WO2020176207A1

WO2020176207A1 - Finger cuff device with non-volume clamp plethsmography method for continuous non-invasive blood pressure measurement

Info

Publication number: WO2020176207A1
Application number: PCT/US2020/016850
Authority: WO
Inventors: Andrew Victor BARAJAS; Ernest William HEFLIN
Original assignee: Edwards Lifesciences Corporation
Priority date: 2019-02-25
Filing date: 2020-02-05
Publication date: 2020-09-03

Abstract

Disclosed is a finger cuff that includes: an optical source and sensor pair to perform measurements of a plethysmography signal from an artery of the finger; a bladder to apply an equal constant pressure to the finger; and a pressure sensor connected to the bladder used to measure the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger. The finger cuff device further includes a processor connected to the optical source and sensor pair and to the pressure sensor that is used to extract the patient's arterial blood pressure waveform signal from the plethysmography signal, the patient's arterial blood pressure waveform signal being extracted from the plethysmography signal based upon an equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger as measured by the pressure sensor.

Description

FINGER CUFF DEVICE WITH NON- VOLUME CLAMP PLETHSMOGRAPHY METHOD FOR CONTINUOUS NON-INVASIVE BLOOD PRESSURE

MEASUREMENT

BACKGROUND

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62/809,904 filed February 25th, 2019, which is incorporated by reference herein in its entirety.

Field

[0002] Embodiments of the invention relate generally to non-invasive blood pressure measurement. More particularly, embodiments of the invention relate to a finger cuff device to be used in measuring the patient’s blood pressure information.

Relevant Background

[0003] Absolute non-invasive blood pressure measurements are typically performed using external cuffs that apply pressure to one or more arteries and the response of the arteries is observed to determine the blood pressure. Auscultatory and oscillometric blood pressure cuffs use this technique to obtain discrete (non-continuous) blood pressure (BP) measurements. The volume clamp with a finger cuff uses related techniques to obtain continuous BP measurements.

[0004] Much work is being done to develop“cuff-less” BP measurement techniques that do not require applying an external force to the arteries or require very low forces. Pulse wave analysis (PWA) techniques that obtain an arterial“pulsatility” waveform, extract amplitude and timing features, and track changes in those features over time that correlate with changes in BP over time are a successful class of cuff-less BP measurements - but they are unable to obtain absolute BP values from which to track changes. Examples of PWA techniques include CSEM photoplethysmography techniques.

[0005] Non-invasive blood pressure measurements typically fall into two categories: a discrete but absolute blood pressure measurement, such as, a brachial cuff measurement performed by the auscultatory or oscillometric methods, and, tracking of relative changes in blood pressure values, such as the techniques by CSEM. Known methods of performing absolute blood pressure measurements on a patient require the application of pressure to some part of the patient’s body, such as the upper arm and/or finger, in a way that at least partially occludes blood flow. The occlusion of blood flow requires there to be times when pressure is not applied in order to allow blood to flow to tissues under and downstream from the occlusion location.

[0006] One example of non-invasively measuring blood pressure is utilizing a finger cuff with the volume clamping technique in which pressure is applied to a patient’s finger in such a manner that arterial pressure may be balanced by a time varying pressure to maintain a constant arterial volume. In a properly fitted and calibrated system, the applied time varying pressure is equal to the arterial blood pressure in the finger. The applied time varying pressure may be measured to provide a reading of the patient’s arterial blood pressure.

[0007] This may be accomplished by a finger cuff that is arranged or wrapped around a finger of a patient. The finger cuff may include an infrared light source, an infrared sensor, and an inflatable bladder. The infrared light may be sent through the finger in which a finger artery is present. The infrared sensor picks up the infrared light and the amount of infrared light registered by the sensor may be inversely proportional to the artery diameter and indicative of the pressure in the artery. Therefore, the finger cuff provides optical signals and an optical system.

