JP2014045917A - Fetal heart beat-measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fetal heart beat-measuring device having a sound-collecting structure easy to search fetal heart beat.SOLUTION: Fetal heart beat microphones 20 and 30 collect sound of fetal heart beat. A signal processing part 40 outputs fetal heart beat signals based on sound signals collected by the fetal heart beat microphones 20 and 30. When a distance between the fetal heart beat microphone 20 and the fetal heart beat microphone 30 is denoted by L and a radius of a detection range of the fetal heart beat microphone 20 and the fetal heart beat microphone 30 is denoted by R, L is larger than R (a prescribed distance) and R is equal to or more than one-half of L.

Description

  The present invention relates to a fetal heart sound measuring apparatus that measures fetal heart sounds, and more particularly to a fetal heart sound measuring apparatus that measures fetal heart sounds using two fetal heart sound microphones.

  The health condition of the fetus in the mother's body is generally examined by an examination device used by a doctor or the like. The inspection apparatus performs processing such as image diagnosis using ultrasonic echoes, heart beat detection using an ultrasonic Doppler, and a synthetic sound added to the heart beat. Pregnant women can check fetal heart sounds by regularly going to the hospital and undergoing screening using these examination devices. However, diagnosis using the above-described inspection apparatus using ultrasonic waves cannot be performed in a private home. Therefore, pregnant women cannot check fetal heartbeats on a daily basis. However, the demand for pregnant women and the like to check the health condition of the fetus on a daily basis is very high. Therefore, further development of a commercial fetal heart sound measuring device is strongly desired.

  The normal range of fetal heartbeat is 110 to 160 bpm (beats per minute), which is a pulse rate twice or more that of an adult. If the pulse rate is within this range, the fetus is determined to be well-being. A tachycardia higher than the normal range and a bradycardia lower than the normal range are treated as a state of caution unless they are transient.

  The fetus is surrounded by amniotic fluid in the maternal body and buried in the soft tissue of the maternal body. Therefore, it is not easy to hear the fetal heart sound emitted from the fetus from the maternal surface. Of course, the fetal heart is very small compared to adults. For example, fetuses aged 36 to 40 weeks (10 months of age) on average have a height of about 50 cm, a body weight of about 3 kg, a shoulder width of about 11 cm, and a lateral heart diameter (cross section length of the heart) of about 36 mm to 40 mm. On the other hand, the adult horizontal heart diameter is 12 to 15 cm, which is about 4 to 5 times that of the fetus. In the case of adults, heart sounds can be auscultated from more than half of the chest, and pulsation can be confirmed from other parts (for example, wrist). Therefore, it is not difficult to collect adult heart sounds. On the other hand, as described above, since the fetal heart is very small and the fetus is in the mother's body, the sound pressure sensitivity of the fetal heart sound is -20 dB to -40 dB. This sound pressure sensitivity is 1 to 2 orders of magnitude worse than that of adults. Therefore, it is not easy to measure heart sounds using a technique equivalent to adult heart sounds.

  For example, Patent Document 1 is cited as a related art related to a civil fetal heart sound measuring device. Patent Document 1 discloses a bioacoustic signal system provided with a dedicated vibration sensor provided with two or more piezo elements to facilitate the search for fetal heart sounds.

Japanese Patent Laid-Open No. 10-216123

  The present invention mainly relates to a fetal heart sound measuring device used for civilian purposes. As described above, the sound pressure sensitivity of the fetal heart sound is very low, and the fetal heart sound cannot be properly heard unless the microphone of the fetal heart sound measuring device is brought into contact with an appropriate position on the surface of the mother's body. However, the conventional technology does not sufficiently study the structure of a fetal heart sound measuring device for listening to fetal heart sounds, and there is a problem that it is difficult for users who are not experts (mainly pregnant women) to use the fetal heart sound measuring device. It was.

  The present invention has been made in view of the above-described problems, and a main object of the present invention is to provide a fetal heart sound measuring device having a sound collection structure that facilitates searching for fetal heart sounds.

