JPH0642879B2 - Respiratory tuning sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention detects the temperature difference between exhaled air and inhaled air,
The present invention relates to a respiratory sensor for detecting a respiratory rate, a respiratory aspect, etc., and more particularly to a medical respiratory tuning sensor for accurately detecting the time points at which breathing begins to be exhaled and when breathing begins.

[Prior art]

Respiratory modality monitoring plays an important role in medical activities such as health condition management and utilization of respiratory assistance devices.

As means for sensing this respiration, conventionally, for example, Japanese Patent Laid-Open No. 55-108343 and Japanese Patent Laid-Open No. 56-63341 are used to measure the impedance of the chest, and Japanese Patent Publication No. 58-300.
For measuring the change in resistance value due to expansion and contraction of the electric resistor attached to the chest band as disclosed in Japanese Patent No. 47, the pressure of the respiratory airflow as disclosed in Japanese Patent Laid-Open Nos. 50-39544 and 59-48106. One that detects breathing sound with a microphone as in Japanese Patent Laid-Open No. 58-112529, one that detects changes in the exhaled air and inhaled humidity by changes in capacitance as in Japanese Laid-Open Patent Application No. 58-183143, JP-A-51-124080, JP-A-56-31736, JP-A-60-836870, etc., which detects a temperature difference between exhalation and inspiration using a thermometer such as a thermistor, There is known a device for measuring both chest impedance and temperature as disclosed in JP-A-58-173534.

Although such conventional means for detecting respiration are effective for measuring the presence or absence of respiration, respiratory waveform, and some kinds of respiratory flow, for example, respiration in patients with neuromuscular diseases such as muscular dystrophy and patients with chronic respiratory failure. As with assisting, the timing of assisting breathing, i.e., triggering air or oxygen when the patient wants to breathe, is either imperceptible because the breath is weak or irrelevant Signals (body movements, electromagnetic interference, etc.) have a large influence, and as a result, malfunctions often occur.

Further, according to Japanese Patent Laid-Open No. 59-4694, a method is known in which two thermistors are self-heated in a member for guiding a respiratory airflow and are thermally coupled to each other so that the respiratory airflow is applied thereto. . Since the element on the side that hits the airflow has a large heat removal effect, the change in the resistance value is large, and by detecting the difference in the resistance value of both elements, it is possible to determine from which element side the airflow is coming. Is. That is, both thermistors must be kept isothermally in the absence of air flow, and the temperature difference inevitably generated in one thermistor is immediately transmitted to the other thermistor, giving an extremely weak temperature difference. Absent. Therefore, there is a drawback that electromagnetic signals unrelated to breathing have a large influence, resulting in malfunction.

A pyroelectric element is extremely effective as a temperature-sensitive element for a respiratory sensor capable of avoiding such a malfunction and outputting a sensitive and high-output signal. A capacitor may be coupled to the signal output conductor with a combination of a pyroelectric element and an impedance buffer circuit (consisting of an FET, that is, a field effect transistor and a resistor). However, if the sensitivity of this is too high, there is a tendency for false alarm due to overshoot in the opposite direction when returning from the output peak to the O level.

[Object of the Invention]

INDUSTRIAL APPLICABILITY The present invention avoids the malfunction of the sensor which has been used and has been tried so far, and can accurately detect the exhalation and inspiration of a wide range of subjects, including patients with attenuated breathing and patients with large and weak turbulence. As a result of conducting research on sensors, we obtained the knowledge that a combination of a pyroelectric element and an impedance buffer circuit as a temperature sensor for a respiratory sensor is highly sensitive and sensitive, and malfunction does not occur. The invention has been completed.

[Structure of Invention]

The present invention has a barrier having a gap through which breathing air can flow in a pipe that serves as a passage for breathing air flow, and at least one pyroelectric element electromagnetically shielded on the exhalation inflow side and the inspiration inflow side with respect to the barrier. A temperature-sensing section arranged, a buffer circuit connected to each pyroelectric element, a pair of comparison circuits connected to each of the expiratory-side and inspiratory-side buffer circuits, and capable of individually setting threshold values, and these. And a detection circuit section composed of a flip-flop circuit that generates an ON / OFF signal by using the outputs of the pair of comparison circuits as a signal source.

The breathing synchronization sensor according to the present invention comprises a temperature sensing unit installed in the respiratory airflow and a detection circuit unit connected to the temperature sensing unit.

The structure of the temperature sensing portion in the present invention is the most important requirement of the present invention and will be described below with reference to the drawings.