[0008] In the finger cuff implementation, by inflating the bladder in the finger cuff, a pressure is exerted on the finger artery. If the pressure is high enough, it will compress the artery and the amount of light registered by the sensor will increase. The amount of pressure necessary in the inflatable bladder to compress the artery is dependent on the blood pressure. By controlling the pressure of the inflatable bladder such that the diameter of the finger artery is kept constant, the blood pressure may be monitored in very precise detail as the pressure in the inflatable bladder is directly linked to the blood pressure. In a typical present-day finger cuff implementation, a volume clamp system is used with the finger cuff. The volume clamp system typically includes a pressure generating system and a regulating system that includes: a pump, a valve, and a pressure sensor in a closed loop feedback system that is used in the measurement of the arterial volume. To accurately measure blood pressure, the feedback loop provides sufficient pressure generating and releasing capabilities to match the pressure oscillations of the patient’s blood pressure.

[0009] The current issues that have to do with non-invasive blood pressure measurement devices out on the market today have to deal with accuracy, and the

restrictiveness of the design of how these systems are often implemented. [0010] Currently, even with the most advanced continuous non-invasive devices that are currently on the market, they still rely on the method of volume clamping which is the method of continuous measuring blood pressure through the pressurization of the finger.

Even though volume clamping allows for accurate measurement and tracking of blood pressure through the finger using plethysmography, there is a large period, where even this method, can become extremely inaccurate due to the volume clamping process. Also, the act of volume clamping can affect the measurement itself artificially, putting it at risk of being inaccurate from the beginning due to certain patient populations and instances. This type of measurement is also very sensitive to movement making it difficult for this type of continuous blood pressure monitoring to move out of the OR/Critical Care sector of healthcare. Volume clamping also requires hardware and implementation that causes complications in the manufacturing and everyday use of those types of products (e.g., specially designed pressure measurement instrumentation circuits, sensors, highly controlled and accurate pump mechanisms, expensive material costs, etc.).

[0011] Further, other methods of continuous non-invasive blood pressure

measurement are simply inaccurate or too discrete for much health value in comparison to measurements that use volume clamping. And even though these methods may be used outside of the OR/Critical Care sector, these methods are not as accurate as the volume clamp method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a diagram of an example of a finger cuff device according to an optional example.

[0013] FIG. 2 is a block diagram of a portion of the finger cuff device shown in FIG. 1, according to an optional example.

[0014] FIG. 3 is a flow diagram of a process of measuring blood pressure according to an optional example.

DETAILED DESCRIPTION

[0015] Various optional examples are related to the principles of plethysmography (also known as“plethysmography”) measurement and performing the plethysmography measurement at the finger with a finger cuff and finger cuff techniques. The arterial waveform signal (e.g.,“the arterial blood pressure waveform signal”) itself is extracted from the plethysmography signal based on the relationship between blood flow in the finger and arterial blood pressure in the finger. As they are inversely related, by allowing the plethysmography signal to oscillate, the arterial waveform signal itself may be captured. Digital signal processing (DSP) may then be used to filter out artifacts such as respiration and high frequency noise to allow for a clean arterial waveform signal.

[0016] In one optional example, a specially designed finger cuff may be utilized to achieve this with a bladder to apply equal and constant pressure to the finger. In particular, instead of a bladder filled with air by a pump utilized in conventional finger cuffs, the bladder may be filled with an incompressible fluid (e.g., saline, medical grade hydraulic fluid, etc.). With the incompressible fluid applying an equal amount of constant pressure across the finger, the finger itself becomes a constant rigid form allowing the natural signal of the artery to penetrate the finger and into the bladder. These pressure changes may be picked up by a pressure sensor, such as, a strain gauge, that is attached to the bladder, allowing these pressure variations to be picked up by the strain gauge sensor. These pressure fluctuations will be used as a reference for the plethysmography signal and ultimately for the resulting pressure signal translated itself.

[0017] In one optional example, with the arterial waveform signal extracted, the pressure references measured by the strain gauge can be used to interpolate a translation of blood flow to pressure algorithm based on plasticity of the patient. This would be initially done by taking readings with the finger cuff applying zero pressure, and then taking readings with the cuff cam on at maximum to the patient’s finger. The result will be a deformity of the patient’s plethysmography signal according to pressure allowing for references to be used for interpolation as well as for future pressure changes made by the strain gauge.