Therefore, the present invention collects the first fetal heart sound microphone (20) for collecting fetal heart sounds, the second fetal heart sound microphone (30) for collecting fetal heart sounds, and the first fetal heart sound microphone (20). A signal processing unit (40) for outputting a fetal heart sound signal based on the first sound signal and the second sound signal collected by the second fetal heart sound microphone (30),
The distance L between the first fetal heart sound microphone (20) and the second fetal heart sound microphone (30) is set as the radius R of the detection range of the first and second heart sound microphones (20, 30). Provided is a fetal heart sound measuring device (1) characterized by satisfying the following formula when the average shoulder width of the moon is a predetermined distance.
Predetermined distance <= L + R ――― Formula (1)
R> = L / 2 ――― Formula (2)
In the fetal heart sound measuring device (1), the radius R may be configured to be approximately equal to the distance L.
In the fetal heart sound measuring device (1), the predetermined distance may be substantially equal to an average shoulder width of a fetus month of October.
In the fetal heart sound measuring device (1), the signal processing unit (40) calculates a signal difference value between the first audio signal and the second audio signal in a predetermined period, and the signal difference value is equal to or greater than a predetermined threshold value. If the signal difference value between the first sound signal and the second sound signal is output as the fetal heart sound signal, and the signal difference value is less than a predetermined threshold value, the first sound signal and the second sound signal are output. A signal sum with a signal may be output as the fetal heart sound signal.
In the fetal heart sound measuring device (1), each of the first fetal heart sound microphone (20) and the second fetal heart sound microphone (30) includes a microphone element (201) for collecting fetal heart sound and a contact surface (206). ) Through a vibration transmitting portion (203) made of a material having a Shore A hardness of 40 or more, and a surface facing the contact surface (206) is in contact with the microphone element (201). The vibration transmission unit (201) and the inner case (202) for accommodating the microphone element (201) may be provided.
In the fetal heart sound measuring device (1), the inner case (202) extends from a plane parallel to the contact surface (206), and the upper surface of the inner case (202) and the microphone element (201). A vibration damping portion (207) provided so as to cover the upper surface may be further included.
The fetal heart sound measuring device (1) may further include an information output unit (50) for displaying fetal heart sound information on a display device or printing on a printing device based on the fetal heart sound signal.

  The present invention can provide a fetal heart sound measuring device having a sound collection structure that facilitates searching for fetal heart sounds.

It is a block diagram which shows the structure of the fetal heart sound measuring apparatus 1 concerning Embodiment 1 of this invention. It is a perspective view which shows the external appearance of the fetal heart sound collection unit 10 concerning Embodiment 1 of this invention. It is sectional drawing of the fetus heart sound microphone 20 concerning Embodiment 1 of this invention. It is an example from which sectional drawing of the fetus heart sound microphone 20 concerning Embodiment 1 of this invention differs. It is a table | surface which shows each state containing the magnitude | size (lateral heart diameter) of the fetal heart after 16 weeks of age. It is the schematic which looked at the fetal heart sound collection unit 10 concerning Embodiment 1 of this invention from the bottom face (contact surface with a pregnant woman mother body). It is a figure which shows the example of a measurement which measured the fetal heart sound in the maternal body of a 36-week-old pregnant woman using the fetal heart sound collection unit 10 concerning Embodiment 1 of this invention. It is a figure which shows the measurement result at the time of measuring the fetal heart sound in the 36-week-old pregnant mother body using the fetal heart sound-collecting unit 10 concerning Embodiment 1 of this invention. It is a figure which shows the measurement result at the time of measuring the fetal heart sound in the 36-week-old pregnant mother body using the fetal heart sound-collecting unit 10 concerning Embodiment 1 of this invention. It is a figure which shows the example of a measurement which measured the fetal heart sound in the maternal body of a 36-week-old pregnant woman using the fetal heart sound collection unit 10 concerning Embodiment 1 of this invention. It is a figure which shows the measurement result at the time of measuring the fetal heart sound in the 36-week-old pregnant mother body using the fetal heart sound-collecting unit 10 concerning Embodiment 1 of this invention. It is a figure which shows the measurement result at the time of measuring the fetal heart sound in the 36-week-old pregnant mother body using the fetal heart sound-collecting unit 10 concerning Embodiment 1 of this invention. FIG. 6 is a graph showing changes in fetal heart sounds when the signal difference between the sound signals (first sound signal and second sound signal) collected by both microphones in the first measurement example according to the first embodiment of the present invention is a monaural signal. is there. FIG. 7 is a graph showing changes in fetal heart sound when a signal difference between sound signals (first sound signal and second sound signal) collected by both microphones in the measurement example 2 according to the first embodiment of the present invention is a monaural signal. is there. FIG. 7 is a graph showing changes in fetal heart sound when the signal sum of the sound signals (first sound signal and second sound signal) collected by both microphones is a monaural signal in Measurement Example 1 according to the first embodiment of the present invention. is there. FIG. 7 is a graph showing changes in fetal heart sound when the signal sum of the sound signals (first sound signal and second sound signal) collected by both microphones is a monaural signal in Measurement Example 2 according to the first embodiment of the present invention. is there. It is a graph which shows the relationship between the Shore A hardness of the fetus heart sound conduction layer in the fetus heart sound microphone which concerns on Embodiment 1 of this invention, and a frequency.

  Hereinafter, an example of an embodiment to which the present invention is applied will be described. It goes without saying that other embodiments may also belong to the category of the present invention as long as they match the gist of the present invention. In addition, the sizes and ratios of the members in the following drawings are for convenience of explanation, and the actual ones may not necessarily be those sizes and ratios. Further, in the following embodiments and modifications, the same type members are denoted by the same reference numerals, and the description thereof is omitted as appropriate.

<Embodiment 1>
FIG. 1 is a block diagram showing a configuration of a fetal heart sound measuring apparatus 1 according to the present embodiment. The fetal heart sound measuring device 1 includes a fetal heart sound collecting unit 10 and an information output unit 50. The fetal heart sound collecting unit 10 includes a fetal heart sound microphone 20, a fetal heart sound microphone 30, and a signal processing unit 40. FIG. 1 also shows a schematic diagram of a pregnant woman and a fetus in the mother's body.

