JP2005080722A - Pulse pressure measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a variation of a background component in the output signal of a pressure sensor in a pulse pressure measurement. <P>SOLUTION: A pulse pressure measuring device main body 22 is constituted in such a manner that a contact section 30 which comes into contact with a measuring area, and a sensor section 50 in which the pressure sensor 54 is arranged are superposed. The pressure sensor 54 outputs a pulse pressure detecting signal in response to a pressure difference between a measuring pressure air chamber 38 and a back pressure air chamber 58. By a thin and long communication passage 70 which communicates with the back pressure air chamber 58, an internal pressure difference between the measuring pressure air chamber 38 and the back pressure air chamber 58 is softened by a sufficiently longer softening time than the pulse pressure cycle. Thus, even when the body is moved after the pulse pressure measuring device main body 22 is attached, the background component which appears in the pulse pressure detecting signal varies with a favorable reproductivity conforming to a specified softening time characteristic, and the variation can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pulse pressure measuring device, and more particularly to a pulse pressure measuring device that measures a pulse pressure of an artery using a pressure sensor.

  As a non-invasive method of measuring blood pressure, the measurement site is measured by auscultating Korotkoff sounds that accompany arterial pulse pressure fluctuations in the process of pressurizing the measurement site with a cuff and then gradually reducing the pressure. Is widely used in medical settings. This method uses auscultation, measures the pressure at the height of the mercury column or water column, and because the measurement site is fixed, it is inconvenient for the person to measure. There have been proposed various types of electronic sphygmomanometers that improve convenience by using them. For example, Patent Document 1 discloses that a pressure and a pulse wave in a cuff are detected by a pressure sensor, and blood pressure is measured by calculating output data of the pressure sensor.

JP 2001-198093 A

  In order to extract the pulse pressure component of the artery with the pressure sensor, for example, it is necessary to pick up a pulsation component of about several tens to 100 mV in a signal change in the 3V range. That is, in order to extract the pulse pressure component of a small artery from the output of the pressure sensor, it is necessary to remove the background component of the signal. However, when the pressure sensor is attached to the measurement site and the pulse pressure is to be detected, the background component is greatly shifted if the body is moved. An example is shown in FIG. Here, the pressure sensor is fixed in the vicinity of the wrist radial artery by an appropriate attachment method, and the time change of the detection signal of the pressure sensor is shown with time on the horizontal axis and detection voltage on the vertical axis. As shown in FIG. 1, the detection signal of the pressure sensor includes a small pulsation component 10 indicating the pulse pressure of the artery. Here, when the wrist is slightly moved, the entire detection signal waveform greatly fluctuates at 12 and the measurement range is swung away. As the wrist stops moving, the fluctuation of the detection signal waveform tries to return to the original state, but it does not return completely, and the return method is not reproducible. That is, the background component 14 indicated by a broken line changes without reproducibility each time the wrist is moved.

  In order to remove the background component from the detection signal of the pressure sensor, for example, a high-pass filter is provided, or a background component curve is obtained by calculation such as a least square method, and this is subtracted. In addition, the background component changes greatly even with a slight movement, and the method of change is not reproducible, resulting in a complicated electronic circuit configuration or complicated arithmetic processing.

  An object of the present invention is to provide a pulse pressure measuring device that can solve the problems of the prior art and suppress the fluctuation of the background component in the output signal of the pressure sensor.

  In order to achieve the above object, a pulse pressure measurement device according to the present invention is a pulse pressure measurement device that detects a pulse pressure by pressing against a site where blood pressure is measured, and has an elastic plate on the surface pressed against the measurement site. A housing containing air having a predetermined pressure inside, a flexible thin film that divides the inside of the housing into a measurement pressure air chamber and a back pressure air chamber on the elastic plate side, and a pulse pressure from the measurement site. A pressure sensor that detects the pressure difference between the internal pressure of the measurement pressure air chamber and the back pressure air chamber, which changes according to the pressure, by the deformation of the flexible thin film, and the measurement pressure air chamber and the back pressure air chamber communicate with each other. And an elongate communication path that relaxes the internal pressure difference between the measured pressure air chamber and the back pressure air chamber with a relaxation time longer than the period.

  The communication path preferably has a diameter of 5 μm or more and 50 μm or less. Moreover, it is preferable that the length of a communicating path is 0.5 mm or more and 1.5 mm or less. The predetermined pressure is preferably 90 mbar or more and 150 mbar. The elastic plate is preferably formed by stacking a metal screen mesh thin plate and a plastic thin plate.

