JP2006006897A - Method and apparatus for measurement of blood pressure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for measurement of blood pressure to estimate the blood pressure of the subject by only analyzing a measured pulse wave. <P>SOLUTION: In this method for measurement of blood pressure, an acceleration pulse wave is obtained by twice differentiating a volume pulse wave measured on the subject. Blood pressure of the subject is estimated by using phenomena that a time interval t from the maximum point of the a wave (protosystole positive wave) to the maximum point of the e wave (protodiastole positive wave) becomes shorter when blood pressure is high and the time interval t longer when blood pressure is low. When the maximum point of the c wave (midsystole re-elevation wave) or the minimum point of the d wave (late systolic re-descent wave) are unclear and the maximum point and the minimum point of each component cannot be discriminated, the acceleration pulse wave is further differentiated twice to obtain the maximum point and the minimum point in the acceleration pulse wave. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a blood pressure measurement method and apparatus for estimating blood pressure of a subject by analyzing measured pulse waves.

  Conventionally, methods for measuring blood pressure include a method in which an artery is compressed using a cuff (compression band) and the blood pressure is measured in the process of changing the pressure, and a method in which blood pressure is measured without using a cuff. Among them, the blood pressure measurement method using a cuff has been used in clinical practice for many years, and its accuracy is recognized by society. On the other hand, as a method not using a cuff, for example, there is a method as shown in Patent Document 1 below.

  The blood pressure measurement device described in Patent Document 1 includes a pair of electrocardiogram electrodes, an electrocardiogram processing means for processing an electrocardiogram signal from the electrocardiogram electrodes, a fingertip photoelectric pulse wave detection sensor, and a detected pulse wave signal. A pulse wave processing means for processing the blood pressure, a second differential processing means for differentiating the processed pulse wave signal twice, and calculating a blood pressure based on the processed electrocardiogram signal, pulse wave signal and the second differential signal And calculating means. And a calculating means calculates | requires a pulse wave propagation time, a pulse wave interval, and a heart rate from a cardiac potential waveform and a pulse wave waveform, and calculates blood pressure based on these. That is, the technique disclosed in Patent Document 1 uses a phenomenon that the propagation speed of a pulse is generally increased when blood pressure is increased, and an electrocardiographic waveform that has little delay from the time of occurrence in the heart even in the periphery because of electrical propagation. The blood pressure is estimated from the pulse delay time observed in the periphery with respect to the electrocardiographic waveform.

JP-A-8-140948

  However, in the technique described in Patent Document 1, two parameters having different propagation principles of cardiac potential and pulse must be measured in order to obtain the pulse wave propagation time, and a pair of cardiac potential electrodes and fingertip light are measured. It was necessary to attach the radio wave detection sensor to the subject, which was troublesome and complicated.

  The present invention has been proposed in view of such a conventional situation, and an object of the present invention is to provide a blood pressure measurement method and apparatus for estimating the blood pressure of a subject only by analyzing the measured pulse wave.

  In order to achieve the above-described object, the present inventors have conducted intensive research from various viewpoints. As a result, among the acceleration pulse waves obtained by differentiating the pulse wave (volume pulse wave) twice, the time interval from the maximum point of the contraction initial positive wave to the maximum point of the expansion initial positive wave shows a significant correlation with the blood pressure. I found it. The present invention has been completed based on such findings.

  That is, the blood pressure measurement method according to the present invention includes a pulse wave detection step for detecting a pulse wave generated by blood circulation, a differential calculation step for differentiating the pulse wave waveform detected in the pulse wave detection step twice, A blood pressure calculation step of calculating blood pressure based on a time interval from the maximum point of the contraction initial positive wave to the maximum point of the expansion initial positive wave among the waveforms obtained in the differential calculation step.

  Further, the blood pressure measurement device according to the present invention includes a pulse wave detection means for detecting a pulse wave generated by blood circulation, a differential calculation means for differentiating the pulse wave waveform detected by the pulse wave detection means twice, Blood pressure calculating means for calculating blood pressure based on the time interval from the maximum point of the contraction initial positive wave to the maximum point of the extended initial positive wave among the waveforms obtained by the differential calculation means.

  Here, when detecting a pulse wave, light is projected from the light emitting unit to a part for detecting the pulse wave, and transmitted light or reflected light obtained from this part is detected by the light receiving unit.

