WO1999039634A1 - Method and device for arterial blood pressure measurement - Google Patents

Method and device for arterial blood pressure measurement Download PDF

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Publication number
WO1999039634A1
WO1999039634A1 PCT/IL1999/000082 IL9900082W WO9939634A1 WO 1999039634 A1 WO1999039634 A1 WO 1999039634A1 IL 9900082 W IL9900082 W IL 9900082W WO 9939634 A1 WO9939634 A1 WO 9939634A1
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Prior art keywords
pressure
signals
region
cuff
subject
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PCT/IL1999/000082
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French (fr)
Inventor
Meir Nitzan
Original Assignee
Abp Tek Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Abp Tek Ltd. filed Critical Abp Tek Ltd.
Priority to AU24392/99A priority Critical patent/AU2439299A/en
Priority to GB0021870A priority patent/GB2356709B/en
Publication of WO1999039634A1 publication Critical patent/WO1999039634A1/en

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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/02108Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics
    • A61B5/02125Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics of pulse wave propagation time
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/022Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
    • A61B5/02233Occluders specially adapted therefor
    • A61B5/02241Occluders specially adapted therefor of small dimensions, e.g. adapted to fingers
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/022Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
    • A61B5/0225Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds

Definitions

  • the present invention relates to a method and device for the measurement of arterial blood pressure (ABP). More particularly, the present invention relates to a method and a device for measuring systolic and diastolic blood pressure.
  • ABSP arterial blood pressure
  • Blood supply to the tissues of a living body is essential for maintaining their metabolism and proper function.
  • systole heart contraction
  • SBP systolic blood pressure
  • DBP diastolic blood pressure
  • plethysmography which can be performed by means of several methods, including photoplethysmography (PPG), which is the measurement of light absorption in tissue.
  • PPG photoplethysmography
  • Fig. 1 shows a known PPG probe attached to a finger.
  • the light source L emits light into the tissue and the photodetector D measures the light scattered from the tissue under the skin.
  • the output of the photodetector depends on the tissue blood volume, and oscillates with the oscillations of the latter.
  • Fig. 2 shows the blood pressure and the PPG signal measured simultaneously in the finger arteries as a function of time.
  • the blood pressure measurement was performed on a fingertip by means of a continuous, non- invasive blood pressure meter (Finapres, Ohmeda, U.S.A.).
  • the curve of oscillations (at the heart rate) of the tissue blood volume as measured by the PPG signal is similar, but not identical, to the ABP curve.
  • Blood pressure can change because of exercise, mental stress, or excitement. It also changes spontaneously due to activity of the autonomic nervous system. For adults aged below 40 years, the values of normal blood pressure (at rest) are 120 mmHg and 80 mmHg for systolic and diastolic blood pressures, respectively; If the ABP is too high (hypertension), the subject is at higher risk of cerebral stroke and heart attack. Lower than normal blood pressure (hypotension) is acutely hazardous, since it may cause low blood supply to the brain, resulting in fainting or even in brain damage. Decreasing blood pressure for patients after trauma, surgery or heart attack is a reliable indication of critical deterioration of the cardiovascular system.
  • Blood pressure can be measured invasively by inserting a catheter into an artery and measuring the pressure by means of a piezoelectric device. This measurement is the most reliable one, and it is done in intensive care units where an arterial line is present for additional reasons. Due to its invasiveness, this method is not used for routine applications.
  • the auscultatory method is the most common method for non-invasive measurement of blood pressure, and is based on hearing (via stethoscope or microphone) the turbulence sounds which appear in a compressed artery when it is intermittently closed and opened by means of an inflatable cuff having air pressure of a value between that of diastolic and systolic blood pressure.
  • the cuff air pressure is increased above the SBP, then decreased.
  • the cuff air pressure at which the turbulence sounds appear is the SBP; the pressure at which they disappear is the DBP.
  • the manual auscultatory method (using a stethoscope) has been accepted as the gold standard for non-invasive ABP measurement, and is routinely used in clinics and hospitals.
  • the automatic auscultatory method (using a microphone), is also used for monitoring ABP in hospital wards. In spite of its extensive use, the auscultatory method is not accurate, because of the difficulty in
  • Automatic blood pressure measurement can also be done by means of the oscillometric method.
  • a cuff is applied to the arm or finger and a sensor for detecting blood volume changes in the arteries, such as a piezoelectric pressure transducer or PPG device, is attached to the cuff or to the skin under the cuff, respectively. Oscillations in the heart rate can then be seen in the sensor output, due to the systolic pulsatile increase in arterial blood volume.
  • these oscillations also increase until the air pressure is equal to the mean blood pressure, and then they decrease.
  • the systolic and diastolic blood pressure can be derived from the curve of the amplitude of oscillation as a function of the air pressure, using empirical formulae.
  • This method which is called oscillometry, can be used for monitoring blood pressure, but the measurement time is long: more than 20 heart beats, depending on the patient and on the required accuracy. In any case, the method and the commercial devices which are based thereon, are not considered to be accurate.
  • the systolic blood pressure can be non-invasively measured by means of PPG, by using a PPG device and a cuff around the arm or finger, increasing the air pressure in the cuff, and determining the air pressure at which the PPG signal disappears. This air pressure is equal to the systolic blood pressure in the artery under the cuff. The determination of the diastolic blood pressure is more difficult.
  • the DBP and SBP for each heartbeat is determined from the minimum and maximum points of the PPG signal.
  • the method is not accurate, since DBP or SBP, and the maximum or minimum of the PPG signal, are not related by a constant k.
  • an exponential relationship is assumed between the ABP and the blood volume changes measured by PPG, for the assessment of the cardiac-induced blood pressure oscillations from the simultaneous blood volume oscillations in the heart rate.
  • ABP blood pressure
  • PPG blood pressure clamp method
  • the device utilized for this method is composed of a finger cuff with a PPG probe, and the method is based on the determination of the cuff air pressure which is required to keep the arterial blood volume constant.
  • the device enables the measurement of ABP changes during the cardiac cycle via very rapid changes of the cuff air pressure.
  • the method is very sophisticated, but it was not found to reliably record ABP.
  • the device is expensive, due to the need to swiftly change the cuff air pressure in accordance with the blood pressure changes during the cardiac cycle.
  • the present invention is a device and method for measurement of arterial blood pressure and, in particular, the diastolic blood pressure.