  Prior to the description of the processing of each processing unit, the appearance and configuration of the fetal heart sound collecting unit 10 and the configuration of the fetal heart sound microphone 20 (30) will be described with reference to FIGS. FIG. 2 is a perspective view showing an example of the appearance of the fetal heart sound collecting unit 10.

  The fetal heart sound collecting unit 10 includes an outer case 100, a fetal heart sound microphone 20, and a fetal heart sound microphone 30. The outer case 100 and the fetal heart sound microphone 20 are connected by two cylindrical support members (204-1, 204-2). Similarly, the outer case 100 and the fetal heart sound microphone 30 are connected by two cylindrical support members (204-3, 204-4). The distance between the fetal heart sound microphone 20 and the fetal heart sound microphone 30 will be described later with reference to FIG. Although not shown in FIG. 2, it is assumed that the fetal heart sound collecting unit 10 appropriately includes a circuit or the like constituting the signal processing unit 40. The fetal heart sound unit 10 appropriately includes a cable (not shown) for outputting a fetal heart sound signal generated from the collected sound signal to an arbitrary device (including an information output unit 50 described later). The fetal heart sound unit 10 may have a configuration that does not include the cable and appropriately communicates with an external device using a wireless function.

  The outer case 100 is a housing that is gripped by a user (for example, a pregnant woman). Fetal heart sound microphones 20 and 30 house a microphone element and the like, which will be described later, and have a contact surface with the mother's body on the surface facing the upper surface of outer case 100. Here, a direction in which the contact surface of the fetal heart sound microphone 20 or 30 is viewed from the upper surface of the outer case 100 is defined as a downward direction or a vibration detection direction, and a reverse direction is defined as an upward direction. The support members 204-1 and 204-2 that connect the outer case 100 and the fetal heart sound microphone 20 are provided on the same axis, and the axial direction is substantially parallel to the contact surface. Similarly, support members 204-3 and 204-4 that connect the outer case 100 and the fetal heart sound microphone 30 are provided on the same axis, and the axial direction is substantially parallel to the contact surface.

  FIG. 3A is a cross-sectional view showing the configuration of the fetal heart sound microphone 20. The cross-sectional view includes an axis connecting the support members 204-1 and 204-2. The fetal heart sound microphone 20 includes a microphone element 201, an inner case 202, a vibration transmission unit 203, a support member 204-1, a support member 204-2, and a vibration control unit 207. The microphone element 201 has a diaphragm 205 exposed in the vibration detection direction (downward). A lower surface (bottom surface) of the vibration transmitting unit 203 has a contact surface 206 that comes into contact with the surface of the mother's body.

  The microphone element 201 detects vibration in the diaphragm 205. The microphone element 201 supplies an electric signal (first audio signal described later) corresponding to the detected vibration to the signal processing unit 40. The microphone element 201 may be any type of microphone element such as an electric capacitor type, a capacitor type, a piezoelectric type, and a dynamic type. The type of the microphone element 201 is selected according to the use environment and the detection target, but it is most effective to use an electric capacitor type from the viewpoints of weight reduction, size reduction, circuit signal processing, and the like. .

  The diaphragm 205 that contacts the microphone element 201 is in contact with the vibration transmission unit 203. The diaphragm 205 is a plate-like member that is in contact with the vibration transmission unit 203, but is not necessarily limited to the plate-like member, and may be a diaphragm, for example.

  The inner case 202 is disposed so as to cover the outer surfaces of the microphone element 201 and the vibration transmitting unit 203. The inner case 202 has a cylindrical shape as shown in FIG. 2, but is not necessarily limited thereto, and may have another shape (for example, a hexagonal cylinder, an octagonal cylinder, etc.). The material of the inner case 202 is not particularly limited, but may be formed of a highly vibration-damping metal such as aluminum, brass, or stainless steel, a resin such as ABS resin, PET resin, or PC (polycarbonate).

  The vibration transmission unit 203 is a vibration transmission medium that transmits the vibration of the fetal heart sound generated from the contact surface 206 on the maternal body surface to be detected (vibration source) to the diaphragm 205. The vibration transmitting unit 203 uses an acoustic impedance characteristic that is close to the acoustic impedance characteristic of the region where fetal heart sounds are collected. Here, the acoustic impedance in the subject refers to an acoustic impedance obtained by synthesizing a conduction sound of a hard tissue including a soft tissue part such as skin, subcutaneous tissue, organ, and muscle, and a skeleton.