  In the blood pressure measurement method and apparatus according to the present invention, an expanded initial positive wave from a maximum point of a contraction initial positive wave in a waveform (acceleration pulse wave) obtained by differentiating a pulse wave waveform (volume pulse wave) generated by blood circulation twice. Since the blood pressure of the subject is estimated based on the time interval up to the maximum point, blood pressure data can be obtained simply by measuring the pulse wave.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to a blood pressure measurement method and apparatus for estimating a blood pressure of a subject by analyzing a pulse wave. In the following, a method for estimating blood pressure from a pulse wave will be described first, and then an example of a blood pressure measurement apparatus that performs processing for measuring a pulse wave and analyzing the blood pressure to analyze the pulse wave will be described.

  A volume pulse wave is obtained by electrically and mechanically capturing the expansion / contraction of skin blood vessels (peripheral blood vessels) from the skin surface. A general waveform of the detected volume pulse wave is shown in FIG. Also, a so-called velocity pulse wave obtained by differentiating the volume pulse wave once and a so-called acceleration pulse wave obtained by differentiating the volume pulse wave twice are shown in FIGS. 1B and 1C, respectively.

  Here, each component of the acceleration pulse wave shown in FIG. 1C is given a name as a convention. That is, the positive wave having the first maximum point showing the maximum amplitude is referred to as a wave (contraction initial positive wave), and the negative wave following the a wave is referred to as b wave (contraction initial negative wave). These waves are referred to as wave (mid-systolic re-rising wave), d wave (late systolic re-falling wave), and e wave (expanded initial positive wave).

  The inventors of the present invention have found that the time interval t from the a-wave maximum point to the e-wave maximum point has a significant correlation with the blood pressure, based on extensive experiments and statistical results in the process leading to the present invention. It was. Specifically, it has been found that the time interval t between a and e decreases when the blood pressure is high, and the time interval t between a and e increases when the blood pressure is low.

  In an anatomical explanation, the maximum point of the a wave indicates the minimum point in the volume pulse wave, that is, the point where the pressure of the pulse ejected from the heart is the lowest, and the left ventricle begins to contract and the blood In contrast to the time immediately before ejection, the maximum point of the e-wave is a point where a pulse ejected from the heart exhibits a hydrodynamically nonlinear behavior in the arterial system, for example, branching or stenosis of the artery. It can be said that it represents a point in time immediately before the re-elevation of the trunk artery pressure due to reflection and superimposition of the reflected pulse on the original pulse.

  In this way, the blood pressure measurement method according to the present embodiment estimates blood pressure based on the time interval t from the maximum point of the a wave to the maximum point of the e wave. In this blood pressure measurement method, since the blood pressure can be estimated only from the time interval t between a and e, it is only necessary to measure one system of pulse wave data in any living body part of the subject, which is very simple. is there.

Hereinafter, a procedure for identifying the maximum points of the a wave and the e wave from the characteristics of the waveform of the pulse wave will be described.
In the acceleration pulse wave shown in FIG. 1C, the waveform shapes of the a wave, b wave, c wave, d wave, and e wave are clear, and it is easy to specify the maximum point and the minimum point. However, when actually measured by a human body, an acceleration pulse wave with unclear waveform shapes of c and d waves may be obtained. That is, for example, as shown in FIG. 2, the minimum value of the d wave is not sufficiently smaller than the maximum value of the c wave, and in the process from the b wave to the e wave, there is a clear polarity of increase-decrease-increase. An acceleration pulse wave without reversal may be obtained.

  Generally, the acceleration pulse wave is further differentiated once more, and the point at which the value becomes zero (the zero cross point that intersects the horizontal axis when drawn on the graph) is obtained, whereby the maximum point in the acceleration pulse wave, Although the local minimum point can be specified, in the case of the waveform as shown in FIG. 2, the process from the b wave to the e wave is close to a simple increase.

  Therefore, in this case, in order to reliably specify the maximum point of the e wave most important for blood pressure estimation, in this embodiment, a waveform obtained by further differentiating the acceleration pulse wave twice is obtained.

  FIGS. 3A to 3C show the acceleration pulse wave, its once differentiated waveform, and its twice differentiated waveform on the same time axis. These waveforms correspond to those obtained by differentiation from the original volume pulse wave twice, three times, and four times, respectively.

