A human body respiratory heat metabolism detection device and method based on a piston-type air cylinder

Abstract

The present invention discloses a human body respiratory heat metabolism detection device and method based on a piston-type cylinder. The detection device includes a flow rate detection module, a respiratory gas sampling module, a gas concentration analysis module, a control unit, and a computer. The flow rate detection module is used for bidirectional flow rate detection of respiratory gas; the respiratory gas sampling module is used for sampling collection, physical averaging, and constant flow discharge of respiratory gas; the gas concentration analysis module is used for detecting and calibrating the concentrations of oxygen and carbon dioxide in respiratory gas; the control unit is responsible for controlling and signal acquisition of various motors, valves, sensors, etc. in the device; the computer is responsible for data collection, calculation and analysis, human-computer interaction, and result display. The detection method is to first carry out concentration calibration, then implement metabolic tests on subjects based on a respiratory mask or a ventilator, and finally calculate metabolic indicators according to the measured gas concentration and flow rate parameters. The present invention can be applied to two metabolic detection scenarios of mechanical ventilation and spontaneous breathing, and the test is reliable and easy to be implemented in engineering.

Description

Technical Field

[0001] The present invention relates to the field of human energy metabolism detection, and particularly relates to a human respiratory heat metabolism detection device and method based on a piston-type cylinder. Background Art

[0002] Human respiratory heat metabolism detection equipment plays an important role in medical applications such as nutritional support, prevention and diagnosis of metabolic diseases. For example, the metabolic detection results of critically ill patients are an important basis for physicians to formulate nutritional support plans. The principle of indirect calorimetry is the "gold standard" for human metabolism detection, which is achieved by detecting the oxygen consumption and carbon dioxide production of the subject. Currently, the detection methods of equipment based on the principle of indirect calorimetry mainly include:

[0003] (1) Hood dilution method. The metabolic detection equipment using this method draws the human breath gas into the corresponding analysis unit after mixing and diluting it with air through a collecting hood to achieve flow and concentration detection, and complete the calculation of oxygen consumption and carbon dioxide production. This method has the advantages of high comfort, simple gas path, and good accuracy. However, due to the application of the collecting hood structure, it cannot be adapted to the ventilator pipeline, making it unable to be applied to the metabolic detection scenario of mechanically ventilated subjects, and it is difficult to identify the real-time metabolic changes of the subjects.

[0004] (2) Mixed chamber method. The metabolic detection equipment using this method first collects the human exhaled breath based on the mixed chamber, physically averages it, then discharges it after diluting it with air, and finally detects the component concentrations of the gas in the mixed chamber, the diluted gas, and the inhaled gas, and combines the flow detection of the diluted exhaust gas to achieve the calculation of oxygen consumption and carbon dioxide production. This method has the advantages of high stability, high accuracy, and can be adapted to the application scenarios of subjects under spontaneous breathing and mechanical ventilation. In addition, although the design of the mixed chamber reduces the frequency response requirements of the concentration sensor, it increases the complexity of the gas path structure, the equipment volume is large, and it is difficult to carry out disinfection and sterilization of medical equipment, making it difficult to control the risk of cross-infection between subjects.

[0005] (3) Breath-by-breath method. The metabolic detection equipment using this method respectively detects the flow rate in the respiratory passage and the concentration by using the bypass gas sampling method in the respiratory passage to complete the detection of the flow rate and concentration signals of each breath of the subject, and achieve the calculation of oxygen consumption and carbon dioxide production. This method has the advantages of strong real-time performance and high adaptability of the application scenario. However, it has very high requirements for the frequency response of the concentration sensor, and highly depends on the time alignment algorithm of the flow signal and the concentration signal, with complex implementation and difficult engineering implementation. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a human respiratory heat metabolism detection device and method based on a piston cylinder, which is a piston cylinder human respiratory heat metabolism detection device and method applicable to two application scenarios of mechanically ventilated and spontaneously breathing subjects, with a reliable gas path structure and low requirements for the dynamic performance of gas concentration sensors, and can achieve high-safety and high-comfort human energy metabolism detection.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A human respiratory heat metabolism detection device based on a piston cylinder, which consists of a flow rate detection module, a respiratory gas sampling module, a gas concentration analysis module, a control unit and a computer. The flow rate detection module is used for bidirectional flow rate detection of the subject's respiratory gas; the respiratory gas sampling module is used for sampling collection, physical averaging and constant flow discharge of the subject's respiratory gas; the gas concentration analysis module is used for detecting the oxygen and carbon dioxide concentrations in the subject's respiratory gas and calibrating the sensor concentration; the control unit is responsible for controlling and signal acquisition of various motors, valves, sensors, etc. in the device; the computer is responsible for data collection, calculation and analysis, human-computer interaction and result display.

[0009] Preferably, the flow rate detection module is a detachable tubular structure composed of a porous air resistance plate, a main pressure difference sensor, sampling hole A, sampling hole B, a pipeline and an air pipe. The porous air resistance plate is vertically and centrally installed inside the pipeline, and when the respiratory gas passes through, an air flow resistance is generated to form a pressure difference; the sampling hole A and the sampling hole B are installed on both sides of the porous air resistance plate at equal intervals, providing an air flow path for sampling and analyzing the respiratory gas flow rate and the respiratory gas concentration; the main pressure difference sensor is connected to the sampling hole A and the sampling hole B through an air pipe, and is used for detecting the pressure difference at both ends of the porous air resistance plate of the respiratory gas in the pipeline, and then calculating and obtaining a bidirectional flow rate signal.

[0010] Preferably, the respiratory gas sampling module consists of a pressure difference detection unit and a piston cylinder sampling unit. The pressure difference detection unit is used for detecting the pressure difference between the inside of the piston cylinder and the pipeline of the flow rate detection module; the design purpose of the piston cylinder sampling unit is: firstly, it is used for proportionally pumping and collecting the subject's respiratory gas; secondly, it is used for physically averaging the concentrations of various gas components in the respiratory gas; thirdly, it is used for constantly flowing the collected subject's respiratory gas out to the gas concentration analysis module.

[0011] Preferably, the air pressure difference detection unit is composed of a micro pressure difference sensor, a fifth switching valve, a sixth switching valve, a seventh switching valve, an eighth switching valve, and an air pipe. Sampling hole C and sampling hole D are respectively the air inlet holes of the exhalation piston cylinder and the inhalation piston cylinder. The X end of the fifth switching valve is connected to sampling hole A through an air pipe, the X end of the sixth switching valve is connected to sampling hole D through an air pipe, the X end of the seventh switching valve is connected to sampling hole B through an air pipe, and the X end of the eighth switching valve is connected to sampling hole C through an air pipe. The X end of the micro pressure difference sensor is interconnected with the Y end of the fifth switching valve and the Y end of the seventh switching valve through an air pipe, and the Y end of the micro pressure difference sensor is interconnected with the Y end of the sixth switching valve and the Y end of the eighth switching valve through an air pipe.