  The vibration transmission unit 203 has high hardness, Young's modulus (elastic modulus), high anti-sliding noise characteristics, small acoustic impedance difference from the maternal mother surface, and the speed of sound in the vibration transmission unit 203 is in vivo. What has a characteristic substantially equivalent to a sound speed is preferable. By setting the Shore A hardness of the vibration transmitting unit 203 to 40 or more, the low frequency side band can be shifted in a lower direction, and the high frequency side band can be shifted in a higher direction, thereby achieving a wider band. As a result, the frequency characteristics can be improved, and fetal heart sounds can be extracted with high efficiency. Since the upper limit value of the Shore A hardness of the vibration transmitting portion 203 can be suitably applied even in the recommended measurement range 90 for a member having rubber elasticity, the preferable upper limit value of the Shore A hardness cannot be defined by the measurement limit. In addition, Shore A hardness is performed by the method as described in ASTM standard (ASTM D2240) or JIS standard (JIS K6523).

  The material of the vibration transmitting portion 203 may be any material that satisfies the above-described characteristics. Preferred examples include viscoelastic bodies and rubber elastic bodies, and particularly preferred examples include silicone elastomer. That is, it is desirable to form the vibration transmitting portion 203 by filling it with silicone elastomer.

  The vibration transmitting unit 203 is in contact with the microphone element 201 via the diaphragm 205. The vibration transmitting portion 203 has a straight cone shape in cross section as shown in the figure. By making the vibration transmitting portion 203 into a straight cone shape, the microphone element 201 can obtain a flat frequency characteristic. Note that it is possible to increase the bandwidth by making the vibration transmitting portion 203 a curved cone shape or a parabolic cone shape. By changing the angle and depth of the straight cone shape of the vibration transmitting unit 203, the frequency characteristics can be adjusted, and the detection range can be adjusted. Here, the detection range is a detection region in which the fetal heart sound microphone 20 or 30 in contact with the pregnant woman's mother can stably collect the peak of the heart sound of the fetal heart. Increasing the aperture of the vibration transmitting unit 203 increases the sound collection sensitivity and widens the detection range. However, the greater the depth of the vibration transmission unit 203 (the distance from the contact surface 206 to the microphone element 201), the more the attenuation occurs.

The contact surface 206 functions as a fetal heart sound conduction layer for acoustic impedance matching and microphone surface protection. Moreover, since the contact surface 206 is in contact with the pregnant woman's mother body, it is desirable to have sufficient cushioning properties.
Further, the fetal heart sound microphones 20 and 30 are configured as shown in FIG. 3B, and a fetal heart sound conducting layer 209 is provided on the contact surface 203 side of the vibration transmitting unit 203. The vibration transmitting unit 203 has a shear A hardness lower than that of the fetal heart sound conducting layer. You may comprise with a raw material. By filling the vibration transmitting unit 203 with a large difference in acoustic impedance with the maternal body, the fetal heart sound conduction layer 209, and the inner case 202, it is possible to effectively increase the attenuation of external noise and suppress noise mixing. it can. In the fetal heart sound microphone provided with such a fetal heart sound conduction layer 209, FIG. 10 shows the result of plotting the frequency characteristics of the measured sound of each sample by changing the Shore A hardness of the fetal heart sound conduction layer 209. The low-frequency side frequency and the high-frequency range frequency shown in the figure indicate the low-frequency range and high-frequency range frequencies of the sound pressure that is −10 dB from the maximum sound pressure peak. It can be seen that when the Shore A hardness is 40 or more, the low frequency range is shifted to the low frequency range, the high frequency range is shifted to the high frequency range, and the bandwidth is increased. Therefore, the Shore A hardness of the fetal heart sound conduction layer 209 is preferably 40 or more.

  In the inner case 202, the damping unit 207 extends from the parallel surface of the contact surface 206 in a direction substantially parallel to the outer surface of the inner case 202. Furthermore, the vibration control unit 207 is installed so as to cover the upper surfaces of the inner case 202 and the microphone element 201. Since the vibration control unit 207 plays a role of blocking external noise, it is desirable that the vibration damping unit 207 has excellent sliding noise resistance and external environmental noise characteristics. As the damping part 207, a viscoelastic body or a rubber elastic body is preferable as a preferable example, and a urethane nest lamar or the like is particularly preferable.

  Two support members 204-1 and 204-2 are provided on the outer surface of the inner case 202. Support members 204-1 and 204-2 are cylindrical. The straight line connecting the support members 204-1 and 204-2 is substantially parallel to the contact surface 206. The support members 204-1 and 204-2 can be made of the same material as that of the inner case 202, or may be configured using other materials. The support members 204-1 and 204-2 are provided on the same axis and connect the inner case 202 and the outer case 100.

  The outer case 100 is disposed so as to cover the outer surface of the inner case 202. The outer case 100 is a portion that is held by a user (for example, a pregnant woman).

  The outer case 100 has two holes 208-1 and 208-2 corresponding to the support members 204-1 and 204-2, respectively, on the inner surface. The holes 208-1 and 208-2 are provided on the same axis. The holes 208-1 and 208-2 are fitted with the support members 204-1 and 204-2, respectively. Thereby, the outer case 100 and the inner case 202 are connected. The inner case 202 has the support members 204-1 and 204-2 pivoted by making the holes 208-1 and 208-2 into cylindrical grooves having substantially the same diameter as the support members 204-1 and 204-2. Is configured to be rotatable. The inner case 202 is configured to be rotatable, so that the contact surface 206 is easily brought into close contact with the surface of the pregnant mother even when the fetal heart sound collecting unit 100 is moved on the surface of the pregnant mother.