  If the minimum points are ignored, the a-wave maximum point a, the c-wave maximum point c, and the e-wave maximum point e in the acceleration pulse wave are zero-cross points in the one-time differential waveform (FIG. 3B). It corresponds to a ′, b ′ and c ′, respectively, and corresponds to the minimum points a ″, b ″ and c ″ in the twice differentiated waveform (FIG. 3C).

  As described above, in the waveform in which the maximum and minimum of the c wave and the d wave are not remarkable, the one-time differential waveform corresponding to the maximum point of the c wave and the minimum point of the d wave does not become zero, that is, the horizontal axis May not intersect. However, even in that case, the minimum points a ", b", and c "appear in the twice-differentiated waveform of the acceleration pulse wave (FIG. 3C). By defining each as the maximum point of e wave, the position of each maximum and minimum can be specified regardless of the behavior of the maximum and minimum of c wave and d wave.

  A time interval t from the maximum point of the a wave specified in this way to the maximum point of the e wave is measured, and a graph showing the relationship between the time interval t and the diastolic blood pressure of the subject is shown in FIG. . As can be seen from FIG. 4, it can be seen that the time interval t tends to decrease significantly as the blood pressure increases.

  Next, an example of a blood pressure measurement device that measures a pulse wave and analyzes it to estimate blood pressure as described above will be described.

  An outline of the blood pressure measurement device according to the present embodiment is shown in FIG. As shown in FIG. 5, the blood pressure measurement device 1 according to the present embodiment includes an inner-ear type ear receiver-shaped sensor element 10 for measuring a pulse wave, and a pulse measured by the sensor element 10 while reproducing music and the like. A signal analysis unit 30 for analyzing blood waves and obtaining blood pressure data is connected via a wiring 50. The signal analysis unit 30 is provided with a display unit 31, and blood pressure data analyzed by the signal analysis unit 30 is provided to the subject via the display unit 31.

  FIG. 6 is an enlarged view of the sensor element 10 in the blood pressure measurement device 1. As shown in FIG. 6, the sensor element 10 includes a main body 20 having a speaker 21 for outputting music reproduced by the signal analysis unit 30 and a flexible cushioning material such as silicon rubber or low-resilience urethane. As shown in FIG. 7, when measuring blood pressure, the earpiece 22 is inserted into the ear canal and the main body portion 20 is connected to the concha of the subject as shown in FIG. Used to be fixed to the cavity.

  An example of a side sectional view of the earpiece 22 is shown in FIGS. A through hole is provided in the center of the earpiece 22, and sound waves output from the speaker 21 are sent to the ear canal through the through hole and reach the eardrum. Further, the earpiece 22 is embedded with a light emitting unit 23 and a light receiving unit 24 for measuring a pulse wave, and the light emitting unit 23 and the light receiving unit 24 provide the sensor element 10 to the subject as shown in FIG. It is disposed so that the optical axis of the projection light projected from the light emitting unit 23 and the reflected light thereof is at right angles or close to right angles with the ear canal when it is worn and in contact with the skin inside the ear canal. In FIG. 8, only one light receiving unit 24 is provided. However, by providing a plurality of light receiving units 24, reflected light passing through different paths can be received, and the pulse wave can be measured with higher accuracy.

  In the earpiece 22, a light emitting element such as a small LED (Light Emission Diode) element can be used for the light emitting unit 23. For the light receiving unit 24, for example, a photodetector using a photodiode or pyroelectric microsensor using Si, InGaAs, Ge or the like can be used. The light emitting unit 23 projects red light and near infrared light toward the outside of the earpiece 22, that is, the surface in contact with the skin of the ear canal. The projected light passes through the subject and partly reflects and diffuses back. The light receiving unit 24 receives the reflected light, converts it into an electrical signal, and transmits it to the signal analyzing unit 30 via the wiring 50. Here, the blood flow has a pulse, and the blood permeability is lower than that of other biological parts such as the skin. Therefore, the intensity of the reflected light detected by the light receiving unit 24 is synchronized with the pulse. Fluctuate. Therefore, a pulse wave can be obtained by continuously measuring this variation.