[0012] Preferably, the piston cylinder sampling unit is composed of a first switching valve, a second switching valve, a third switching valve, a fourth switching valve, a first electric push rod, a second electric push rod, an inhalation piston cylinder, an exhalation piston cylinder, a pressure difference sensor, and an air pipe. An exhalation phase sampling air flow path is formed by connecting sampling hole A, the first switching valve, the sampling hole C of the exhalation piston cylinder, the air outlet hole of the exhalation piston cylinder, and the air inlet of the third switching valve in sequence through an air pipe; an inhalation phase sampling air flow path is formed by connecting sampling hole B, the second switching valve, the sampling hole D of the inhalation piston cylinder, the air outlet hole of the inhalation piston cylinder, and the air inlet of the fourth switching valve in sequence through an air pipe. One end of the pressure difference sensor is connected to the air outlet of the third switching valve, the air outlet of the fourth switching valve, the air inlet end of the oxygen sensor, and the air outlet of the proportional valve through an air pipe, and the other end of the pressure difference sensor is connected to the air. The first electric push rod and the second electric push rod are respectively connected to the piston rods of the exhalation and inhalation piston cylinders, and are used to drive and adjust the positions of the piston rods to realize sampling, pumping, and exhausting of the breathing gas of the subject.

[0013] Preferably, during the inhalation phase of the subject. First, the fifth and sixth switching valves in the air pressure difference detection unit are opened, and the seventh and eighth switching valves are closed. At this time, the micro-pressure difference sensor detects the air pressure difference between sampling hole A and sampling hole D; second, the second and third switching valves in the piston cylinder sampling unit are opened, and the first and fourth switching valves are closed. At this time, the inhalation piston cylinder is to be evacuated, the piston rod of the inhalation piston cylinder is at the topmost position, the exhalation piston cylinder is to be exhausted, and the piston rod of the exhalation piston cylinder is at the bottommost position; then, after the inhalation phase starts, the second electric push rod pulls the piston rod of the inhalation piston cylinder, and the inhaled air of the subject in the flow detection module is inhaled into the inhalation piston cylinder through the second switching valve. During this period, based on the ADRC negative feedback control algorithm, taking the air pressure difference between sampling hole A and sampling hole D as the observation signal, the second electric push rod is controlled to pull the piston rod of the inhalation piston cylinder, so that the air pressure difference between sampling hole A and sampling hole D is 0, thereby realizing that the evacuation flow rate of the inhalation piston cylinder is proportional to the inhaled air flow rate of the subject in the flow detection module, completing the proportional evacuation to collect the inhaled air of the subject and the physical averaging of the gas component concentrations based on the inhalation cylinder; finally, simultaneously after the inhalation phase starts, the first electric push rod pushes the piston rod of the exhalation piston cylinder, and the exhaled air of the subject in the exhalation piston cylinder is discharged to the gas concentration analysis module through the third switching valve. During this period, based on the PID negative feedback control algorithm, taking the air pressure at the inlet of the oxygen sensor detected by the pressure difference sensor as the observation signal, the first electric push rod is controlled to adjust the pushing rate of the piston rod in the exhalation piston cylinder, so that the air pressure at the outlet of the third switching valve is constant until the gas in the exhalation piston cylinder is exhausted, realizing the constant pressure and constant flow discharge of the exhaled air of the subject in the exhalation piston cylinder to the oxygen sensor in the gas concentration analysis module. During the exhalation phase of the subject. First, the seventh and eighth switching valves in the air pressure difference detection unit are opened, and the fifth and sixth switching valves are closed. At this time, the micro-pressure difference sensor detects the air pressure difference between sampling hole B and sampling hole C; second, the first and fourth switching valves in the piston cylinder sampling unit are opened, and the second and third switching valves are closed. At this time, the exhalation piston cylinder is to be evacuated, the piston rod of the exhalation piston cylinder is at the topmost position, the inhalation piston cylinder is to be exhausted, and the piston rod of the inhalation piston cylinder is at the bottommost position; then, after the exhalation phase starts, the first electric push rod pulls the piston rod of the exhalation piston cylinder, and the exhaled air of the subject in the flow detection module is inhaled into the exhalation piston cylinder through the first switching valve. During this period, based on the ADRC negative feedback control algorithm, taking the air pressure difference between sampling hole B and sampling hole C as the observation signal, the first electric push rod is controlled to pull the piston rod of the exhalation piston cylinder, so that the air pressure difference between sampling hole B and sampling hole C is 0, thereby realizing that the evacuation flow rate of the exhalation piston cylinder is proportional to the exhaled air flow rate of the subject in the flow detection module, completing the proportional evacuation to collect the exhaled air of the subject and the physical averaging of the gas component concentrations based on the exhalation cylinder; finally, simultaneously after the exhalation phase starts, the second electric push rod pushes the piston rod of the inhalation piston cylinder, and the inhaled air of the subject in the inhalation piston cylinder is discharged to the gas concentration analysis module through the fourth switching valve.During this period, based on the PID negative feedback control algorithm, the air pressure at the intake port of the oxygen sensor detected by the differential pressure sensor is used as the observation signal to control the second electric push rod to adjust the pushing rate of the piston rod in the suction piston cylinder, so that the air pressure at the outlet of the fourth switching valve is constant until the gas in the suction piston cylinder is exhausted, realizing the constant-pressure and constant-flow discharge of the inhaled gas of the subject in the suction piston cylinder to the oxygen sensor in the gas concentration analysis module. Among them, the inhalation and exhalation phases of the subject are identified by the main differential pressure sensor in the flow detection module. In particular, during the first breath of the subject, the exhaust gas from the exhalation piston cylinder is air.

[0014] Preferably, the gas concentration analysis module is composed of an oxygen sensor, a carbon dioxide sensor, a first high-pressure calibration gas source, a second high-pressure calibration gas source, a first pressure reducing valve, a second pressure reducing valve, a first pressure relief valve, a second pressure relief valve, a proportional valve and a trachea. The first high-pressure calibration gas source, the first pressure reducing valve, the first pressure relief valve and the proportional valve are connected in sequence through the trachea to form a first set of calibration gas flow paths, and the second high-pressure calibration gas source, the second pressure reducing valve, the second pressure relief valve and the proportional valve are connected in sequence through the trachea to form a second set of calibration gas flow paths. The outlet end of the oxygen sensor is connected to the inlet end of the carbon dioxide sensor. The outlet end of the carbon dioxide sensor is connected to the air. The oxygen sensor and the carbon dioxide sensor are used to detect the oxygen and carbon dioxide concentration signals in the sampled gas.

