JPH0257417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a respiration sensor that detects the temperature difference between exhaled and inhaled air, and detects the presence or absence of respiration, the rate of respiration, the manner of respiration, etc.

[Prior art]

In post-surgical respiratory management, neonatal life support, etc., sensing breathing and monitoring its state by some means plays the most important role in quickly responding to abnormal situations and ultimately ensuring patient survival. It is something.

As a means for sensing this respiration, conventional methods such as those disclosed in Japanese Patent Application Laid-open No. 108343/1983 and Japanese Patent Application Laid-Open No. 56-1983
Those that measure the impedance of the chest as in Japanese Patent Publication No. 63341, those that measure changes in resistance due to expansion and contraction of electrical resistors attached to the chest strap as in Japanese Patent Publication No. 58-30047, and Japanese Patent Application Laid-Open No. 50-39544. Those that detect the pressure of respiratory airflow as in Japanese Patent Application Laid-Open No. 59-48106, those that detect breathing sounds with a microphone as in Japanese Patent Application Laid-Open No. 112529-1982, and those that detect breathing sounds with a microphone as in Japanese Patent Application Laid-Open No. 183-143.
JP-A No. 1989-1973, which captures changes in humidity between exhaled and inhaled air by changes in capacitance.
Publication No. 124080, Japanese Patent Application Publication No. 1983-31736, Japanese Patent Application Publication No. 1987-31736
59-46940, JP 60-836870, etc., which use a thermometer such as a thermistor to detect the temperature difference between expiration and intake air;
There are known devices that measure both chest impedance and temperature, as disclosed in Japanese Patent No. 173534.

These conventional means of detecting breathing are effective in measuring the presence or absence of breathing, respiratory waveforms, and in some cases, respiratory flow rate, but they are useful in patients with neuromuscular diseases such as muscular dystrophy, chronic respiratory failure, etc. When assisting a patient with breathing, the timing of assisting breathing, that is, the trigger for delivering air or oxygen when the patient wants to breathe, may be because the breathing is so weak that it cannot be detected.
or signals unrelated to breathing (body movement, electromagnetic interference, etc.)
This had a large influence, often resulting in malfunctions.

For example, FIG. 4 is a waveform diagram of thermoelectromotive force measured during normal breathing using the conventional method of placing a chromel-allomel thermocouple at the tip of the nose. As can be seen from Figure 4, in the case of exhalation, the air that has risen due to body temperature hits the temperature sensing part, the temperature rises, and an upwardly convex curve is drawn. The temperature increase is greatest at the beginning of exhalation, reaching its peak in about 1 second, but due to the decrease in exhalation flow rate and cooling due to the outside temperature, the temperature begins to decrease even during the exhalation period, and at the moment of expiration, the temperature rises. Cooled by the rapid flow of outside air, the temperature drops until exhalation begins. Therefore, it is relatively easy to detect at the moment when breathing begins, but it is not so clear at the moment when inspiration begins.

[Purpose of the invention]

The present invention aims to avoid such malfunctions and to obtain a completely new type of respiratory sensor that can accurately detect exhalation and inspiration even in patients with weakened breathing, by examining various temperature-sensitive elements. As a result, they discovered that the most sensitive and high-output respiratory signals could be extracted by using a pyroelectric element.
Further research led to the completion of this respiration sensor.

[Structure of the invention]

That is, in the present invention, a pyroelectric element is disposed in a respiratory airflow passage, the pyroelectric element detects a temperature change in the passage, and the temperature change obtained from an electric circuit including the pyroelectric element is responded to. This breathing sensor is characterized by knowing when to start exhaling and inhaling based on the differential waveform of the electrical signal.

As mentioned earlier, when assisting the breathing of patients with muscular dystrophy, chronic respiratory failure, etc., it is necessary to mainly assist with inhalation, and if the patient has the intention of spontaneous breathing, it is necessary to assist the patient with breathing. It is said that a breathing assistance method that synchronizes with the patient's breathing, which assists breathing by blowing air at the moment of thought, will speed up the weaning of such patients from breathing aids. However, the timing at which inspiration begins is unclear as described above, and detection is extremely difficult, especially in patients suffering from respiratory failure.
Therefore, by taking the differential value of this respiratory waveform, the present inventors determined that the exhaled breath has the highest rate of change in temperature,
We decided to detect the beginning of inspiration, and found that it was suitable to use a pyroelectric element as a temperature sensing element, which can obtain a differential waveform of the respiratory waveform, and completed this respiratory sensor.

