Pulse wave measurement method

Abstract

To provide a method for non-invasively and directly measuring a PWV in only a straight section of the aorta from outside the body in order to solve such problems that the conventional pulse wave velocity (PWV) measurement method is theoretically incorrect because it obtains the propagation velocity from a difference in the propagation times of pulse waves traveling in different directions from the heart, and an issue easily occurs in measurement accuracy even though a method to obtain the PWV including the aorta from a time difference between the ejection time of the heart and the pulse wave of annulment, and a method to obtain the PWV of the aorta from the time difference by dividing the pulse waves measured by the annulment into the ejection wave and the reflected wave have been proposed.SOLUTION: The above-mentioned problems are solved by focusing on the fact that the pulse waves of the aorta propagate through small arteries and arterioles connected to the aorta, and the propagated pulse waves can be detected on the body surface near the aorta by photoelectric pulse wave sensors 100 and 110.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pulse wave measuring method and a biological information measuring method. [Background technology]

[0002] In recent years, with the aging of society, measures for early diagnosis and early treatment of arteriosclerosis are urgently needed. Aortic pulse wave velocity testing, which measures the pulse wave velocity (PWV) between two points on the aorta, is known as one method for non-invasive quantitative diagnosis of arteriosclerosis.

[0003] Aortic pulse wave velocity testing shows that pulse wave velocity is faster in hard materials and slower in soft materials. In the aortic pulse wave velocity test, first, the pulse wave is measured from the heart. The time it takes for the light to travel between two points in the aorta in the same direction is measured, and then the measured time is multiplied by 2. The pulse wave velocity is calculated from the distance between the points (arterial length). Based on the fact that healthy arterial walls are soft and elastic, while arteriosclerotic blood vessel walls are hard and brittle, the faster the measured pulse wave velocity, the more advanced the arteriosclerosis is diagnosed.

[0004] Types of PWV include cfPWV (carotid-femoral PWV: PWV between the carotid artery and femoral artery) and baPWV (brachial-ankle PWV: PWV between the upper arm and ankle) (see Guidelines for Non-invasive Assessment of Vascular Function).

[0005] Furthermore, CAVI (Cardio-Ankle Vascular Index) is an index of arteriosclerosis using PWV (see Guidelines for Non-invasive Assessment of Vascular Function). CAVI measures blood pressure and pulse waves using cuffs attached to the upper arm and ankle (or popliteal fossa), and measures heart sounds using a heart sound microphone attached to the sternum.

[0006] However, although these PWV measurement methods and the indices that use them are all called aortic pulse wave velocity testing methods, they do not measure the pulse wave velocity of the aorta alone, but the pulse wave velocity including the aorta, and moreover, they do not measure the pulse wave velocity between two points, but rather calculate the propagation velocity from the difference in propagation time of the pulse wave traveling in different directions from the heart.

[0007] To solve this problem, two methods have been proposed for calculating the pulse wave velocity of the aorta itself. The first method uses various sensors to determine the cardiac ejection time, and calculates the aorta or PWV including the aorta from the time difference between this and the peripheral pulse wave. The second method separates the peripherally measured pulse wave into an ejection wave and a reflected wave, and calculates the aorta's PWV from the time difference between them. These are listed below as prior art documents. The first four documents relate to the first method, and the remaining three to the second method. [Prior art documents] [Patent documents]

[0008] <Prior art related to the first method> Patent Publication No. 2005-278965 The technique combines electrocardiogram and phonocardiogram signals with cardiac mechanical efficiency to determine the cardiac ejection time, and calculates the PWV between the aortic valve and the upper arm from the time difference between this and the upper arm pulse wave. The problem with this technique is that the ejection time is estimated by inputting electrocardiogram and phonocardiogram information into a cardiac motion model. In addition, since the measurement is based on the time difference from the opening of the aortic valve, it includes the curved portion of the arch of the ascending aorta, so it is not easy to estimate the blood vessel length with high accuracy from outside the body.

[0009] Patent No. 6399852 This involves detecting the aortic pulse wave accompanying ejection using a magnetic sensor. As with the previous case, this involves measuring the time difference from the time the aortic valve opens, and includes the curved portion of the arch of the ascending aorta, so it is not easy to estimate the blood vessel length with high accuracy from outside the body.