  The material of the outer case 100 is not particularly limited, but may be formed of a highly vibration-damping metal such as aluminum, brass, or stainless steel, a resin such as ABS resin, PET resin, or PC (polycarbonate).

  In FIG. 3, the inner case 202 and the outer case 100 are connected by two support members. However, the present invention is not limited to this, and the inner case 202 and the outer case 100 may be connected by one support member. The configuration of the fetal heart sound microphone 30 is substantially the same as that of the fetal heart sound microphone 20 shown in FIG.

  Refer to FIG. 1 again. The signal processing unit 40 includes a signal relating to the fetal heart sound heard by the fetal heart sound microphone 20 (hereinafter referred to as a first audio signal) and a signal relating to the fetal heart sound heard by the fetal heart sound microphone 30 (described below). Then, the second audio signal is input. The signal processing unit 40 obtains a difference (dB) between the first audio signal and the second audio signal at regular intervals (for example, every 1 second) for a certain period (for example, 0.05 seconds), and calculates an average difference value thereof. To do. If the difference value is equal to or greater than a predetermined threshold value, the signal processing unit 40 generates an audio signal obtained by subtracting the other audio signal from the audio signal having a high sound pressure among the first audio signal and the second audio signal. The generated audio signal is supplied to the information output unit 50 as a fetal heart sound signal. On the other hand, when the difference value is less than the predetermined threshold value, the signal processing unit 40 supplies an audio signal obtained by adding the first audio signal and the second audio signal to the information output unit 50 as a fetal heart sound signal.

  The information output unit 50 is a processing unit that displays the fetal heart sound signal input from the signal processing unit 40 in an arbitrary format. The information output unit 50 is configured to be integrated or connectable with, for example, a display device. The information output unit 50 displays the heart rate of the fetus on the display surface of the display device based on the input fetal heart sound signal. The information output unit 50 can also graph a long-term change in fetal heart sound based on the fetal heart sound signal and display it on the display surface of the display device. The information output unit 50 can also output the fetal heart sound based on the fetal heart sound signal. At this time, the information output unit 50 can also output a sound after performing a pitch shift process or the like for conversion into a frequency band that is easier to hear.

  The information output unit 50 may be configured to be connected to or integrated with a printing device such as a simple printer. In this case, the information output unit 50 outputs a printed paper on which a graph or the like indicating the transition of the fetal heart sound is printed based on the input fetal heart sound signal. The information output unit 50 may be configured to transmit fetal heart sound information to another communication device (for example, a mobile phone or a smartphone held by a pregnant woman).

  Next, general properties of the fetus will be described. The fetus repeats sleeping and waking up at intervals of about 20 minutes in the maternal amniotic fluid while it is young and moves relatively freely. Thus, while the fetus is young, the orientation of the fetus in the mother's body is not fixed and changes frequently. Therefore, it is known that it is difficult to specify the position of the fetus while the age of the fetus is young. According to the diagnosis by a doctor, when the fetus is about 20 weeks old, the sound pressure is such that the fetal heart sound can be heard.

  The average value of each state including the size of the fetal heart after 16 weeks of age (cardiac transverse diameter) is shown in FIG. FIG. 4 is a table showing the average size of each fetus at each age. For example, when the age is 16 to 19 weeks, the weight of the fetus is about 280 to 300 g, the height is about 25 to 26 cm, the shoulder width is about 4 cm, and the transverse diameter is about 16 to 19 mm.

  The fetal heart sound needs to be heard from the back side of the fetus, and the sound collection unit (in this embodiment, the fetal heart sound microphone 20 or 30) needs to be almost directly above the fetal heart. The fetal heart sound does not propagate isotropically and has directivity in a narrow range. Therefore, when the posture of the fetus changes or when the fetus moves, auscultation of the fetal heart sound becomes difficult unless the sound collection unit is moved.

  In general, doctors and the like can detect the fetal posture by palpation from the abdominal body surface of the pregnant woman when the fetus in the mother's body is 30 weeks of age or later. During this palpation, doctors first find the position of one shoulder of the fetus. The fetal heart is between the shoulders. Therefore, a pregnant woman who uses the fetal heart sound collecting unit 10 first searches for a shoulder on one side of the fetus by palpation. Then, the pregnant woman places one fetal heart sound microphone 20 at the searched position and moves the fetal heart sound collecting unit 10 so as to slide on the mother's body, thereby searching for an optimal auscultation position, Collect sound.