[0015] Preferably, when calibrating the oxygen sensor and the carbon dioxide sensor in the gas concentration analysis module based on the concentration of the first set of calibration gases: First, close the second high-pressure calibration gas source and open the first high-pressure calibration gas source. The calibration gas is reduced in pressure by the first pressure reducing valve and then reaches the first pressure relief valve. Then, open the first pressure relief valve. After the calibration gas is depressurized, it reaches the inlet of the proportional valve. Finally, open the proportional valve, and the calibration gas is sent to the oxygen sensor and the carbon dioxide sensor through the proportional valve. During this period, the differential pressure sensor in the piston cylinder sampling unit detects the outlet pressure of the proportional valve outlet as the observation signal, and controls the opening size of the proportional valve based on the PID negative feedback control algorithm to keep the outlet pressure of the proportional valve constant, and the calibration gas of the first high-pressure calibration gas source is sent to the oxygen sensor at a constant pressure and constant flow rate. When calibrating the oxygen sensor and the carbon dioxide sensor in the gas concentration analysis module based on the concentration of the second set of calibration gases: First, close the first high-pressure calibration gas source and open the second high-pressure calibration gas source. The calibration gas is reduced in pressure by the second pressure reducing valve and then reaches the second pressure relief valve. Then, open the second pressure relief valve. After the calibration gas is depressurized, it reaches the inlet of the proportional valve. Finally, open the proportional valve, and the calibration gas is sent to the oxygen sensor and the carbon dioxide sensor through the proportional valve. During this period, the differential pressure sensor in the piston cylinder sampling unit detects the outlet pressure of the proportional valve outlet as the observation signal, and controls the opening size of the proportional valve based on the PID negative feedback control algorithm to keep the outlet pressure of the proportional valve constant, and the calibration gas of the second high-pressure calibration gas source is sent to the oxygen sensor at a constant pressure and constant flow rate. When the subject conducts a metabolic test: close the proportional valve, and the breathing gas of the subject is discharged to the oxygen sensor at a constant pressure and constant flow rate by the breathing gas sampling module, and then discharged to the air after passing through the carbon dioxide sensor, so as to detect the oxygen concentration and carbon dioxide concentration of the breathing gas of the subject.

[0016] The present invention also provides a method for detecting human respiratory heat metabolism based on a piston-type cylinder. Based on the above detection device, it includes the following steps:

[0017] Step 1: The operator calibrates the gas concentrations of the oxygen sensor and the carbon dioxide sensor.

[0018] First, when calibrating with the first set of gas standards, open the first high-pressure calibration gas source. The calibration gas is reduced in pressure by the first pressure reducing valve and then reaches the first pressure relief valve. Then, open the first pressure relief valve. The calibration gas passes through the outlet of the proportional valve to realize the flow path of the first set of calibration gases. After ventilation and waiting for the air flow to stabilize, collect the average value of the gas concentration within a period of time to complete the calibration of the range point of the oxygen sensor and the zero point calibration of the carbon dioxide sensor. Secondly, when calibrating with the second set of gas standards, open the second high-pressure calibration gas source. The calibration gas is reduced in pressure by the second pressure reducing valve and then reaches the second pressure relief valve. Then, open the second pressure relief valve. The calibration gas passes through the outlet of the proportional valve to realize the flow path of the second set of calibration gases. After ventilation and waiting for the air flow to stabilize, collect the average value of the gas concentration within a period of time to complete the zero point calibration of the oxygen sensor and the calibration of the range point of the carbon dioxide sensor. Finally, close each high-pressure calibration gas source and valve to complete the calibration of the gas concentrations of the oxygen sensor and the carbon dioxide sensor.

[0019] Step 2: The subject completes user registration and login on the computer, makes preparations before the metabolic test, and starts the test.

[0020] When applied to subjects with spontaneous breathing, the subject wears a breathing mask. One end of the flow detection module is connected to the breathing mask, and the other end is connected to the air. When applied to subjects with mechanical ventilation, the subject is connected to the ventilator, and both ends of the flow detection module are installed in the ventilator patient pipeline between the Y-shaped interface of the ventilator and the subject. The main differential pressure sensor in the flow detection module measures the air pressure difference across the porous air resistance plate, thereby identifying the inhalation and exhalation phases of the subject and obtaining the bidirectional flow of the subject's breathed air. When the subject starts to inhale, the inhalation piston cylinder is ready to draw air, and the exhalation piston cylinder is ready to exhaust air. During inhalation, the inhalation piston cylinder draws air to collect the inhaled air of the subject, and the exhalation piston cylinder discharges the collected exhaled air of the subject from the previous breath to the gas concentration analysis module at a constant pressure and constant flow rate through the third switching valve. The oxygen sensor and carbon dioxide sensor detect the average oxygen concentration and average carbon dioxide concentration of the subject's exhaled air from the previous breath. When the subject starts to exhale, the exhalation piston cylinder is ready to draw air, and the inhalation piston cylinder is ready to exhaust air. During exhalation, the exhalation piston cylinder draws air to collect the exhaled air of the subject, and the inhalation piston cylinder discharges the collected inhaled air of the subject from the previous breath to the gas concentration analysis module at a constant pressure and constant flow rate through the fourth switching valve. The oxygen sensor and carbon dioxide sensor detect the average oxygen concentration and average carbon dioxide concentration of the subject's inhaled air from the previous breath.

[0021] Step 3: The computer calculates the metabolic-related indicators: oxygen uptake per minute and carbon dioxide production per minute based on the data collected and uploaded by the control unit. The formula derivation is expressed as follows:

[0022] Volume of exhaled gas per breath:

[0023] (1)

[0024] (2)

[0025] Where, is the volume of exhaled gas (mL) during a certain respiratory cycle; is the start time (s) of exhalation during a certain respiratory cycle; is the end time (s) of exhalation during a certain respiratory cycle; is the respiratory flow rate (mL / s) of the subject; is the time (s); is the gas standard state correction coefficient; is the ambient atmospheric pressure (kPa).

[0026] Oxygen uptake per minute ( ) :

[0027] (3)

[0028] Carbon dioxide production per minute ( ):

[0029] (4)

[0030] Wherein, is the start time of inhalation (s) in a certain respiratory cycle; is the average oxygen concentration of each exhaled breath of the subject (%); is the average carbon dioxide concentration of each exhaled breath of the subject (%); is the average oxygen concentration of each inhaled breath of the subject (%); is the average carbon dioxide concentration of each inhaled breath of the subject (%); is the oxygen uptake per minute (mL / min); is the carbon dioxide production per minute (mL / min).

[0031] The respiratory quotient (RQ) can be calculated through the above oxygen uptake per minute and carbon dioxide production per minute, and then the resting metabolic rate (REE) can be calculated based on the Weir formula, thereby realizing a human respiratory heat metabolism detection based on a piston-type cylinder.

