JPH0357207Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a cardiac sensor that detects, as an electrical signal, a change in inductance of a coil element of a sensor body in response to the displacement of a magnet fixed to the skin of a human body, and in particular, Regarding the setting of the distance between and the magnet.

(Prior Art) Conventionally, cardiac sensors that detect chest wall vibrations or blood vessel site vibrations that occur with myocardial activity have been used that have semiconductor pressure sensing elements or piezoelectric elements. This conventional method involves manually pressing a sensor onto the carotid artery and femoral artery, and analyzing the signal waveform (cardiac diagram) in response to pressure changes caused by myocardial activity, or comparing the cardiac diagram with an electrocardiogram. Based on this, he diagnosed arteriosclerosis, various valvular diseases, etc. However, since the output signal of cardiac sensors using semiconductor pressure sensing elements or piezoelectric elements changes when the sensor is pressed against the skin, testing requires skill.

Cardiac sensors shown in FIGS. 5 to 9 have been developed to solve this drawback.
As shown in FIG. 5, this cardiac sensor has a magnet 3 attached to a part of the skin 1 corresponding to an artery 2 such as the carotid artery.
It is attached by adhering the adhesive thin film 4 covering this to the skin 1. A separate sensor body 6 is attached to the thin film 4 and magnet 3.
The magnet 3 is set in the bottom recess 8 of the outer case 7.
A shield case 9 made of non-magnetic metal is fitted, and an even number of coil elements 12 each having a winding 11 around a magnetic wire 10 are inserted in the shield case 9 radially and circumferentially as shown in FIG. The resin 13 is arranged at equal intervals (that is, so that the elements 12 facing each other across the center are in point-symmetrical positions).
It accommodates an element stand 14 molded with a mold and a substrate 16 provided with a signal processing circuit 15 for processing output signals of the group of elements 12, and a lead wire 17 is connected to the signal processing circuit 15 to be drawn to the outside. .

As shown in FIG. 7, the connection of the winding 11 of the element 12 is divided into the solid line a and the dotted line b for each element 12, and the connection of the solid line a is for one of the DC power sources. The poles, for example, the positive electrode common terminal 18 side are connected to the outer end of each winding 11, and the negative electrode terminal 19 side is connected to the inner end of each winding 11, so that they are connected in series, and the connection indicated by dotted line b is
On the contrary, they are connected in series so that the positive electrode common terminal 18 side is connected to the inner end of the winding 11 and the negative electrode terminal 19 side is connected to the outer end of the winding 11.

The sum of the inductances of the two sets of elements 12 connected by these lines a and b differs depending on the position of the magnet 3. That is, as shown in FIG. 7, the magnetic flux Bφ generated in the element 12 by the current flowing through the line b and the magnetic flux Mφ caused by the magnet
However, with respect to the magnetic flux Aφ generated in the element 12 due to the current flowing through the wire a, the magnetic flux Mφ caused by the magnet 3 is biased in the forward direction, and the magnetic wire 10 is saturated, resulting in a difference in inductance. Note that, for example, the winding 11 connected to the wire b
If the winding direction of the magnetic wire 10 is reversed,
A current is passed through line b in the opposite direction to that shown.

As a circuit for detecting the difference in inductance depending on the position of the magnet 3, for example, a circuit as shown in FIG. 8 is used. That is, a winding group 11a connected to the wire a and a winding group 1 connected to the wire b.
One end of 1b is commonly connected to the power terminal 18 side,
The other ends are connected to the collectors of transistors 21 and 22, respectively, and the emitters of transistors 21 and 22 are connected to the other ends (ground) of the electrodes via resistors 25 and 26, respectively, and the bases of one of transistors 21 and 22 are connected to the other transistor 22,
By connecting the collector of transistor 21 to the collector of transistor 2 through parallel circuits 24 and 23 consisting of a capacitor and a resistor, an astable multivibrator is constructed.
The difference between the emitter voltages of magnets 1 and 22 is converted into a DC voltage by a high-cut filter (integrator circuit) 27, and the DC voltage is amplified by an amplifier circuit 28 to obtain an output voltage from an output terminal 29. The relationship between the position and the output voltage from the output terminal 29 is as shown in FIG. In other words, the closer the magnet is to the element 12, the higher the operating frequency of the multivibrator (for example, configured to vary in the range of 60kHz to 500kHz) and the higher the emitter voltage. L1 is uniquely determined
The linear region of ~L2 is designed to fall within the operating range of the magnet 3. Also, magnet 3 and element 1
2 (i.e., the sensor body 6)
0 is set to a distance corresponding to approximately the midpoint A of the region where the distance and the output have a linear relationship, as shown in FIG. Furthermore, the responsiveness of the sensor can be changed by changing the time constant of the high-cut filter 27, and the time constant is determined by the frequency of change in the signal to be measured.

