A breath ketone detection instrument and a gas collection and concentration calculation method thereof

Abstract

The application discloses a breath ketone detection instrument and a gas collection and concentration calculation method thereof, and relates to the technical field of breath gas detection. The instrument comprises a shell, a variable-diameter airway assembly, a line board of integrated control and calculation module and a sensor group arranged in the shell. The variable-diameter airway assembly has a taper structure with an inlet diameter larger than an outlet diameter, which can inhibit reverse backflow of gas. The method comprises the following steps: directional collection of the gas blown by a subject through the variable-diameter airway assembly; obtaining the total volume of the airway, the incident flow and the exit flow, calculating the effective blowing time based on the volume and flow difference, realizing quantitative collection and ensuring the collection of the gas at the end of the lung; obtaining the environmental temperature and humidity in real time and performing dynamic compensation; finally, performing three-level calibration in the order of airway volume correction, environmental compensation and standard concentration fitting, and outputting the final breath ketone concentration. The application can ensure that the collected gas sample is derived from the end of the lung, eliminate measurement errors through three-level sequential calibration, and improve the detection accuracy.

Description

Technical Field

[0001] This invention relates to the field of respiratory gas detection technology, and in particular to a respiratory ketone detection instrument and its gas collection and concentration calculation method. Background Technology

[0002] Ketone bodies are metabolic byproducts produced by the liver when carbohydrate intake is insufficient, primarily consisting of acetoacetic acid, β-hydroxybutyric acid, and acetone. Acetone is volatile and can be expelled through respiration; therefore, detecting the concentration of acetone in exhaled breath can indirectly reflect ketone body levels and lipid metabolism status in the body. Breath ketone detection has significant applications in scenarios such as early warning of diabetic ketoacidosis, management of ketogenic diets, and monitoring of weight loss effectiveness.

[0003] However, existing equipment and methods for detecting respiratory ketones (acetone) have the following shortcomings: First, interference from dead space gases in the oral cavity and upper respiratory tract. Human exhaled air contains two types of components: the initial "dead space gas" originates from areas such as the oral cavity, pharynx, and trachea that do not participate in gas exchange; its composition is similar to ambient air, with extremely low acetone concentration. The subsequent "alveolar gas" originates from the alveoli at the end of the lungs where gas exchange occurs; its acetone concentration accurately reflects the ketone body level in the blood. Current respiratory gas detection equipment typically lacks the ability to effectively distinguish between dead space gas and alveolar gas, resulting in the collected sample being diluted by dead space gas, severely impacting the representativeness and accuracy of the test results.

[0004] Second, the systematic errors introduced by the airway structure of the detector are not included in the concentration calculation model. When exhaled gas flows through the internal airway of the detector, due to factors such as changes in airway cross-section, flow velocity, and uneven airflow distribution, there is an inherent deviation between the actual gas concentration that the sensor comes into contact with and the original concentration of the subject's exhaled gas. Existing methods typically assume that the sensor output value directly corresponds to the exhaled gas concentration, without considering the errors introduced by the airway structure as a correction factor for concentration calculation.

[0005] Third, ambient temperature and humidity significantly affect sensor response. The detection sensitivity of acetone gas sensors, especially those based on oxide semiconductor principles, drifts with changes in ambient temperature and humidity. Existing methods often rely on offline calibration or empirical fixed corrections for environmental compensation, lacking an adaptive compensation mechanism integrated with the detection process and based on dynamic calculations of real-time environmental parameters.

[0006] Fourth, the existing methods involve independent correction steps that do not form a complete, multi-level calibration system with a defined operational order. If steps such as airway structure correction and temperature and humidity compensation are performed in isolation or their order is arbitrarily interchanged, the mutual coupling effects between these steps cannot be eliminated, leading to a systematic deviation in the final output concentration. Summary of the Invention

[0007] The technical problem to be solved by this invention is as follows: This invention aims to provide a respiratory ketone detection instrument and its gas collection and concentration calculation method to solve the following technical problems: eliminating the interference of oral and upper respiratory tract dead space gas on the accuracy of detection results; incorporating the deviation introduced by the internal airway structure of the detector into the concentration calculation model to achieve structural error correction; realizing real-time and dynamic compensation for ambient temperature and relative humidity; and constructing a three-level calibration system with a defined operation order to ensure the synergistic consistency between each correction link and eliminate coupling errors.

