Metabolic chamber accuracy online verification method and system

Abstract

The application provides a metabolic chamber accuracy online verification method and system, comprising: propane gas is accurately controlled by a mass flow controller to set a flow rate into a burner placed in a metabolic chamber, and the propane gas is ignited to be completely combusted; according to a complete combustion stoichiometric ratio of the propane gas, a theoretical oxygen consumption and a theoretical carbon dioxide generation are calculated from the set flow rate; mixed gas discharged from the metabolic chamber is sampled, the sampled gas is dehumidified, a dew point temperature before dehumidification is measured, a volume of the sampled gas is corrected to a dry gas volume under a standard state based on the obtained dew point temperature, and then actual measured oxygen consumption and carbon dioxide generation of the metabolic chamber are obtained; oxygen consumption recovery and / or carbon dioxide recovery are calculated; and whether the recovery is within a preset qualified range is judged, and if yes, it is determined that the metabolic chamber accuracy verification is passed. End-to-end verification of the whole system of the metabolic chamber is realized.

Description

Technical Field

[0001] This invention relates to the field of medical device testing, specifically to a method and system for online verification of the accuracy of metabolic chambers. Background Technology

[0002] The metabolic chamber is a core device for measuring energy consumption in humans or animals based on the principle of open-loop indirect calorimetry. Its measurement accuracy directly determines the reliability of data in fields such as clinical nutrition assessment, exercise physiology research, and diagnosis and treatment of metabolic diseases. Therefore, it is of great significance to establish scientific and efficient system-level accuracy verification and quality control methods. Currently, the mainstream verification methods mainly include the alcohol combustion method, the pure standard gas calibration method, and the manually adjusted propane combustion method. Among them, the alcohol combustion method, as the traditional "gold standard," has inherent defects such as the combustion rate being greatly affected by the burner structure, alcohol evaporation loss, and combustion temperature; the combustion products containing a large amount of water vapor that seriously interferes with the gas analyzer; the need for precise weighing before and after combustion, resulting in long single-experiment time and the fact that it can only be performed offline; and the inability to distinguish between alcohol evaporation loss and combustion consumption, leading to mass balance errors. The pure standard gas calibration method can only verify the accuracy of the gas analyzer itself and cannot cover the entire system measurement link of "flow rate × concentration difference," making it difficult to detect system-level problems such as gas leakage in the sampling branch, drying efficiency reduction, and flow meter drift. The propane combustion method using manually adjusted valves combined with a rotor flow meter, which is used by a few laboratories, has a flow control accuracy of only about ±5%, is highly subjective in operation, and cannot achieve automated and repeatable online acceptance. More importantly, all the aforementioned combustion verification methods require the metabolic chamber to be equipped with a constant temperature and humidity control system. Otherwise, the superposition of water vapor generated during combustion and ambient humidity will significantly reduce the accuracy of acceptance testing, making it impossible to conduct effective combustion verification for small, mobile, and outdoor metabolic chambers that are not equipped with constant temperature and humidity systems. Therefore, developing an online verification method for the accuracy of metabolic chambers that does not require weighing, is free from water vapor interference, can be automatically and repeatedly executed, does not rely on a constant temperature and humidity environment, and can achieve end-to-end verification of the entire chain from chamber airtightness to energy consumption calculation output has become an urgent technical problem to be solved. Summary of the Invention

[0003] To overcome at least one of the aforementioned technical problems, this invention proposes an online verification method and system for the accuracy of metabolic chambers.

[0004] The first aspect of this invention provides a method for online verification of the accuracy of a metabolic chamber, comprising: The propane gas is precisely controlled by a mass flow controller to enter the burner located in the metabolic chamber at a set flow rate, and the propane is ignited to ensure complete combustion. Based on the stoichiometric ratio of propane's complete combustion, the theoretical oxygen consumption VO is calculated from the set flow rate. 2_true Theoretical carbon dioxide production (VCO) 2_true ; The mixed gas discharged from the metabolic chamber was sampled, and the sampled gas was dehumidified. The dew point temperature before dehumidification was measured. Based on the obtained dew point temperature, the volume of the sampled gas was corrected to the volume of dry gas under standard conditions, thereby obtaining the measured oxygen consumption (VO) of the metabolic chamber. 2_measured and carbon dioxide production (VCO) 2_measured ; Calculate oxygen recovery rate: Recovery(O2) = VO 2_measured / VO 2_true ×100% and / or CO2 recovery rate Recovery(CO2) = VCO 2_measured / VCO 2_true ×100%, where Recovery(O2) represents the oxygen consumption recovery rate, and Recovery(CO2) represents the carbon dioxide recovery rate; and Determine whether the recovery rate is within the preset acceptable range; if so, the accuracy verification of the metabolic chamber is deemed to have passed.

[0005] In some optional embodiments, the respiratory quotient (RQ) and carbon monoxide concentration measured in real time meet preset threshold ranges as criteria for complete combustion.