  Next, the detection operation of the fetal heart sound by the fetal heart sound collecting unit 10 will be described with reference to FIG. FIG. 5 is a schematic view of the fetal heart sound collecting unit 10 as seen from the bottom surface (contact surface with the pregnant woman's mother). FIG. 5 also shows a conceptual diagram of a 10 month old fetus. The distance L between the fetal heart sound microphone 20 and the fetal heart sound microphone 30 (the distance from the center position of the contact surface of the fetal heart sound microphone 20 to the center position of the contact surface of the fetal heart sound microphone 30. Hereinafter, the distance L between the microphones is described. )) And the radius (detection radius) of the detection range of the fetal heart sound microphone 20 and the fetal heart sound microphone 30 is R (hereinafter referred to as detection radius R).

As described above, the heart is between both shoulders of the fetus, and the shoulder on one side of the fetus can be detected by palpation. Therefore, the fetal heart sound microphone 20 (or 30) is placed at the shoulder position on one side, and the maternal surface is searched. Here, when the sum of the distance L between the microphones and the detection radius R is equal to or larger than the fetal shoulder width, it is easy to detect the fetal heart sound without omission by moving the fetal heart sound unit 10 as illustrated. That is, the relationship between the distance L between microphones, the detection radius R, and the fetal shoulder width is expressed by the following formula (1).
Fetal shoulder width <= Microphone distance L + Detection radius R ――― Formula (1)

  As shown in FIG. 4, the fetal shoulder width varies depending on the age and the pregnant woman. Therefore, the fetal shoulder width in the above formula (1) can be read as an arbitrary distance (predetermined distance) in the range of the shoulder width that can be taken by a week-old fetus capable of detecting heart sounds. However, the heart position of the fetus can be detected most easily (with few scans) by setting the average fetal shoulder width at the age of 10 months immediately before giving birth to the fetal shoulder width of the above-described formula (1).

Next, the detection radius R will be examined. When the detection radius R is smaller than half of L, a range in which the fetal heart sound cannot be detected in the section of the distance L between the microphones occurs. Therefore, the detection range R needs to satisfy the following formula (2).
R> = L / 2 ――― Formula (2)

However, increasing the detection range R causes difficulty in designing the microphone and increasing the cost. Therefore, as shown in FIG. 5, it is desirable that the detection range of the fetal heart sound microphone 20 (dotted line portion in the figure) and the detection range of the fetal heart sound microphone 30 (dotted line portion in the figure) be in contact with each other. That is, it is desirable that the inter-microphone distance L and the detection radius R satisfy the following expression (3).
R ≒ L / 2 ――― Formula (3)

  Even if it is not possible to grasp the shoulder on one side of the fetus by palpation, a wide range including the fetal shoulder width can be covered by adopting the configuration satisfying the above formulas (1) and (3). A wide range of searches can be performed with this scan. In addition, when the fetal shoulder width (month of October) and the sum of the distance L between the microphones and the detection radius R are completely equal in the formula (1), it corresponds to almost all fetal shoulder widths while keeping the detection radius R small. Can do.

(Measurement Example 1)
Below, the 1st measurement example which measured the fetal heart sound in the maternal body of a 36-week-old pregnant woman using the fetal heart sound collection unit 10 concerning this Embodiment is shown. FIG. 6A shows a conceptual diagram of the measurement. In FIG. 6A and later-described FIG. 7A, the structure of the fetal heart sound collecting unit 10 is schematically shown. In this measurement, the fetal heart sound collecting unit 10 is placed on the pregnant woman's mother so that the fetal heart sound is located almost directly below the fetal heart sound microphone 20. Further, the distance L between the microphones satisfies the above formula (1), and the detection radius R satisfies the above formula (3).

  FIG. 6B shows the first audio signal detected by the fetal heart sound microphone 20. FIG. 6C shows the second audio signal detected by the fetal heart sound microphone 30. Note that both the first audio signal and the second audio signal are subjected to band-pass filter processing of 50 Hz to 200 Hz. As apparent from FIG. 6B, the fetal heart sound microphone 20 can detect the I sound and the II sound of the fetal heart sound. On the other hand, as apparent from FIG. 6C, the fetal heart sound microphone 30 cannot detect the I sound and the II sound of the fetal heart sound. That is, the fetal heart is not within the detection range of the fetal heart sound microphone 30.

(Measurement example 2)
The 2nd measurement example which measured the fetal heart sound in the maternal body of a 36-week-old pregnant woman using the fetal heart sound collection unit 10 is shown. FIG. 7A shows a conceptual diagram of the measurement. In the measurement, the fetal heart sound collecting unit 10 is placed on the pregnant woman's mother so that the fetal heart sound is located between the fetal heart sound microphone 20 and the fetal heart sound microphone 30. Further, the distance L between the microphones satisfies the above formula (1), and the detection radius R satisfies the above formula (3).

  FIG. 7B shows the first audio signal detected by the fetal heart sound microphone 20. FIG. 7C shows the second audio signal detected by the fetal heart sound microphone 30. Note that both the first audio signal and the second audio signal are subjected to band-pass filter processing of 50 Hz to 200 Hz. In this case, as is apparent from FIG. 7B, the fetal heart sound microphone 20 can detect the I sound and the II sound of the fetal heart sound. Similarly, the fetal heart sound microphone 30 can detect the I sound and the II sound of the fetal heart sound. The first audio signal detected by the fetal heart sound microphone 20 and the second audio signal detected by the fetal heart sound microphone 30 were at substantially the same level.