In a pyroelectric element, when a temperature change occurs, the spontaneous polarization value of the element, which is a ferroelectric substance, changes, and the surface charge of the element changes. At this time, when an external load is connected, a current (pyrocurrent) flows, and the surface returns to its original state with neither excess nor deficiency, and no current flows until the temperature changes again. Therefore, the pyroelectric element responds only when there is a temperature change, and when used as a respiration sensor, a differential waveform of the respiration waveform can be obtained. Therefore, this waveform has a sharp peak at the beginning of exhalation and inspiration, and by applying a trigger at an appropriate voltage level, it is possible to accurately detect the beginning of exhalation and inspiration. Moreover,
Pyroelectric elements can provide much higher output than other temperature-sensitive elements such as thermistors and thermocouples, so they have the advantage of not requiring amplification and can simplify subsequent signal processing.

The greatest advantage of using a pyroelectric element as a sensor is its high sensitivity and high output. for example,
The output of the chromel-allomel thermocouple shown in Fig. 4 is about 0.04 mv/°C, while the output of a pyroelectric element varies depending on the type and size, but for example, it is 1.3 mv/°C. A very high output of sec is obtained, and this fact greatly simplifies subsequent signal processing. Furthermore, as mentioned above, the output is differential with respect to temperature, which is very advantageous in detecting the timing of switching between expiration and inspiration.

The pyroelectric elements used in the respiratory sensor of the present invention include single crystals such as lithium tantalate (L _i T _a O ₃ ), triglycine sulfate (TGS), lead titanate (P _b T _i O ₃ ), and titanium. Examples include, but are not limited to, sintered bodies such as lead zirconate (PZT), polymeric ferroelectric materials such as polyvinylidene fluoride (PVDF), and composites of ceramic sintered body powder and plastic materials. It's not something you can do. but,
Since the rise in the output of the respiration sensor according to the present invention is controlled by the rate of change in the temperature of the pyroelectric element,
If the thickness is made as thin as possible in order to reduce the heat capacity, the responsiveness will be better and the timing of breathing can be more sensitively determined. From this point of view, the maximum thickness of a single crystal or ceramic sintered body is 80 to 100 μm, and such a thickness makes it easy to break and makes work such as mounting it on a support stand difficult. In contrast, films or sheets made of single polymer ferroelectric materials or composites of ceramic sintered powder and polymer materials have good processability, and devices with a thickness of several tens of micrometers or less can be easily produced. This method is suitable because it is easy to use and has good workability.

The temperature-sensitive element of a breathing sensor is generally installed inside a nasal cannula or mask, that is, in a position close to the nostrils, but the breathing sensor using the pyroelectric element of the present invention has high sensitivity. As long as respiratory airflow flows through the device, it can be installed in a hood that covers the entire body of a newborn or patient, or in an oxygen tent, in a way that does not come into direct contact with the patient's body. Pyroelectric elements have a large output per unit area, so when installed inside a nasal cannula or mask, an element with a small area of about 3 mm x 3 to 8 mm is sufficient.
Even when installed at the top of a hood or oxygen tent, sufficient sensitivity can be obtained with an element approximately 10 to 20 mm x 10 to 40 mm in size.

FIG. 1 is a circuit diagram showing an example of an electrical circuit of a respiratory sensor according to the present invention. The charge generated on the pyroelectric element 1 due to temperature change depends on the electric properties of the element such as capacitance, resistance, pyroelectricity, size, speed of temperature change, etc. Generally, its impedance is as high as 10 ⁸ to 10 ¹¹ Ω, and it cannot be detected as it is. Therefore, a recorder with a built-in buffer amplifier circuit for converting impedance is used, or a field effect transistor 2 is used to lower the impedance. The output impedance is determined by the output resistor 4, but it is usually desirable to set it to about 10 ³ to ^{10 5} Ω. The capacitor 5 is used to preferentially pass the high frequency component of the obtained signal, that is, the signal component at a time point when the rate of change is large, and the obtained waveform differs depending on the size of its capacitance. Therefore, the capacitance of the capacitor to be used may be determined depending on the purpose, and the capacitor 5 may not be used in some cases.