[0006] In some optional embodiments, the volume of the sampled gas is corrected to the volume of dry gas under standard conditions based on the obtained dew point temperature using the following conversion formula: V _STPD =V _measured ×(P _measured- P _H2O ) / P _STP ×T _STP / T _measured Among them, V _STPD V represents the volume of dry gas corrected to standard conditions. _measured P represents the measured volume of moist gas. _measured P represents the measured atmospheric pressure. _H2O P represents the partial pressure of water vapor derived from the dew point temperature. _STP T represents standard atmospheric pressure. _STP T represents the thermodynamic temperature under standard conditions. _measured This represents the measured thermodynamic temperature.

[0007] In some optional embodiments, the initial verification also includes a baseline measurement phase: shutting off the propane supply and recording baseline O2 and CO2 concentrations inside the chamber; and / or, The verification process also includes a recovery phase: automatic shutdown, waiting for the gas concentration inside the metabolic chamber to return to baseline.

[0008] In some optional embodiments, a multi-level calibration step is also included: Set at least two different propane flow rates in sequence and obtain oxygen consumption recovery rate and / or carbon dioxide recovery rate data for each flow rate. By performing regression fitting with the theoretical oxygen consumption and / or theoretical carbon dioxide production at each level as the x-axis and the corresponding measured oxygen consumption and / or measured carbon dioxide production as the y-axis, an error correction function is obtained, which is used to correct the original measurements in subsequent experiments.

[0009] In some optional embodiments, the experimental data are fitted using the following regression fitting relationship: VO 2_measured =k _O2 ·VO 2_true+ b _O2 VCO 2_measured =k _CO2 VCO 2_true+ b _CO2 Among them, VO 2_measured This represents the measured oxygen consumption, VO2+. 2_true k represents the theoretical oxygen consumption. _O2 b represents the slope of the linear regression of oxygen consumption. _O2 This represents the intercept of the linear regression of oxygen consumption; VCO 2_measured VCO represents the measured amount of carbon dioxide produced. 2_true k represents the theoretical carbon dioxide production. _CO2 b represents the slope of the linear regression of carbon dioxide. _CO2 This represents the intercept of the linear regression of carbon dioxide. The corresponding correction formula is: VO 2_corrected = (VO 2_measured - b _O2 ) / k _O2 VCO 2_corrected = (VCO 2_measured - b _CO2 ) / k _CO2 Among them, VO 2_corrected VCO represents the corrected oxygen consumption. 2_corrected This indicates the corrected amount of carbon dioxide produced.

[0010] In some optional embodiments, the preset qualified range is 98% to 102%, and the verification is deemed successful when both the oxygen consumption recovery rate and the carbon dioxide recovery rate fall within this range.

[0011] In some optional embodiments, the metabolic chamber is connected to a gas sampling pretreatment system, which includes at least: a Nafion drying tube, a dew point meter, an O2 analyzer, and a CO2 analyzer.

[0012] In some optional embodiments, the set flow rate of propane is selected according to the rated exhaust volume of the metabolic chamber, so that the difference between the decrease in O2 concentration and the increase in CO2 concentration in the chamber caused by combustion are within the linear measurement range of the analyzer.

[0013] A second aspect of the present invention provides an online verification system for the accuracy of a metabolic chamber, comprising: Propane gas source; A mass flow controller is connected between the propane gas source and the burner located in the metabolic chamber to control the propane gas to enter the burner at a set flow rate. An ignition device used to ignite propane in the burner; The gas sampling and analysis unit, including sampling pipelines, dehumidification device, dew point measuring device, O2 analyzer, and CO2 analyzer, is used to sample the mixed gas discharged from the metabolic chamber to obtain the measured oxygen consumption (VO). 2_measured and carbon dioxide production (VCO) 2_measured ;as well as The control and computing unit is configured to perform the method described in any of the first aspects.

[0014] The technical solution of the present invention has the following advantages or beneficial effects: (1) The solution provided by this invention eliminates the error caused by the volatilization loss of volatile combustion media at its source. By burning propane online in the metabolic chamber, the actual operating conditions such as gas mixing, chamber leakage, and airflow disturbance are fully reproduced, realizing end-to-end verification of the entire metabolic chamber system (from chamber airtightness, exhaust flow rate, sampling mixing to analyzer accuracy), rather than just single-point calibration of the analyzer itself. At the same time, through dehumidification and dew point volume correction, the interference of water vapor in the combustion products on the measurement is eliminated, allowing the verification to be carried out under any ambient humidity without relying on expensive constant temperature and humidity systems. The entire verification process can be fully automated, and the time for a single verification is greatly shortened.