FIG. 1 (1) is a perspective view having a cutout portion showing the inside of the structure in the example of the temperature sensing portion in the present invention, and FIG. 1 (2), (3),
(4) is a sectional view of each portion of the same structure. 1 (2) and 1 (3) show the internal structure by vertical division of AA 'and BB', and FIG. 1 (4) shows the internal structure by horizontal division of CC '. The pipe 11 serving as a passage for the respiratory airflow has a diameter of about the nostril or less, and the inside of the pipe is separated by a barrier 22 into two chambers, an expiratory inflow side 3 and an inspiratory inflow side 4. The barrier 22 has a gap 5 through which breathing air can flow, and each chamber 3, 4
At least one piece of the pyroelectric elements 33, 44 is arranged in each of them. This element is provided with a ground electrode and an output signal electrode, each of which is connected by a lead wire 7 to a detection circuit outside the tube 11. By using waterproof and moisture-proof coating for the electrode and the connection with the lead wire and the lead wire, and using the wire mesh coating wire for the shield for the lead wire, it is possible to prevent the characteristic deterioration due to moisture proof and waterproof and to protect the general electrical noise. preferable.

The barrier provided in the tube may be orthogonal to the axis of the tube or may be parallel to the tube, and one or more barriers may be formed in a range that does not prevent the arrangement of the pyroelectric element. Since this barrier with a gap is installed to promote the heat exchange with the respiratory airflow, it may be a breathable foam and its shape does not matter as long as the heat exchange can be performed efficiently. The arrangement of the pyroelectric elements in the present invention is important for the pyroelectric elements (3 and 4) on the inflow side of the exhaled air and the inhaled air to come into contact with the airflow in the state where the temperature difference is large, but the barrier is extended to both sides thereof. It is effective whether it is fixed to the wall of the pipe or to the barrier if it exists.

For electromagnetic shielding of the pyroelectric element, the entire temperature sensitive part may be covered with a conductive shield material, the inner wall of the tube may be metalized, and the pyroelectric element layer may be a shield layer. The stacking method is effective and desirable because it is advantageous in reducing the space. One side is grounded from the electrodes on both sides of each pyroelectric element,
The other side is a signal line, which is connected to a pair of impedance buffer circuits as shown in the circuit diagram of FIG.
In FIG. 2, 31 and 32 are the signal of the element on the exhalation inflow side and the ground terminal, 33 output terminal, 34 FET, 35 gate resistance, 36 output resistance. Similarly, 41 to 46 correspond to elements on the intake inflow side. P indicates a power supply and G indicates ground. FE
T is preferably, for example, NF-5301-3 (National Semiconductor Company). If the gate resistance is too high, the output becomes unstable, but if the resistance is too low, the output becomes small and the rise tends to be slow. 200 MΩ to 1,200
It is preferable to select in the range of MΩ. The output resistance may be selected according to the application, but normally 10 to 100 KΩ is used.

In the present invention, when designed to be sensitively applied to a weak respiratory airflow, there may be an overshoot at the time of returning to the O level that occurs after the rising due to the strong respiratory airflow.
In the temperature sensing portion of the present invention, the pyroelectric element on the exhalation injection side receives a strong air flow due to exhalation, so that the output may overshoot after rising. However, due to the structure of the intake airflow, the output peak becomes weak and overshoot does not occur. Similarly, the pyroelectric element on the intake inflow side may cause overshoot due to inspiration, but does not overshoot for expiration.

Further, in the present invention, two comparison circuits (FIGS. 37 and 47) to which the output signal from the impedance buffer circuit is input, and a flip-flop circuit which receives a signal from the comparison circuit and generates an ON / OFF signal to open / close the switch section ( F
F) and. Here, the function of the comparison circuit is to set the lower limit or the upper limit of the voltage values to be compared, to output if the input signal voltage is within the set range, and not to output if it is outside the set range. The output V ₃ from the expiratory inflow side impedance buffer circuit is input to 37 and the inspiratory inflow side output V ₄ is input to 47. Assuming that both changes in V ₃ and V ₄ at the time of exhalation inflow increase and decrease at the time of inflow of inspiration, the lower limit value VO ₃ below the O level is set in the comparison circuit 37, and the upper limit value VO ₄ below the O level is set at 47. If there is an input signal voltage within this set range, a positive or negative signal is immediately emitted from each comparison circuit. The flip-flop circuit maintains a positive output after positive input and a negative output after negative input. The relationship of these signal changes in the present invention will be schematically described with reference to FIG. In each case, the horizontal axis is time.