  • a method for measuring arterial diastolic blood pressure in a subject comprising: (a) applying a variable pressure to a first region of the subject's body so as to affect blood flow through at least one artery in the first region, the variable pressure being varied as a function of time; (b) generating first and second signals indicative, respectively, of systolic pulsatile variations in tissue blood volume in a second region and a third region of the subject's body; (c) processing the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals; (d) calculating values of a ratio of the parameter for corresponding pulses of the first and second signals and identifying a current value of the variable pressure corresponding to each value of the ratio, the first, the second and the third regions being chosen such that the ratio varies as a function of the variable pressure; and (e) identifying as the diastolic pressure a value of the variable pressure
  • the size information is the amplitude of a pulse.
  • the size information is an integral of a signal over at least part of a pulse.
  • the first and second signals are generated by use of non-invasive sensors, preferably photoplethysmography sensors.
  • a device for use in blood pressure measurement comprising: (a) a cuff having an operative inflatable portion, locations beyond the operative inflatable portion in a first direction being termed “proximal” and locations beyond the operative inflatable portion in a second direction being termed “distal”; (b) a first photoplethysmography sensor attached to the cuff so as to produce a signal indicative of variations in subcutaneous blood volume in a first proximal region; and (c) a second photoplethysmography sensor attached to the cuff so as to produce a signal indicative of variations in subcutaneous blood volume in a second non-proximal region.
  • the second non- proximal region is distal.
  • a device for measuring arterial diastolic blood pressure in a subject comprising: (a) a pressure cuff applicable to a first region of the subject's body so as to affect blood flow through at least one artery in the first region; (b) a pressure controller operatively connected to the pressure cuff so as to vary a current pressure of the pressure cuff; (c) first and second plethysmography sensors for application to a second region and a third region of the subject's body, the first and second plethysmography sensors being configured to produce first and second signals, respectively, indicative of variations in tissue blood volume in the second and third regions, respectively; and (d) a processor associated with the pressure controller and with the first and second plethysmography sensors, the processor being configured to: (i) process the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals at a range of different values of the current pressure
  • Fig. 1 illustrates a prior art PPG probe attached to a finger of a subject
  • Fig. 2 shows curves of the cardiac-induced oscillations of the blood pressure in a finger's arteries and the cardiac-induced oscillations of the tissue blood volume as a function of time;
  • Fig. 3 is a plot of arterial blood pressure as a function of time
  • Fig, 4 is an illustration of an embodiment of the device for diastolic blood pressure measurement according to the present invention.
  • Fig. 5 is a block diagram of the device of Fig. 4;
  • Fig. 6 shows curves of PPG signals in the fingers of the right and left hands of a subject, for different air pressures applied to the subject's right arm;
  • Fig. 7 illustrates a further embodiment of the device for diastolic blood pressure measurement
  • Fig. 8 illustrates a still further embodiment of the device for diastolic blood pressure measurements
  • Fig. 9 is a cross-sectional view of the pressure application means and the PPG probe of Fig. 8;
  • Fig. 10 illustrates a first example of the variation in ratio of affected to unaffected signal amplitudes and integrals as a function of applied cuff pressure;
  • Fig. 11 illustrates a second example of the variation in ratio of affected to unaffected signal amplitudes and integrals as a function of applied cuff pressure.
  • the present invention is a device and method for measurement of arterial blood pressure and, in particular, the diastolic blood pressure.
  • the principles and operation of devices and methods according to the present invention may be better understood with reference to the drawings and the accompanying description.
  • Figures 4, 5 and 7-9 show various embodiments of a device, constructed and operative according to the teachings of the present invention, for measuring the arterial blood pressure of a subject.
  • the invention is based on the application of a pressure cuff with air pressure Pa around the limb of a subject on a pressure application site, and a first PPG probe on a measurement site, distal to the pressure application site, said first PPG probe producing the first PPG signal.
  • a pressure cuff with air pressure Pa around the limb of a subject on a pressure application site
  • a first PPG probe on a measurement site distal to the pressure application site, said first PPG probe producing the first PPG signal.
  • the arteries under the cuff will be compressed and closed for those short periods of time (between t and t 2 ) in which the arterial blood pressure is below the cuff air pressure Pa 0 .
  • the blood stops flowing through the momentarily closed artery and no systolic increase in the tissue blood volume occurs, resulting in a reduction in said first PPG signal amplitude and a delay in the start of the systolic increase in said first PPG signal. Both the change in the PPG amplitude and the delay of the systolic increase are not easy to detect, since the PPG signal changes spontaneously.
  • This small change in the first PPG signal can, however, be detected by measuring the first PPG signal simultaneously with a second (reference) PPG signal in a second PPG probe, which is not placed distal to the cuff so that it is not directly affected by the cuff, and comparing the two PPG signals.
  • the air pressure reaches a value between that of the diastolic and systolic blood pressure, the first PPG signal in the site distal to the cuff deviates from the second (reference) signal of the second PPG probe.
  • both the amplitude and integral of the PPG signal increase due to the increased proportion of time during the cardiac cycle for which the artery below the cuff is open.
  • the air pressure becomes less than the diastolic blood pressure
  • the artery remains always open and the ratio between the first and second signal amplitudes or integrals ceases to increase.
  • the veins remain closed with the result that blood volume in the finger increases.
  • the consequent stretching of the blood vessels reduces their capacity for systolic blood volume increase, thereby reducing the ratio with further decrease in air pressure.
  • the result is that the diastolic pressure corresponds to a local maximum in the relation between the ratio of affected/unaffected amplitude or area and air pressure.
  • Figures 10 and 11 show two examples of the variation of amplitude ratio and integral ratio as a function of decreasing pressure.
  • both ratios reach a maximum value at a cuff pressure of about 70 mmHg and then decrease.
  • the value of the diastolic blood pressure in this case was measured by sphygmomanometry and was found to be 72 mmHg.
  • the invention provides a device for measuring arterial blood pressure in a subject, including a pressure cuff
  • First and second plethysmography sensors 2 and 4 applicable to second and third regions of the subject's body, are configured to produce first and second signals, respectively, indicative of systolic pulsatile variations in tissue blood volume in the second and third regions, respectively.
  • a processor 12b is associated with pressure controller 12a, optionally in a single unit 12, and with first and second plethysmography sensors 2 and 4.
  • Processor 12b is configured to: (i) process the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals at a range of different values of the current pressure, (ii) calculate values of a ratio of the parameter for corresponding pulses of the first and second signals, (iii) identify a current pressure corresponding to each of the values of the ratio, and (iv) identify as the diastolic pressure a value of the variable pressure corresponding substantially to a stationary point in a relationship between the ratio and the current pressure.