[0015] (2) This invention uses the real-time measured respiratory quotient (RQ) and carbon monoxide concentration meeting preset threshold ranges as criteria for complete combustion; it completely solves the defect of "no complete combustion criteria" in related technologies, ensures the accuracy of theoretical true value calculation, and avoids errors in verification results caused by incomplete combustion. Compared with manual visual judgment, the objectivity and sensitivity of the criteria are greatly improved, and it can promptly detect slight incomplete combustion that is not visible to the naked eye, ensuring the reliability of verification results. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the online verification method for the accuracy of the metabolic chamber according to the first embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the main structure of the online verification system for the accuracy of the metabolic chamber according to the second embodiment of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0019] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0020] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0021] To address at least one problem existing in the accuracy measurement schemes of metabolic chambers mentioned in the background section, such as the alcohol combustion method requiring precise manual weighing of alcohol, which is cumbersome and the alcohol is volatile during combustion, leading to high calculation errors in theoretical oxygen consumption and carbon dioxide production. Offline verification methods can only perform single-point calibration of the gas analyzer itself and cannot simulate real operating conditions such as chamber leakage, airflow disturbance, and uneven gas mixing during actual operation of the metabolic chamber, resulting in large deviations between verification results and actual measurements. Furthermore, some schemes cannot be automated, and each verification is too time-consuming, making them unsuitable as a routine quality control method. The first aspect of this invention provides an online verification method for the accuracy of a metabolic chamber. This includes: using a mass flow controller to precisely control propane gas to enter a burner placed inside the metabolic chamber at a set flow rate, and igniting the propane to achieve complete combustion; calculating the theoretical oxygen consumption (VO) based on the stoichiometric ratio of complete propane combustion from the set flow rate. 2_true Theoretical carbon dioxide production (VCO) 2_true The mixed gas discharged from the metabolic chamber was sampled, and the sampled gas was dehumidified. The dew point temperature before dehumidification was measured. Based on the obtained dew point temperature, the volume of the sampled gas was corrected to the dry gas volume under standard conditions, thereby obtaining the measured oxygen consumption (VO) of the metabolic chamber. 2_measured and carbon dioxide production (VCO) 2_measured ; Calculate oxygen recovery rate Recovery(O2) = VO 2_measured / VO 2_true ×100% and / or CO2 recovery rate Recovery(CO2) = VCO 2_measured / VCO 2_true ×100%, where Recovery(O2) represents the oxygen consumption recovery rate and Recovery(CO2) represents the carbon dioxide recovery rate; and determining whether the recovery rate is within the preset qualified range, if so, the accuracy verification of the metabolic chamber is deemed to have passed.

[0022] like Figure 1 and 2 In the illustrated embodiment, the verification scheme of the present invention is based on the indirect calorimetry method. First, the burner is placed in the metabolic chamber, preferably in the center, and connected to a propane gas source, a mass flow controller, an ignition device, and a gas sampling and analysis system to check the airtightness of the pipeline. The mass flow controller precisely controls the propane gas to enter the burner in the metabolic chamber at a set flow rate; preferably, the control accuracy of the mass flow controller is better than ±1% FS. After the flow rate stabilizes, the automatic ignition device is activated to ignite the propane and ensure complete combustion. Then, based on the stoichiometric ratio of complete propane combustion, the theoretical oxygen consumption (VO) is calculated from the set flow rate. 2_true Theoretical carbon dioxide production (VCO) 2_trueIn practice, a control unit can be set up in the measurement system to automatically calculate oxygen consumption and carbon dioxide production. The control system can be a computer, server, etc. This invention uses propane combustion instead of alcohol combustion; the chemical reaction equation for complete combustion is: C3H8 + 5O2 → 3CO2 + 4H2O. According to the stoichiometric ratio, theoretically, burning 1 volume of propane consumes 5 volumes of oxygen and produces 3 volumes of carbon dioxide. Therefore, the control system automatically calculates the theoretical oxygen consumption (VO). 2_true =5×Q _C3H8 Theoretical carbon dioxide production (VCO) 2_true =3×Q _C3H8 Q _C3H8 This refers to the supply of propane; the theoretical respiratory quotient RQ. _true = VCO2 / VO2 = 0.60. Then, gas sampling and correction are performed. Specifically, a mixed gas is collected from the exhaust port of the metabolic chamber. The dew point temperature before dehumidification is measured, and after water vapor is removed by the dehumidification device, the gas is sent to an O2 / CO2 analyzer to measure the concentration. Based on the dew point temperature, the water vapor partial pressure is calculated, and the measured wet gas volume is corrected to the dry gas volume under standard conditions, thus obtaining the measured oxygen consumption (VO2) of the metabolic chamber. 2_measured and carbon dioxide production (VCO) 2_measured Then calculate the oxygen recovery rate (O2) and / or carbon dioxide recovery rate (CO2); finally determine whether the recovery rate is within the preset qualified range. If it is, the accuracy verification of the metabolic chamber is deemed to have passed.

[0023] As described above, this stoichiometric relationship provides a precise and traceable system-level truth value, eliminating the need for weighing steps in related technologies and fundamentally eliminating errors caused by the evaporation loss of volatile combustion media (such as alcohol). Furthermore, by burning propane online within the metabolic chamber, the actual operating conditions, including gas mixing, chamber leakage, and airflow disturbances, are fully reproduced. This enables end-to-end verification of the entire metabolic chamber system (from chamber airtightness, exhaust flow rate, sampling mixing to analyzer accuracy), rather than just single-point calibration of the analyzer itself. Compared to the alcohol combustion method in related technologies, this significantly reduces measurement errors. Simultaneously, dehumidification and dew point volume correction eliminate the interference of water vapor from combustion products on measurements, allowing verification to be conducted under any ambient humidity without relying on expensive constant temperature and humidity systems. The entire verification process can be fully automated, significantly reducing the time required for a single verification run.