[0018] In one optional example, disclosed is a finger cuff device to measure a patient’s blood pressure from a finger of the patient, the finger cuff device including a finger cuff. The finger cuff includes: a cavity to receive the finger, the finger cuff to extend around the finger; an optical source and an optical sensor to form an optical source and sensor pair to perform measurements of a plethysmography signal from an artery of the finger; a bladder to apply an equal constant pressure to the finger; and a pressure sensor connected to the bladder. The pressure sensor is used to measure the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger. In one optional example, the finger cuff device further includes a processor connected to the optical source and sensor pair and to the pressure sensor. The processor is used to extract the patient’s arterial blood pressure waveform signal from the plethysmography signal, the patient’s arterial blood pressure waveform signal being extracted from the plethysmography signal based upon an equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger as measured by the pressure sensor (e.g., the strain gauge). As has been described, in one optional example, the strain gauge may measure pressure fluctuations that will be used as a reference for the plethysmography signal and ultimately for the resulting pressure signal translated itself utilizing the equation or algorithm.

[0019] As one example, with reference to FIG. 1, which illustrates an optional example of a finger cuff device 102, finger cuff device 102 includes a finger cuff 104 that may be attached to a patient’s finger and a processor 108, in which processor 108 may be attached to the patient’s body (e.g., a patient’s wrist or hand) as shown, as part of a suitable housing. Processor 108 may be attached on the patient’s hand or wrist with an attachment bracelet or band 106 that wraps around the patient’s wrist or hand. Attachment bracelet 106 may be metal, plastic, Velcro, etc. Cable 114 couples finger cuff 104 to processor 108. In other optional examples, processor 108 may be included in the finger cuff 104, itself, such that, only one integrated device is attached to the patient’ s finger.

[0020] Continuing with this optional example, as shown in FIG. 1, a patient’s hand may be placed on the face 110 of an arm rest 112 for measuring a patient’s blood pressure with processor 108. Processor 108 may be coupled to a patient monitoring device (not shown) through a power/data cable (not shown) or may be wirelessly connected to the patient monitoring device (e.g., without a cable). The patient monitoring device may be any type of medical electronic device that may read, collect, process, display, etc., physiological readings/data of a patient including blood pressure, as well as any other suitable physiological patient readings. Accordingly, data may be transmitted (wired or wirelessly) to and from the patient monitoring device and processor 108 of the finger cuff.

[0021] With reference to Figures 1 and 2, as one optional example, a finger cuff device 102 to measure a patient’ s blood pressure from a finger of the patient includes a finger cuff 104 and, in some optional examples, a processor 108. Finger cuff 104 includes a cavity to receive the finger, the finger cuff to extend around the finger. Further, finger cuff 104 includes: an optical source and an optical sensor to form an optical source and sensor pair 202 to perform measurements of a plethysmography signal from an artery of the finger; a bladder 206 to apply an equal constant pressure to the finger; and a pressure sensor 204 connected or attached to bladder 206, in which, pressure sensor 204 is used to measure the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger. Additionally, in one optional example, finger cuff device 102 includes processor 108 (and/or appropriate electronics, control circuitry, etc.) connected to optical source and sensor pair 202 and to pressure sensor 204, in which, processor 108 is used to extract the patient’s arterial blood pressure waveform signal from the plethysmography signal, the patient’s arterial blood pressure waveform signal being extracted from the plethysmography signal based upon an equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger as measured by the pressure sensor 204 (e.g., as one optional example, a strain gauge). However, any type of pressure sensor (e.g., electronic, strain gauge, mechanical, magnetic, optical, combinations thereof, etc.) may be used.

[0022] As one optional example, the arterial blood pressure waveform signal itself is extracted from the plethysmography signal based on the relationship between blood flow in the finger and the arterial blood pressure in the finger. As they are inversely related, by allowing the plethysmography signal to oscillate, the arterial blood pressure waveform signal itself may be captured. Suitable digital signal processing (DSP) techniques may then be used to filter out artifacts such as respiration and high frequency noise to allow for a clean arterial blood pressure waveform signal. In one optional example, optical source and optical sensor pair 202 includes a light emitting diode (LED) and photodiode (PD) (LED-PD) pair that may be used to obtain the plethysmography signal. However, it should be appreciated that utilizing an optical source and sensor pair is only an optional example of acquiring a plethysmography signal from an artery of the finger and that other devices and processes may be used.