  As described above, the signal processing unit 40 acquires the difference (dB) between the first audio signal and the second audio signal at regular intervals (for example, every 1 second) for a certain period (for example, 0.05 seconds). Then, the fetal heart sound signal calculated by the signal sum or the signal difference according to whether or not the difference value is equal to or greater than a predetermined threshold is supplied to the information output unit 50. However, FIG. 8 below shows the fetal heart sound signal generated by the signal difference regardless of the comparison with the threshold value. Similarly, FIG. 9 shows a fetal heart sound signal generated by signal sum without comparison with this threshold value.

  FIG. 8A is a graph showing changes in fetal heart sound when the signal difference between the sound signals (first sound signal and second sound signal) collected by both microphones in the measurement example 1 is a monaural signal. FIG. 8B is a graph showing changes in fetal heart sound when the signal difference between the sound signals (first sound signal and second sound signal) collected by both microphones in the measurement example 2 is a monaural signal. 8A and 8B, the S / N (signal-noise ratio) ratio of the output monaural signal is higher in FIG. 8A. The reason for this will be described below.

  When the fetal heart sound microphone 20 is placed immediately above the fetal heart (Measurement Example 1), the detection range of the fetal heart sound microphone 30 does not include the position of the fetal heart. Thereby, in the measurement example 1, the fetal heart sound microphone 30 collects only noise that is not related to the fetal heart sound. For this reason, it is possible to obtain a fetal heart sound with good quality from which noise is removed by taking a signal difference (subtracting the second audio signal from the first audio signal).

  FIG. 9A is a graph showing changes in heart sounds when the signal sum of the sound signals (first sound signal and second sound signal) collected by both microphones in the measurement example 1 is a monaural signal. FIG. 9B is a graph showing changes in heart sounds when the signal sum of the sound signals (first sound signal and second sound signal) collected by both microphones in the measurement example 2 is a monaural signal. As is apparent from a comparison between FIG. 9B and FIG. 8B, the S / N ratio in the measurement example 2 when the signal sum is a monaural signal (FIG. 9B) is greater than when the signal difference is a monaural signal (FIG. 8B). Is expensive. This is because in the measurement example 2, since the fetal heart sounds are collected almost equally by both microphones, the fetal heart sounds can be obtained more clearly by taking the signal sum.

  Thus, depending on the positional relationship between each microphone and the fetal heart, each microphone collects noise or fetal heart sound. Therefore, the signal processing unit 40 switches between outputting the signal sum or outputting the signal difference depending on whether or not the difference between the first audio signal and the second audio signal is equal to or greater than a predetermined threshold value. A fetal heart sound signal with a high N ratio can be output. Here, for the threshold value, for example, a value determined empirically may be used.

  When the difference between the first audio signal and the second audio signal is greater than or equal to a predetermined threshold, the signal processing unit 40 does not output the signal difference but outputs only the audio signal having a high sound pressure as the fetal heart sound signal. It is also possible.

  Next, effects of the fetal heart sound measuring apparatus 1 according to the present embodiment will be described. First, the effect of the fetal heart sound collecting unit 10 that satisfies the above-described equations (1) and (2) will be described. As a comparative example, consider the case where the distance L between the microphones is extremely narrow. In this case, if the fetal heart position can be surely grasped, the fetal heart sound can be properly heard, but if the fetal heart position cannot be grasped, the heart sound of the fetal heart sound collecting unit 10 as a whole. The detection range is narrow. Therefore, it takes time to grasp the heart position of the fetus. Consider a case where the distance L between the microphones is extremely wide. In this case, within the distance L between the microphones, a section that does not enter either the search radius R of the fetal heart sound microphone 20 or the search radius R of the fetal heart sound microphone 30 occurs. Thereby, even if the fetal heart sound collecting unit 10 is located almost directly above the fetal heart, fetal heart sound may not be detected.

  On the other hand, the fetal heart sound collecting unit 10 according to the present embodiment is configured to satisfy the above formulas (1) and (2). In other words, the fetal heart sound collecting unit 10 is configured such that the sum of the inter-microphone distance L and the detection radius R is larger than the fetal shoulder width. The pregnant woman detects the shoulder position on one side of the fetus by palpation, places the fetal heart sound microphone 20 almost directly above the position, and moves the fetal heart sound collecting unit 10 so that the position of the fetal heart sound microphone 30 changes. The position of the fetal heart within the fetal shoulder width range can be detected efficiently. That is, even a pregnant woman who is not a fetal medical specialist can easily detect fetal heart sounds.

  Even if the position of the shoulder of the fetus cannot be detected by palpation, the fetal heart sound collecting unit 10 that satisfies the above formulas (1) and (2) cannot detect the fetal heart sound in the section of the distance L between the microphones. There is no section, and the total detection range of both microphones can cover a sufficiently wide range. Thereby, the fetal heart position can be easily detected.