[0024] In some optional embodiments, the respiratory quotient (RQ) and carbon monoxide concentration measured in real time meet preset threshold ranges as criteria for complete combustion. Complete combustion of propane is the foundation of the accuracy of this verification method. Addressing the shortcomings of existing technologies: judging combustion status solely by visually observing flame color is highly subjective and cannot promptly detect slight incomplete combustion; when combustion is incomplete (e.g., insufficient oxygen supply, burner blockage), byproducts such as carbon monoxide are produced, at which point the stoichiometric ratio no longer holds, and the theoretical VO calculated based on complete combustion becomes invalid. 2_true and VCO 2_true Deviations from the true value will lead to distorted verification results, and such errors cannot be detected by visual inspection. Therefore, some embodiments of this invention employ dual objective criteria to achieve online real-time monitoring of combustion completeness. Specifically, this is achieved through the following two criteria: ① Respiratory Quotient (RQ) Criterion: Theoretically, the RQ for complete propane combustion is 0.60. When combustion is incomplete, carbon dioxide production decreases, and the RQ will be less than 0.60. Therefore, considering measurement errors, an acceptable RQ range is set to determine whether combustion is normal. For example, the RQ range is set to 0.59-0.61; exceeding this range indicates abnormal combustion. ② Carbon Monoxide Concentration Criterion: Complete combustion requires a carbon monoxide concentration lower than a set value. If the concentration exceeds the set value, combustion is considered incomplete. In some embodiments, the analyzer detection limit is used as the set value, for example, a carbon monoxide concentration ≤ 10 ppm. If the concentration is higher than 10 ppm, incomplete combustion is determined.

[0025] During the verification process, the control unit calculates RQ in real time and reads the carbon monoxide analyzer data. Only when both criteria are met simultaneously is complete combustion of propane confirmed and subsequent verification steps continue. If either criterion is not met, the propane gas supply is immediately and automatically cut off, the burner is extinguished, and an alarm is triggered to prompt troubleshooting.

[0026] As described above, this embodiment completely solves the defect of "no incomplete combustion criterion" in related technologies, ensuring the accuracy of theoretical truth value calculation and avoiding errors in verification results caused by incomplete combustion. Compared with manual visual judgment, the objectivity and sensitivity of the criterion are greatly improved, enabling timely detection of slight incomplete combustion that is imperceptible to the naked eye, thus ensuring the reliability of verification results.

[0027] In some optional embodiments, the volume of the sampled gas is corrected to the volume of dry gas under standard conditions based on the obtained dew point temperature using the following conversion formula: V _STPD =V _measured ×(P _measured -P _H2O ) / P _STP ×T_STP / T _measured Among them, V _STPD V represents the volume of dry gas corrected to standard conditions. _measured P represents the measured volume of moist gas. _measured P represents the measured atmospheric pressure. _H2O P represents the partial pressure of water vapor derived from the dew point temperature. _STP T represents standard atmospheric pressure. _STP T represents the thermodynamic temperature under standard conditions. _measured This represents the measured thermodynamic temperature.

[0028] During the verification process, the complete combustion of propane produces a large amount of water vapor (i.e., 4 moles of water vapor per mole of propane). This water vapor dilutes the concentrations of O2 and CO2 and alters the gas volume. Related techniques typically use fixed humidity values ​​(e.g., assuming a relative humidity of 50%) or measurements from ordinary temperature and humidity sensors for correction. However, ordinary temperature and humidity sensors can only measure relative humidity and cannot accurately reflect absolute water vapor content, resulting in large humidity correction errors and inaccurate measurements in the metabolic chamber. Furthermore, the measurement methods in these techniques require the metabolic chamber to be equipped with a constant temperature and humidity system; otherwise, accurate verification is impossible. The use of a constant temperature and humidity system significantly increases equipment costs and imposes usage limitations.

[0029] Therefore, some embodiments of the present invention employ an STPD (Standard Temperature Pressure Dry Gas) correction method based on dew point temperature, the specific execution steps of which are as follows: The dew point temperature T of the sampled gas before dehumidification was measured using a dew point meter. _d Dew point temperature is a direct function of water vapor partial pressure, and its measurement accuracy is much higher than that of relative humidity. The partial pressure of water vapor P can be inversely derived from the dew point temperature using the Magnus or Antoine formula. _H2O ; Real-time measurement of atmospheric pressure P _measured and gas temperature T _measured ; Substituting into the STPD conversion formula above, the measured wet gas volume is gradually corrected to the dry gas volume under standard conditions (0℃, 101.325kPa).

