Differential pressure pneumotachograph

Abstract

To provide a differential pressure type respiration rate meter which does not use an air tube for detection of a differential pressure.SOLUTION: A differential pressure type respiration rate meter comprises: a channel component 3 which is communicated with a mask 1, and generates a differential pressure in an air flow following breathing; a differential pressure sensor 6 for detecting a differential pressure; a calculation part for calculating a breathing amount on the basis of the detected differential pressure, in which the channel component 3 comprises: a main body 4 on which, a plurality of channels 40 is formed; and a sensor storage part 5 which is integrated with the main body 4. Out of the channels 40, a first side and a second side of a channel 40' close to the sensor storage part 5 are communicated with the sensor storage part 5 for forming a bypass, and a differential pressure sensor 6 is stored in the sensor storage part 5.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a differential pressure pneumotachograph. [Background technology]

[0002] In an expiratory gas analyzer, it is necessary to measure the air volume for both the amount of air inhaled into the human body and the amount of air exhaled from the body. The main types of expiratory flow meters used are ultrasonic, hot wire, and differential pressure.

[0003] Differential pressure pneumotachometers, also known as pneumotachometers, obtain flow rates based on the differential pressure of airflow measured across a resistor, and are disclosed in, for example, Patent Documents 1 to 3. Known differential pressure pneumotachometers, depending on the type of resistor, include primarily Fleisch-type flow meters using a tube bundle, Lilly-type flow meters using wire mesh, and orifice-type flow meters. For example, the barriers disclosed in Patent Documents 1 and 2 use resistors similar to wire mesh, while Patent Document 3 discloses an orifice-type flow meter using a Venturi. Differential pressure pneumotachometers measure flow rates using an appropriate differential pressure-to-flow rate conversion formula depending on the type of resistor.

[0004] In the differential pressure respiratory flow meters disclosed in Patent Documents 1 to 3, the air flows before and after the resistor are connected to a differential pressure detection sensor via air tubes. The inventors have investigated how to arrange the sensor directly in the differential pressure detection unit without using an air tube by providing a unique resistor configuration. It is also important to note that the differential pressure-flow characteristics can be affected by the resistor configuration. [Patent Document 1] Patent Publication No. 7-8472 [Patent Document 2] Patent Publication No. 2021-35441 [Patent Document 3] US2019 / 0110714A1 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a differential pressure pneumotachograph that does not use an air tube to detect differential pressure. [Means for solving the problem]

[0006] The technical means adopted by the present invention are: a flow path component that communicates with the mask and generates a differential pressure in an airflow caused by breathing; a differential pressure sensor for detecting the differential pressure; a calculation unit that calculates a respiratory volume based on the detected differential pressure; A differential pressure pneumotachograph comprising: The flow path component is a main body having a plurality of flow paths formed therein; a sensor housing portion integrally formed with the main body; Equipped with Among the plurality of flow paths, a first side and a second side of a flow path close to the sensor housing portion are respectively connected to the sensor housing portion to form a bypass, The sensor housing accommodates a differential pressure sensor. It is a differential pressure respiratory flow meter.

[0007] In one aspect, the differential pressure sensor has a nonlinear differential pressure-flow characteristic in relation to the flow path component; the calculation unit calculates the flow rate using a correction formula that approximates the differential pressure-flow rate characteristics, The correction formula is made up of two linear approximations that sandwich a predetermined differential pressure value in a double logarithmic graph of differential pressure vs. flow rate.

[0008] In one embodiment, a filter is provided between the mask and the flow path part, and exhaled air passes through the filter and is introduced into the sensor accommodating portion.