  In addition, when the fetal heart sound microphone 20 and the fetal heart sound microphone 30 satisfy the above-described formula (3), it is possible to appropriately detect the fetal heart position, to facilitate the microphone design, and to reduce the design cost. Become.

  Further, the fetal heart sound microphones 20 and 30 are configured as shown in FIG. 3, and the vibration transmitting unit 203 is made of a material having a Shore A hardness of 40 or more, thereby effectively attenuating fetal heart sounds in the high sound range at the interface with the pregnant mother. The fetal heart sound with high sensitivity and broadband can be collected. This is because by setting the Shore A hardness of the vibration transmitting portion 203 to 40 or more, the Young's modulus and the sound speed can be more efficiently maintained at approximately the same level as the surface of the mother's body that is the subject.

  Furthermore, the detection range can be appropriately adjusted by adjusting the internal structure of the fetal heart sound microphones 20 and 30 including the vibration transmitting unit 203 as described above. As described with reference to FIG. 3, the fetal heart sound microphones 20 and 30 have a configuration in which acoustic impedance matching with the pregnant woman's mother is sufficiently taken into account, and therefore, highly accurate sound collection processing can be realized.

  In addition, the fetal heart sound microphones 20 and 30 have a vibration damping unit 207 inside and are not easily affected by external vibration. As a result, it is possible to reduce the influence of noise other than fetal heart sounds.

  Further, the information output unit 50 displays fetal heart sound information in any format (displays fetal heart sounds in a graph format, prints and outputs changes in fetal heart sounds in a graph format, transmits information to any communication device, etc.). By presenting, the pregnant woman can grasp the condition of the fetus more accurately and easily.

  Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the configuration of the above embodiment, and can be made by those skilled in the art within the scope of the invention of the claims of the claims of the present application. It goes without saying that various modifications, corrections, and combinations are included.

  For example, the detection range of the fetal heart sound microphone 20 and the detection range of the fetal heart sound microphone 30 may be configured so as to be somewhat overlapped. This further reduces the risk of fetal heart sound detection omission at the distance L between the microphones. Further, it goes without saying that the fetal heart sound collecting unit 10 may be used by being held by, for example, a person other than a pregnant woman (for example, a spouse of the pregnant woman).

1 Fetal heart sound measuring device 10 Fetal heart sound collecting unit 20 Fetal heart sound microphone 30 Fetal heart sound microphone 40 Signal processing unit 50 Information output unit 100 Outer case 201 Microphone element 202 Inner case 203 Vibration transmitting unit 204-1 Support member 204-2 Support member 205 Diaphragm 206 Contact surface 207 Damping portion 208-1 Hole 208-2 Hole 209 Fetal heart sound conduction layer L Distance between microphones R Detection radius

Claims (7)

A first fetal heart sound microphone for collecting fetal heart sounds;
A second fetal heart sound microphone that collects fetal heart sounds;
A signal processing unit that outputs a fetal heart sound signal based on the first audio signal collected by the first fetal heart sound microphone and the second audio signal collected by the second fetal heart sound microphone;
When the distance L between the first fetal heart sound microphone and the second fetal heart sound microphone is set as the radius R of the detection range of the first and second heart sound microphones, and the average shoulder width of the fetus month of October is a predetermined distance, A fetal heart sound measuring device satisfying the following formulas (1) and (2):
Predetermined distance <= L + R ――― Formula (1)
R> = L / 2 ――― Formula (2)   The fetal heart sound measuring apparatus according to claim 1, wherein twice the radius R is substantially equal to the distance L.   The fetal heart sound measuring apparatus according to claim 1, wherein the predetermined distance is substantially equal to an average shoulder width of a fetus month of October. The signal processing unit
Calculating a signal difference value between the first audio signal and the second audio signal in a predetermined period;
When the signal difference value is greater than or equal to a predetermined threshold, the signal difference between the first audio signal and the second audio signal is output as the fetal heart sound signal,
The signal sum of the first audio signal and the second audio signal is output as the fetal heart sound signal when the signal difference value is less than the predetermined threshold. The fetal heart sound measuring device according to item. Each of the first fetal heart sound microphone and the second fetal heart sound microphone is:
A microphone element that collects fetal heart sounds;
A contact with the pregnant mother through the contact surface, a surface facing the contact surface is in contact with the microphone element, and a vibration transmission unit composed of a material having a Shore A hardness of 40 or more;
The fetal heart sound measuring apparatus according to any one of claims 1 to 4, further comprising an inner case that houses the vibration transmitting unit and the microphone element.   The apparatus further comprises a vibration damping portion that extends from a surface parallel to the contact surface to the inside of the inner case and is provided to cover the upper surface of the inner case and the upper surface of the microphone element. 5. The fetal heart sound measuring device according to 5.   The fetal heart sound according to any one of claims 1 to 6, further comprising an information output unit that displays fetal heart sound information on a display device or prints it on a printing device based on the fetal heart sound signal. measuring device.

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