[0030] As described above, to overcome the problem of large humidity correction errors in related technologies, this invention effectively eliminates the dilution effect of water vapor on O2 and CO2 concentration measurements through dew point measurement and thermodynamic correction. Even under conditions of large fluctuations in ambient humidity, stable and accurate measurement results can be obtained, making this method applicable to various scenarios such as small metabolic chambers, mobile metabolic chambers, and outdoor metabolic chambers that lack constant temperature and humidity systems, significantly lowering the barrier to entry for equipment use.

[0031] In some optional embodiments, the initial verification also includes a baseline measurement phase: shutting off the propane supply and recording the baseline O2 and CO2 concentrations inside the chamber; and / or, the final verification also includes a recovery phase: automatic flameout, waiting for the gas concentrations inside the metabolic chamber to return to the baseline.

[0032] In related technologies, the verification process is incomplete, lacking automated baseline measurement and recovery stages; manual recording of baseline concentrations is prone to introducing reading errors and cannot guarantee baseline stability; high residual CO2 concentrations in the chamber after verification can affect the accuracy of subsequent verifications or human experiments, requiring lengthy manual waiting times and resulting in low efficiency. Some embodiments of this invention add baseline measurement and recovery stages, achieving closed-loop control of the verification process.

[0033] Specifically, during the baseline measurement phase: before the verification begins, the propane gas supply is shut off, the metabolic chamber ventilation system is activated, and after the gas inside the chamber stabilizes, the O2 and CO2 concentrations are measured continuously for 5 minutes, and the average value is taken as the baseline concentration. 2_baseline and CO 2_baseline When calculating the concentration change, use ΔO2=O 2_baseline- O 2_measured and ΔCO2=CO 2_measured- CO 2_baseline This eliminates the impact of initial concentration fluctuations.

[0034] Recovery Phase: After verification, the mass flow controller automatically shuts off the propane supply, extinguishes the burner, and the ventilation system continues to operate. The gas concentration inside the chamber is monitored in real time. The recovery phase ends when the concentration returns to the set baseline concentration range, and the system automatically generates a verification report. For example, the set range can be ±0.01%.

[0035] In some optional embodiments, a multi-level calibration step is also included: at least two different propane flow rates are set sequentially, and oxygen consumption recovery rate and / or carbon dioxide recovery rate data are obtained for each flow rate level; regression fitting is performed with the theoretical oxygen consumption and / or theoretical carbon dioxide production of each level as the abscissa and the corresponding measured oxygen consumption and / or measured carbon dioxide production as the ordinate to obtain an error correction function, which is used to correct the original measurement values ​​of subsequent experiments.

[0036] Related technologies typically use a single flow point for verification, which can only determine whether the system is qualified, but cannot detect the nonlinear response of the gas analyzer in different concentration ranges. The measurement error of the metabolic chamber is inconsistent under low and high metabolic states; for example, the error can reach ±8% under low metabolic state and ±6% under high metabolic state. Single flow point verification cannot detect these nonlinear errors, let alone correct them, resulting in low reliability of measurement results under different metabolic levels. Some embodiments of this invention propose a multi-level calibration procedure, specifically: Based on the measurement range of the metabolic chamber, at least three different propane flow rates should be set to cover the low, medium, and high measurement ranges (e.g., 0.05 SLPM, 0.20 SLPM, and 0.40 SLPM, corresponding to VO2max, etc.). 2_true =0.25L / min, 1.00L / min, 2.00L / min); Following the verification method described above, complete the full verification process for each traffic level and record the theoretical and measured values ​​for each level. A scatter plot was drawn with theoretical values ​​on the x-axis and measured values ​​on the y-axis. The least squares method was used for regression fitting to obtain the system-level error correction function. The correction function is written into the data processing system of the metabolic chamber to automatically correct the raw measurements of all subsequent experiments.

[0037] In some optional embodiments, the experimental data are fitted using the following regression fitting relationship: VO 2_measured =k _O2 ·VO 2_true+ b _O2 VCO 2_measured =k _CO2 VCO 2_true+ b _CO2 Among them, VO 2_measured This represents the measured oxygen consumption, VO2+. 2_true k represents the theoretical oxygen consumption. _O2 b represents the slope of the linear regression of oxygen consumption. _O2 This represents the intercept of the linear regression of oxygen consumption; VCO 2_measured VCO represents the measured amount of carbon dioxide produced. 2_true k represents the theoretical carbon dioxide production. _CO2 b represents the slope of the linear regression of carbon dioxide. _CO2 This represents the intercept of the linear regression of carbon dioxide. The corresponding correction formula is: VO 2_corrected = (VO2_measured - b _O2 ) / k _O2 VCO 2_corrected = (VCO 2_measured - b _CO2 ) / k _CO2 wherein, VO 2_corrected represents the corrected oxygen consumption, and VCO 2_corrected represents the corrected carbon dioxide production.

[0038] In related technologies, there is no quantitative error correction method, and whether the system is qualified can only be judged through single-point verification, so that quantitative correction of system errors cannot be achieved; even if the system is found to have deviations, it can only be solved by replacing sensors or recalibrating the analyzer, which has high cost, long cycle and cannot completely eliminate non-linear errors. The solution provided by the present invention clarifies that the linear regression fitting relational expression and the corresponding correction formula can quantitatively describe the system error characteristics of the metabolic chamber, and realize error correction through mathematical operations, which greatly reduces the deviation between the corrected measured value and the true value. After writing the correction coefficient into the control device of the metabolic chamber, automatic correction of all experimental data can be realized without manual intervention, which greatly improves the convenience and accuracy of measurement.