[0023] As shown in FIG. 2, in one optional example, bladder 206 includes an incompressible fluid (e.g., saline, medical grade hydraulic fluid, etc.) such that the

incompressible fluid filled bladder 206 is to apply an equal amount of constant pressure across the finger, such that the finger becomes a constant rigid form allowing a natural signal of the artery to penetrate the finger into the bladder to be measured by the pressure sensor. Any suitable incompressible fluid may be used in bladder 206.

[0024] As seen as an example, in FIG. 1, the patient’s finger with finger cuff 104, as well as their hand and arm, may be placed on the surface 110 of a table 112. Alternatively, the person may wear the finger cuff 104 anywhere and it does not have to be on a table.

Also, the processor 108 or other circuitry may be connected to the finger cuff by tube or cable 114 that is connected by a band around the person’s wrist (as part of finger cuff device 102). As another optional example, all of the electronic components (e.g., including processor 108) may present in the finger cuff 104, as an integrated device, to perform the functions.

Similarly, finger cuff 104 and/or processor 108 may be connected (wirelessly/or by wire) to a display monitoring device (not shown) to show the patient’s blood pressure and/or other physiological measurements. Further, in some optional examples, a processor is not utilized for blood pressure measurement and only the pressure sensor is utilized for blood pressure measurement.

[0025] Continuing with FIG. 2, as one optional example, pressure sensor 204 may include a strain gauge sensor coupled to incompressible fluid filled bladder 206 allowing pressure variations of the bladder from the artery to be measured by the strain gauge sensor, such that, pressure fluctuations are used in the equation relating the plethysmography signal to the blood flow in the finger and arterial blood pressure of the finger in extracting the patient’s arterial blood pressure waveform signal from the plethysmography signal. It should be appreciated that the use a processor is an optional example and that in some optional examples the finger cuff device 104 only includes the bladder 206 that contains a fluid to apply a constant pressure to the patient’s finger and the pressure sensor 206, in which, the pressure sensor is used to measure the pressure applied to the bladder by the patient’s artery to measure the arterial blood pressure of the finger. In this case, only the pressure sensor (alone or in combination with other devices) is used for blood pressure measurement and a processor is not utilized.

[0026] In one optional example, the plasticity of the patient’s finger is utilized in the equation relating the plethysmography signal to the blood flow in the finger and arterial blood pressure of the finger by taking reference readings of the finger cuff at an applied zero pressure reading, intermediate pressure readings, and a maximum pressure reading, such that the patient’s plethysmography signal in relation to pressure accounting for the plasticity of the finger is included. This is a method of calibration for the algorithm that may be actively performed on every patient before measurement. Interpolation may be used to generate algorithm constants to help scew the patient population curve that best fits interpolation from resulting calibration. In one optional example, the patient’s blood pressure measurement values from the patient’s arterial blood pressure waveform signal includes systolic pressure, mean arterial pressure (MAP), and diastolic pressure.

[0027] With reference to FIG. 3, a flow diagram 300 of a process, according to one optional example, for measuring a blood pressure of a patient includes receiving a finger of the patient in a cavity of a finger cuff at 302, performing, by an optical source and sensor pair, measurements of a plethysmography signal from an artery of the finger at 304, applying, by a bladder, an equal constant pressure to the finger at 306, measuring, by a pressure sensor, the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger at 308, and extracting, by a processor, the patient’s arterial blood pressure waveform signal from the plethysmography signal, the patient’s arterial blood pressure waveform signal being extracted from the plethysmography signal based upon an equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger as measured by the pressure sensor at 310.