  In the blood pressure measurement device 1 according to the present embodiment, since the light emitting unit 23 and the light receiving unit 24 are embedded in the earpiece 22 made of a flexible buffer material, the light emitting unit 23 and the light receiving unit 24 are repelled by the buffer material. It is brought into contact with the skin on the inner surface of the ear canal with an appropriate pressure by force. Thereby, it can suppress effectively that the distance from the light emission part 23 and the light-receiving part 24 to skin by the influence of test subject's own movement and gravity can be suppressed, and the stable measurement is attained. Further, since the earpiece 22 is inserted into the ear canal and is not exposed outside the body, there is an advantage that the earpiece 22 is not easily affected by external light during measurement. In addition, since the inside of the external auditory canal is far from muscles that can be moved arbitrarily such as arms and fingers, there is an advantage that there is little influence of the subject's own movement and there is no need to restrain the subject during measurement.

  Furthermore, in the blood pressure measurement device 1 according to the present embodiment, the sensor element 10 has an inner-ear ear receiver shape, and music or the like can be output through the speaker 21 of the main body unit 20. The blood pressure can be measured in a relaxed state unconsciously and unconsciously. For this reason, it can be worn for a long time, and it is also possible to observe trends such as blood pressure transitions and fluctuations. In particular, since the light emitting unit 23 and the light receiving unit 24 embedded in the earpiece 22 are small in size, a decrease in acoustic performance can be minimized, and the design as an ear receiver is not impaired. In the blood pressure measurement device 1 according to the present embodiment, since the main body 20 having the speaker 21 and the earpiece 22 having the light emitting part 23 and the light receiving part 24 are separated, the blood pressure was measured while listening to music or the like. Even in this case, it is hardly affected by acoustic vibration.

  FIG. 10 shows a schematic configuration of a portion related to blood pressure measurement in the blood pressure measurement device 1 described above. The electrical signal transmitted from the light receiving unit 24 of the earpiece 22 is first input to the preamplifier unit 40 of the signal analysis unit 30. The preamplifier unit 40 is induced by noise that is electromagnetically induced from a power supply frequency or light from a lighting fixture by removing a component having a frequency higher than about 20 Hz from the input electric signal by a low-pass filter. Remove noise. Further, the preamplifier unit 40 amplifies the electric signal from which this noise has been removed. The signal processing circuit 41 separates the pulse wave signal and the baseline fluctuation component from the electrical signal.

  The separated baseline fluctuation component is integrated with a long time constant of about 5 to 10 seconds in the feedback circuit 42 and supplied to the light emitting unit driving circuit 43. The light emitting unit drive circuit 43 conversely detects the pulse wave detected by the light receiving unit 24 so as to increase the light emission amount of the light emitting unit 23 to obtain a larger change when the pulse wave voltage detected by the light receiving unit 24 is small. When the voltage is large, the light emission amount of the light emitting unit 23 is decreased to control the light receiving unit 24 and the subsequent signal processing circuit from being saturated.

  On the other hand, the separated pulse wave signal is quantized by an A / D (Analogue / Digital) converter 44 and sent to the processor 45 as numerical data. The processor 45 estimates the blood pressure of the subject by analyzing the waveform by performing the numerical calculation processing including the above-described double differentiation on the data, and records the result in the storage medium 46. Displayed on the display unit 31 by characters or other methods.

  In addition, in the light emission part 23 and the light-receiving part 24 mentioned above, a blood glucose level and a blood cholesterol level can also be measured by projecting the light of the wavelength which is easy to be absorbed by the blood component (glucose, cholesterol, etc.) to measure. . Further, the oxygen saturation level in blood can be measured by utilizing the difference in light absorption rate between hemoglobin to which oxygen is bound and hemoglobin to which oxygen is not bound. Thus, according to the blood pressure measurement device 1 in the present embodiment, in addition to blood pressure, a plurality of biological information such as pulse rate, blood sugar level, blood cholesterol value, blood oxygen saturation and the like are measured in parallel. Therefore, it is beneficial for the health management of the subject. Further, higher-order analysis such as analysis of the correlation between the respective pieces of biological information is possible.

  Although specific embodiments to which the present invention is applied have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. Of course there is.

  For example, in the above-described embodiment, the sensor element having the inner ear type ear receiver shape as shown in FIG. 5 has been described as being used in the blood pressure measurement device. However, the present invention is not limited to this shape, and the fingertip, earlobe, wrist The shape may be such that the peripheral tissue of the human body is sandwiched between them. Even in this case, it is possible to measure the pulse wave by projecting light from the light emitting unit to the peripheral tissue and detecting the transmitted light or reflected light by the light receiving unit, and analyzing the pulse wave Blood pressure can be estimated.