[0009] The present invention can be provided as an exhaled gas analyzer including the above-described differential pressure pneumotachometer. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a differential pressure pneumotachometer that does not use an air tube to detect differential pressure. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an overall view of a respiratory flow meter (excluding a calculation unit) according to an embodiment of the present invention. [Figure 2] FIG. 2 is an assembled perspective view of the flow path component according to the embodiment. [Figure 3] FIG. 2 is an exploded perspective view of the flow path component according to the embodiment. [Figure 4] FIG. 2 is a front view of the flow path component according to the embodiment. [Figure 5] 10A and 10B are diagrams illustrating airflows in the flow path component according to the embodiment. [Figure 6] FIG. 1 is a block diagram of a pneumotachograph according to an embodiment of the present invention. [Figure 7] 1 is a block diagram of an exhaled gas analyzer using a pneumotachograph according to an embodiment of the present invention. [Figure 8] 1 is a graph showing a differential pressure-flow rate characteristic curve based on sample data. [Figure 9] 9 is a log-log transformed graph based on the graph of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0012] As shown in FIGS. 1 to 5, the differential pressure respiratory flow meter according to this embodiment is provided with a flow path component 3 that is attached to a tubular section 2 that communicates with a mask 1 and generates a differential pressure in the airflow associated with breathing. The flow path component 3 includes a main body 4 having a first surface on the mask side and a second surface on the side away from the mask, multiple flow paths 40 that penetrate between the first and second surfaces of the main body 4, and a sensor housing 5 that is integrally formed with the main body 4. Of the multiple flow paths 40, the first and second sides of flow paths 40' that are closer to the sensor housing 5 communicate with the sensor housing 5, respectively, to form bypasses. The sensor housing 5 houses a differential pressure sensor 6 (a sensor module in which a sensor and an AD converter are integrated) that includes an A / D converter. A box-shaped sensor housing 8 is formed by covering the sensor housing 5 with the differential pressure sensor 6 housed therein with a lid 7.

[0013] In this embodiment, a differential pressure sensor 6 is provided in a sensor housing 5 integrally formed with the flow path component 3, allowing the sensor to be placed directly on the flow path component 3 to detect differential pressure without using an air tube. In conventional differential pressure respiratory flow meters, the differential pressure generating unit and the differential pressure detecting unit are separated by an air tube, whereas in the differential pressure respiratory flow meter of this embodiment, the flow path component 3 provides the differential pressure generating unit and the differential pressure detecting unit. This enables pressure detection over a wide dynamic range without having to consider pressure loss due to the length of the air tube.

[0014] The main body 4 of the flow path component 3 according to this embodiment has a robust tube bundle structure formed by cutting resin, and performance is not affected by structural deterioration. For example, in a conventional type that detects differential pressure using a resistor made of mesh, there is a risk that the characteristics of the resistor will change or deteriorate if the mesh is accidentally touched. However, the flow path component 3 may also be integrally molded using a mold or the like.

[0015] 3, the peripheral wall of the cylindrical portion 2 is partially cut out to form an insertion portion for the main body 4 of the flow path part 3, and the flow path part 3 is attached to the cylindrical portion 2 such that the block-shaped main body 4 of a predetermined thickness is inserted to close the cross section of the cylindrical portion 2 and the sensor accommodating portion 5 is positioned outside the cylindrical portion 2. In addition, one end of an air tube (not shown) is connected to the peripheral wall of the cylindrical portion 2, and the other end of the air tube is connected to an exhaled gas analyzer so that exhaled gas is supplied to the exhaled gas analyzer (oxygen sensor, CO2 sensor 2).

[0016] In the embodiment shown in FIG. 1 , a filter 9 is provided in the tubular portion 2, positioned between the mask 1 and the flow path component 3. The filter 9 is used to remove contaminating microdroplets such as saliva exhaled from the subject. When breathing, saliva may unintentionally mix with exhaled air depending on the dynamics of the breathing. The differential pressure respiratory flow meter of this embodiment does not use the air tube used in conventional differential pressure respiratory flow meters, and therefore the distance between the mask 1 and the differential pressure detection unit is relatively short. Therefore, there is a risk of saliva directly adhering to the differential pressure detection unit, and the adhering matter may affect the performance of the sensor. Therefore, a filter is connected to prevent exhaled air from directly contacting the differential pressure detection unit. Note that the filter 7 is an optional element.

[0017] The differential pressure sensor 6 is electrically connected to a calculation unit that calculates the respiration rate based on the detected differential pressure. The differential pressure sensor 6 has a nonlinear differential pressure-flow rate characteristic in relation to the flow path component 3. The calculation unit calculates the flow rate using a correction formula that approximates the differential pressure-flow rate characteristic, and the correction formula consists of two linear approximation formulas that sandwich a predetermined differential pressure value on a double logarithmic graph of differential pressure-flow rate.

[0018] The calculation method for the two-stage approximation conversion formula based on the differential pressure characteristic curve is explained below. First, Fig. 8 is a graph plotting sample data (a large amount of corresponding data between differential pressure and flow rate), with the horizontal axis representing differential pressure (DP) [pa] and the vertical axis representing flow rate [standard liter per minute: slm]. In Fig. 8, it can be observed that the differential pressure-flow rate characteristic is a nonlinear characteristic (curve).