[0028] With this technique that uses plethysmography readings to extract the arterial blood pressure waveform signal, this technique allows for more accurate continuous arterial blood pressure measurement because active pressure translation with a pump is no longer required. With no physical pressure translation needed for the measurement, the

fundamentals of the continuous blood pressure measurement are changed in a way that there is no longer a risk of actively artificially altering the measurement from the beginning as may happen with previous volume clamping techniques.

[0029] Further, by utilizing this technique with the method of extracting arterial blood pressure measurement, the measurement is greatly simplified, no longer requiring additional complicated circuitry, sensors, or mechanics required for previous volume clamping techniques, while still maintaining the same amount of accuracy. Only circuit implementation to perform the plethysmography measurement as well as static mechanical elements are needed. This simplification also allows the device to work outside of the OR/Critical Care sector of healthcare so that it may be used in other health spaces that would benefit from continuous blood pressure measurement. Spaces that in the past have been closed to finger volume clamp devices due to the environment may now be open. Lastly, with the

measurement simplified using this technique along with moving into new spaces, the finger cuff device may be used with wireless capabilities and particularly designed virtual applications.

[0030] It should be appreciated that FIG. 2 illustrates a non-limiting example of a processor implementation to implement the previously described functions. As an example, a processor may comprise a processing unit, a memory, and an input/output connected with a bus. Under the control of the processing unit, data may be received from an external source through the input/output interface and stored in the memory, and/or may be transmitted from the memory to an external destination through the input/output interface. The processing unit may process, add, remove, change, or otherwise manipulate data stored in the memory.

Further, code may be stored in the memory. The code, when executed by the processing unit, may cause the processor to perform operations relating to data manipulation and/or transmission and/or any other possible operations.

[0031] It should be appreciated that aspects of the invention previously described may be implemented in conjunction with the execution of instructions by processors, control circuitry, circuitry, controllers, etc. (e.g., processor 108 of FIG. 2). As an example, control circuitry may operate under the control of a program, algorithm, routine, or the execution of instructions to execute methods or processes in accordance with embodiments previously described (e.g., the method 300 of FIG. 3, as well as other functions). For example, such a program may be implemented in firmware or software (e.g. stored in memory and/or other locations) and may be implemented by control circuitry, processors, and/or other circuitry, these terms being utilized interchangeably. Further, it should be appreciated that the terms processor, microprocessor, circuitry, control circuitry, circuit board, controller,

microcontroller, etc., refer to any type of logic or circuitry capable of executing logic, commands, instructions, software, firmware, functionality, etc., which may be utilized to execute embodiments.

[0032] The various illustrative blocks, processors, modules, and circuitry described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a specialized processor, circuitry, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field

programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor may be a microprocessor or any conventional processor, controller, microcontroller, circuitry, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0033] The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module/firmware executed by a processor, or any combination thereof. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.

[0034] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0035] The disclosure also includes the following clauses:

1. A finger cuff device to measure a patient’s blood pressure from a finger of the patient, the finger cuff device comprising:

a finger cuff including:

a cavity configured to receive the finger, the finger cuff configured to extend around the finger;

an optical source and an optical sensor configured to form an optical source and sensor pair to perform measurements of a plethysmography signal from an artery of the finger;

a bladder configured to apply an equal constant pressure to the finger; and

a pressure sensor connected to the bladder, the pressure sensor configured to measure the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger; and

a processor connected to the optical source and sensor pair and to the pressure sensor, the processor configured to extract the patient’s arterial blood pressure waveform signal from the plethysmography signal, the patient’s arterial blood pressure waveform signal being extracted from the plethysmography signal based upon an equation relating the

plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger as measured by the pressure sensor.

2. The finger cuff device of claim 1, wherein the optical source and optical sensor pair includes a light emitting diode (LED) and photodiode (PD) (LED-PD) pair.

3. The finger cuff device of any of the claims 1-2, wherein the bladder is an incompressible fluid filled bladder to apply an equal amount of constant pressure across the finger, such that, the finger becomes a constant rigid form allowing a natural signal of the artery to penetrate the finger into the bladder to be measured by the pressure sensor.

