, shown therein is a method 200 for initializing the PPG module 112 in connection with a blood pressure measurement process. The same initialization method 200 can be adapted for use with other biometric measurements, including pulse rate and blood oxygenation (pulse-ox). The method 200 can be carried out as a computer- implemented routine by the control circuits 110 or other onboard or remote processor connected to the biometric monitoring device 100.

[0017] The method begins at step 202 by placing the user’s body part (e.g., fingertip) on the biometric monitoring device 100 in a position in which the vascular structures of the body part (including brachial arteries) are positioned over the PPG module 1 12 such that light emitted by the photoemitters 106 is reflected by the vascular structures and returned to the photoreceptors 108. Next, at step 204, the PPG module 112 is activated such that the photoemitters 106 are set to emit light at an initial intensity and the gain of the photoreceptors 108 is set to an initial output level. The PPG module 1 12 can be configured to automatically activate once the photoreceptors 108 begin to detect light or when contact is initially detected by the pressure sensor 114.

[0018] At step 206, the body part is pressed into the biometric monitoring device 100 with increasing force until an initial pressure target is measured by the pressure sensor 114. The pressure target may include, for example, pressures between about 70 mmHg to about 110 mmHg. The pressure target may also be in a narrower range between about 80 mmHg to about 100 mmHg. In a non-limiting example, the pressure target may be about 90 mmHg. At that level of force, the pulsative (AC) features of the PPG signal should be apparent for most users and a baseline optical signal (e.g., a baseline PPG level) will be produced by the PPG module 112.

[0019] Once the pressure target has been met, the PPG module 112 can be adjusted such that the photoemitters 106 emit light at an adjusted intensity and the photoreceptors 108 output PPG signals at an adjusted sensitivity. With these adjusted settings, an initial PPG signal is acquired at step 208.

[0020] At step 210, the method 200 queries whether the PPG signal produced by the photoreceptors 108 is adequate. The adequacy of the PPG signal can be quantitatively or qualitatively determined, but the adequacy standard is intended to provide a PPG signal in which the cardiac component of the PPG signal (AC) is maximized without saturating the photoreceptors 108 and control circuits 110 with high baseline PPG signal (DC). It is important to maximize the pulsative (AC) portion of the PPG signal because this portion of the signal provides the primary diagnostic benefits.

[0021] If the PPG signal is determined to be adequate at step 210, the method 200 moves to step 218 and the biometric monitoring device 100 terminates the initialization process and begins to obtain PPG measurements with the photoemitters 106 and photoreceptors 108 operating with the current intensity and sensitivity, respectively. If, however, the PPG signal is determined to be inadequate at step 210, the method 200 moves to step 212, where the photoemitters 106 are adjusted to increase or decrease the intensity of the light emitted by the photoemitters 106. At step 214, the photoreceptors 108 are adjusted to increase or decrease the sensitivity or output of the signals output by the photoreceptors 108, which may include increasing or decreasing the gain of the photoreceptors 108. Steps 212 and 214 may take place simultaneously or with step 214 occurring before step 212.

[0022] At step 216, a new PPG signal is obtained using the adjusted output from the PPG module 112. The process returns to step 210, where the adequacy of the PPG signal is once again evaluated. If the PPG signal is determined to be adequate the initialization process is terminated and the PPG module 112 obtains live measurements at step 218 that can be processed for diagnostic purposes. If the PPG signal is determined to be inadequate at step 210, the process iterates through steps 212-216 until the adjustments made to both the photoemitters 106 and the photoreceptors 108 provide an adequate PPG signal at step 210. In some embodiments, the method 200 can include a timeout feature to terminate the initialization method 200 if an adequate PPG signal is not achieved over a preset period of time (e.g., 20 seconds).

[0023] In certain embodiments, the method 200 is carried out separately for individual photoemitters 106 and photoreceptors 108 in a biometric monitoring device 100 that includes multiple photoemitters 106 and photoreceptors 108. For example, in a biometric monitoring device 100 that includes three different photoemitters 106 (e.g., green, red, and infrared LEDs), the above initialization process 200 may be used to separately determine the optimal brightness for each variant of the photoemitters 106 (e.g., green, red or infrared) and the optimal gain for each variant of the photoreceptors 108 (e.g., green, red or infrared), and then repeat the process for the remaining variants of the photoemitters 106 and photodetectors 108. Where the initialization method 200 is repeated for different photoemitters 106 and photoreceptors 108, the initial pressure and the pressure target for each round of the initialization process may be the same as in previous rounds or different. Alternatively, a single round of the initialization process may be used to optimize the optimal brightness and optimal gain for all photoemitters in the biometric monitoring device at the same time. [0024] In the foregoing specification, the invention has been described with reference to specific embodiments thereof. However, it will be evident that various modifications and changes can be made thereto without departing from the broader scope of the invention as set forth in the appended claims. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, different photoemitters, initial pressures, pressure targets, biometric monitoring devices, optical sensors, and electronic circuits not specifically identified or described in this disclosure or not evaluated in a particular embodiment are still expected to be within the scope of this invention.

[0025] The present invention may suitably comprise, consist of, or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “about” in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Claims

It is claimed:

1. A method for measuring blood pressure with a biometric monitoring device that includes a photoemitter, a photoreceptor and a pressure sensor, the method comprising the steps of: placing a body part on the biometric monitoring device such that the body part is covering the photoemitter, the photoreceptor and the pressure sensor; applying light with the photoemitter at an initial intensity; outputting a signal from the photoreceptor at an initial gain; increasing the pressure applied by the body part to the biometric monitoring device until a target pressure is reached; obtaining an initial PPG signal from the photoreceptor; determining that the initial PPG signal is inadequate; adjusting the intensity of the light emitted by the photoemitter; adjusting the gain of the photoreceptor; obtaining an adjusted PPG signal from the photoreceptor; determining that the adjusted PPG signal is adequate; terminating the initialization routine; and using the adjusted intensity and adjusted gain to obtain a blood pressure measurement with the biometric monitoring device.