[0010] Patent No. 6541214 The aortic pulse wave accompanying ejection is detected by the pulse wave detection unit as an induced voltage generated by the magnetic flux generation unit and blood flow. As in the previous case, the time difference is measured from the time of opening of the aortic valve, and the curved portion of the arch of the ascending aorta is included, so it is not easy to estimate the blood vessel length with high accuracy from outside the body.

[0011] Re-table 2020 / 071480 The ballistocardiogram, which is the vibration caused by ejection, is detected by a piezoelectric vibration sensor. As in the previous case, the time difference is measured from the time of the aortic valve opening, and since it includes the curved part of the arch of the ascending aorta, it is not easy to estimate the blood vessel length with high accuracy from outside the body.

[0012] <Prior art related to the second method> Patent No. 3495348 This method determines the peaks of the forward and reflected wave components of the carotid artery wave detected by a pressure pulse wave detection probe, and calculates the pulse wave velocity from the time difference between them. The method of deconvoluting a single waveform, splitting it into two peaks, and determining the time difference between them is prone to problems with measurement accuracy, as there are large individual differences in waveforms.

[0013] Patent No. 5681434 The pulse wave velocity detection unit calculates the pulse wave velocity PWV by correcting the propagation velocity PWV (=2h / ΔT: h is the distance from the heart to the abdominal aortic bifurcation) calculated based on the time difference ΔT between the reference time T1 of the ejection wave component of the pulse wave detected by the reference time detection unit and the reference time T2 of the reflected wave component, using a correction coefficient (augmentation index) AI (=W1 / W2) calculated from the amplitude W1 of the pulse wave corresponding to the reference time T1 of the ejection wave component detected by the pulse wave amplitude detection unit and the amplitude W2 of the pulse wave S corresponding to the reference time T2 of the reflected wave component. Since correction is done with AI, it is considered to be more accurate than the previous example, but the method of deconvoluting one waveform, dividing it into two peaks, and calculating the time difference between them remains unchanged. This is likely to cause problems with measurement accuracy due to the large individual differences in the waveform.

[0014] Patent No. 5741087 The reflection coefficient of blood at the measurement site is calculated using a value representing the difference in vascular diameter between the measurement site in avascular occlusion and the peripheral side, and a value representing the hardness of the subject's blood vessels. These are then used to calculate a transfer function, which is then applied to the pressure pulse wave obtained from the measurement site to calculate the blood pressure waveform in the aorta. This is used to estimate the PWV between the heart and the abdominal aortic bifurcation. This method still uses the same method of deconvoluting one waveform, dividing it into two peaks, and determining the time difference between them. This method is prone to problems with measurement accuracy as there are many individual differences in the waveform. Summary of the Invention [Problem to be solved by the invention]

[0015] As described above, in all of the prior art related to the first method, measurements are taken from the aortic valve opening side at the center of the body, which means that the curved part of the aortic arch is included. This makes it difficult to estimate the blood vessel length from the body surface, which reduces the accuracy of PWV measurement. In addition, the prior art related to the second method uses a method of deconvoluting one waveform, dividing it into two peaks, and calculating the time difference between them, which is likely to cause problems in measurement accuracy. In particular, there are many individual differences in pulse waveforms, which is likely to cause problems in analysis accuracy.

[0016] The present invention aims to provide a method for directly measuring PWV of only the straight portion of the aorta from outside the body in a non-invasive manner, without using indirect methods such as deconvolving the waveform into two peaks. [Means for solving the problem]

[0017] The present invention has solved the above-mentioned problems by focusing on the fact that the aortic pulse wave propagates through small arteries and arterioles connected to the aorta, and that this propagated pulse wave can be detected by a photoplethysmographic sensor on the body surface near the aorta.

[0018] Conventionally, photoplethysmography sensors have been used to evaluate pulse waves and blood oxygen concentration at peripheral sites such as the fingertip and radius, but in the present invention, this photoplethysmography sensor is used to measure the pulse wave velocity of the aorta. Photoplethysmography sensors are of the transmissive type that uses near-infrared light and the reflective type that uses green light, but any photoelectric sensor of any wavelength range that can detect pulse waves can be used in the present invention.

[0019] The propagation of the pulse wave is unrelated to the velocity of blood flow. When the blood flow ejected from the heart due to the opening of the aortic valve collides with the aortic wall, vibrations are generated. This is a wave that is transmitted using the blood vessel walls and blood as a medium, and it is said that the further one gets to the periphery, the faster the propagation speed becomes.