A sensor consisting of such radially arranged elements 12 cancels out the disturbance magnetic field, and the magnet 3
This has the advantage that the effects of uneven magnetization can also be canceled out.

Note that since there is also a correlation between the distance of the magnet 3 and the operating frequency of the multivibrator, it is possible to obtain a signal corresponding to the operating frequency as a signal indicating the distance, but the signal processing circuit 15 is complicated.

(Problem to be solved by the invention) In the cardiac sensor that detects changes in inductance due to the movement of the magnet 3 as changes in electrical signals, the carotid and femoral arteries that are actually measured are As shown in Figure 1A in Figure 5, it forms a protruding surface, so when the magnet is actually attached to the skin, it
The operating point becomes as indicated by A, and the operating point becomes as indicated by B, as shown in FIG. Therefore, since the magnet 3 is close to the sensor body 6 at a distance L3, the change in output D2 with respect to the change in distance C2 is smaller than the change in output D1 with respect to the change in distance C1 at the time of design, resulting in poor measurement accuracy. There is a problem.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a cardiac sensor that detects as an electrical signal the change in inductance of the coil element of the sensor body in response to the displacement of a magnet fixed to the human skin. , the off-reset between the element and the magnet is set to be a distance greater than the distance corresponding to the midpoint of the output range where the relationship between the change in the output of the sensor main body and the change in the distance between the two is a linear relationship. shall be.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. First, the configuration of the cardiac sensor of this embodiment will be explained with reference to FIGS. 1 and 2. 30 is a sensor body, and 38 is a resin holder to which the magnet 3 is attached with the following structure. The holder 38 is provided with a plurality of (preferably 4 or more, but 8 in the illustrated example) rising pieces 40 around a ring-shaped bottom plate 39, and the above-mentioned sensor main body is provided on the upper part of each rising piece 40. A locking protrusion 40a that protrudes inward and locks a protrusion 32a formed around the resin case 32 of No. 30 is formed.

Furthermore, three or more (eight in the illustrated example) protrusions 41 (which may be cylindrical protrusions) are formed on the upper surface of the bottom plate portion 39 of the holder 38 to abut and support the bottom surface of the case 32. ing. Further, an adhesive 42 (which may be applied by thermal welding) is applied to the lower surface of the bottom plate portion 39.
Stretchable membrane 4 made of nonwoven fabric, resin membrane, etc.
The magnet 3 is fixed to the center of the upper surface of the stretchable film 43 using an adhesive 44. Further, an adhesive 45 is applied to the lower surface of the membrane 3, that is, the surface facing the human skin, and the applied surface is covered with a release paper 45.
6, and a part of the outer periphery of the release paper 46 has a tongue piece 46a for facilitating its peeling.

Further, as shown in FIG. 2, the sensor main body 30 of this embodiment has an even number of elements 12 each having a winding 11 wound around a magnetic gland 10 on one side of the substrate 16, that is, the surface facing the magnet 3. , as described above, are arranged radially and at equal intervals in the circumferential direction so that the elements facing each other across the center are point symmetrical and molded with resin 47, thereby preventing relative movement of the element 12 with respect to the substrate 16. In addition, the signal processing circuit 15 of the element 12 is provided on the opposite side of the board 16, and the signal processing circuit 15 is covered with a shield case 31 made of a non-magnetic material such as brass or aluminum. The lead wire 17 connected to the signal processing circuit 15 is pulled out from the case 32, and the element 12, the substrate 16, and the shield case 31 are integrated with resin, thereby forming the sensor body 30 and achieving a thinner structure. ing.

Further, in this embodiment, a grip part 48 that also serves as a lead wire accommodating part through which the lead wire 17 is passed is formed on the upper surface of the case 32 in a radial direction and protrudes upward. A grip portion 49, which also serves as a lead wire accommodating portion, is provided so as to protrude laterally in the form of a rod.