  • the size-related parameter is typically either the pulse amplitude or the integral of the signal over the cardiac pulse cycle. Either of these quantities may readily be derived from the signal waveforms by conventional and well-known algorithms.
  • the hardware required for implementing processor 12b will be clear to one ordinarily skilled in the art. Typically, a microprocessor unit is employed operating conventional computational software under a suitable operating system. Alternatively, a custom hardware implementation, or a combination of hardware and software (referred to as "firmware") may be used.
  • sensors 2 and 4 may be applied to any two regions of the subject's body chosen such that the ratio obtained varies as a function of the pressure applied to cuff 18. In the case of Figure 4, the reference signal from sensor 4 is substantially unaffected by variations in the applied pressure. In alternative implementations such as that of Figure 7, the two regions in which measurements are taken may both be affected so long as they are affected to a
  • the device consists of a first PPG probe 2, fitted with per se known means for attaching the probe to a finger of one hand of a subject and similarly, a second PPG probe 4 fitted with means for attaching it to a finger of the second hand of said subject.
  • the probes 2 and 4 each include a light source L modulated by a modulator 6 and a photodetector D, the output of which is advantageously amplified, filtered and demodulated at 8 before being digitized by an A/D converter 10.
  • the outputs for converter 10 are applied to a processor/controller 12.
  • the latter also governs the operation of pump 16, which affects the inflation and deflation of a pressure application means 18, e.g., a cuff, configured to be attached to the arm of one of the subject's hands and receives information from an air pressure monitor 14.
  • a pressure application means e.g., a cuff
  • the modulator 6, amplifiers/filters 8 and A/D converters 10 are shown for the sake of clarity as being a separate assembly, it should be understood that in practice, these functions are performed by circuits physically constituting parts of the processor/controller 12.
  • the device also includes a display 20 for displaying the arterial blood pressure and other selectable, useful information.
  • the method for measuring arterial diastolic blood pressure in a subject is as follows. First, a variable pressure is applied to a first region of the subject's body so as to affect blood flow through at least one artery in the first region, the variable pressure being varied as a function of time; then, first and second signals are generated indicative, respectively, of systolic pulsatile variations in tissue blood volume in a second region and a third region of the subject's body; these first and second signals are then processed to derive a parameter relating to a size of pulses in each of the first and second signals; values of a ratio of the parameter for corresponding pulses of the first and second signals are calculated and a current value of the variable pressure corresponding to each value of the ratio is identified. The first, the second and the third regions are chosen to ensure that this ratio varies as a function of the variable pressure. Finally, the diastolic pressure is
  • variable pressure 12 identified as the value of the variable pressure corresponding substantially to a stationary point in the function of the variable pressure.
  • the size-related parameter is preferably either the amplitude of a pulse of the signal or the integral of the signal over at least part of a pulse.
  • the choice of numerator and denominator when defining the ratio in question is somewhat arbitrary and is not essential to the implementation of the method of the present invention.
  • a convention is chosen such that the ratio tends to zero at air pressure above systolic blood pressure, i.e., that the more strongly pressure-affected signal is employed as the numerator of the ratio.
  • the stationary point corresponding to the diastolic blood pressure is defined as a local maximum value of the function with respect to the variable pressure.
  • a minimum upper value of the variable pressure is identified above which the value of the parameter is substantially zero for one of the first and second signals. This minimum upper value corresponds substantially to the systolic blood pressure.
  • the local maximum value is then taken as the local maximum occurring at the highest value of the variable pressure which lies at least 20 mmHg below the minimum upper value.
  • Fig. 6 shows the PPG signals in the fingers of both the right and left hands simultaneously measured when a pressure application means 18 is attached to the right arm and the air pressure in it is between the systolic and diastolic blood pressures. In the right hand curve, a reduced amplitude and area of pulses of the PPG signal when the external air pressure exceeds the diastolic ABP can be clearly seen.
  • the basis for the invention is to compare the first PPG signal in the first site which is distal to the pressure application means with another reference signal in the second site which is not affected by the pressure of means 18, or which is affected in a different manner from the signal of the first site. Hence, the measurement of the diastolic blood pressure can also be obtained
  • a combined pressure application means 18 and PPG probes may be formed, which can be affixed at any suitable location on a subject's body in such a way that one of the PPG probes, e.g., probe 2, will be located to provide measurements of light absorption in tissue distal to the pressure application means 18 relative to the heart, while the other PPG probe 4 will be located to provide measurements of light absorption in tissue proximal thereof.
  • Figs. 8 and 9 illustrate another embodiment of the device in accordance with the present invention, in which the PPG probe 2, which measures the blood volume changes which are affected by the pressure application means 18, is attached to the skin of the forearm under the pressure application means.
  • the second probe 4 which measures the blood volume changes which are not affected by the pressure application means 18, is attached to the skin of the contralateral forearm.
  • the signals of the two probes are compared, and the appearance of significant deviation between the two signals as the air pressure in the means 18 is increased, provides an indication that the air pressure is higher than the diastolic blood pressure.
  • plethysmography sensors such as electrical impedance plethysmography sensors may equally be used.
  • detectors of another cardiovascular parameter such as blood flow, blood velocity or tissue blood pressure, could be utilized.
  • the method according to the present invention can be used for non- invasively measuring and monitoring diastolic and systolic blood pressure more accurately than that measured by the oscillometric method.
  • it is needed only to scan the air pressure around the diastolic and around the systolic blood pressure, which can also be done simultaneously with two probes, while oscillometry requires the scanning of the air pressure for the whole region between the systolic and the diastolic blood pressures.
  • the present method will be more accurate than oscillometry, because the derivation of the diastolic and the systolic blood pressure from the PPG signal is straightforward, without any assumptions, calibrations or empirical formulae, which are not always correct.
  • the pressure application means has been shown and described to be attached to a subject's arm or hand, it should be understood that it can just as well be attached to a subject's leg or foot; hence, the pressure application means can be applied to any of a subject's limbs.
  • the probes are shown and described as being attached to a subject's fingers, it should be understood that such probes can just as well be attached to a subject's toes; hence, the probes can be applied to any of a subject's digits.