[0020] In the present invention, the photoelectric pulse wave sensor is placed at two locations on the body surface, one on the upper back and the other on the lower back or waist, and the time difference between the pulse waves detected by both sensors is calculated to accurately estimate the pulse wave velocity of the aortic main body. This will be explained in detail below with reference to Figure 1 and Table 1.

[0021] [Table 1]

[0022] Two photoelectric pulse wave sensors, an upper back arteriole photoelectric pulse wave sensor 100 and a lower back arteriole photoelectric pulse wave sensor 110, are placed on the body surface of the upper back and lower back (or lumbar region) between the aortic arch 10 and the abdominal aortic bifurcation (not shown). These two body surfaces are connected to the aorta by the upper back arteriole 30 and the lower back arteriole 40, respectively. Therefore, pulse waves can be detected on each body surface.

[0023] Both sensors are connected to a photoelectric pulse wave control device 120 via a connection cable 140. The photoelectric pulse wave control device 120 is connected to a pulse wave display analysis device 130, which displays an upper back arteriolar wave 60 and a lower back arteriolar wave 70, and the pulse wave display analysis device 130 analyzes the time difference between these waves to calculate the pulse wave velocity of the aorta.

[0024] The time difference Tm between the two photoplethysmographic sensors, photoplethysmographic sensor 100 for the upper back arteriole and photoplethysmographic sensor 110 for the lower back arteriole, is calculated from the propagation time Ta of the straight portion 20 of the aorta to be measured, the propagation speed T1 of the upper back arteriole 30 to the body surface, and the propagation speed T2 of the lower back arteriole 40 to the body surface, using the following formula. Tm = (Ta + T2) - T1…(1)

[0025] By modifying the formula, the pulse wave propagation time Ta of the aortic straight section 20 to be measured is Ta = Tm - (T2 - T1) ... (2) It becomes.

[0026] Therefore, the pulse wave velocity Va of the aortic straight portion 20 to be measured is Va = Da / Ta = Da / (Tm ‐(T2 ‐T1)) = Da / (Tm ‐(D2 / V2 ‐D1 / V1))…(3) It becomes.

[0027] According to MRI tomographic image analysis, in the straight part of the aorta, the upper dorsal arteriole length D1 and the lower dorsal arteriole length D2 are independent of body type and can be considered as D2 ≒ D1. Va = Da / (Tm ‐(D1(1 / V2 ‐1 / V1)))…(4) In addition, the propagation speed of the dorsal arterioles from the aorta to the body surface is estimated to be approximately the same in both the upper and lower back, so V2 ≒ V1. Va = Da / Tm…(5)

[0028] Furthermore, MRI analysis of the lateral body image showed that in the straight part of the aorta, the aorta is arranged along the spine, so the aortic straight part distance Da is almost the same value as the corresponding inter-sensor body surface distance Dm. Therefore, Da ≒ Dm, Va = Dm / Tm…(6) It can be regarded as:

[0029] From the above, the pulse wave velocity Va of the straight aortic section is calculated from the body surface distance Dm between the sensors and the time difference Tm between the sensors. Va = Dm / Tm…(7) It can be calculated by: Effect of the Invention

[0030] According to the present invention, it is possible to easily measure the aortic Pulse Wave Velocity, which has been difficult to measure accurately and non-invasively until now, and to perform early diagnosis of arteriosclerosis of the aorta, mainly the abdominal aorta, where calcification of the vascular wall is believed to occur first in humans. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 illustrates an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing an example of a measurement result of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, the mode for carrying out the present invention will be described in detail based on examples. EXAMPLES

[0033] Here, a first embodiment of the present invention will be described. In the first embodiment, two photoplethysmographic sensor evaluation boards BH1792GLC-EVK-001 manufactured by ROHM Co., Ltd. were prepared and connected to a Sensor Shield-EVK-003 also manufactured by ROHM Co., Ltd. An Arduino Uno microcomputer was mounted on the Sensor Shield-EVK-003, which was connected to a PC via a USB cable. The waveform data of the two photoplethysmographic sensors was synchronously imported into the PC at a sampling frequency of 1 kHz, and the pulse wave velocity and other parameters were analyzed using a self-made PWV analysis software AYA-PMulti.