A shows a change in temperature near the nostril due to breathing. a
In the period of the expiratory flow, the rising is in the positive direction, and b is in the period of the inspiratory flow, and the rising is in the negative direction. B and D represent strengths when the exhalation-side and inspiration-side pyroelectric elements of the temperature sensing portion according to the present invention are received. Due to the effect of the barrier provided in the tube, the intensity of a is large for the element on the exhalation side, the absolute value of the intensity of b is small, the intensity of a is small for the pyroelectric element on the inspiration side, and the intensity of B is the absolute value. Is large. C and E are outputs from the corresponding impedance buffer circuits. Although the output rises due to the stimulation regardless of the strength, when the absolute value of the strength is large, Ca and Eb tend to overshoot when returning to the O level immediately. Next, in the comparison circuit, for C, the lower limit d (chain line) and for E the upper limit f (chain line).
By setting the values, the rising point e of exhalation and the rising point g of inspiration can be captured regardless of overshoot. The output of this signal in the flip-flop circuit is F
Is. Corresponding to the respiratory stimulus of A, it is possible to convert the expiratory period and the inspiratory period into corresponding level signals with extremely high accuracy. For comparison, one pyroelectric element is placed in the temperature sensing part and combined with the impedance buffer circuit. FIG. 5 shows the case where both the exhaled air and the inhaled airflow are directly contacted and detected. In FIG. 5, A represents the temperature change of the respiratory airflow. The buffer circuit output when the strength of the respiratory airflow is appropriate is shown in B.
d is the squeeze value in the comparison circuit for finding the start of exhalation, and point e can be captured, and f is the upper limit in the comparison circuit for the start of inspiration, and point g, which cuts this point, can be captured. Therefore, if these are input to the flip-flop circuit, a relatively good respiratory sensor as shown in FIG. 5C is obtained.

However, when the respiratory stimulus is too strong, the rising like D tends to exhale and inhale, but tends to overshoot on return. In this case, the comparison circuit picks up i, j, etc. as a breathing start point in addition to h for the same squeeze values d and f.
Is an output signal with a large deviation. That is, when the breathing intensity fluctuates greatly, the chances of overshooting increase and the reliability decreases.

According to the present invention, the obstacle due to this overshoot is removed, and a highly accurate and highly reliable respiratory sensor can be obtained. The pyroelectric element used in the present invention includes single crystals of lithium tantalate (LiTaO ₃ ), triglycine sulfate (TGS), lead titanate (PbTiO ₃ ), lead zirconate titanate (PZT), etc. Examples thereof include, but are not limited to, a sintered body such as or a modified product thereof, a polymer ferroelectric such as polyfucht vinylidene (PVDF), or a composite of a ceramic sintered body powder and a plastic material. Not a thing. Among them, the polymer ferroelectric film and the ferroelectric ceramic composite polymer film are preferable materials because they have good workability and can easily form an element having a thickness of several tens of μm.

[Effect on invention]

The respiratory sensor according to the present invention is very accurate in exhalation and inspiration,
Moreover, it is possible to detect with high sensitivity, and a respiratory assist tuning device for a patient with respiratory failure, which has been difficult with a conventional respiratory sensor, an incubator, and the like are greatly effective.
Furthermore, when this is combined with an oxygen supply device, oxygen is released only during inhalation, and economical usage can be realized. Further, not only medical applications but also other fields such as wind instruments can be expected, which is extremely useful industrially.

[Brief description of drawings]

FIG. 1 (1) is a perspective view having a notched portion showing the inside of the temperature sensing portion according to the present invention, and FIGS. 1 (2), (3) and (4) are A in FIG. 1 (1).
-A ', BB' are vertical sectional views, CC 'are transverse sectional views,
FIG. 2 is an impedance buffer circuit diagram, FIG. 3 is a block diagram showing a combination of a comparison circuit and a flip-flop circuit, and FIG. 4 is a diagram showing a correspondence between a stimulation value due to respiration and an output to the sensor of the present invention. The figure shows the output of the sensor as a comparative example.

Continuation of front page (56) References JP-A-61-28869 (JP, A)

Claims (1)

[Claims] 1. At least one piece of a pyroelectric element having a barrier having a gap through which breathing air can flow in a pipe that serves as a passage for breathing airflow, and electromagnetically shielded on the exhalation inflow side and the inspiration inflow side with respect to the barrier. Each of the temperature-sensing parts arranged one by one, the buffer circuit connected to each pyroelectric element, the buffer circuit connected to each of the expiratory side and the inspiratory side, and the thresholds thereof can be set individually 1
A respiratory tuning sensor comprising a pair of comparison circuits, and a detection circuit section composed of a flip-flop circuit that generates an ON / OFF signal using outputs of the pair of comparison circuits as a signal source.