The sensor of this embodiment is manufactured by holding the tongue 46a of the release paper 46 shown in FIG. 1 and peeling off the membrane 46.
The adhesive 45 applied to 3 is exposed, and the holder 38 is adhered to the skin together with the membrane 43 so that the magnet 3 is positioned above the artery (carotid artery or femoral artery, etc.) 2, as shown in FIG. Then, the grip part 49 is held between the thumb and middle finger (or index finger) of the examiner's hand 50, and in the case of the femoral artery, the part of the holder 38 is detected and fitted by palpation with the middle finger or ring finger,
Measure. At this time, the bottom surface of the case 32 comes into contact with the protrusion 41, and at the same time, the protrusion 32a around the case 32 is elastically engaged with the engagement protrusion 40a of the rising piece 40, so that the magnet 3 is attached to the element. 12, and as the skin 1 in that area protrudes and retracts as the artery 2 moves, the magnet 3 follows and operates, and the signal processing circuit 15 causes the magnet 3 to move according to the principle described above. An output corresponding to the position is outputted to a measuring device (not shown) via the lead wire 17.

As shown in FIG. 3, since the skin 1 has a protruding surface, when the holder 38 is adhered to the skin 1, the membrane 43 is not a flat surface as shown by the two-dot chain line 43A, but a solid line. Since the magnet 3 has a curved surface as shown, when the holder 38 is actually fixed to the skin, the magnet 3 is attached to the sensor body 30 (element 1
2) Close to. Considering this point, in the present invention, the offset between the magnet 3 and the element 12 (distance when the holder 38 is set on a flat surface) is
The distance is set to (L0+ΔL), which is the sum of the distance L0 corresponding to point A (the midpoint of the straight line area) in FIG. Such a setting sets the height of the protrusion 41 to the height H of the protrusion 41 corresponding to the distance L0 plus the above-mentioned ΔL (correspondingly, the height of the locking protrusion 40a is also set). This is realized by

If such a distance is set, when the holder 38 is actually adhered to the skin 1, the magnet 3 will protrude from the curved surface of the skin 2, so the magnet 3 and the element 12 will be separated as shown in FIGS. 3 and 4. As shown in FIG. 4, the change in distance C
The change D1 in the output relative to 1 is made from the set operating point C to the vicinity of point A.

In the above embodiment, an example in which the sensor body 30 is attached to the holder 38 has been described, but the present invention can also be applied to a structure in which the magnet 3 is fixed with an adhesive film 4 and the sensor body is set thereon, as in the conventional example. can be applied.

(Effects of the invention) As described above, in the invention, the offset between the coil element and the magnet corresponds to the midpoint of the output range where the relationship between the change in the output of the sensor body and the change in the distance between the two is a linear relationship. In actual measurement, the operating point will be near the midpoint of the region where the linear relationship holds true, and the operation will occur in the region where the distance and output form a linear relationship. measurement accuracy is not compromised.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the present invention with the holder and sensor main body separated, and Fig. 2 is a longitudinal cross-section showing the cardiac sensor of the embodiment in a state where the holder and sensor main body are fitted. 3 is a sectional view explaining the offset setting in this embodiment, FIG. 4 is a relationship diagram between the distance of the magnet and the output voltage of the signal processing circuit in this embodiment, and FIG. FIG. 6 is a cross-sectional view showing the sensor; FIG. 6 is a plan view showing the arrangement of elements of a conventional cardiac sensor; FIG.
8 is a circuit diagram showing an example of a signal processing circuit of the element. FIG. 9 is a circuit diagram showing an example of a signal processing circuit of the element.
The figure is a diagram showing the relationship between the distance between magnets and the output voltage of a signal processing circuit in a conventional cardiac sensor.

Claims (1)

[Scope of utility model registration request] In a cardiac sensor that detects as an electrical signal the change in inductance of a coil element of the sensor body in response to the displacement of a magnet fixed to the human skin, off-reset between the element and the magnet is
A cardiac sensor characterized in that the relationship between the change in the output of the sensor body with respect to the change in the distance between the two is set to be a distance greater than the distance corresponding to the midpoint of the output region where the relationship is a linear relationship.