  Moreover, it is preferable that the pulse pressure measuring device according to the present invention further includes a transmission unit that wirelessly transmits the output of the pressure sensor.

  With the above configuration, the inside of the housing is partitioned into a measurement pressure air chamber on the elastic plate side and a back pressure air chamber by a flexible thin film, and an elongated communication path is provided between the measurement pressure air chamber and the back pressure air chamber. Communicate with Here, the flexible thin film becomes a pressure sensor that can detect a pressure difference between both sides of the thin film by deformation. The frequency component of the background component is on the lower frequency side than the frequency band of the pulse pressure component. The elongated communication path between the measurement pressure air chamber and the back pressure air chamber serves as a bypass filter for the pressure difference between both sides of the flexible thin film. Therefore, the frequency band of the bypass filter can be adjusted according to the diameter of the communication path, thereby suppressing the fluctuation of the background component in the output signal of the pressure sensor. The length of the elongated communication passage is set so that the measured pressure air chamber and the back pressure air chamber communicate with each other and the internal pressure difference between the measured pressure air chamber and the back pressure air chamber is relaxed in a relaxation time longer than the cycle of the pulse pressure. Is done. The condition that the diameter is 5 μm or more and 50 μm or less is a value obtained experimentally as a range in which the fluctuation of the background component can be suppressed. In this case, a small flexible thin film type pressure sensor was used, and the length of the communication path was set to about 0.5 to 1.5 mm.

  The predetermined pressurization is set to 90 mbar or more and 150 mbar, which is a value close to the blood pressure value. In this way, the elastic plate can easily transmit the fluctuation of the pulse pressure to the measurement pressure air chamber by substantially balancing the pressurization pressure and the pulse pressure of the measurement pressure air chamber. In addition, the elastic plate is configured by stacking a metal screen mesh thin plate and a plastic thin plate. The metal screen mesh thin plate expands and contracts only within the elastic range, and its periphery is held by the housing, so the surface shape changes as a whole according to the pulse pressure fluctuation, and the pulse pressure fluctuation is measured Uniform transmission to the compressed air chamber is possible. The plastic thin film serves to prevent air from leaking from the mesh portion of the screen mesh thin film.

  Further, since the output of the pressure sensor can be transmitted wirelessly, the signal line from the pulse pressure measuring device to the outside is eliminated, and handling becomes convenient.

  As described above, according to the pulse pressure measuring device of the present invention, the fluctuation of the background component in the output signal of the pressure sensor can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a diagram showing a state in which the pulse pressure measuring device 20 according to the embodiment of the present invention is pressed against or attached to the measurement site 18. As a place where the arterial pulse pressure can be easily detected, the measurement site 18 near the wrist radial artery inside the wrist can be used. The pulse pressure measuring device 20 is of a size that can be held by several fingers in one hand, and includes a pressure sensor that detects the pulse pressure inside, and an external signal line that extracts the output signal to the outside. The external signal line is connected to an appropriate waveform monitor or blood pressure calculator. In order to detect the pulse pressure, the pulse pressure measurement device 20 is held with one hand and pressed against the measurement site 18 or the pulse pressure measurement device 20 is attached to the measurement site 18 using a fixture such as an appropriate adhesive tape. Then, the output waveform of the pressure sensor can be displayed on the waveform monitor to observe fluctuations in pulse pressure or the like, or a blood pressure value based on the pulse pressure can be calculated using a blood pressure calculator.

  FIG. 3 is a cross-sectional view of the pulse pressure measuring device main body 22 with the external signal line removed from the pulse pressure measuring device 20. The pulse pressure measuring device main body 22 has a shape in which a contact portion 30 having a slightly larger outer shape that comes into contact with a measurement site and a sensor portion 50 in which the pressure sensor 54 is disposed inside is slightly smaller than the contact portion 30. doing. As an example, the outer diameter of the contact portion 30 is about 15-20 mm, the outer diameter of the sensor portion 50 is about 10-15 mm, and the overall height is about 2-3 mm.

  The contact portion 30 includes a lower housing 32 having a wide opening, an elastic plate 34 attached to the wide opening of the lower housing, and measured compressed air in an internal space surrounded by the lower housing 32 and the elastic plate 34. Chamber 38.

  The lower housing 32 is a flat cup-shaped member having a function of preventing the deformation of the measurement pressure air chamber 38 except for the elastic plate 34 at the wide opening, and the peripheral wall and ceiling wall thereof are made of a rigid material, for example, Consists of hard plastic. As shown in FIG. 3, the lower housing 32 can be obtained by assembling a rigid plastic annular peripheral wall member and a ceiling disk in an airtight manner, or by integral molding. As the rigid material, ceramic or metal having a necessary insulation treatment may be used. A common hole 40a and a communication hole 60a are provided in the ceiling wall of the lower housing, and details thereof will be described later.