[0039] In some optional embodiments, the preset qualification range is 98% to 102%, and the verification is determined to pass when both the oxygen consumption recovery rate and the carbon dioxide recovery rate fall within the range.

[0040] Aiming at the problem that inconsistent or loose verification standards in related technologies lead to low credibility of clinical and scientific research data and cannot meet the requirements of high-precision metabolic measurement, in some embodiments of the present invention, the preset qualification range is set to 98% to 102%, and only when both the oxygen consumption recovery rate and the carbon dioxide recovery rate meet this range can the overall performance of the metabolic chamber be determined to be qualified. If any recovery rate exceeds this range, it indicates that the system has excessive system error (such as chamber leakage, exhaust flowmeter drift, sampling pipeline blockage, Nafion drying tube efficiency attenuation, analyzer linear drift, etc.), and maintenance or recalibration is required.

[0041] In some optional embodiments, the metabolic chamber is connected with a gas sampling pretreatment system, and the system at least comprises: a Nafion drying tube, a dew point meter, an O2 analyzer and a CO2 analyzer.

[0042] Related technologies typically employ condensation dehumidification systems. During the condensation process, some CO2 dissolves in the condensate, leading to lower CO2 readings. Furthermore, condensation dehumidification systems have slow response times and cannot track humidity changes in real time. Additionally, existing systems lack dedicated dew point measurement devices, relying solely on relative humidity to calculate water vapor partial pressure, resulting in significant errors. To address these issues, some embodiments of this invention provide a Nafion drying tube, which allows only water vapor molecules to pass through. This efficiently removes moisture from the sampled gas, ensuring O2 and CO2 measurements are based on a dry gas standard, avoiding interference from water vapor to the analyzer sensor, and eliminating the problem of condensate dissolving the gas. A dew point meter is installed upstream of the Nafion drying tube to measure the dew point temperature of the sampled gas before dehumidification, providing accurate water vapor partial pressure data for STPD volume correction. The O2 analyzer can employ a paramagnetic sensor, offering advantages such as fast response, good stability, and no cross-interference. The CO2 analyzer can employ a non-dispersive infrared (NDIR) sensor, capable of accurately measuring changes in low concentrations of CO2.

[0043] The orderly combination of the above-mentioned devices in the embodiments of the present invention realizes the whole process of gas sampling and preprocessing, namely "measuring dew point before dehumidification → analyzing gas concentration after dehumidification → correcting volume based on STPD", and realizes the key hardware support for verification without constant temperature and humidity environment.

[0044] In some optional embodiments, the set flow rate of propane is selected according to the rated exhaust volume of the metabolic chamber, so that the difference between the decrease in O2 concentration and the increase in CO2 concentration caused by combustion are within the linear measurement range of the analyzer.

[0045] In practice, selecting a propane flow rate that is too high or too low can lead to large variations in O2 and CO2 concentrations within the chamber, exceeding the analyzer's linear range, significantly increasing measurement errors, and making verification results unreliable. Therefore, some embodiments of this invention propose a principle for selecting the propane flow rate: based on the metabolic chamber's rated exhaust volume Q. _vent Calculate the maximum allowable flow rate of propane to ensure that the difference in O2 concentration decrease (ΔO2) and the difference in CO2 concentration increase (ΔCO2) are within the effective linear measurement range of the analyzer. For example, this can be calculated using the following formula: Q _C3H8 ≤ 0.004×Q _vent For example, for a metabolic chamber with a rated exhaust volume of 3000 SLPM, the maximum allowable flow rate of propane is 12 SLPM. If a flow rate of 0.20 SLPM is actually selected, then ΔO2≈0.033% and ΔCO2≈0.020%, which is exactly within the optimal operating range of the analyzer.

[0046] A second aspect of this invention provides an online verification system for the accuracy of a metabolic chamber, comprising: a propane gas source; a mass flow controller connected between the propane gas source and a burner placed inside the metabolic chamber, used to control the propane gas to enter the burner at a set flow rate; an ignition device for igniting the propane in the burner; piezoelectric ignition can be used, combined with a thermocouple and an ultraviolet flame sensor to achieve automatic ignition and flameout monitoring. Preferably, a fume hood can be installed above the burner to collect combustion products. A gas sampling and analysis unit, including sampling pipelines, a dehumidification device, a dew point measuring device, an O2 analyzer, and a CO2 analyzer, is used to sample the mixed gas discharged from the metabolic chamber to obtain the measured oxygen consumption (VO). 2_measured and carbon dioxide production (VCO) 2_measured ; and a control and computing unit, configured to perform the method described in any of the first aspects.