[0032] The beneficial effects achieved by the present invention are as follows:

[0033] 1. The breathing sampling module of the present invention based on the piston cylinder sampling unit realizes the cyclic and proportional collection, physical buffering and constant pressure and constant flow gas component concentration analysis of the inhaled and exhaled breaths of the human body respectively, avoiding the real-time human breath analysis at the millisecond level, and not requiring the dynamic performance of the oxygen sensor and carbon dioxide sensor (i.e., the concentration sensor in the per-breath method), making the human metabolism detection and analysis easier to be realized in engineering;

[0034] 2. The present invention realizes the constant pressure and constant flow control of the air flow during the analysis of the human breath component concentration through the breathing gas sampling module and the gas concentration analysis module, avoiding the errors of the oxygen sensor and carbon dioxide sensor caused by the fluctuations of air pressure and air flow, and improving the accuracy of human metabolism detection;

[0035] 3. The present invention based on the flow detection module can realize the detection of the flow rate and component concentration of the human breath when the subject wears a mask or is connected to a ventilator, supporting two application scenarios of human metabolism tests for subjects with spontaneous breathing and subjects under mechanical ventilation. Description of the Drawings

[0036] Figure 1It is a schematic structural diagram of a human respiratory heat metabolism detection device based on a piston-type cylinder according to the present invention;

[0037] Figure 2 It is a schematic structural diagram of a flow detection module device for subject metabolism testing under mechanical ventilation and spontaneous breathing;

[0038] Figure 3 It is a schematic diagram of the structure of a piston-type cylinder device and its air extraction and exhaust;

[0039] Figure 4 It is a flowchart of a method for detecting human respiratory heat metabolism based on a piston-type cylinder according to the present invention.

[0040] Among them, the reference numerals are: 1 - computer, 2 - control unit, 3 - porous air resistance plate, 4 - main pressure difference sensor, 5 - first switching valve, 6 - second switching valve, 7 - exhalation piston cylinder, 8 - inhalation piston cylinder, 9 - first electric push rod, 10 - second electric push rod, 11 - third switching valve, 12 - fourth switching valve, 13 - oxygen sensor, 14 - carbon dioxide sensor, 15 - proportional valve, 16 - first pressure relief valve, 17 - first pressure reducing valve, 18 - first high-pressure calibration gas source, 19 - pressure difference sensor, 20 - second pressure relief valve, 21 - second pressure reducing valve, 22 - second high-pressure calibration gas source, 23 - micro pressure difference sensor, 24 - fifth switching valve, 25 - sixth switching valve, 26 - seventh switching valve, 27 - eighth switching valve, 2.1 - sampling hole A, 2.2 - sampling hole B, 2.4 pipeline. Specific embodiments

[0041] To make the purpose, technical solution and advantages of the present invention clearer, the embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0042] As Figure 1 shown, this embodiment provides a human respiratory heat metabolism detection device based on a piston-type cylinder, including a flow detection module, a respiratory gas sampling module, a gas concentration analysis module, a control unit 2 and a computer 1.

[0043] As Figure 2As shown, the flow detection module is a detachable tubular structure composed of a porous air resistance plate 3, a main differential pressure sensor 4, a sampling hole A 2.1, a sampling hole B 2.2, a pipeline 2.4 of the flow detection module, and an air pipe. The porous air resistance plate 3 is vertically and centrally installed inside the pipeline 2.4. When the breathing air passes through, it generates air flow resistance to form a pressure difference. The sampling hole A 2.1 and the sampling hole B 2.2 are installed on both sides of the porous air resistance plate 3 at equal intervals, providing an air flow path for the pressure taking analysis of the breathing air flow and the sampling analysis of the breathing air concentration. The main differential pressure sensor 4 is connected to the sampling hole A 2.1 and the sampling hole B 2.2 through an air pipe, and is used to obtain the pressure difference between the breathing air in the pipeline 2.4 and both ends of the porous air resistance plate 3, and then calculate the two-way flow signal.

[0044] Specifically, when applied to a subject with spontaneous breathing, the subject wears a breathing mask, and one end of the flow detection module is connected to the breathing mask and the other end is connected to the air. When applied to a subject with mechanical ventilation, the subject wears a ventilator, and both ends of the flow detection module are installed in the ventilator patient pipeline between the Y-shaped interface of the ventilator and the subject.

[0045] The breathing gas sampling module is composed of a differential pressure detection unit and a piston cylinder sampling unit. The differential pressure detection unit is used to detect the pressure difference between the inside of the piston cylinder and the pipeline of the flow detection module. The design purpose of the piston cylinder sampling unit: Firstly, it is used to extract and collect the breathing gas of the subject in equal proportion; Secondly, it is used for the physical averaging of the concentrations of various gas components in the breathing gas; Thirdly, it constantly discharges the collected breathing gas of the subject to the gas concentration analysis module.

[0046] The differential pressure detection unit is composed of a micro differential pressure sensor 23, a fifth switching valve 24, a sixth switching valve 25, a seventh switching valve 26, an eighth switching valve 27, and an air pipe. The sampling hole C and the sampling hole D are respectively the air inlet holes of the exhalation piston cylinder 7 and the inhalation piston cylinder 8. The X end of the fifth switching valve 24 is connected to the sampling hole A 2.1 through an air pipe, the X end of the sixth switching valve 25 is connected to the sampling hole D through an air pipe, the X end of the seventh switching valve 26 is connected to the sampling hole B 2.2 through an air pipe, and the X end of the eighth switching valve 27 is connected to the sampling hole C through an air pipe. The X end of the micro differential pressure sensor 23 is interconnected with the Y end of the fifth switching valve 24 and the Y end of the seventh switching valve 26 through an air pipe, and the Y end of the micro differential pressure sensor 23 is interconnected with the Y end of the sixth switching valve 25 and the Y end of the eighth switching valve 27 through an air pipe.

[0047] The piston cylinder sampling unit consists of a first switching valve 5, a second switching valve 6, a third switching valve 11, a fourth switching valve 12, a first electric push rod 9, a second electric push rod 10, an inhalation piston cylinder 8, an exhalation piston cylinder 7, a differential pressure sensor 19 and an air pipe. The sampling hole A 2.1, the first switching valve 5, the sampling hole C of the exhalation piston cylinder 7, the air outlet of the exhalation piston cylinder 7 and the air inlet of the third switching valve 11 are connected in sequence through the air pipe to form an exhalation phase sampling air flow path; the sampling hole B 2.2, the second switching valve 6, the sampling hole D of the inhalation piston cylinder 8, the air outlet of the inhalation piston cylinder 8 and the air inlet of the fourth switching valve 12 are connected in sequence through the air pipe to form an inhalation phase sampling air flow path. One end of the differential pressure sensor 19 is connected to the air outlet of the third switching valve 11, the air outlet of the fourth switching valve 12, the air inlet end of the oxygen sensor 13 and the air outlet of the proportional valve 15 through the air pipe at the same time, and the other end of the differential pressure sensor 19 is connected to the air. The first electric push rod 9 and the second electric push rod 10 are respectively connected to the piston rods of the exhalation piston cylinder 7 and the inhalation piston cylinder 8, and are used to drive and adjust the positions of the piston rods to realize sampling, pumping and exhausting of the breathing gas of the subject.