On the other hand, when a pyroelectric element 1 is used in combination with a field effect transistor 2 and an output resistor 4 as shown in FIG. 1, the lead wire connecting each element acts as an antenna and noise enters from the outside. It is expected that this will interfere with accurate detection of temperature changes.
However, since the output of the pyroelectric element is large, it is possible to compactly combine the pyroelectric element 6, field effect transistor 7, and output resistor 8 into one component as in the embodiment shown in FIG. Although the influence of external noise can be almost ignored, the entire electric circuit system consisting of the pyroelectric element 6, field effect transistor 7, and output resistor 8 is surrounded by a layer of conductive material to block external electromagnetic waves. If you block it (electromagnetic wave shield), you can be even more careful. When formed as a single component, the material of the mantle 9 shown in FIG. 2 can be plastic, rubber, metal, etc., and is not particularly limited. If a conductive material such as metal is used, it can be used as an electromagnetic shielding material. It can also be used effectively. However, metal has the problem of coldness because it comes into direct contact with the patient's body.
It is preferable to use plastic or rubber, and when metal is used, it is preferably covered with plastic or rubber. Further, it is more effective to use conductive plastic or rubber because it can also serve as an electromagnetic shield.

In addition to being compactly assembled as a single component as shown in the embodiment shown in Figure 2, it is also possible to install each component as separate components when installed inside a hood or oxygen tent as described above. . Conductive materials for electromagnetic shielding used in these cases include box-shaped or can-shaped bodies made of metal plates such as aluminum, copper, and iron, mesh bodies made from metal wire, and die-cut metal plates. metal mesh, expanded metal, conductive plastic (molded product, film, sheet, etc.), conductive paint, etc. can be used, and there are no particular limitations, and they can be selected as appropriate depending on the arrangement and shape of the electromagnetic shielding part. do it.

The respiration sensor according to the present invention can be applied to a wide range of medical devices that require sensing of respiration, and examples of its application include respiration assist devices, respiration monitors, apnea monitors, anesthesia machines, incubators, oxygen administration system, ventilator, respirator, X
Radiography equipment (timing synchronization during chest X-ray photography),
Examples include rehabilitation exercise equipment for respiratory diseases, and synchronization of various treatment devices that stimulate the living body with breathing. The material, shape, size, and signal processing method of the pyroelectric element vary depending on its use.

Hereinafter, specific examples of the respiratory sensor of the present invention will be explained with reference to the drawings.

FIG. 2 is a diagram showing the structure of a respiration sensor according to an embodiment of the present invention, in which a is a side sectional view and b is a bottom view. This example is a nasal cannula-type breathing sensor, which can be used as a timing sensor for breathing monitoring or breathing assistance by simply attaching it to the nose in cases where the patient's condition is not so serious that oxygen supply is required and only air is required. belongs to.

The breathing sensor in this embodiment has two conduits 11 inserted into the nostrils, a breathing vent 12 communicating with the outside air on the opposite side, and a mantle with supports 13 attached on both sides for supporting and fixing the head. 9 includes a pyroelectric element 1 and a field effect transistor (hereinafter referred to as
FET 7), an output resistor 8, and a shielding metal mesh 10 are arranged.
The three conductors 14 coming out from are signal output, FET
For power supply and grounding. The FET 7 and the output resistor 8 are installed in a small room separated by a drip-proof partition 15 at one end of the breathing sensor to protect them from water droplets that are generated when moisture in exhaled air condenses. A conductor 14 is led along or through the support 13 and is connected to a measuring device. The support device 13 may be in the form of a tube made of soft vinyl chloride resin, such as a nasal cannula used for oxygen inhalation, that can be wrapped around the head and fixed, or it can be worn around the ear like glasses, etc. You can do it like this. Note that the DC power supply 3 and capacitor 5 shown in FIG. 1 are provided in the measuring instrument.