[0047] In some examples, the propane gas source uses high-pressure steel cylinders containing high-purity propane (purity ≥99.5%), with the pressure regulated to 0.1-0.3 MPa via a two-stage pressure reducing valve. A thermal mass flow controller is used, with a flow range of 0-5 SLPM, control accuracy ±1% FS, and repeatability ±0.2% FS, enabling precise and stable control of the propane flow rate. The ignition device employs a high-voltage electric spark igniter with automatic ignition and flameout protection functions. The gas sampling and analysis unit includes a Nafion drying tube, dew point meter, paramagnetic O2 analyzer, non-dispersive infrared CO2 analyzer, and carbon monoxide analyzer, realizing gas sampling, pretreatment, and concentration analysis. The control and calculation unit uses an embedded industrial computer with built-in verification control software, capable of automatically executing the entire process of baseline measurement, flow regulation, ignition control, data acquisition, calculation and analysis, result judgment, and report generation.

[0048] This system integrates all hardware and software modules, including precision flow control, automatic ignition and monitoring, gas sampling pretreatment, concentration analysis and humidity measurement, and host computer control and calculation. It can be directly deployed in existing metabolic chamber equipment without requiring modifications. This system upgrades the accuracy verification of metabolic chambers from a "one-time acceptance upon construction and delivery" to a routine quality control method that is "periodic, automated, and online," significantly improving the ease of use and data reliability of the metabolic chamber.

[0049] The technical solution of the present invention will be further illustrated below through two specific embodiments.

[0050] Example 1: Verification of Standard Recovery Rate for a Single Gear This embodiment uses a large clinical metabolic chamber with a volume of approximately 13m³ and a rated exhaust volume of approximately 3000SLPM as an example.

[0051] The specific verification process is as follows: the propane gas source is reduced to 0.2 MPa through a two-stage pressure reducing valve, and the propane flow rate is set to 0.20 SLPM by the mass flow controller. The propane gas enters the straight-tube liquid propane Bunsen burner placed in the center of the metabolic chamber through a polytetrafluoroethylene pipeline, and is ignited by an automatic high-voltage electric spark ignition device.

[0052] Real-time monitoring of the respiratory quotient (RQ) and carbon monoxide concentration of combustion products: Complete propane combustion is confirmed when RQ stabilizes within the range of 0.59-0.61 and the carbon monoxide concentration is below 5 ppm. Theoretical values ​​are calculated based on stoichiometry: VO 2_true =5 × 0.20 = 1.00 SLPM (standard conditions), VCO 2_true =3×0.20=0.60SLPM (standard conditions).

[0053] The gas sampling and analysis unit collects mixed gas from the exhaust port of the metabolic chamber, sequentially passes it through a PTFE filter membrane to remove particulate matter, and then measures the dew point temperature using a dew point meter (e.g., if the measured dew point temperature is 18°C, the water vapor partial pressure P is calculated). _H2O The dry gas concentration was measured using a Nafion drying tube (2.06 kPa) and a paramagnetic O2 analyzer and a non-dispersive infrared CO2 analyzer. Simultaneously, a wall-mounted temperature and humidity transmitter recorded the dry-bulb temperature T = 25℃ (thermodynamic temperature 298.15 K), and a barometer recorded the atmospheric pressure P = 101.3 kPa.

[0054] Substituting the measured wet gas volume into the STPD conversion formula, the measured wet gas volume is corrected to the standard dry gas volume, and then the measured value is calculated: VO 2_measured= 0.992 SLPM, VCO 2_measured= 0.595 SLPM. Calculated recovery rates: Recovery (O2) = 0.992 / 1.00 × 100% = 99.2%, Recovery (CO2) = 0.595 / 0.60 × 100% = 99.2%. Both recovery rates fall within the range of 98%–102%, indicating that the accuracy verification of the metabolic chamber has passed.

[0055] Example 2: Multi-level nonlinear calibration This embodiment uses the same metabolic chamber as in Embodiment 1 as an example to perform multi-level calibration. The process is as follows: Four propane flow rates were sequentially set: 0.05 SLPM, 0.10 SLPM, 0.20 SLPM, and 0.40 SLPM, covering the typical measurement range of the metabolic chamber from low to high metabolism. The validation process was performed on each flow rate according to the method described in Example 1, and the theoretical and measured values ​​for each flow rate are shown in the table below:

[0056] With theoretical VO 2_true x-axis, measured VO 2_measured A linear regression was performed on the ordinate to obtain the relationship. The correction coefficient was written into the data processing system of the metabolic chamber, and after correcting the original measured values, the recovery rates of each level stabilized within the set target range.

