JPS63143034A - Respiration detection method and apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention detects the temperature difference in or near the nostrils due to expiration and inspiration, and detects the presence or absence of breathing, the rate of breathing, and the timing of transition from the exhalation phase to the inhalation phase. This relates to a respiration sensor that detects, etc.

[Prior art]

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

As means for detecting this respiration, there are conventional methods such as those disclosed in Japanese Patent Application Laid-open No. 55-108343 and Japanese Patent Application Laid-Open No. 56-63341.
One that measures the impedance of the chest as in the publication,
Those that measure the change in resistance value due to expansion and contraction of an electrical resistor attached to the chest as in Japanese Patent Publication No. 58-30047;
6, which detects the pressure of the respiratory airflow, JP-A-58-112529, which detects breathing sounds with a microphone, and JP-A-58-183143, which detects the pressure of breathing airflow. Those that capture changes in humidity by changes in capacitance, such as those disclosed in JP-A-51-124080, JP-A-56-31736, JP-A-59-46940, JP-A-60-836870, etc. There are known devices that use a thermometer such as a thermistor to detect the temperature difference between exhaled air and inhaled air, and those that measure both chest impedance and temperature as disclosed in Japanese Patent Application Laid-Open No. 173534/1983.

Among these means for detecting breathing, especially in the case of an open system in which exhaled air does not pass through the breathing circuit, the method of detecting the temperature difference between exhaled and inhaled air is the most sensitive, has the least noise, and is the most common.
When assisting breathing in an open system, such as in an oxygen supply system or respiratory synchronization in a positive pressure ventilator known as an iron lung, it is especially important to It is necessary to clearly detect the transition period and provide effective treatment. These methods are disclosed in Japanese Patent Application Laid-open No. 59-8972 and Japanese Patent Application Laid-open No. 61-13.
Methods such as those disclosed in Japanese Patent Application Laid-open No. 1756 and Japanese Patent Application Laid-open No. 176325/1988 are known, but these methods require complicated calculation processing and may not be able to follow changes in the patient's breathing pattern, or the breathing may be weak. However, there are drawbacks such as the inability to sense the air, or the large influence of signals unrelated to breathing (body movement, electromagnetic interference, etc.), resulting in frequent malfunctions.

[Purpose of the invention]

The present invention avoids such malfunctions of conventional respiratory sensors, can accurately detect exhalation and inhalation even in patients with weakened breathing, and can accurately follow changes in the patient's breathing pattern. The purpose of this research was to provide a breathing detection method and device that could detect respiration.We discovered that good judgments could be made by performing differential processing on the electrical signals detected by temperature sensors, and we continued our research. This led to the completion of the present invention.

[Structure of the invention]

That is, the present invention is characterized in that a temperature change in the respiratory airflow is detected as an electrical signal, the electrical signal is differentiated, and the time when the differential value reaches a predetermined value is set as the start time of exhalation or inspiration. A respiration detection method, a temperature sensor that detects a temperature change in a respiratory airflow, an amplifier that amplifies the output from the temperature sensor, a differentiation circuit that differentiates the signal amplified by the amplifier, a variable resistor that adjusts a threshold level, It is a respiration detection device used to control oxygen supply systems, positive pressure ventilators, etc., and consists of a comparator that compares the differential waveform obtained by the differential circuit with a pre-adjusted threshold level.

Figure 1 shows the change in temperature output value over time when a chrome-allomel thermocouple was installed near the nostril.

When exhaled air warmed by body temperature hits a thermocouple that is isothermal to the outside temperature, the temperature rises. This temperature increase is greatest due to the temperature difference between the thermocouple and exhaled air, and the exhalation rate is fastest at the beginning of exhalation, and reaches almost O at the end of expiration.
At some distance from the nostrils, as shown in FIG. 1, the temperature may drop due to being cooled by the outside air. Therefore, for example, in a determination method in which the process of temperature rise is considered as exhalation and the process of temperature decrease as inhalation, an erroneous operation occurs in which the end of expiration is already determined to be the start of inhalation. This also applies when a thermistor is used as the temperature sensing element.

Therefore, the present inventors focused on the fact that the absolute value of the rate of change in temperature is greatest at the beginning of expiration and inspiration, and by differentiating the signal proportional to temperature, a signal that clearly indicates the transition between expiration and inspiration was obtained. I was able to get it. This differential signal is as shown in FIG. 2, and shows a sharp peak at the transition between exhalation and inspiration. This peak can be detected using a method that is generally used for measuring heart rate on an electrocardiogram monitor. It is possible to obtain a signal synchronized with breathing without any time delay.