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Abstract

A device for measuring arterial blood pressure in a subject, includes a pressure cuff (18) applicable to a first region of the subject's body so as to affect blood flow through at least one artery in the first region, and a pressure controller (12a) connected to the pressure cuff (18) so as to vary a current pressure of the pressure cuff (18). First and second plethysmography sensors (2)(4), applicable to second and third regions of the subject's body, are configured to produce first and second signals, respectively, indicative of systolic pulsatile variations in tissue blood volume in the second and third regions, respectively. A processor (12b) is associated with the pressure controller (12a) and with the first and second plethysmography sensors (2)(4). The processor (12b) is configured to process the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals at a range of different values of the current pressure; calculate values of a ratio of the parameter for corresponding pulses of the first and second signals; identify a current pressure corresponding to each of the values of the ratio; and identify as the diastolic pressure a value of the variable pressure corresponding substantially to a stationary point in a relationship between the ratio and the current pressure.

Description

Method and Device for Arterial Blood Pressure Measurement
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method and device for the measurement of arterial blood pressure (ABP). More particularly, the present invention relates to a method and a device for measuring systolic and diastolic blood pressure.
Blood supply to the tissues of a living body is essential for maintaining their metabolism and proper function. During systole (heart contraction), blood is ejected from the heart into the arterial system, thereby increasing the arterial blood pressure. The maximal arterial blood pressure (ABP) is the systolic blood pressure (SBP). During and after systole, blood flows from the arteries, through the capillaries, into the veins, and from them back into the heart. The period between two systoles is called diastole. During diastole, the arterial blood pressure decreases; the minimal arterial blood pressure (at the end of diastole) is called diastolic blood pressure (DBP). Similar to blood pressure, blood volume in the tissue also shows oscillations at the heart rate. During systole, blood is ejected from the left ventricle into the peripheral tissues, thereby increasing their blood content. The measurement of the systolic pulsatile increase of tissue blood volume is called plethysmography, which can be performed by means of several methods, including photoplethysmography (PPG), which is the measurement of light absorption in tissue. The PPG signal originates from the increase of tissue blood volume during systole, and the consequent higher light absorption. Fig. 1 shows a known PPG probe attached to a finger. The light source L emits light into the tissue and the photodetector D measures the light scattered from the tissue under the skin. The output of the photodetector depends on the tissue blood volume, and oscillates with the oscillations of the latter.
Fig. 2 shows the blood pressure and the PPG signal measured simultaneously in the finger arteries as a function of time. The blood pressure measurement was performed on a fingertip by means of a continuous, non- invasive blood pressure meter (Finapres, Ohmeda, U.S.A.). As can be seen in Fig. 2, the curve of oscillations (at the heart rate) of the tissue blood volume as measured by the PPG signal, is similar, but not identical, to the ABP curve.
Blood pressure can change because of exercise, mental stress, or excitement. It also changes spontaneously due to activity of the autonomic nervous system. For adults aged below 40 years, the values of normal blood pressure (at rest) are 120 mmHg and 80 mmHg for systolic and diastolic blood pressures, respectively; If the ABP is too high (hypertension), the subject is at higher risk of cerebral stroke and heart attack. Lower than normal blood pressure (hypotension) is acutely hazardous, since it may cause low blood supply to the brain, resulting in fainting or even in brain damage. Decreasing blood pressure for patients after trauma, surgery or heart attack is a reliable indication of critical deterioration of the cardiovascular system.
Blood pressure can be measured invasively by inserting a catheter into an artery and measuring the pressure by means of a piezoelectric device. This measurement is the most reliable one, and it is done in intensive care units where an arterial line is present for additional reasons. Due to its invasiveness, this method is not used for routine applications.
The auscultatory method is the most common method for non-invasive measurement of blood pressure, and is based on hearing (via stethoscope or microphone) the turbulence sounds which appear in a compressed artery when it is intermittently closed and opened by means of an inflatable cuff having air pressure of a value between that of diastolic and systolic blood pressure. Usually, the cuff air pressure is increased above the SBP, then decreased. The cuff air pressure at which the turbulence sounds appear is the SBP; the pressure at which they disappear is the DBP. The manual auscultatory method (using a stethoscope) has been accepted as the gold standard for non-invasive ABP measurement, and is routinely used in clinics and hospitals. The automatic auscultatory method (using a microphone), is also used for monitoring ABP in hospital wards. In spite of its extensive use, the auscultatory method is not accurate, because of the difficulty in
2 detecting the correct sounds and also because of the unclear relationship between the disappearance of the turbulence sounds and DBP.
Automatic blood pressure measurement can also be done by means of the oscillometric method. A cuff is applied to the arm or finger and a sensor for detecting blood volume changes in the arteries, such as a piezoelectric pressure transducer or PPG device, is attached to the cuff or to the skin under the cuff, respectively. Oscillations in the heart rate can then be seen in the sensor output, due to the systolic pulsatile increase in arterial blood volume. When the air pressure is continuously increased above diastolic blood pressure, these oscillations also increase until the air pressure is equal to the mean blood pressure, and then they decrease. The systolic and diastolic blood pressure can be derived from the curve of the amplitude of oscillation as a function of the air pressure, using empirical formulae. This method, which is called oscillometry, can be used for monitoring blood pressure, but the measurement time is long: more than 20 heart beats, depending on the patient and on the required accuracy. In any case, the method and the commercial devices which are based thereon, are not considered to be accurate.
The low accuracy of the auscultatory and the oscillometry methods for the measurement of diastolic and systolic blood pressure, and the need for a reliable method, resulted in several attempts to develop a more accurate device. Some of these attempts are based on PPG measurement. The systolic blood pressure can be non-invasively measured by means of PPG, by using a PPG device and a cuff around the arm or finger, increasing the air pressure in the cuff, and determining the air pressure at which the PPG signal disappears. This air pressure is equal to the systolic blood pressure in the artery under the cuff. The determination of the diastolic blood pressure is more difficult.
In U.S. Patent No. 5,269,310, there is disclosed a method for measuring, by means of PPG, changes of blood volume in the arteries during systole together with the patient's blood pressure, and for determining a constant k particular to the patient's arterial blood pressure- volume relationship. By means of this calibration,