[0008] The technical solution adopted by the present invention to solve its technical problem is: a respiratory ketone detection instrument, including a housing, wherein a variable diameter airway assembly and a circuit board integrating control and calculation modules are disposed inside the housing, and a sensor group electrically connected to the circuit board is installed inside the variable diameter airway assembly. The variable diameter airway assembly is provided with a mouthpiece sleeve, an intermediate airway structure and an exhaust pipe from left to right; The diameter of the right tail section airway chamber in the intermediate airway structure is smaller than that of the left section, and the opening diameter of the mouthpiece sleeve is larger than that of the left section airway chamber in the intermediate airway structure. This causes a pressure gradient to be generated when the exhaled gas flows through the variable diameter airway assembly due to the contraction of the cross-sectional area, thereby inhibiting the backflow of gas from the outlet end to the inlet end. The intermediate airway structure can be an airway structure formed by the upper air guide plate, the lower sealing cover and the shell, or an airway structure formed by a single air intake pipe.

[0009] Furthermore, the sensor group described in this invention includes an exhaled airflow gas sensor, an acetone gas sensor, a temperature sensor, and a humidity sensor.

[0010] Furthermore, the intermediate airway structure of the present invention is provided with a sensor mounting cavity near the right tail section, and the sensor group is installed in the sensor mounting cavity with the working end face of the sensor group protruding into the airway cavity of the intermediate airway structure.

[0011] Furthermore, the right end of the housing of the present invention is provided with an exhaust chamber that communicates with the exhaust pipe of the variable diameter air passage assembly, an exhaust fan is provided in the exhaust chamber, and an exhaust port is provided on the housing at the exhaust chamber.

[0012] Furthermore, the housing described in this invention is composed of a front cover and a rear cover that can be detachably assembled.

[0013] This invention also employs a gas collection and concentration calculation method for a respiratory ketone detection instrument, comprising the following steps: Step 1: Directional collection of respiratory gases: The subject blows exhaled air into the variable-diameter airway assembly through the mouthpiece. The air flows through the intermediate airway structure, passes the working end face of the sensor group, enters the exhaust pipe, and is then drawn out by the exhaust fan in the exhaust chamber and discharged from the exhaust port. The diameter of the right tail section of the intermediate airway structure is smaller than that of the left section, and the opening diameter of the mouthpiece is larger than that of the left section of the intermediate airway structure. When the air flows through the variable-diameter airway assembly, a pressure gradient is generated due to the gradual contraction of the cross-sectional area, which inhibits the backflow of gas in the sensor mounting cavity towards the mouthpiece. Step 2: Quantitative acquisition and control based on airway volume: Obtain the total internal volume of the variable diameter airway assembly, the incident flow rate flowing through the back of the mouthpiece sleeve, and the outgoing flow rate flowing through the sensor mounting cavity, and calculate the flow rate difference between the incident flow rate and the outgoing flow rate. Based on the ratio of the total volume to the flow rate difference, and combined with a preset safety factor, the effective blowing time is calculated. When the blowing time reaches the effective blowing time, it is determined that the gas in the sensor mounting cavity has been filled and reached a stable airflow state. The acquisition window is then opened, and the signal output by the sensor group at this time is taken as the effective detection signal. Step 3: Real-time compensation of environmental parameters: During the gas collection process, the ambient temperature and relative humidity are acquired in real time through the temperature and humidity sensors in the sensor group; The temperature compensation factor is calculated based on the deviation between the ambient temperature and the standard calibration temperature, combined with the preset temperature compensation coefficient. The humidity compensation factor is calculated based on the deviation between the relative humidity and the standard calibrated humidity, combined with the preset humidity compensation coefficient. Step 4: Concentration Calculation and Output: Obtain the raw concentration rough value output by the acetone gas sensor; firstly, use the preset airway volume correction coefficient to correct the structural error of the raw concentration rough value to obtain the first-level corrected concentration; then use the temperature compensation factor and humidity compensation factor obtained in step three to compensate for environmental error of the first-level corrected concentration to obtain the second-level corrected concentration; finally, use the preset standard concentration fitting equation to convert the second-level corrected concentration into the calibrated final respiratory ketone concentration and output it; wherein, the operation order of the structural error correction, environmental error compensation and standard concentration fitting in step four is executed sequentially and cannot be changed.