[0048] As Figure 1 and Figure 3As shown, during the inhalation phase of the subject, first, the fifth switching valve 24 and the sixth switching valve 25 in the air pressure difference detection unit are opened, and the seventh switching valve 26 and the eighth switching valve 27 are closed. At this time, the micro-pressure difference sensor 23 detects the air pressure difference between the sampling hole A2.1 and the sampling hole D; then, the second switching valve 6 and the third switching valve 11 in the piston cylinder sampling unit are opened, and the first switching valve 5 and the fourth switching valve 12 are closed. At this time, the inhalation piston cylinder 8 is to be evacuated, the piston rod of the inhalation piston cylinder 8 is at the topmost position, the exhalation piston cylinder 7 is to be exhausted, and the piston rod of the exhalation piston cylinder 7 is at the bottommost position; then, after the inhalation phase starts, the second electric push rod 10 pulls the piston rod of the inhalation piston cylinder 8, and the inhaled air of the subject in the flow detection module is inhaled into the inhalation piston cylinder 8 through the second switching valve 6. During this period, based on the ADRC (active disturbance rejection control) algorithm, with the air pressure difference between the sampling hole A 2.1 and the sampling hole D as the observation signal, the second electric push rod 10 is controlled to pull the piston rod of the inhalation piston cylinder 8, so that the air pressure difference between the sampling hole A2.1 and the sampling hole D is 0, thereby realizing that the evacuation flow rate of the inhalation piston cylinder 8 is proportional to the inhaled air flow rate of the subject in the flow detection module, completing the evacuation of the inhaled air of the subject in equal proportion and the physical averaging of the gas component concentration based on the inhalation cylinder; finally, simultaneously after the inhalation phase starts, the first electric push rod 9 pushes the piston rod of the exhalation piston cylinder 7, and the exhaled air of the subject in the exhalation piston cylinder 7 is discharged to the gas concentration analysis module through the third switching valve 11. During this period, based on the PID negative feedback control algorithm, with the air pressure at the inlet of the oxygen sensor 13 detected by the pressure difference sensor 19 as the observation signal, the first electric push rod 9 is controlled to adjust the pushing rate of the piston rod in the exhalation piston cylinder 7, so that the air pressure at the outlet of the third switching valve 11 is constant until the gas in the exhalation piston cylinder 7 is exhausted, realizing the constant pressure and constant flow discharge of the exhaled air of the subject in the exhalation piston cylinder 7 to the oxygen sensor 13 in the gas concentration analysis module.

[0049] During the exhalation phase of the subject, first, the seventh switching valve 26 and the eighth switching valve 27 in the air pressure difference detection unit are opened, and the fifth switching valve 24 and the sixth switching valve 25 are closed. At this time, the micro-pressure difference sensor 23 detects the air pressure difference between the sampling hole B 2.2 and the sampling hole C; secondly, the first switching valve 5 and the fourth switching valve 12 in the piston cylinder sampling unit are opened, and the second switching valve 6 and the third switching valve 11 are closed. At this time, the exhalation piston cylinder 7 is ready to be evacuated, the piston rod of the exhalation piston cylinder 7 is at the topmost position, the inhalation piston cylinder 8 is ready to exhaust, and the piston rod of the inhalation piston cylinder 8 is at the bottommost position; then, after the exhalation phase starts, the first electric push rod 9 pulls the piston rod of the exhalation piston cylinder 7, and the exhaled breath of the subject in the flow detection module is inhaled into the exhalation piston cylinder through the first switching valve 5. During this period, based on the ADRC auto-disturbance rejection control algorithm, with the air pressure difference between the sampling hole B 2.2 and the sampling hole C as the observation signal, the first electric push rod 9 is controlled to pull the piston rod of the exhalation piston cylinder 7, so that the air pressure difference between the sampling hole B 2.2 and the sampling hole C is 0, thereby realizing that the evacuation flow rate of the exhalation piston cylinder 7 is proportional to the exhaled breath flow rate of the subject in the flow detection module, completing the evacuation collection of the exhaled breath of the subject in proportion and the physical averaging of the gas component concentrations based on the exhalation cylinder; finally, simultaneously with the start of the exhalation phase, the second electric push rod 10 pushes the piston rod of the inhalation piston cylinder 8, and the inhaled gas of the subject in the inhalation piston cylinder 8 is discharged to the gas concentration analysis module through the fourth switching valve 12. During this period, based on the PID negative feedback control algorithm, with the air pressure at the inlet of the oxygen sensor 13 detected by the pressure difference sensor 19 as the observation signal, the second electric push rod 10 is controlled to adjust the pushing rate of the piston rod in the inhalation piston cylinder 8, so that the air pressure at the outlet of the fourth switching valve 12 is constant until the gas in the inhalation piston cylinder 8 is exhausted, realizing the constant-pressure and constant-flow discharge of the inhaled gas of the subject in the inhalation piston cylinder 8 to the oxygen sensor 13 in the gas concentration analysis module. Among them, the inhalation and exhalation phases of the subject are identified by the main pressure difference sensor 4 in the flow detection module. In particular, during the first breath phase of the subject, the gas discharged from the exhalation piston cylinder is air.

[0050] The gas concentration analysis module consists of an oxygen sensor 13, a carbon dioxide sensor 14, a first high-pressure calibration gas source 18, a second high-pressure calibration gas source 22, a first pressure reducing valve 17, a second pressure reducing valve 21, a first pressure relief valve 16, a second pressure relief valve 20, a proportional valve 15 and air pipes. The first high-pressure calibration gas source 18, the first pressure reducing valve 17, the first pressure relief valve 16 and the proportional valve 15 are connected in sequence through the air pipes to form a first set of calibration gas flow paths, and the second high-pressure calibration gas source 22, the second pressure reducing valve 21, the second pressure relief valve 20 and the proportional valve 15 are connected in sequence through the air pipes to form a second set of calibration gas flow paths. The outlet end of the oxygen sensor 13 is connected to the inlet end of the carbon dioxide sensor 14. The outlet end of the carbon dioxide sensor 14 is connected to the air. The oxygen sensor 13 and the carbon dioxide sensor 14 are used to detect the oxygen and carbon dioxide concentration signals in the sampled gas.

[0051] Specifically, when calibrating the oxygen sensor 13 and the carbon dioxide sensor 14 in the gas concentration analysis module based on the concentration of the first set of calibration gas, first, close the second high-pressure calibration gas source 22 and open the first high-pressure calibration gas source 18. The calibration gas is reduced in pressure by the first pressure reducing valve 17 and then reaches the first pressure relief valve 16. Then, the first pressure relief valve 16 is opened, and the calibration gas is depressurized and then reaches the inlet of the proportional valve 15. Finally, the proportional valve 15 is opened, and the calibration gas is sent to the oxygen sensor 13 and the carbon dioxide sensor 14 through the proportional valve 15. During this period, the differential pressure sensor 19 in the piston cylinder sampling unit detects the outlet air pressure of the proportional valve 15 as the observation signal, and controls the opening size of the proportional valve 15 based on the PID negative feedback control algorithm to keep the outlet air pressure of the proportional valve 15 constant, and the calibration gas of the first high-pressure calibration gas source 18 is sent to the oxygen sensor 13 at a constant pressure and constant flow rate.