3 the DBP and SBP for each heartbeat is determined from the minimum and maximum points of the PPG signal. The method is not accurate, since DBP or SBP, and the maximum or minimum of the PPG signal, are not related by a constant k. In another U.S. Patent, No. 5,423,322, an exponential relationship is assumed between the ABP and the blood volume changes measured by PPG, for the assessment of the cardiac-induced blood pressure oscillations from the simultaneous blood volume oscillations in the heart rate. There are several drawbacks to this method: 1) The relationship between the arterial blood pressure and the blood volume is not strictly exponential. Furthermore, the volume vs. pressure curve changes as a function of time; it even changes between the period of increasing pressure (systole) to the period of decreasing pressure (diastole) within the same cardiac cycle (as can be seen in Fig. 2 of the present application), and 2) The blood volume changes not only in a single artery, but also in the small arteries and in the arterioles (resistance vessels). It is not possible to simulate the entire group of arteries and arterioles as a single artery, since the pressure therein is not constant as the blood pressure is reduced in the arterioles relative to the arteries. Another approach, suggested by a number of academic papers but not implemented in practice, proposes to measure diastolic blood pressure on the basis of a delay in the pulse caused by pressure from a cuff. This approach was detailed by L. A. Geddes et al. in a paper entitled "Pulse Arrival Time as a Method of Obtaining Systolic and Diastolic Blood Pressure Indirectly", (Medical & Biological Engineering & Computing, September 1981, pp. 671-672). Geddes et al., experimenting on dogs, compared the measurements of an invasive pressure sensor with either another similar sensor or an ECG reference to detect a delay in the pulse reaching a location beyond a pressure cuff. The use of ECG as a time reference is particularly problematic, giving broad scattering of results. Even with a second sensor as a reference, however, the point at which the diastolic pressure
4 is supposedly indicated appears poorly defined. It also remains unclear whether the method could be adapted to non-invasive techniques for clinical applications.
Another known method for continuous measurement of finger ABP is the arterial volume clamp method, which is based on PPG. The device utilized for this method is composed of a finger cuff with a PPG probe, and the method is based on the determination of the cuff air pressure which is required to keep the arterial blood volume constant. The device enables the measurement of ABP changes during the cardiac cycle via very rapid changes of the cuff air pressure. The method is very sophisticated, but it was not found to reliably record ABP. The device is expensive, due to the need to swiftly change the cuff air pressure in accordance with the blood pressure changes during the cardiac cycle.
Other methods for the measurement of ABP have been suggested, but the only methods which have been accepted for routine and comprehensive clinical use are the oscillometric and auscultatory methods, which indicates that the other suggested methods are either not reliable enough, or are too complicated, for clinical use.
There is therefore a need for a device and method for accurately measuring diastolic blood pressure to ameliorate the above-described drawbacks of the prior art blood pressure measuring devices and methods.
SUMMARY OF THE INVENTION
The present invention is a device and method for measurement of arterial blood pressure and, in particular, the diastolic blood pressure.
According to the teachings of the present invention there is provided, a method for measuring arterial diastolic blood pressure in a subject, the method comprising: (a) applying a variable pressure to a first region of the subject's body so as to affect blood flow through at least one artery in the first region, the variable pressure being varied as a function of time; (b) generating first and second signals indicative, respectively, of systolic pulsatile variations in tissue blood volume in a second region and a third region of the subject's body; (c) processing the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals; (d) calculating values of a ratio of the parameter for corresponding pulses of the first and second signals and identifying a current value of the variable pressure corresponding to each value of the ratio, the first, the second and the third regions being chosen such that the ratio varies as a function of the variable pressure; and (e) identifying as the diastolic pressure a value of the variable pressure corresponding substantially to a stationary point in the function of the variable pressure.
According to a further feature of the present invention, the size information is the amplitude of a pulse.
According to an alternative feature of the present invention, the size information is an integral of a signal over at least part of a pulse.
According to a further feature of the present invention, the first and second signals are generated by use of non-invasive sensors, preferably photoplethysmography sensors.
There is also provided according to the teachings of the present invention, a device for use in blood pressure measurement, the device comprising: (a) a cuff having an operative inflatable portion, locations beyond the operative inflatable portion in a first direction being termed "proximal" and locations beyond the operative inflatable portion in a second direction being termed "distal"; (b) a first photoplethysmography sensor attached to the cuff so as to produce a signal indicative of variations in subcutaneous blood volume in a first proximal region; and (c) a second photoplethysmography sensor attached to the cuff so as to produce a signal indicative of variations in subcutaneous blood volume in a second non-proximal region.
According to a further feature of the present invention, the second non- proximal region is distal.
There is also provided according to the teachings of the present invention, a device for measuring arterial diastolic blood pressure in a subject, the device comprising: (a) a pressure cuff applicable to a first region of the subject's body so as to affect blood flow through at least one artery in the first region; (b) a pressure controller operatively connected to the pressure cuff so as to vary a current pressure of the pressure cuff; (c) first and second plethysmography sensors for application to a second region and a third region of the subject's body, the first and second plethysmography sensors being configured to produce first and second signals, respectively, indicative of variations in tissue blood volume in the second and third regions, respectively; and (d) a processor associated with the pressure controller and with the first and second plethysmography sensors, the processor being configured to: (i) process the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals at a range of different values of the current pressure, (ii) calculate values of a ratio of the parameter for corresponding pulses of the first and second signals, (iii) identify a current pressure corresponding to each of the values of the ratio, and (iv) identify as the diastolic pressure a value of the variable pressure corresponding substantially to a stationary point in a relationship between the ratio and the current pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.
With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
In the drawings:
Fig. 1 illustrates a prior art PPG probe attached to a finger of a subject; Fig. 2 shows curves of the cardiac-induced oscillations of the blood pressure in a finger's arteries and the cardiac-induced oscillations of the tissue blood volume as a function of time;
Fig. 3 is a plot of arterial blood pressure as a function of time;
Fig, 4 is an illustration of an embodiment of the device for diastolic blood pressure measurement according to the present invention;