The method of the present invention can be realized by a simple combination of circuits as shown below. In other words, there are no particular restrictions on the temperature-sensitive element constituting the temperature sensor used in the device of the present invention, as long as it exhibits an output proportional to temperature, such as a thermistor or thermocouple; For processing by circuits, it is desirable to have one that can output a signal all at once. Further, the size of the temperature sensing element is desirably as small as possible for reasons such as thermal responsiveness and wearability. Further, the amplifier used in the present invention amplifies the output from the temperature sensor, and is no different from those used as instruments for general thermistors and thermocouple thermometers.

According to the method of the present invention, it is necessary to sequentially time differentiate the amplified signal described above to obtain a differentiated waveform.

However, if the signal indicating the temperature change is given as an electrical signal, a differential waveform can be easily obtained by using, for example, a general differential circuit as shown in FIG. The differential waveform obtained by the differential circuit is as shown in FIG. 2, and the rise of the peak of this waveform is the start of exhalation, and the start of fall of the lower peak is the start of inspiration. Therefore, it is sufficient to input the threshold level of a constant voltage that allows cylinder production using a variable resistor and the differential waveform to a comparator, and detect the first point at which the difference becomes O as the starting point of exhalation or inspiration. It goes without saying that two types of threshold levels are required at this time, one for exhalation and one for inhalation. This threshold level can be adjusted using a variable resistor to accommodate differential waveforms that vary depending on individual patient differences, breathing strength, conversation, etc., making it possible to judge expiration and inspiration without malfunction. .

Furthermore, for example, when the respiratory waveform is as shown in Figure 4, two exhalation start points are detected in one breath, but for example, continuous identical signals are ignored and the inhalation and exhalation start points are detected. If the switching method is adopted using a flip 70 knob that ensures that the start signals are input alternately, in the example shown in Fig. 4, it is possible to prevent the expiration start signal from being counted more than once in a row unless the inhalation start signal is input. can. Further, the circuit may be configured such that, for example, once an exhalation signal is input, the exhalation signal is not detected for several seconds thereafter. By using these methods, “respiration rate can also be measured accurately,
For example, it can also be used as a neonatal monitor.

〔Effect of the invention〕

According to the method of the present invention, there is no need for complicated circuit systems or calculation processing, so there is very little time delay, it is possible to sufficiently follow changing breathing patterns, and malfunctions can be greatly reduced. Furthermore, since the device of the present invention can be realized with a simple circuit configuration, it is inexpensive and has few failures.
Therefore, the present invention is extremely useful in the medical industry.

〔Example〕

According to the method of the present invention, a device having the configuration shown in the block diagram shown in FIG. 5 was created, and a temperature sensor using a thermistor as a temperature sensing element was inserted into the patient's nostril and fixed with a clip.

Adjust the threshold level with a variable resistor,
In addition, by changing the time constant of the differential circuit, we were able to perform respiratory synchronization accurately without any time lag.

In addition, the signals from this device were used to synchronize the breathing of a positive pressure ventilator. That is, during inspiration, the valve of the positive pressure line was opened to make the pressure inside the dome positive and negative pressure outside the thoracic cavity was created, and during expiration, this was closed and the release valve was opened to release to the atmosphere.

By using this device, we were able to provide respiratory assistance that matched the patient's wishes.

[Brief explanation of the drawing]

Figure 1 shows the change over time in the temperature output value when a chrome-allomel thermocouple is installed near the nostril, and Figure 2 shows the change over time in the differential signal obtained by time-differentiating the temperature change signal due to breathing and the threshold. Figure 3 is a diagram showing an example of a differential circuit used in the present invention; Figure 4 is an example of a differential waveform of temperature change due to respiration; Figure 5 is an example of an embodiment of the present invention. This is a block diagram of a breathing detection device. Patent applicant Sumitomo Bakelite Co., Ltd. First page Lie Figure 2

Claims (3)

[Claims] (1) Breathing detection characterized by detecting temperature changes in respiratory airflow as electrical signals, differentiating the electrical signals, and determining the time when the differential value reaches a predetermined value as the start time of exhalation or inspiration. Method. (2) A temperature sensor that detects temperature changes in the respiratory airflow, an amplifier that amplifies the output from the temperature sensor, a differentiation circuit that differentiates the signal amplified by the amplifier, a variable resistor that adjusts the threshold level, and a differentiation circuit. A respiration detection device comprising a comparator that compares a differential waveform obtained by a circuit with a pre-adjusted threshold level. (3) A temperature sensor that detects temperature changes in respiratory airflow, an amplifier that amplifies the output from the temperature sensor, a differentiation circuit that differentiates the signal amplified by the amplifier, a variable resistor that adjusts the threshold level, and a differentiation circuit. It is characterized by comprising a comparator that compares the level of the differentiated signal with a pre-adjusted threshold level, and a flip-flop that ignores consecutive identical signals and ensures that exhalation and inspiration signals are output alternately. Breathing detection device.