[0052] When calibrating the oxygen sensor 13 and the carbon dioxide sensor 14 in the gas concentration analysis module based on the concentration of the second set of calibration gas, first, close the first high-pressure calibration gas source 18 and open the second high-pressure calibration gas source 22. The calibration gas is reduced in pressure by the second pressure reducing valve 21 and then reaches the second pressure relief valve 20. Then, the second pressure relief valve 20 is opened, and the calibration gas is depressurized and then reaches the inlet of the proportional valve 15. Finally, the proportional valve 15 is opened, and the calibration gas is sent to the oxygen sensor 13 and the carbon dioxide sensor 14 through the proportional valve 15. During this period, the differential pressure sensor 19 in the piston cylinder sampling unit detects the outlet air pressure of the proportional valve 15 as the observation signal, and controls the opening size of the proportional valve 15 based on the PID negative feedback control algorithm to keep the outlet air pressure of the proportional valve 15 constant, and the calibration gas of the second high-pressure calibration gas source 22 is sent to the oxygen sensor 13 at a constant pressure and constant flow rate. When the subject conducts a metabolic test: close the proportional valve 15, and the breathing gas of the subject is discharged from the breathing gas sampling module to the oxygen sensor 13 at a constant pressure and constant flow rate, and then discharged to the air after passing through the carbon dioxide sensor 14, so as to detect the oxygen concentration and carbon dioxide concentration of the breathing gas of the subject.

[0053] AsFigure 4 As shown in the figure, the present invention also provides a method for detecting human respiratory heat metabolism based on a piston-type cylinder, including the following steps:

[0054] Step 1: The operator calibrates the gas concentrations of the oxygen sensor 13 and the carbon dioxide sensor 14, including:

[0055] First, during the first set of gas calibrations, the first high-pressure calibration gas source 18 is opened, and the calibration gas is reduced in pressure by the first pressure reducing valve 17 and then reaches the first pressure relief valve 16; then, the first pressure relief valve 16 is opened, and the calibration gas passes through the outlet of the proportional valve 15 to realize the flow path of the first set of calibration gas. After ventilation and waiting for the gas flow to stabilize, the average value of the gas concentration within a period of time is collected to complete the calibration of the range point of the oxygen sensor 13 and the zero point calibration of the carbon dioxide sensor 14; then, during the second set of gas calibrations, the second high-pressure calibration gas source 22 is opened, and the calibration gas is reduced in pressure by the second pressure reducing valve 21 and then reaches the second pressure relief valve 20; then, the second pressure relief valve 20 is opened, and the calibration gas passes through the outlet of the proportional valve 15 to realize the flow path of the second set of calibration gas. After ventilation and waiting for the gas flow to stabilize, the average value of the gas concentration within a period of time is collected to complete the zero point calibration of the oxygen sensor and the calibration of the range point of the carbon dioxide sensor. Finally, each high-pressure calibration gas source and valve is closed to end the gas concentration calibration of the oxygen sensor and the carbon dioxide sensor.

[0056] Step 2: The subject completes user registration and login on the computer, makes preparations before the metabolic test, and starts the test, including:

[0057] When applied to a subject with spontaneous breathing, the subject wears a breathing mask, one end of the flow detection module is connected to the breathing mask, and the other end is connected to the air. When applied to a subject with mechanical ventilation, the subject wears a ventilator, and both ends of the flow detection module are installed in the ventilator patient pipeline between the Y-shaped interface of the ventilator and the subject. The main pressure difference sensor 4 in the flow detection module measures the pressure difference at both ends of the porous air resistance plate 3, thereby identifying the inhalation and exhalation phases of the subject and obtaining the bidirectional flow of the subject's breathing gas. When the subject starts to inhale, the inhalation piston cylinder 8 waits to draw air, and the exhalation piston cylinder 7 waits to exhaust air. The exhaled gas of the subject in the exhalation piston cylinder 7 is discharged to the gas concentration analysis module at a constant pressure and constant flow through the third switching valve 11, and the oxygen sensor 13 and the carbon dioxide sensor 14 detect the average oxygen concentration and the average carbon dioxide concentration of the exhaled gas of the subject last time. When the subject starts to exhale, the exhalation piston cylinder waits to draw air, and the inhalation piston cylinder waits to exhaust air. The inhaled gas of the subject in the inhalation piston cylinder is discharged to the gas concentration analysis module at a constant pressure and constant flow through the fourth switching valve 12, and the oxygen sensor 13 and the carbon dioxide sensor 14 detect the average oxygen concentration and the average carbon dioxide concentration of the inhaled gas of the subject last time.

[0058] Step 3: Based on the data collected and uploaded by the control unit 2, computer 1 calculates the metabolic-related indicators: oxygen uptake per minute and carbon dioxide production per minute. The formula derivation is as follows:

[0059] Volume of exhaled gas per breath:

[0060] (1)

[0061] (2)

[0062] where is the volume of exhaled gas during a certain respiratory cycle (unit: mL); is the start time of exhalation during a certain respiratory cycle (unit: s); is the end time of exhalation during a certain respiratory cycle (unit: s); is the respiratory flow rate of the subject (unit: mL / s); is the time (unit: s); is the gas standard state correction coefficient; is the ambient atmospheric pressure (unit: kPa).

[0063] Oxygen uptake per minute is:

[0064] (3)

[0065] Carbon dioxide production per minute is:

[0066] (4)

[0067] where is the start time of inhalation during a certain respiratory cycle (unit: s); is the average oxygen concentration of the exhaled gas per breath of the subject (%); is the average carbon dioxide concentration of the exhaled gas per breath of the subject (%); is the average oxygen concentration of the inhaled gas per breath of the subject (%); is the average carbon dioxide concentration of the inhaled gas per breath of the subject (%); is the oxygen uptake per minute (unit: mL / min); is the carbon dioxide production per minute (unit: mL / min).

[0068] Through the above oxygen uptake per minute and carbon dioxide production per minute, the respiratory quotient RQ can be calculated. Then, based on the Weir formula, the resting metabolic rate REE can be calculated, and further, a human respiratory heat metabolism detection based on a piston-type cylinder can be realized.

[0069] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A human body breathing heat metabolism detection device based on a piston cylinder, characterized in that: It includes a flow detection module, a breathing gas sampling module, a gas concentration analysis module, a control unit and a computer; The flow detection module is used for bidirectional flow detection of the subject's respiratory gas; The respiratory gas sampling module is used for sampling, collecting, physically averaging and discharging the subject's respiratory gas at a constant flow rate; The gas concentration analysis module is used for oxygen and carbon dioxide concentration detection and concentration calibration in the subject's breath; The control unit is responsible for the control and signal collection of each motor, valve, and sensor; The computer is responsible for data collection, calculation and analysis, human-computer interaction and result display; The respiratory gas sampling module is composed of a pressure difference detection unit and a piston cylinder sampling unit; the pressure difference detection unit comprises a micro-pressure difference sensor (23), a fifth switch valve (24), a sixth switch valve (25), a seventh switch valve (26), an eighth switch valve (27) and an air pipe, and is used to detect the pressure difference in the piston cylinder and in the pipeline of the flow detection module; the piston cylinder sampling unit comprises a first switch valve (5), a second switch valve (6), a third switch valve (11), a fourth switch valve (12), a first electric push rod (9), a second electric push rod (10), an inhalation piston cylinder (8), an exhalation piston cylinder (7), a pressure difference sensor (19) and an air pipe, and is used to proportionally extract and collect the respiratory gas of the subject, and physically average and discharge it to the gas concentration analysis module at a constant flow.