Fig. 5 is a block diagram of the device of Fig. 4;
Fig. 6 shows curves of PPG signals in the fingers of the right and left hands of a subject, for different air pressures applied to the subject's right arm;
Fig. 7 illustrates a further embodiment of the device for diastolic blood pressure measurement ;
Fig. 8 illustrates a still further embodiment of the device for diastolic blood pressure measurements;
Fig. 9 is a cross-sectional view of the pressure application means and the PPG probe of Fig. 8; Fig. 10 illustrates a first example of the variation in ratio of affected to unaffected signal amplitudes and integrals as a function of applied cuff pressure; and
Fig. 11 illustrates a second example of the variation in ratio of affected to unaffected signal amplitudes and integrals as a function of applied cuff pressure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is a device and method for measurement of arterial blood pressure and, in particular, the diastolic blood pressure. The principles and operation of devices and methods according to the present invention may be better understood with reference to the drawings and the accompanying description.
Referring now to the drawings, Figures 4, 5 and 7-9 show various embodiments of a device, constructed and operative according to the teachings of the present invention, for measuring the arterial blood pressure of a subject.
Generally speaking, the invention is based on the application of a pressure cuff with air pressure Pa around the limb of a subject on a pressure application site, and a first PPG probe on a measurement site, distal to the pressure application site, said first PPG probe producing the first PPG signal. When the cuff is inflated to an air pressure above the SBP, the arteries under the cuff will be compressed and closed. Hence, the SBP can be measured by determining the air pressure at which the PPG signal disappears, as described above. When the cuff air pressure is held at a given value of Pa0, which is below the SBP but above the DBP (see Fig. 3), the arteries under the cuff will be compressed and closed for those short periods of time (between t and t2) in which the arterial blood pressure is below the cuff air pressure Pa0. During the time at which the blood pressure decreases below the applied air pressure Pa0, the blood stops flowing through the momentarily closed artery and no systolic increase in the tissue blood volume occurs, resulting in a reduction in said first PPG signal amplitude and a delay in the start of the systolic increase in said first PPG signal. Both the change in the PPG amplitude and the delay of the systolic increase are not easy to detect, since the PPG signal changes spontaneously. This small change in the first PPG signal can, however, be detected by measuring the first PPG signal simultaneously with a second (reference) PPG signal in a second PPG probe, which is not placed distal to the cuff so that it is not directly affected by the cuff, and comparing the two PPG signals. When the air pressure reaches a value between that of the diastolic and systolic blood pressure, the first PPG signal in the site distal to the cuff deviates from the second (reference) signal of the second PPG probe. More specifically, when the air pressure decreases after it was elevated to above systolic blood pressure (but is still above diastolic blood pressure), both the amplitude and integral of the PPG signal increase due to the increased proportion of time during the cardiac cycle for which the artery below the cuff is open. When the air pressure becomes less than the diastolic blood pressure, the artery remains always open and the ratio between the first and second signal amplitudes or integrals ceases to increase. In fact, since the pressure is still above venous blood pressure, the veins remain closed with the result that blood volume in the finger increases. The consequent stretching of the blood vessels reduces their capacity for systolic blood volume increase, thereby reducing the ratio with further decrease in air pressure. The result is that the diastolic pressure corresponds to a local maximum in the relation between the ratio of affected/unaffected amplitude or area and air pressure.
Parenthetically, it should be noted that, while reference is made herein to a preferred embodiment in which measurements are made while decreasing the applied air pressure, alternative embodiments may be implemented in which measurements are taken while increasing the pressure.
Figures 10 and 11 show two examples of the variation of amplitude ratio and integral ratio as a function of decreasing pressure. In Figure 10, both ratios reach a maximum value at a cuff pressure of about 70 mmHg and then decrease. The value of the diastolic blood pressure in this case was measured by sphygmomanometry and was found to be 72 mmHg.
In certain cases, exemplified here by Figure 11, an additional maximum is observed in both the amplitude and integral ratios at cuff pressures just below the systolic blood pressure. This additional peak has been found always to fall within a range of about 20 mmHg below the systolic blood pressure. The second peak of each ratio again accurately corresponded to the independently measured diastolic blood pressure to within a few mmHg.
In structural terms, with reference to Figure 4, the invention provides a device for measuring arterial blood pressure in a subject, including a pressure cuff
10 18 applicable to a first region of the subject's body so as to affect blood flow through at least one artery in the first region, and a pressure controller 12a operatively connected to the pressure cuff so as to vary a current pressure of pressure cuff 18. First and second plethysmography sensors 2 and 4, applicable to second and third regions of the subject's body, are configured to produce first and second signals, respectively, indicative of systolic pulsatile variations in tissue blood volume in the second and third regions, respectively. A processor 12b is associated with pressure controller 12a, optionally in a single unit 12, and with first and second plethysmography sensors 2 and 4. Processor 12b is configured to: (i) process the first and second signals to derive a parameter relating to a size of pulses in each of the first and second signals at a range of different values of the current pressure, (ii) calculate values of a ratio of the parameter for corresponding pulses of the first and second signals, (iii) identify a current pressure corresponding to each of the values of the ratio, and (iv) identify as the diastolic pressure a value of the variable pressure corresponding substantially to a stationary point in a relationship between the ratio and the current pressure.
As mentioned above, the size-related parameter is typically either the pulse amplitude or the integral of the signal over the cardiac pulse cycle. Either of these quantities may readily be derived from the signal waveforms by conventional and well-known algorithms. The hardware required for implementing processor 12b will be clear to one ordinarily skilled in the art. Typically, a microprocessor unit is employed operating conventional computational software under a suitable operating system. Alternatively, a custom hardware implementation, or a combination of hardware and software (referred to as "firmware") may be used. It will be noted that sensors 2 and 4 may be applied to any two regions of the subject's body chosen such that the ratio obtained varies as a function of the pressure applied to cuff 18. In the case of Figure 4, the reference signal from sensor 4 is substantially unaffected by variations in the applied pressure. In alternative implementations such as that of Figure 7, the two regions in which measurements are taken may both be affected so long as they are affected to a
11 different extent, thereby also allowing measurement of a ratio which varies as a function of the applied pressure.