  The elastic plate 34 is a thin plate member having a function of deforming into a concave-convex shape as a whole according to fluctuations in pulse pressure at the measurement site, and having an overall thickness of, for example, about 40-50 μm. Specifically, it can be constituted by a double structure of a metal screen mesh 35 that does not expand and contract except a very small elastic range and a plastic rubber 36 that can expand and contract in a large range. Alternatively, it may be composed of a single polyimide thin plate.

  The sensor unit 50 includes a sensor housing 52 having a recess through which the common hole 40b passes, a pressure sensor 54 that covers the common hole 40b and is attached to the recess of the sensor housing 52, and covers the recess of the sensor housing 52. The lid 56 includes a back pressure air chamber 58 that is an internal space surrounded by the sensor casing 52, the pressure sensor 54, and the lid 56.

  The sensor housing 52 has a substantially cylindrical shape, and is formed with a step having several steps so as to be dug from the outer peripheral portion toward the center portion, and a common hole 40b passes through the center of the recess. It is a member provided. There are at least two steps, and the first step that is closest to the common hole 40b and is dug down holds the periphery of the pressure sensor 54. An electrode pattern is provided on the second step that is less on the outer periphery side than the first step and less than the first step, and the electrode pattern and the electrode pad on the pressure sensor 54 are connected by a metal wire. The electrode pattern is connected to an external signal line drawn out of the pulse pressure measuring device main body 22. The depth of the second step is set to a sufficient depth so that the metal wire loop does not contact the lid 56. As shown in FIG. 3, in order to secure the volume of the back pressure air chamber 58, a third step with a small amount of digging may be provided further on the outer peripheral side of the second step to which the metal wire is connected. In addition, shapes other than those shown in FIG. 3 can be taken according to the shape of the pressure sensor. Such a sensor housing 52 can be obtained by, for example, molding ceramic or hard plastic into a predetermined shape, and wiring an electrode pattern or the like at a required location by a technique such as thick film printing. In addition, although the communication hole 60b is provided in the sensor housing | casing 52 toward a back pressure air chamber from the bottom part, the detail is mentioned later.

  The lid 56 is a disk-like member having the same outer diameter as the outer diameter of the sensor housing 52 and has a function of covering the recess of the sensor housing 52 and isolating the back pressure air chamber 58 from the outside. Specifically, the peripheral portion of the lid 56 is airtightly fixed to the uppermost edge of the recess in the sensor housing 52. The lid 56 may be formed of the same material as that used for the sensor housing 52, or may be a different material. For fixing to the sensor casing 52, adhesion or a hermetic seal can be used.

  The pressure sensor 54 is an element having a flexible thin film portion. For example, silicon having a predetermined plane orientation is locally etched in a larger area than the common hole 40b by selective etching, and the portion is flexible film portion. And a thick peripheral portion that is not etched can be used as an attachment portion to be attached to the sensor housing 52. A pressure sensor can be obtained by forming a resistance element in the flexible thin film portion using a semiconductor element forming technique. That is, since one surface of the flexible thin film portion faces the common hole 40b and the other surface faces the back pressure air chamber 58, the air pressure of the common hole 40b side and the air pressure of the back pressure air chamber 58 are Depending on the differential pressure, which is the difference, the flexible thin film portion bends upward or downward. The resistance element is subjected to stress according to the deflection of the flexible thin film portion and causes distortion, so that the resistance value changes. Therefore, the magnitude of the differential pressure can be detected from the change in resistance value.

  FIG. 4 is a diagram showing a circuit unit 80 for pressure detection. The resistance bridge 82 is formed by connecting four resistors provided in the flexible thin film portion of the pressure sensor 54 so as to form a bridge circuit. By using the resistance bridge circuit in this manner, the change in resistance value is set as a voltage value, and the change amount can be detected in an enlarged manner compared to the case of using one resistance element, and the output can be stabilized. The amplifier 84 is a circuit having a function of amplifying the detection signal in the resistance bridge 82. The output I / F 86 is a conversion circuit such as level adjustment for outputting the amplified signal via an external signal line. From the output I / F 86, a pulse pressure detection signal including a pulsation component of an artery as a background component is output. As an example of the pulse pressure detection signal, a pulsation component of about several tens to 100 mV can be output in the 3V range.