2. A human body breathing heat metabolism detection device based on a piston cylinder according to claim 1, characterized in that: The flow detection module is a detachable tubular structure consisting of a porous air block plate (3), a main pressure difference sensor (4), a sampling hole A (2.1), a sampling hole B (2.2), a pipeline (2.4) and an air pipe; the porous air block plate (3) is vertically and centrally mounted inside the pipeline (2.4); the sampling hole A (2.1) and the sampling hole B (2.2) are mounted on both sides of the porous air block plate (3) at equal intervals; the main pressure difference sensor (4) is connected to the sampling hole A (2.1) and the sampling hole B (2.2) via the air pipe; the main pressure difference sensor (4) is connected to the sampling hole A (2.1) and the sampling hole B (2.2) via the air pipe, and is used to obtain the pressure difference between the respiratory gas in the pipeline and the two ends of the porous air block plate (3); when the respiratory gas flows through the porous air block plate (3), a pressure difference is generated, and a bidirectional respiratory flow signal is obtained.

3. A human body breathing heat metabolism detection device based on a piston cylinder according to claim 1, characterized in that: In the air pressure difference detection unit, the sampling hole C and the sampling hole D are respectively the air inlet hole of the exhalation piston cylinder (7) and the air inlet hole of the inhalation piston cylinder (8); the X end of the fifth switch valve (24) is connected to the sampling hole A through an air pipe, the X end of the sixth switch valve (25) is connected to the sampling hole D through an air pipe, the X end of the seventh switch valve (26) is connected to the sampling hole B through an air pipe, and the X end of the eighth switch valve (27) is connected to the sampling hole C through an air pipe; the X end of the micro-pressure difference sensor (23) is connected to the Y end of the fifth switch valve (24) and the Y end of the seventh switch valve (26) through an air pipe, and the Y end of the micro-pressure difference sensor (23) is connected to the Y end of the sixth switch valve (25) and the Y end of the eighth switch valve (27) through an air pipe.

4. The human body breathing heat metabolism detection device based on a piston cylinder according to claim 1 is characterized in that: The sampling hole A, the first switch valve (5), the sampling hole C of the exhalation piston cylinder (7), the air outlet hole of the exhalation piston cylinder (7) and the air inlet of the third switch valve (11) are connected in sequence through the trachea to form an exhalation phase sampling airflow path; the sampling hole B, the second switch valve (6), the sampling hole D of the inhalation piston cylinder (8), the air outlet hole of the inhalation piston cylinder (8) and the air inlet of the fourth switch valve (12) are connected in sequence through the trachea to form an inhalation phase sampling airflow path; a pressure difference sensor (19) is connected to the first The first end of the electric push rod (9) and the second electric push rod (10) are connected to the outlet of the third switch valve (11), the outlet of the fourth switch valve (12), the air inlet end of the oxygen sensor (13) and the outlet of the proportional valve (15) through the trachea, and the other end of the differential pressure sensor (19) is connected to the air; the first electric push rod (9) and the second electric push rod (10) are respectively connected to the piston rods of the exhalation piston cylinder (7) and the inhalation piston cylinder (8), and are used to drive and adjust the position of the piston rods to achieve sampling of the subject's respiratory gas. In the inhalation phase, first, the fifth switch valve (24) and the sixth switch valve (25) of the air pressure difference detection unit are opened, and the seventh switch valve (26) and the eighth switch valve (27) are closed at the same time, and the air pressure difference between the sampling holes A (2.1) and D is detected by the micro-pressure difference sensor (23); then, in the piston cylinder sampling unit, the second switch valve (6) and the third switch valve (11) are opened, and the first switch valve (5) and the fourth switch valve (12) are closed. At this time, the inhalation piston cylinder (8) is ready to be inhaled, and the exhalation piston cylinder (7) is ready to be exhausted; after the inhalation phase begins, the second electric push rod (10) pulls the piston rod of the inhalation piston cylinder (8), and the inhaled gas of the subject enters the cylinder through the second switch valve (6); during this period, based on the ADRC negative feedback control algorithm, the air pressure difference between the sampling holes A and D is used as an observation signal to control the second electric push rod (10) to pull the piston rod of the inhalation piston cylinder (8), so that the sampling hole A (2.1) is closed.1) and the pressure difference between the sampling hole D and the sampling hole D is 0, thereby ensuring that the suction flow is proportional to the inhaled gas flow of the subject and completing the physical average of the gas component concentration in the cylinder; finally, at the same time as the inhalation phase begins, the first electric push rod (9) pushes the exhalation piston cylinder (7), and the exhaled gas is discharged to the gas concentration analysis module through the third switch valve (11); during this period, based on the PID negative feedback control algorithm, the pushing speed of the piston rod of the exhalation piston cylinder (7) is adjusted to ensure that the exhaust port pressure is constant until the gas is completely discharged to the gas concentration analysis module; in the exhalation phase In the first stage, the seventh switch valve (26) and the eighth switch valve (27) of the air pressure difference detection unit are opened, and the fifth switch valve (24) and the sixth switch valve (25) are closed at the same time, and the air pressure difference between the sampling holes B and C is detected by the micro-pressure difference sensor (23); then, in the piston cylinder sampling unit, the first switch valve (5) and the fourth switch valve (12) are opened, and the second switch valve (6) and the third switch valve (11) are closed; at this time, the exhalation piston cylinder (7) is ready to be evacuated, and the inhalation piston cylinder (8) is ready to be exhausted; secondly, after the exhalation stage begins, the first electric The push rod (9) pulls the piston rod of the exhalation piston cylinder (7), and the exhaled gas of the subject enters the cylinder through the first switch valve (5); during this period, based on the ADRC negative feedback control algorithm, the pressure difference between the sampling holes B (2.2) and C is used as an observation signal to control the first electric push rod (9) to pull the piston rod of the exhalation piston cylinder (7), so that the pressure difference between the sampling holes B (2.2) and the sampling hole C is 0, thereby ensuring that the suction flow rate is proportional to the exhaled gas flow rate of the subject, and completing the physical average of the gas component concentration in the cylinder; finally, the exhalation stage At the same time as the start, the second electric push rod (10) pushes the inhalation piston cylinder (8), and the inhaled gas is discharged to the gas concentration analysis module through the fourth switch valve (12); during this period, based on the PID negative feedback control algorithm, the pushing rate of the piston rod of the inhalation piston cylinder (8) is adjusted to ensure that the gas pressure at the exhaust port is constant until the gas is completely discharged to the gas concentration analysis module; wherein, the inhalation and exhalation phases of the subject are detected and identified by the main pressure difference sensor (4) in the flow detection module; during the subject's first breathing phase, the exhalation gas of the exhalation piston cylinder (7) is air. .