[0034] Two photoelectric pulse wave sensor evaluation boards manufactured by ROHM were attached to the upper and lower back of a subject (male, 51 years old) with surgical tape. Both sensors were attached 2 cm to the right of the spine. The subject was laid on his back with the aorta aligned with the spine. The body surface distance between the sensors was 20 cm.

[0035] Figure 2 shows the measurement results of the pulse wave velocity (PWV) of the straight aortic portion, analyzed by AYA-PMulti. The peak position for measuring the time difference was determined using the 5% rise point of the waveform, without differentiation of the waveform. The average time difference was 22.8 msec, and the PWV value was 8.77 m / sec, calculated using equation (7). EXAMPLES

[0036] As in Example 1, two photoelectric pulse wave sensor evaluation boards (sensors) manufactured by ROHM were attached to the upper and lower back of a 21-year-old female subject using surgical tape. The body surface distance between the sensors was 19 cm. As in Example 1, PWV analysis was performed using AYA-PMulti, and the average time difference was 45 msec, resulting in a PWV value of 4.22 m / sec. EXAMPLES

[0037] As in Examples 1 and 2, two ROHM photoelectric pulse wave sensor evaluation boards (sensors) were attached to the upper back and dorsum of the foot of a 22-year-old male subject with surgical tape. The body surface distance between the sensors was 135 cm. As in Examples 1 and 2, PWV analysis was performed using AYA-PMulti, resulting in an average time difference of 156 msec and a PWV value of 8.65 m / sec. In this way, this patented technology can be used to measure PWV not only in the aorta but also in peripheral arteries. EXAMPLES

[0038] As in Examples 1, 2, and 3, two ROHM photoelectric pulse wave sensor evaluation boards (sensors) were attached to the back of the knee and the back of the foot of a 55-year-old female subject with surgical tape. The sensor-to-body surface distance was 38 cm. As in Examples 1 and 2, PWV analysis was performed using AYA-PMulti, and the average time difference was 30 msec, resulting in a PWV value of 12.7 m / sec. In this way, this patented technology can also be used to measure PWV, which is an index of arteriosclerosis in peripheral areas not including the aorta.

[0039] Other Embodiments The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit and scope of the present invention. (1) In the above embodiment, the photoplethysmographic sensor is a photoplethysmographic sensor evaluation board BH1792GLC-EVK-001 manufactured by ROHM Co., Ltd., which is a sensor equipped with a green LED. However, a photoplethysmographic sensor equipped with a red or near-infrared LED, which is used for measuring blood oxygen levels, may also be used. (2) In the above embodiment, the upper back, lower back, back of the knee, and back of the foot are used as the measurement sites for the pulse wave, but it has been found that the pulse wave can be detected by the photoelectric pulse wave sensor via the arterioles in other sites, and the whole body surface can be used as the measurement site for the pulse wave velocity PWV. For example, by attaching a pulse wave sensor to the body surface of the upper arm and radius, the PWV of the local upper arm can be measured. [Industrial Applicability]

[0040] According to the present invention, the pulse wave velocity PWV of only the straight portion of the aorta can be measured directly and simply from outside the body in a non-invasive manner without using an indirect method such as deconvoluting the waveform into two peaks. This makes it possible to perform early diagnosis of arteriosclerosis of the aorta, particularly the abdominal aorta, where calcification of the vascular wall is believed to occur first in humans. [Explanation of symbols]

[0041] 10: Aortic arch 20: Straight aortic section 30: Upper dorsal arteriole 40: Inferior dorsal arteriole 60: Upper dorsal arteriolar wave 70: Inferior dorsal arteriolar wave 100: Photoelectric pulse wave sensor for upper back arterioles 110: Photoelectric pulse wave sensor for lower back arterioles 120: Photoelectric pulse wave control device 130: Pulse wave display and analysis device 140: Connection cable

Claims

1. A method for measuring aortic pulse wave velocity using multiple photoelectric pulse wave sensors

2. 2. The method for measuring pulse wave velocity according to claim 1, further comprising attaching at least one photoelectric pulse wave sensor to the back.

3. 2. The method for measuring pulse wave velocity according to claim 1, wherein a first photoplethysmographic sensor is attached to the upper back and a second photoplethysmographic sensor is attached to the lower back.

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