  The output I / F 86 is connected to an appropriate waveform monitor or blood pressure calculator via an external signal line. Moreover, it is good also as what transmits a pulse pressure detection signal to an external waveform monitor and a blood pressure calculator by a radio signal, without using an external signal line. In this case, after being amplified by the amplifier 84, conversion to a transmission signal is performed at the output I / F 86. The amplifier 84 and the output I / F 86 can be configured by independent circuit components or the like, and can be formed by using a semiconductor integrated circuit technique in the thick silicon of the pressure sensor 54.

  The contact part 30 and the sensor part 50 are fixed by positioning and fixing the ceiling wall of the lower housing 32 of the contact part 30 and the bottom part of the sensor housing 52 of the sensor part 50, as a whole. Become. The positioning is performed by matching the positions of the common hole 40a and the communication hole 60a provided in the ceiling wall of the lower housing 32 with the positions of the common hole 40b and the communication hole 60b provided in the bottom of the sensor housing 52. Is called. In order to facilitate positioning, the hole diameter on one side may be larger than the hole diameter on the other side. For fixing after positioning, fixing means such as adhesion or a small screw can be used.

  As shown in FIG. 3, the pulse pressure measuring device main body 22 assembled in this way has the function of the entire housing with the lower housing 32, the sensor housing 52, and the lid 56. Further, the pressure sensor 54 has a function of partitioning the measured pressure air chamber 38 and the back pressure air chamber 58 on the elastic plate side by positioning the common holes 40a and 40b. The positioned communication holes 60 a and 60 b have a function of communicating the measured pressure air chamber 38 and the back pressure air chamber 58 with a narrow communication passage 70.

  The measured pressure air chamber 38 and the back pressure air chamber 58 are shut off from the outside by the lower housing 32, the sensor housing 52, the lid 56, and the elastic plate 34, and communicated by a narrow communication passage 70. The measurement pressure air chamber 38 and the back pressure air chamber 58 that are communicated with each other are preliminarily filled with air having a pressure close to that of blood pressure. Encapsulation can be performed at the time of assembly of the pulse pressure measuring device main body 22 by attaching the elastic plate 34 or attaching the lid 56 as the last step. Alternatively, a separate air feed hole may be provided at an appropriate place such as the lower housing 32, air may be supplied from the hole to the inside, and the air may be stopped by closing the hole when a predetermined pressure is reached. . The pressurization can be, for example, 90 mbar or more and 150 mbar. Preferably it is around 120 mbar. In addition, although general air can be used for the air enclosed, it is preferable to manage the temperature and humidity at the time of enclosure in a predetermined range. Further, dry nitrogen gas or the like may be enclosed instead of air. Although it is possible to enclose a gas whose component is significantly different from that of air, in that case, it is necessary to convert the pressure into standard air so that the pressure is close to the blood pressure.

  The elongated communication passage 70 has a function of relaxing the internal pressure difference when there is an internal pressure difference between the measurement pressure air chamber 38 and the back pressure air chamber 58, and the relaxation time is a period of the pulse pressure, that is, The dimension of the communication path 70 is set so as to be sufficiently longer than the pulse period. For example, the diameter and length of the communication path 70 are set so that the relaxation time is about several times the pulse period minus 10 times. Specifically, the diameter and length of the communication path 70 can be set based on the size of the measured pressure air chamber 38 and the back pressure air chamber 58, the performance of the pressure sensor 54, and the like. As an example, as described above, the outer diameter of the contact part 30 is about 15-20 mm, the outer diameter of the sensor part 50 is about 10-15 mm, the overall height is about 2-3 mm, the measured pressure air chamber 38 and the back pressure. When the volume of the air chamber 58 is about 0.1-0.6 ml, and the pulse pressure detection signal is about several tens to 100 mV in the 3V range, the length of the communication path 70 is about 0.5 mm or more. It can be set to about 5 mm or less. With the length of the communication path 70 in this range, the diameter of the communication path can be set to 5 μm or more and 50 μm or less. Preferably, the thickness is about 8-10 μm. The cross section of the communication path 70 may not be circular. In that case, the diameter condition may be converted to an arbitrary cross section so that the cross-sectional areas are equal.