5. The human body breathing heat metabolism detection device based on a piston cylinder according to claim 1, characterized in that: The gas concentration analysis module comprises an oxygen sensor (13), a carbon dioxide sensor (14), a first high-pressure calibration gas source (18), a second high-pressure calibration gas source (22), a first pressure reducing valve (17), a second pressure reducing valve (21), a first pressure relief valve (16), a second pressure relief valve (20), a proportional valve (15) and an air pipe; the first high-pressure calibration gas source (18), the first pressure reducing valve (17), the first pressure relief valve (16) and the proportional valve (15) are sequentially connected through the air pipe to form a first group of calibration gas flow paths; the second high-pressure calibration gas source (22), the second pressure reducing valve (21), the second pressure relief valve (20) and the proportional valve (15) are sequentially connected through the air pipe to form a second group of calibration gas flow paths; the gas outlet end of the oxygen sensor (13) is connected to the gas inlet end of the carbon dioxide sensor (14); the gas outlet end of the carbon dioxide sensor (14) is connected to air; the oxygen sensor (13) and the carbon dioxide sensor (14) are used to detect oxygen and carbon dioxide concentration signals in the sampled gas.

6. The human body breathing heat metabolism detection device based on a piston cylinder according to claim 5, characterized in that: When calibrating the oxygen sensor (13) and the carbon dioxide sensor (14), the calibration gas is introduced through the first high-pressure calibration gas source (18) or the second high-pressure calibration gas source (22), passes through the pressure reducing valve and the pressure relief valve to reach the proportional valve (15), and during this process, the proportional valve (15) is adjusted based on the PID negative feedback control algorithm to ensure that the gas pressure at the gas outlet is constant; the calibration gas from the first high-pressure calibration gas source (18) or the second high-pressure calibration gas source (22) is delivered to the oxygen sensor (13) at a constant pressure and flow; when the subject is undergoing a metabolic test, the proportional valve (15) is closed, and the subject's respiratory gas is discharged from the respiratory gas sampling module at a constant pressure and flow to the oxygen sensor (13), and then discharged to the air after passing through the carbon dioxide sensor (14), thereby realizing the detection of the oxygen concentration and carbon dioxide concentration of the subject's respiratory gas.

7. A method for detecting human respiratory heat metabolism based on a piston cylinder, characterized in that: The steps include: Step 1: The operator performs gas concentration calibration of the oxygen sensor (13) and the carbon dioxide sensor (14); first, during the first group of gas calibration, the first high-pressure calibration gas source (18) is opened, and the calibration gas is reduced in pressure by the first pressure reducing valve (17) and then flows to the first pressure relief valve (16); then, the first pressure relief valve (16) is opened, and the calibration gas flows through the gas outlet of the proportional valve (15) to realize the first group of calibration gas flow passages, and after the gas flow is ventilated and stabilized, the average gas concentration over a period of time is collected to complete the range point calibration of the oxygen sensor (13) and the zero point calibration of the carbon dioxide sensor (14); secondly, the first pressure relief valve (16) is opened, and the calibration gas flows through the gas outlet of the proportional valve (15) to realize the first group of calibration gas flow passages, and after the gas flow is ventilated and stabilized, the average gas concentration over a period of time is collected to complete the range point calibration of the oxygen sensor (13) and the zero point calibration of the carbon dioxide sensor (14); When the two groups of gases are calibrated, the second high-pressure calibration gas source (22) is opened, and the calibration gas is reduced in pressure by the second pressure reducing valve (21) and then flows to the second pressure relief valve (20); then, the second pressure relief valve (20) is opened, and the calibration gas flows through the gas outlet of the proportional valve (15) to realize the second group of calibration gas flow passage, and after the gas flow is ventilated and stabilized, the average gas concentration over a period of time is collected to complete the zero point calibration of the oxygen sensor (13) and the range point calibration of the carbon dioxide sensor (14); finally, each high-pressure calibration gas source and valve are closed to end the gas concentration calibration of the oxygen sensor (13) and the carbon dioxide sensor (14); Step 2: The subject completes user registration and login on the computer, makes preparations for the metabolic test, and starts the test, including: When used on a spontaneously breathing subject, the subject wears a breathing mask, one end of the flow detection module is connected to the breathing mask, and the other end is connected to air; When the subject is mechanically ventilated, the subject wears a ventilator, and both ends of the flow detection module are installed in the ventilator patient circuit between the Y-shaped interface of the ventilator and the subject; the main pressure difference sensor (4) in the flow detection module measures the pressure difference at both ends of the porous air block plate (3), thereby identifying the inhalation and exhalation phases of the subject and obtaining the bidirectional flow rate of the subject's respiratory gas; when the subject starts to inhale, the inhalation piston cylinder (8) is ready to be evacuated, and the exhalation piston cylinder (7) is ready to be exhausted; the last exhaled gas of the subject in the exhalation piston cylinder (7) is discharged to the gas outlet through the third switch valve (11) at a constant pressure and constant flow. In the gas concentration analysis module, the oxygen sensor (13) and the carbon dioxide sensor (14) detect and obtain the average oxygen concentration and the average carbon dioxide concentration of the last exhaled air of the subject; when the subject starts to exhale, the exhalation piston cylinder (7) is ready to draw air, and the inhalation piston cylinder (8) is ready to exhaust air; the last inhaled air of the subject in the inhalation piston cylinder (8) is discharged to the gas concentration analysis module through the fourth switch valve (12) at a constant pressure and constant flow, and the oxygen sensor (13) and the carbon dioxide sensor (14) detect and obtain the average oxygen concentration and the average carbon dioxide concentration of the last inhaled air of the subject; Step 3: The computer calculates metabolism-related indicators based on the data collected and uploaded by the control unit: oxygen uptake per minute and carbon dioxide production per minute.

8. The method for detecting human respiratory heat metabolism based on a piston cylinder according to claim 7, characterized in that: The formula involved in step 3 is derived as follows: Exhaled air volume per breath: （1） （2） in, It is the volume of exhaled air in a certain breathing cycle, in mL; It is the time when exhalation starts in a breathing cycle, in seconds; It is the end time of exhalation in a breathing cycle, in seconds; is the subject's respiratory flow rate, in mL / s; is the time, in seconds; is the gas standard state correction factor; is the ambient atmospheric pressure, in kPa; Oxygen uptake per minute for: （3） Carbon dioxide production per minute for: （4） in, It is the time when inspiration starts in a breathing cycle, in seconds; The average oxygen concentration of each breath exhaled by the subject; The mean carbon dioxide concentration of each breath exhaled by the subject; The average oxygen concentration of each breath inhaled by the subject; is the average carbon dioxide concentration of each breath inhaled by the subject; is the oxygen uptake per minute, in mL / min; is the amount of carbon dioxide produced per minute, in mL / min; The respiratory quotient RQ can be calculated through the above-mentioned oxygen uptake per minute and carbon dioxide production per minute, and the resting metabolic rate REE can be calculated based on the Weir formula, thereby realizing a human respiratory heat metabolism detection based on a piston cylinder.

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