[0014] Furthermore, in step two, when it is determined that the gas in the sensor mounting cavity has been filled and reached a stable airflow state, the signal strength output by the sensor group must also reach its maximum value or enter a stable plateau period.

[0015] Furthermore, the temperature compensation factor and humidity compensation factor are multiplicative factors, and in step four, the secondary correction concentration = primary correction concentration × temperature compensation factor × humidity compensation factor.

[0016] Furthermore, the ratio of the mouthpiece opening diameter to the diameter of the left side section of the intermediate airway structure in step one is in the range of 1.5:1 to 3:1.

[0017] Furthermore, the standard calibration temperature in step three is 25°C, and the standard calibration humidity is 50% relative humidity.

[0018] The beneficial effects of this invention are: 1. The present invention uses a variable diameter airway with an inlet diameter larger than the outlet diameter and a gradually shrinking cross-sectional area to create a pressure gradient as exhaled gas flows through the airway. This effectively suppresses backflow of gas without the need for an additional one-way valve, achieving one-way gas collection. The structure is simple and highly reliable. 2. This invention accurately calculates the effective blowing time based on the difference between the total airway volume and the incident and outgoing flow rates, ensuring that the gas collected in the sensor installation cavity is the exhaled gas from the end of the lungs, fundamentally eliminating dead space gas interference and improving the representativeness and repeatability of the detection results; 3. This invention significantly reduces measurement errors introduced by environmental factors by performing real-time dynamic compensation for temperature and humidity based on calibration coefficients, enabling the equipment to maintain stable detection accuracy under different environmental conditions; 4. This invention uses a three-level sequential calibration algorithm to organically link structural correction, environmental compensation, and standard fitting in a predetermined order, eliminating the coupling effects between various error sources and making the final output concentration closer to the true value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a structural schematic diagram of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the sealing cap structure in Embodiment 1; Figure 3 This is a structural schematic diagram of the sealing cap from another perspective in Embodiment 1; Figure 4 This is a schematic diagram of the air guide plate in Embodiment 1; Figure 5 This is a structural schematic diagram of the air guide plate from another perspective in Embodiment 1; Figure 6 This is a schematic diagram of the structure of Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of the structure of the front cover of the shell in Embodiment 2; Figure 8 This is a schematic diagram of the intake pipe in Embodiment 2; Figure 9 A schematic diagram illustrating the specific data processing flow of a complete detection cycle in this invention.

[0021] The following are the labels in the diagram: 1. Housing; 2. Circuit board; 3. Sensor group; 4. Nozzle cover; 5. Exhaust pipe; 6. Air guide plate; 7. Sealing cover; 8. Air inlet pipe; 9. Sensor mounting cavity; 10. Exhaust chamber; 11. Exhaust fan; 12. Exhaust port; 13. Enclosure. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: Variable Diameter Airway Structure and Gas Collection (Airway Structure Formed by the Combination of Air Guide Plate and Sealing Cap) like Figures 1-5 As shown, in this embodiment, the housing 1 is assembled from a front cover and a rear cover that can be detached from each other. A variable diameter air passage assembly is provided inside the housing 1, and the variable diameter air passage assembly is provided with a mouthpiece sleeve 4, an intermediate air passage structure and an exhaust pipe 5 from left to right.