[0057] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art, after considering the specification and practicing the technical solutions disclosed in this application, will readily conceive of other embodiments of this application. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary technical means in the art not disclosed in this application. The specification and embodiments are considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0058] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for online verification of the accuracy of a metabolic chamber, characterized in that, include: The propane gas is precisely controlled by a mass flow controller to enter the burner located in the metabolic chamber at a set flow rate, and the propane is ignited to ensure complete combustion. Based on the stoichiometric ratio of propane's complete combustion, the theoretical oxygen consumption VO is calculated from the set flow rate. 2_true Theoretical carbon dioxide production (VCO) 2_true ; The mixed gas discharged from the metabolic chamber was sampled, and the sampled gas was dehumidified. The dew point temperature before dehumidification was measured. Based on the obtained dew point temperature, the volume of the sampled gas was corrected to the volume of dry gas under standard conditions, thereby obtaining the measured oxygen consumption (VO) of the metabolic chamber. 2_measured and carbon dioxide production (VCO) 2_measured ; Calculate oxygen recovery rate: Recovery(O2) = VO 2_measured / VO 2_true ×100% and / or CO2 recovery rate Recovery(CO2) = VCO 2_measured / VCO 2_true ×100%, where Recovery(O2) represents the oxygen consumption recovery rate and Recovery(CO2) represents the carbon dioxide recovery rate; as well as Determine whether the recovery rate is within the preset acceptable range; if so, the accuracy verification of the metabolic chamber is deemed to have passed.

2. The online verification method according to claim 1, characterized in that, The respiratory quotient (RQ) and carbon monoxide concentration measured in real time meet the preset threshold ranges as the criteria for complete combustion.

3. The online verification method according to claim 1, characterized in that, The volume of the sampled gas is corrected to the volume of dry gas under standard conditions based on the obtained dew point temperature using the following conversion formula: V _STPD =V _measured ×(P _measured- P _H2O ) / P _STP ×T _STP / T _measured Among them, V _STPD V represents the volume of dry gas corrected to standard conditions. _measured P represents the measured volume of moist gas. _measured P represents the measured atmospheric pressure. _H2O P represents the partial pressure of water vapor derived from the dew point temperature. _STP T represents standard atmospheric pressure. _STP T represents the thermodynamic temperature under standard conditions. _measured This represents the measured thermodynamic temperature.

4. The online verification method according to claim 1, characterized in that, The initial validation also includes a baseline measurement phase: shutting off the propane supply and recording baseline O2 and CO2 concentrations inside the chamber; and / or, The verification process also includes a recovery phase: automatic shutdown, waiting for the gas concentration inside the metabolic chamber to return to baseline.

5. The online verification method according to claim 1, characterized in that, It also includes multi-gear calibration steps: Set at least two different propane flow rates in sequence and obtain oxygen consumption recovery rate and / or carbon dioxide recovery rate data for each flow rate. By performing regression fitting with the theoretical oxygen consumption and / or theoretical carbon dioxide production at each level as the x-axis and the corresponding measured oxygen consumption and / or measured carbon dioxide production as the y-axis, an error correction function is obtained, which is used to correct the original measurements in subsequent experiments.

6. The online verification method according to claim 5, characterized in that, The experimental data were fitted using the following regression equation: VO 2_measured =k _O2 ·VO 2_true +b _O2 VCO 2_measured =k _CO2 ·VCO 2_true +b _CO2 Among them, VO 2_measured This represents the measured oxygen consumption, VO2+. 2_true k represents the theoretical oxygen consumption. _O2 b represents the slope of the linear regression of oxygen consumption. _O2 This represents the intercept of the linear regression of oxygen consumption; VCO 2_measured VCO represents the measured amount of carbon dioxide produced. 2_true k represents the theoretical carbon dioxide production. _CO2 b represents the slope of the linear regression of carbon dioxide. _CO2 This represents the intercept of the linear regression of carbon dioxide. The corresponding correction formula is: VO 2_corrected = (VO 2_measured - b _O2 ) / k _O2 VCO 2_corrected = (VCO 2_measured- b _CO2 ) / k _CO2 Among them, VO 2_corrected VCO represents the corrected oxygen consumption. 2_corrected This indicates the corrected amount of carbon dioxide produced.

7. The online verification method according to claim 1, characterized in that, The preset acceptable range is 98% to 102%. When both the oxygen consumption recovery rate and the carbon dioxide recovery rate fall within this range, the verification is deemed successful.

8. The online verification method according to claim 1, characterized in that, The metabolic chamber is connected to a gas sampling pretreatment system, which includes at least: a Nafion drying tube, a dew point meter, an O2 analyzer, and a CO2 analyzer.

9. The online verification method according to claim 1, characterized in that, The set flow rate of propane is selected based on the rated exhaust volume of the metabolic chamber, so that the difference between the decrease in O2 concentration and the increase in CO2 concentration in the chamber caused by combustion are within the linear measurement range of the analyzer.

10. An online verification system for the accuracy of a metabolic chamber, characterized in that, include: Propane gas source; A mass flow controller is connected between the propane gas source and the burner located in the metabolic chamber to control the propane gas to enter the burner at a set flow rate. An ignition device used to ignite propane in the burner; The gas sampling and analysis unit, including sampling pipelines, dehumidification device, dew point measuring device, O2 analyzer, and CO2 analyzer, is used to sample the mixed gas discharged from the metabolic chamber to obtain the measured oxygen consumption (VO). 2_measured and carbon dioxide production (VCO) 2_measured ;as well as The control and computing unit is configured to perform the method according to any one of claims 1 to 9.

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