4. The finger cuff device of claim 3, wherein the pressure sensor includes a strain gauge sensor coupled to the incompressible fluid filled bladder allowing pressure variations of the incompressible fluid filled bladder from the artery to be measured by the strain gauge sensor, such that, pressure fluctuations are used in the equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger in extracting the patient’s arterial blood pressure waveform signal from the plethysmography signal.

5. The finger cuff device of any of the claims 1-4, wherein a plasticity of the finger is utilized in the equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger by taking reference readings of the finger cuff at an applied zero pressure reading, intermediate pressure readings, and a maximum pressure reading, such that, the patient’s plethysmography signal in relation to pressure accounting for the plasticity of the finger is included.

6. The finger cuff device of any of the claims 1-5, wherein the patient’s blood pressure measurement values from the patient’s arterial blood pressure waveform signal includes systolic pressure, mean arterial pressure (MAP), and/or diastolic pressure.

7. A finger cuff for measuring a blood pressure of a patient, the finger cuff comprising:

a cavity configured to receive a finger of the patient, the finger cuff configured to extend around the finger;

an incompressible fluid filled bladder configured to apply an equal constant pressure to the finger; and

a pressure sensor connected to the bladder, the pressure sensor configured to measure the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger.

8. The finger cuff of claim 7, wherein the optical source and optical sensor pair includes a light emitting diode (LED) and photodiode (PD) (LED-PD) pair.

9. The finger cuff of any of the claims 7-8, wherein the incompressible fluid filled bladder is configured to apply an equal amount of constant pressure across the finger, such that the finger becomes a constant rigid form allowing a natural signal of the artery to penetrate from the finger into the bladder to be measured by the pressure sensor.

10. The finger cuff of claim 9, wherein the pressure sensor includes a strain gauge sensor coupled to the incompressible fluid filled bladder allowing pressure variations of the incompressible fluid filled bladder from the artery to be measured by the strain gauge sensor.

11. The finger cuff of any of the claims 7-10, wherein the blood pressure includes systolic pressure, mean arterial pressure (MAP), or diastolic pressure.

12. A method for measuring a blood pressure of a patient, the method comprising: receiving a finger of the patient in a cavity of a finger cuff;

performing, by an optical source and sensor pair, measurements of a plethysmography signal from an artery of the finger;

applying, by a bladder, an equal constant pressure to the finger;

measuring, by a pressure sensor, the pressure applied to the bladder by the artery to measure the arterial blood pressure of the finger; and

extracting, by a processor, the patient’s arterial blood pressure waveform signal from the plethysmography signal, the patient’s arterial blood pressure waveform signal being extracted from the plethysmography signal based upon an equation relating the

13. The method of claim 12, wherein the optical source and sensor pair includes a light emitting diode (LED) and photodiode (PD) (LED-PD) pair.

14. The method of any of the claims 12-13, wherein the bladder is incompressible fluid filled bladder to apply an equal amount of constant pressure across the finger, such that the finger becomes a constant rigid form allowing a natural signal of the artery to penetrate the finger into the bladder to be measured by the pressure sensor.

15. The method of any of the claims 12-14, wherein the pressure sensor includes a strain gauge sensor coupled to the incompressible fluid filled bladder allowing pressure variations of the incompressible fluid filled bladder from the artery to be measured by the strain gauge sensor, such that, pressure fluctuations are used in the equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger in extracting the patient’s arterial blood pressure waveform signal from the plethysmography signal.

16. The method of any of the claims 12-15, wherein a plasticity of the finger is utilized in the equation relating the plethysmography signal to the blood flow in the finger and the arterial blood pressure of the finger by taking reference readings of the finger cuff at an applied zero pressure reading, intermediate pressure readings, and a maximum pressure reading, such that, the patient’s plethysmography signal in relation to pressure accounting for the plasticity of the finger is included.

17. The method of any of the claims 12-16, wherein the patient’s blood pressure measurement values from the patient’s arterial blood pressure waveform signal includes systolic pressure, mean arterial pressure (MAP), or diastolic pressure.

Claims

WHAT IS CLAIMED IS:

a finger cuff including:

a bladder configured to apply an equal constant pressure to the finger; and

applying, by a bladder, an equal constant pressure to the finger;