[0024] The intermediate air passage structure is formed by the upper air guide plate 6, the lower sealing cover 7, and the housing 1. Specifically, the air guide plate 6 is fixedly installed inside the upper side of the housing 1. A baffle 13 is provided on the air guide plate 6 to assist in forming the air passage. The sensor mounting cavity 9 and the sensor group 3 are installed on the air guide plate 6. The sealing cover 7 is located below the air guide plate 6 and cooperates with the air guide plate 6 to form an air passage chamber. The space between the lower surface of the air guide plate 6 and the upper surface of the sealing cover 7 constitutes a gas flow channel.

[0025] In the intermediate airway structure, the diameter of the right tail section airway chamber is smaller than that of the left section, and the opening diameter of the mouthpiece sleeve 4 is larger than that of the left section airway chamber. Preferably, the ratio of the opening diameter of the mouthpiece sleeve 4 to the diameter of the left section of the intermediate airway structure is in the range of 1.5:1 to 3:1. A sensor mounting cavity 9 is provided in the air guide plate 6 near the right tail section. The sensor group 3 is installed in the sensor mounting cavity 9, and the working end face of the sensor group 3 protrudes from the airway chamber of the intermediate airway structure. The sensor group 3 includes an expiratory flow gas sensor, an acetone gas sensor, a temperature sensor, and a humidity sensor.

[0026] An exhaust chamber 10 is provided at the right end of the housing 1, which is connected to the exhaust pipe 5 of the variable diameter air passage assembly. An exhaust fan 11 is provided in the exhaust chamber 10, and an exhaust port 12 is provided on the housing 1 at the exhaust chamber 10.

[0027] When a subject blows exhaled air into the variable-diameter airway assembly through the mouthpiece sleeve 4, the air enters through the large-diameter opening of the mouthpiece sleeve 4, flows in through the left section of the middle airway structure, and because the diameter of the right tail section airway chamber is smaller than that of the left section, the cross-sectional area of ​​the air gradually contracts as it flows towards the outlet, increasing the flow velocity and the air pressure along the flow direction, forming a pressure gradient from the outlet to the inlet. This pressure gradient prevents the air in the sensor mounting cavity 9 from flowing back towards the mouthpiece sleeve 4, thus achieving natural unidirectional gas collection without the need for an additional one-way valve.

[0028] After passing through the working end face of the sensor group 3 via the intermediate air passage structure, the gas enters the exhaust pipe 5, and is then drawn in by the exhaust fan 11 in the exhaust chamber 10 before being discharged from the exhaust port 12. The exhaust fan 11 helps guide the airflow in a predetermined direction, further improving the smoothness and unidirectionality of gas collection.

[0029] Example 2: Variable Diameter Airway Structure and Gas Acquisition (Airway Structure Formed Separately by the Intake Pipe) like Figures 6-8 As shown, the main difference between this embodiment and Embodiment 1 lies in the implementation method of the intermediate airway structure. In this embodiment, the intermediate airway structure is formed by a single intake pipe 8. The intake pipe 8 is a pipe with a variable diameter inner cavity, its left end connected to the mouthpiece sleeve 4, and its right end connected to the exhaust pipe 5. The inner diameter of the right tail section of the intake pipe 8 is smaller than that of the left tail section, forming a tapered structure where the diameter of the inlet end is larger than that of the outlet end. A sensor mounting cavity 9 is provided inside the intake pipe 8 near the right tail section, and the sensor group 3 is installed in the sensor mounting cavity 9.

[0030] In this embodiment, the air intake pipe 8 can be manufactured using a one-piece molding process, such as injection molding from medical-grade plastic or precision machining from stainless steel. Compared to the air passage structure formed by the combination of the air guide plate and the sealing cap in Embodiment 1, the air passage structure formed by the air intake pipe 8 alone has higher airtightness and processing consistency, making it suitable for mass standardized production.