Turning now to the embodiment of Figs. 4 and 5 in more detail, the device consists of a first PPG probe 2, fitted with per se known means for attaching the probe to a finger of one hand of a subject and similarly, a second PPG probe 4 fitted with means for attaching it to a finger of the second hand of said subject. The probes 2 and 4 each include a light source L modulated by a modulator 6 and a photodetector D, the output of which is advantageously amplified, filtered and demodulated at 8 before being digitized by an A/D converter 10. The outputs for converter 10 are applied to a processor/controller 12. The latter also governs the operation of pump 16, which affects the inflation and deflation of a pressure application means 18, e.g., a cuff, configured to be attached to the arm of one of the subject's hands and receives information from an air pressure monitor 14. While the modulator 6, amplifiers/filters 8 and A/D converters 10 are shown for the sake of clarity as being a separate assembly, it should be understood that in practice, these functions are performed by circuits physically constituting parts of the processor/controller 12. The device also includes a display 20 for displaying the arterial blood pressure and other selectable, useful information.
The method for measuring arterial diastolic blood pressure in a subject is as follows. First, a variable pressure is applied to a first region of the subject's body so as to affect blood flow through at least one artery in the first region, the variable pressure being varied as a function of time; then, first and second signals are generated indicative, respectively, of systolic pulsatile variations in tissue blood volume in a second region and a third region of the subject's body; these first and second signals are then processed to derive a parameter relating to a size of pulses in each of the first and second signals; values of a ratio of the parameter for corresponding pulses of the first and second signals are calculated and a current value of the variable pressure corresponding to each value of the ratio is identified. The first, the second and the third regions are chosen to ensure that this ratio varies as a function of the variable pressure. Finally, the diastolic pressure is
12 identified as the value of the variable pressure corresponding substantially to a stationary point in the function of the variable pressure.
The size-related parameter is preferably either the amplitude of a pulse of the signal or the integral of the signal over at least part of a pulse. Clearly, the choice of numerator and denominator when defining the ratio in question is somewhat arbitrary and is not essential to the implementation of the method of the present invention. Preferably, a convention is chosen such that the ratio tends to zero at air pressure above systolic blood pressure, i.e., that the more strongly pressure-affected signal is employed as the numerator of the ratio. In this case, the stationary point corresponding to the diastolic blood pressure is defined as a local maximum value of the function with respect to the variable pressure.
As mentioned earlier, an additional maximum is sometimes observed at pressures just below the systolic blood pressure, as illustrated in Figure 11. To avoid erroneous results, a minimum upper value of the variable pressure is identified above which the value of the parameter is substantially zero for one of the first and second signals. This minimum upper value corresponds substantially to the systolic blood pressure. The local maximum value is then taken as the local maximum occurring at the highest value of the variable pressure which lies at least 20 mmHg below the minimum upper value. Fig. 6 shows the PPG signals in the fingers of both the right and left hands simultaneously measured when a pressure application means 18 is attached to the right arm and the air pressure in it is between the systolic and diastolic blood pressures. In the right hand curve, a reduced amplitude and area of pulses of the PPG signal when the external air pressure exceeds the diastolic ABP can be clearly seen.
As explained above, the basis for the invention is to compare the first PPG signal in the first site which is distal to the pressure application means with another reference signal in the second site which is not affected by the pressure of means 18, or which is affected in a different manner from the signal of the first site. Hence, the measurement of the diastolic blood pressure can also be obtained
13 by increasing the pressure in the pressure application means and measuring the resultant change in the first PPG signal by using two PPG probes on the same limb, one distal to means 18 and the other proximal to it.
Accordingly, and with reference to Fig. 7, there is shown an embodiment similar to the embodiment of Fig. 4, however, in which the PPG probes 2 and 4 are attached to the subject's arm on both edges of the pressure application means 18, instead of on the fingers of both hands, as seen in Fig. 3. Thus, a combined pressure application means 18 and PPG probes may be formed, which can be affixed at any suitable location on a subject's body in such a way that one of the PPG probes, e.g., probe 2, will be located to provide measurements of light absorption in tissue distal to the pressure application means 18 relative to the heart, while the other PPG probe 4 will be located to provide measurements of light absorption in tissue proximal thereof.
Figs. 8 and 9 illustrate another embodiment of the device in accordance with the present invention, in which the PPG probe 2, which measures the blood volume changes which are affected by the pressure application means 18, is attached to the skin of the forearm under the pressure application means. The second probe 4, which measures the blood volume changes which are not affected by the pressure application means 18, is attached to the skin of the contralateral forearm. The signals of the two probes are compared, and the appearance of significant deviation between the two signals as the air pressure in the means 18 is increased, provides an indication that the air pressure is higher than the diastolic blood pressure.
While the above preferred embodiments specifically utilize the measurement of the systolic increase of tissue blood volume by the PPG probes, it should be noted that other plethysmography sensors such as electrical impedance plethysmography sensors may equally be used. Furthermore, it should be understood that detectors of another cardiovascular parameter, such as blood flow, blood velocity or tissue blood pressure, could be utilized.
14 The method according to the present invention can be used for non- invasively measuring and monitoring diastolic and systolic blood pressure more accurately than that measured by the oscillometric method. In the present method, it is needed only to scan the air pressure around the diastolic and around the systolic blood pressure, which can also be done simultaneously with two probes, while oscillometry requires the scanning of the air pressure for the whole region between the systolic and the diastolic blood pressures.
Furthermore, it is expected that the present method will be more accurate than oscillometry, because the derivation of the diastolic and the systolic blood pressure from the PPG signal is straightforward, without any assumptions, calibrations or empirical formulae, which are not always correct.
While in the above embodiments the pressure application means has been shown and described to be attached to a subject's arm or hand, it should be understood that it can just as well be attached to a subject's leg or foot; hence, the pressure application means can be applied to any of a subject's limbs. Similarly, while in the above embodiments the probes are shown and described as being attached to a subject's fingers, it should be understood that such probes can just as well be attached to a subject's toes; hence, the probes can be applied to any of a subject's digits. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
15