At the time of inhalation, the breathing air hole 1 opened in the mantle 9
Air flows in from 2, and the shielding metal mesh 1
0 to the pyroelectric element 6, which cools the pyroelectric element 6 warmed by the exhaled air. This air is divided into left and right parts, guided to a conduit 11 leading to the nostrils, and flows into the body. On the other hand, when exhaling, the process is completely opposite, and the exhaled air is warmed by body temperature and is expelled.
The pyroelectric element 6 is heated.

Before starting the measurement, the capacitance of the capacitor 5 shown in FIG. 1 was determined according to the purpose and inserted, thereby obtaining a respiratory waveform as shown in FIG. 3. FIG. 3a shows the waveform when the capacitor 5 is not inserted, and a negative peak occurs at the moment of warming by exhalation, and turns positive at the time of inspiration. At this time, low frequency components also enter, making it unsuitable for detecting the start of inspiration. Figure 3b is
The waveform when a 0.15 μF capacitor was inserted removed the low frequency components during inspiration, but there was a tendency to overshoot to the positive side during expiration.

Figure 3C shows the waveform when a 10 μF capacitor is inserted, and is an ideal differential waveform in which after a negative peak at the start of expiration, it returns to the baseline, and at the same time as the start of inspiration, a positive peak appears and returns to the baseline again. was gotten. From the above results, when using the respiratory sensor of this example for the purpose of respiratory assistance, for example, by using a capacitor of about 10 μF,
It can be seen that it is possible to accurately detect the beginning of inspiration and begin assistance.

〔Effect of the invention〕

The respiratory sensor according to the present invention can detect expiration and inspiration with high accuracy and high sensitivity, and is highly effective as a synchronization device for respiratory support for patients with respiratory failure, which is difficult to do with conventional respiratory sensors. It can also be applied to incubators, X-ray photography, various stimulating treatments, etc.
Moreover, it is expected to be applied not only to medical applications but also to other fields such as wind instruments, and is extremely useful industrially.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the electrical circuit of a respiratory sensor according to the present invention, and FIG. 2 is a diagram showing the structure of a respiratory sensor according to an embodiment of the present invention, in which a is a cross-sectional view and b is a bottom view. be. Figure 3 shows the respiratory waveforms measured by the respiratory sensor of the present invention, where a is the waveform when no capacitor is inserted, b is the waveform when a 0.15 μF capacitor is inserted, and c is the waveform when a 10 μF capacitor is inserted. It is a diagram. Further, FIG. 4 is a waveform diagram of thermoelectromotive force generated by a conventional respiratory sensor using a chromel-allomel thermocouple.

Claims (1)

[Claims] 1. A pyroelectric element is disposed in a respiratory airflow passage, the pyroelectric element detects a temperature change in the passage, and the temperature change is obtained from an electric circuit including the pyroelectric element. A breathing sensor that determines when to start exhaling and inhaling based on the differential waveform of an electrical signal corresponding to the 2 The respiratory airflow passage is for guiding the respiratory airflow.
It consists of a main conduit and a mantle having a breathing hole opposite the conduit, a pyroelectric element is placed in the center of the mantle, and an electric circuit is constructed with the pyroelectric element in the mantle near the mantle. 2. The respiratory sensor according to claim 1, further comprising a field effect transistor and an output resistor. 3. The field-effect transistor and output resistor that constitute the electric circuit together with the pyroelectric element are installed in a small chamber that is within the path of the respiratory airflow and is isolated from the respiratory airflow by a drip-proof partition. A respiratory sensor according to claim 1 or 2, characterized in that: 4. Claims 1 to 4, characterized in that the entire electric circuit system consisting of a pyroelectric element, a field effect transistor, and a resistance element is surrounded by a layer of a conductive material to block external electromagnetic waves. The respiratory sensor according to any one of Item 3. 5. Claims 1 to 5, characterized in that the pyroelectric element is a film or sheet-like material made of a polymeric ferroelectric material or a composite of ceramic sintered powder and a polymeric material. 4. The respiratory sensor according to any one of Item 4.