[0031] Its gas collection principle is the same as that of Example 1: the subject exhales gas through the mouthpiece sleeve 4 into the air inlet tube 8. When it flows through the variable diameter inner cavity, the cross-sectional area shrinks and a pressure gradient is generated, which inhibits the reverse flow of gas and realizes unidirectional collection.

[0032] Example 3: Obtaining the incident and exit flow rates and calculating the effective blowing time In the gas acquisition process, in order to achieve quantitative acquisition control based on gas channel volume, it is necessary to obtain two key parameters: incident flow rate and outgoing flow rate.

[0033] The incident flow rate refers to the gas flow rate passing through the rear side of the nozzle sleeve 4. In this embodiment, the incident flow rate can be obtained in the following two ways: Method 1: Install a flow sensor in the airway downstream of the mouthpiece sleeve 4, and measure the gas flow rate passing through the back side of the mouthpiece sleeve 4 in real time through the flow sensor, which is used as the incident flow rate L1.

[0034] Method 2: Estimation based on the preset opening diameter of the mouthpiece sleeve 4 and the empirical value of the normal human blowing volume. Specifically, the average value or empirical flow range of the normal human blowing volume corresponding to different mouthpiece sleeve opening diameters is stored in advance. During the test, the corresponding empirical flow value is retrieved according to the mouthpiece sleeve 4 currently in use as the estimated value of the incident flow L1.

[0035] The outflow rate L2 is obtained by real-time measurement using a flow sensor installed at the inlet of sensor mounting cavity 9.

[0036] Let the total internal volume of the variable-diameter airway assembly be V (unit: mL), the incident flow rate be L1 (unit: mL / min), and the exit flow rate be L2 (unit: mL / min), then the flow difference ΔL = L1 L2 (unit: mL / min) represents the volume of gas actually injected into the airway per unit time to fill the airway.

[0037] According to the fluid continuity equation, the rate of change of gas volume within the airway satisfies: d(V_air) / dt = L1 L2 When the airway is fully filled, the following occurs: ∫(L1 L2)·dt = V The effective blowing time t is obtained by calculating the average flow rate within the sampling period: t = k × V / (L1 L2) Where k is a preset safety factor, with a value ranging from 1.1 to 1.5, used to provide a certain filling redundancy to ensure that the airway is fully filled.

[0038] The internal total volume V of the variable diameter air passage assembly can be determined by a standard flow calibration procedure before the equipment leaves the factory. Specifically, a standard gas of known flow rate is introduced into the air passage, and the gas transmission delay time and flow integral value from the nozzle sleeve 4 to the outlet of the exhaust pipe 5 are measured to calculate the specific value of V.

[0039] When the blowing duration reaches the effective blowing time t, it is determined that the gas in the sensor mounting cavity 9 has been filled and reached a stable airflow state. At this time, the acquisition window is opened, and the signal output by the sensor group 3 is used as the effective detection signal.

[0040] Example 4: Lung terminal gas determination During the subject's exhalation process, the signal output by sensor group 3 showed the following characteristics over time: the signal value was low and rose slowly in the initial stage (corresponding to the dead space gas in the oral cavity and upper respiratory tract), then the signal value rose rapidly and finally reached a stable peak or plateau period (corresponding to alveolar gas).

[0041] Since the sensor output signal gradually increases after exhalation, the gas originating from deep within the lungs corresponds to the point where the maximum signal strength is reached. Therefore, in this embodiment, after the exhalation duration reaches the effective exhalation time t, the controller also monitors whether the signal strength output by sensor group 3 has reached its maximum value or entered a stable plateau period.

[0042] The specific determination logic is as follows: The output signal intensity of the acetone gas sensor is monitored in real time. When the signal intensity reaches its maximum value (i.e., the inflection point where the signal change rate changes from positive to negative) or the signal change rate within a continuous time period is lower than a preset threshold (e.g., ±2% / s), the gas sample within that time window is determined to originate from the distal lung region. Only the average sensor output value within this peak time window or the stable plateau period is used as the raw coarse concentration value C_raw for subsequent concentration calculations.