[0019] The inventors have studied the correction of this nonlinear characteristic and found that when the graph of FIG. 8 is converted into a double logarithmic graph as shown in FIG. 9, the th It was observed that two linear approximations are possible with the boundary at x. Based on the log-log graph, the differential pressure (DP) point x th is used as the threshold, and the following conversion formula is obtained by two-step approximation. TIFF0007778352000001.tif46154 The values ​​of α1, β1, α2, and β2 in the conversion formula are determined by the specific values ​​of the sample data, and the specified value of differential pressure (DP) x th is determined as a threshold value, and two linear regression equations are calculated on either side of the threshold value.

[0020] As shown in Figure 6, the differential pressure measured by the differential pressure sensor 6 of the respiratory flow meter is transmitted as digital data to the calculation unit. The calculation unit first calculates the differential pressure and a preset value x th Compare with DP≦x th In this case, the first differential pressure-flow rate conversion formula is selected to convert the differential pressure to flow rate, and DP>x th In this case, the second differential pressure-flow rate conversion formula is selected to convert the differential pressure into a flow rate.

[0021] Based on the obtained flow rate, ventilation volumes, such as tidal volume (VT) and minute ventilation (VE), are calculated. Those skilled in the art will understand that appropriate corrections can be made when calculating ventilation volumes. For example, when calculating tidal volume, corrections can be made according to respiratory rate (RR).

[0022] FIG. 7 shows an exhaled gas analyzer using a respiratory flow meter according to this embodiment. The exhaled gas analyzer comprises an exhaled gas analyzer main body, a calibrator, and an analyzer (computer). The main body includes an oxygen sensor, a CO2 sensor 2, and a processing unit (CPU), which also serves as the processing unit of the respiratory flow meter. The calibrator includes a CO2 sensor 1 and a processing unit (CPU). The differential pressure measured by the differential pressure sensor (flow sensor) of the respiratory flow meter is transmitted as digital data to the processing unit of the exhaled gas analyzer. Exhaled gas is introduced from the respiratory flow meter via an air tube into the exhaled gas analyzer main body. For detailed information about the configuration and calibration method of the exhaled gas analyzer shown in FIG. 7, see Japanese Patent Application Publication No. 2020-192191. [Explanation of symbols]

[0023] 1. Mask 2 Cylindrical part 3 Flow path parts 4 Main unit 40 Flow path 40´ Flow path (bypass) 5 Sensor housing 6 Differential pressure sensor

Claims

1. A differential pressure pneumotachograph having a mask and a tubular portion communicating with the mask, a flow path component provided in the cylindrical portion and generating a differential pressure in an airflow passing through the cylindrical portion in response to breathing; a differential pressure sensor for detecting the differential pressure; a calculation unit that calculates a respiratory volume based on the detected differential pressure; It consists of The flow path component is integrally formed by resin cutting molding, a main body having a first surface on the mask side and a second surface on the side away from the mask, the main body having a plurality of flow channels formed therein and penetrating between the first surface and the second surface; A sensor housing portion is integrally formed with the main body, Among the plurality of flow paths, in a flow path close to the sensor housing portion, a portion on a first surface side and a portion on a second surface side are each in communication with the sensor housing portion to form a bypass, an insertion portion for the main body of the flow path part is formed by partially cutting out a peripheral wall of the cylindrical part, the main body is inserted into the flow path part so as to close a cross section of the cylindrical part, and the sensor accommodating part is positioned outside the cylindrical part, and the flow path part is attached to the cylindrical part; The sensor housing accommodates a differential pressure sensor. Differential pressure pneumotachograph.

2. the differential pressure sensor has a nonlinear differential pressure-flow rate characteristic in relation to the flow path component; the calculation unit calculates the flow rate using a correction formula that approximates the differential pressure-flow rate characteristics, The correction formula is composed of two linear approximation formulas that sandwich a predetermined differential pressure value in a double logarithmic graph of differential pressure vs. flow rate. The differential pressure pneumotachograph according to claim 1 .

3. A filter is provided between the mask and the flow path component, and exhaled air is introduced into the sensor accommodating section through the filter. The differential pressure pneumotachometer according to claim 1 or 2.

4. An exhaled gas analyzer comprising the differential pressure pneumotachometer according to any one of claims 1 to 3.

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