It is a figure explaining a volume pulse wave and its differential waveform, The figure (A) shows the general waveform of a volume pulse wave, The figure (B) is a velocity pulse which differentiated this volume pulse wave once. FIG. 3C shows an acceleration pulse wave obtained by differentiating the volume pulse wave twice. It is a figure which shows an example of the acceleration pulse wave without the clear polarity reversal of increase-decrease-increase in the process from b wave to e wave. It is a figure explaining an acceleration pulse wave and its differential waveform, the figure (A) shows an example of an acceleration pulse wave, the figure (B) shows the waveform which differentiated this acceleration pulse wave once, FIG. (C) shows a waveform obtained by differentiating the acceleration pulse wave twice. It is a figure which shows the relationship between the time interval t from the maximum point of a wave to the maximum point of e wave, and the diastolic blood pressure of a subject. It is the schematic which shows an example of the blood-pressure measurement apparatus in this Embodiment. It is a perspective view which expands and shows the sensor element used for the blood pressure measuring device. It is a figure which shows the state which mounted | wore the test subject with the sensor element. It is a sectional side view which shows the earpiece of the sensor element. It is a figure which shows the state in which the light emission part and light-receiving part of a sensor element are contact | abutted to the skin of a test subject's inner ear canal. It is a figure which shows schematic structure of the part relevant to the measurement of blood pressure among the blood pressure measuring devices.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Blood pressure measuring device, 10 Sensor element, 20 Main body part, 21 Speaker, 22 Earpiece, 23 Light emission part, 24 Light reception part, 30 Signal analysis part, 31 Display part, 40 Preamplifier part, 41 Signal processing circuit, 42 Feedback circuit, 43 Light emitting unit drive circuit, 44 A / D converter, 45 processor, 46 storage medium

Claims (9)

A pulse wave detection step for detecting a pulse wave generated by blood circulation;
A differential operation step of differentiating the pulse wave waveform detected in the pulse wave detection step twice;
A blood pressure calculation step of calculating blood pressure based on a time interval from the maximum point of the contraction initial positive wave to the maximum point of the expansion initial positive wave among the waveforms obtained in the differential calculation step. Measuring method. A second differential calculation step of differentiating the waveform obtained in the differential calculation step twice;
In the blood pressure calculation step, the maximum point of the contraction initial positive wave and the maximum point of the extended initial positive wave are obtained based on the minimum point of the waveform obtained in the second differential calculation step. The blood pressure measurement method according to claim 1. A noise removal step of removing high-frequency noise of the pulse wave detected in the pulse wave detection step;
The blood pressure measurement method according to claim 1, wherein in the differential operation step, the waveform from which noise has been removed in the noise removal step is differentiated twice.   In the pulse wave detection step, the pulse wave is detected by projecting light from the light emitting unit to a part for detecting the pulse wave, and detecting transmitted light or reflected light obtained from the part by the light receiving unit. The blood pressure measurement method according to claim 1. Pulse wave detection means for detecting a pulse wave generated by blood circulation;
Differential calculation means for differentiating the pulse wave waveform detected by the pulse wave detection means twice;
A blood pressure calculating means for calculating blood pressure based on a time interval from the maximum point of the contraction initial positive wave to the maximum point of the extended initial positive wave among the waveforms obtained by the differential calculation means measuring device. A second differential calculation means for differentiating the waveform obtained by the differential calculation means twice;
The blood pressure calculation means obtains a maximum point of the contraction initial positive wave and a maximum point of the extended initial positive wave based on the minimum point of the waveform obtained by the second differential calculation means. The blood pressure measurement device according to claim 5. Noise removing means for removing high-frequency noise of the pulse wave detected by the pulse wave detecting means,
The blood pressure measurement device according to claim 5, wherein the differential calculation means differentiates the waveform from which noise has been removed by the noise removal means twice.   6. The pulse wave detecting means includes: a light emitting unit that irradiates light to a part that detects a pulse wave; and a light receiving part that detects transmitted light or reflected light obtained from the part. The blood pressure measurement device described. 9. The blood pressure measuring device according to claim 8, wherein the pulse wave detecting means has a shape in which the light emitting part and the light receiving part are fixed in contact with the inner surface of the ear canal of the subject.

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