[0043] By combining the dual criteria of "effective blowing time t" and "signal peak / stable plateau period", it is ensured that the gas sample used in the calculation is indeed the exhaled gas from the end of the lungs, thus fundamentally eliminating dead space gas interference.

[0044] Example 5: Calibration of Temperature and Humidity Compensation Coefficient The acetone gas sensor in sensor group 3 is preferably an oxide semiconductor gas sensor. Oxide semiconductor gas sensors have good sensitivity to acetone, but their response characteristics are significantly affected by ambient temperature and humidity, so they need to be calibrated for temperature and humidity compensation.

[0045] Calibration of temperature compensation coefficient α: Under constant relative humidity (e.g., RH0 = 50%RH), the device was placed in different temperature environments (e.g., 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃), and standard acetone gas of known concentration was introduced. The sensor output values ​​at each temperature were recorded. Using the output value at the standard calibration temperature T0 = 25℃ as a benchmark, the output offset at other temperatures was calculated. The temperature compensation function was obtained by least squares fitting. K_T = g(T,T0,α) Where K_T is the temperature compensation factor (dimensionless), T is the real-time ambient temperature (°C), T0 is the standard calibration temperature (25°C), and α is the sensor temperature drift coefficient (factory calibration constant).

[0046] Calibration of humidity compensation coefficient β: Under constant temperature conditions (e.g., T0 = 25℃), the device was placed in environments with different relative humidity levels (e.g., 20%RH, 30%RH, 40%RH, 50%RH, 60%RH, 70%RH, 80%RH, 90%RH), and standard acetone gas of known concentration was introduced. The sensor output values ​​were recorded at each humidity level. Using the output value at the standard calibration humidity RH0 = 50%RH as a benchmark, the output offset at other humidity levels was calculated. The humidity compensation function was obtained by fitting using the least squares method. K_RH = h(RH,RH0,β) Wherein, K_RH is the humidity compensation factor (dimensionless), RH is the real-time ambient relative humidity (%RH), RH0 is the standard calibration humidity (50%RH), and β is the gas diffusion humidity influence coefficient (factory calibration constant).

[0047] In the actual testing process, the temperature sensor and humidity sensor acquire the ambient temperature T and relative humidity RH in real time, and the controller calculates the temperature compensation factor K_T and humidity compensation factor K_RH in real time according to the above calibration function.

[0048] Example 6: Complete Three-Level Sequential Calibration Process The following is a detailed data processing flow for a complete testing cycle, for reference. Figure 9 : (1) Gas sampling and signal acquisition: Subjects continuously exhale through the mouthpiece into the variable-diameter airway assembly. During exhalation, a flow sensor measures the incident flow rate L1 and the outgoing flow rate L2 in real time, while a temperature sensor and a humidity sensor simultaneously acquire the ambient temperature T and relative humidity RH. The controller is based on the known total airway volume V and the flow difference ΔL = L1. L2, combined with the safety factor k, calculate the effective blowing time t = k × V / (L1) L2). When the blowing duration reaches t and the sensor output signal reaches its maximum value or enters a stable plateau period, the acquisition window is opened to obtain the raw concentration coarse value C_raw output by the acetone gas sensor.

[0049] (2) First-level calibration – airway volume correction (structural error correction): The original coarse concentration value C_raw was corrected for structural errors using a preset airway volume correction factor K_V to obtain the first-level corrected concentration C1: C1 = K_V × C_raw K_V is the airway volume correction factor (a factory calibration constant for the equipment), used to correct for systematic deviations introduced by the internal structure of the variable diameter airway assembly (including changes in airway cross-section, uneven airflow distribution, etc.). The specific value of K_V is determined through a standard concentration gas calibration experiment before the equipment leaves the factory.

[0050] (3) Second-level calibration – environmental parameter compensation (environmental error compensation): Based on the real-time acquired ambient temperature T and relative humidity RH, and combined with the calibrated temperature compensation coefficient α and humidity compensation coefficient β, the temperature compensation factor K_T and humidity compensation factor K_RH are calculated respectively.