  The operation of the above configuration will be described. When the pulse pressure measuring device 20 in which a predetermined pressure is sealed in the measurement pressure air chamber 38 and the back pressure air chamber 58 is pressed or attached to the measurement site, the elastic plate 34 receives fluctuations in the pulse pressure of the artery at the measurement site, and the measurement is performed. The internal pressure of the compressed air chamber 38 is changed. Since the communication path 70 is elongated and its relaxation time is sufficiently longer than the pulse pressure cycle, the internal pressure change due to the pulse pressure is not immediately transmitted to the back pressure air chamber 58. Therefore, the pulse pressure detection signal is output from the output I / F 84 in accordance with the differential pressure that is the pressure difference between both sides of the flexible thin film in the pressure sensor 54, but at this time, the background component hardly changes. The above is the operation of the pulse pressure measuring device 20 in a normal case.

  Here, when the body is moved, the state in which the pulse pressure measuring device 20 is pressed against or attached to the measurement site slightly changes, the internal pressure of the measurement pressure air chamber 38 changes greatly, and the internal pressure changes due to the pulsation component of the artery. Greatly changes the background component. This large change in internal pressure is slowly transmitted to the back pressure air chamber 58 by the relaxation time of the communication passage 70. Since the relaxation time can be set in advance by the dimensions of the communication passage 70, etc., the background component of the pressure difference between the measured pressure air chamber 38 and the back pressure air chamber 58 becomes a constant change according to the characteristics of the relaxation time. . That is, the background component appearing in the pulse pressure detection signal when the body is moved changes according to a certain relaxation time characteristic, and can have reproducibility.

  FIG. 5 is a diagram showing this state by a change in the detection signal of the pressure sensor 54. The horizontal axis and the vertical axis are the same as in the case of the conventional example shown in FIG. As shown in FIG. 5, when the wrist is moved, the entire detection signal waveform greatly fluctuates and the measurement range is swung away, but then gradually returns according to the relaxation time characteristic of the communication path 70. The return method follows the same relaxation time characteristic even when the wrist is moved 12, that is, the background component 114 indicated by a broken line changes with the same characteristic with good reproducibility. Therefore, the fluctuation of the background component can be suppressed with good reproducibility from the detection signal of the pressure sensor 54, and the background component can be easily removed.

  It can be used for a pulse pressure measuring device using a pressure sensor. Moreover, it can be used as a pulse pressure measuring unit in an electronic blood pressure monitor.

In a prior art, it is a figure explaining the big change of the detection signal of a pressure sensor when a body is moved. It is a figure which shows a mode that the pulse-pressure measuring apparatus of embodiment which concerns on this invention is pressed or attached to a measurement site | part. It is sectional drawing of the pulse pressure measuring device main body in embodiment which concerns on this invention. It is a figure which shows the circuit part of the pressure detection in embodiment which concerns on this invention. It is a figure explaining the change of the detection signal of a pressure sensor when the body is moved using the pulse pressure measuring apparatus in embodiment which concerns on this invention.

Explanation of symbols

  10 Pulsating component, 14, 114 Background component, 18 Measurement site, 20 Pulse pressure measuring device, 22 Pulse pressure measuring device body, 30 Contact part, 32 Lower housing, 34 Elastic plate, 35 Screen mesh, 36 Plastic rubber, 38 Measurement pressure air chamber, 50 sensor section, 52 sensor housing, 54 pressure sensor, 58 back pressure air chamber, 70 communication path.

Claims (6)

  A pulse pressure measuring device that detects a pulse pressure by pressing against a site where blood pressure is measured, and includes a housing including air having an elastic plate on a surface pressed against the measurement site and having a predetermined pressure inside. A flexible thin film that divides the inside of the body into a measurement pressure air chamber and a back pressure air chamber on the elastic plate side, and the internal pressure of the measurement pressure air chamber and the internal pressure of the back pressure air chamber that change according to the pulse pressure from the measurement site A pressure sensor for detecting a pressure difference by deformation of a flexible thin film, and a measurement pressure air chamber and a back pressure air chamber with a relaxation time longer than a cycle of pulse pressure by communicating the measurement pressure air chamber and the back pressure air chamber. And a long and narrow communication passage that relieves the internal pressure difference between the two.   2. The pulse pressure measuring device according to claim 1, wherein the communication path has a diameter of 5 μm or more and 50 μm or less.   2. The pulse pressure measuring apparatus according to claim 1, wherein the communication path has a length of not less than 0.5 mm and not more than 1.5 mm.   The pulse pressure measuring device according to claim 1, wherein the predetermined pressure is 90 mbar or more and 150 mbar.   2. The pulse pressure measuring device according to claim 1, wherein the elastic plate is formed by stacking a metal screen mesh thin plate and a plastic thin plate. 2. The pulse pressure measuring apparatus according to claim 1, further comprising a transmitter that wirelessly transmits the output of the pressure sensor.

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