Claims

WHAT IS CLAIMED IS:
1. A method for measuring arterial diastolic blood pressure in a subject, the method comprising:
(a) applying a variable pressure to a first region of the subject's body so as to affect blood flow through at least one artery in said first region, said variable pressure being varied as a function of time;
(b) generating first and second signals indicative, respectively, of systolic pulsatile variations in tissue blood volume in a second region and a third region of the subject's body;
(c) processing said first and second signals to derive a parameter relating to a size of pulses in each of said first and second signals;
(d) calculating values of a ratio of said parameter for corresponding pulses of said first and second signals and identifying a current value of said variable pressure corresponding to each value of said ratio, said first, said second and said third regions being chosen such that said ratio varies as a function of said variable pressure; and
(e) identifying as the diastolic pressure a value of said variable pressure corresponding substantially to a stationary point in said function of said variable pressure.
2. The method of claim 1, wherein said size information is the amplitude of a pulse.
3. The method of claim 1, wherein said size information is an integral of a signal over at least part of a pulse.
4. The method of claim 1, wherein said third region is chosen such that variations in said subcutaneous blood volume in said third region are substantially unaffected by variations in said variable pressure.
16
5. The method of claim 1, wherein said ratio is defined such that it tends to zero at air pressure above systolic blood pressure, said stationary point being defined as a local maximum value of said function with respect to said variable pressure.
6. The method of claim 5, further comprising identifying a minimum upper value of said variable pressure above which the value of said parameter is substantially zero for one of said first and second signals, wherein said local maximum value is taken as the local maximum occurring at the highest value of said variable pressure which lies at least 20 mmHg below said minimum upper value.
7. The method of claim 1, wherein said first and second signals are generated by use of non-invasive sensors.
8. The method of claim 1, wherein said first and second signals are generated by use of photoplethysmography sensors.
9. The method of claim 8, wherein said variable pressure is applied using an inflatable cuff, and wherein at least one of said photoplethysmography sensors is attached to said cuff.
10. The method of claim 1, wherein said first and second signals are generated by use of impedance plethysmography sensors.
11. A device for use in blood pressure measurement, the device comprising:
(a) a cuff having an operative inflatable portion, locations beyond said operative inflatable portion in a first direction being termed "proximal" and locations beyond said operative inflatable portion in a second direction being termed "distal";
17 (b) a first photoplethysmography sensor attached to said cuff so as to produce a signal indicative of variations in subcutaneous blood volume in a first proximal region; and
(c) a second photoplethysmography sensor attached to said cuff so as to produce a signal indicative of variations in subcutaneous blood volume in a second non-proximal region.
12. The device of claim 11, wherein said second non-proximal region is distal.
13. A device for measuring arterial diastolic blood pressure in a subject, the device comprising:
(a) a pressure cuff applicable to a first region of the subject's body so as to affect blood flow through at least one artery in said first region;
(b) a pressure controller operatively connected to said pressure cuff so as to vary a current pressure of said pressure cuff;
(c) first and second plethysmography sensors for application to a second region and a third region of the subject's body, said first and second plethysmography sensors being configured to produce first and second signals, respectively, indicative of variations in tissue blood volume in said second and third regions, respectively; and
(d) a processor associated with said pressure controller and with said first and second plethysmography sensors, said processor being configured to:
(i) process said first and second signals to derive a parameter relating to a size of pulses in each of said first and second signals at a range of different values of said current pressure,
(ii) calculate values of a ratio of said parameter for corresponding pulses of said first and second signals,
(iii) identify a current pressure corresponding to each of said values of said ratio, and 18 (iv) identify as the diastolic pressure a value of said variable pressure corresponding substantially to a stationary point in a relationship between said ratio and said current pressure.
19
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WO2007017661A1 (en) * 2005-08-09 2007-02-15 Tarilian Consulting Limited A device for measuring blood pressure
US8657755B2 (en) 2009-05-12 2014-02-25 Angiologix, Inc. System and method of measuring changes in arterial volume of a limb segment
WO2017085716A1 (en) * 2015-11-16 2017-05-26 Jerusalem College Of Technology System and method of measurement of average blood pressure
US10238306B2 (en) 2006-02-20 2019-03-26 Everist Genomics, Inc. Method for non-evasively determining an endothelial function and a device for carrying out said method

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US5439002A (en) * 1993-11-08 1995-08-08 Colin Corporation Blood pressure monitor system

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007017661A1 (en) * 2005-08-09 2007-02-15 Tarilian Consulting Limited A device for measuring blood pressure
US10238306B2 (en) 2006-02-20 2019-03-26 Everist Genomics, Inc. Method for non-evasively determining an endothelial function and a device for carrying out said method
US8657755B2 (en) 2009-05-12 2014-02-25 Angiologix, Inc. System and method of measuring changes in arterial volume of a limb segment
WO2017085716A1 (en) * 2015-11-16 2017-05-26 Jerusalem College Of Technology System and method of measurement of average blood pressure
US11154208B2 (en) 2015-11-16 2021-10-26 Jerusalem College Of Technology System and method of measurement of average blood pressure

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GB2356709B (en) 2002-04-17

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