[0051] In this embodiment, the temperature compensation factor K_T and the humidity compensation factor K_RH are multiplication factors, and the specific calculation method is as follows: K_T = g(T,T0,α) K_RH = h(RH,RH0,β) Multiply the first-level correction concentration C1 by the temperature compensation factor K_T and the humidity compensation factor K_RH to obtain the second-level correction concentration C2: C2 = C1 × K_T × K_RH In an alternative embodiment, the temperature compensation factor and the humidity compensation factor can also be in the form of additive factors, i.e., C2 = C1 + ΔT + ΔRH, where ΔT and ΔRH are the concentration deviation corrections introduced by temperature and humidity, respectively.

[0052] (4) Third-level calibration – Standard concentration fitting output (final true value conversion): Using a pre-defined standard concentration fitting equation, the secondary correction concentration C2 is mapped to the standard concentration value to obtain the calibrated final respiratory ketone concentration C_final. C_final = F(C2), that is: C_final=C_raw × K_v × [1+α(T-T_0)] × [1+β(RH-RH_0) / RH_0].

[0053] (5) Output of results: The calibrated final respiratory ketone concentration C_final is output to the display screen or sent to an external terminal via the communication module. Optionally, C_final can also be compared with a preset ketosis threshold to output a qualitative or semi-quantitative assessment of ketone body metabolism levels.

[0054] Special note regarding the order of operations: The order of operations for the first-level calibration (airway volume correction), the second-level calibration (environmental parameter compensation), and the third-level calibration (standard concentration fitting output) is: airway volume correction → temperature and humidity environmental compensation → standard concentration fitting output. This order is fixed and cannot be changed.

[0055] This is because: airway volume correction decouples the fixed mapping between the sensor's original signal and the hardware structure, and must be performed before environmental compensation to obtain the correct temperature / humidity compensation baseline; environmental compensation must be performed after structural correction because deviations in the sensor signal at the structural level will change the baseline values ​​for temperature and humidity drift; standard concentration fitting, as the final true value conversion step, must be performed after all error corrections are completed. If the above order is reversed (e.g., environmental compensation is performed first, then structural correction), coupling errors will occur between the correction steps, causing the final output concentration to deviate from the true value.

[0056] Industrial applicability The respiratory ketone detection instrument of this invention has a compact structure and is easy to operate, making it suitable for various scenarios such as daily health monitoring at home, auxiliary diagnosis in medical institutions, and weight loss / fitness management. Its core three-level sequential calibration algorithm can be implemented on a general-purpose microcontroller (MCU), resulting in low manufacturing costs and facilitating mass production and widespread application.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A breath ketone detection instrument, characterized in that: Includes a housing (1), inside which is disposed a variable diameter airway assembly and a circuit board (2) integrating a control and calculation module, and inside the variable diameter airway assembly is installed a sensor group (3) electrically connected to the circuit board. The variable diameter airway assembly is provided with a mouthpiece sleeve (4), an intermediate airway structure and an exhaust pipe (5) from left to right. The diameter of the right tail section airway chamber in the intermediate airway structure is smaller than that of the left section, and the opening diameter of the mouthpiece sleeve (4) is larger than that of the left section airway chamber in the intermediate airway structure. This causes the exhaled gas to generate a pressure gradient due to the shrinkage of the cross-sectional area when it flows through the variable diameter airway assembly, thereby inhibiting the backflow of gas from the outlet end to the inlet end. The intermediate airway structure is either an airway structure formed by the upper air guide plate (6), the lower sealing cover (7) and the shell (1) or an airway structure formed by a single air inlet pipe (8).

2. The breath ketone detection instrument as described in claim 1, characterized in that: The sensor group (3) includes an exhaled airflow gas sensor, an acetone gas sensor, a temperature sensor, and a humidity sensor.

3. The breath ketone detection instrument as described in claim 1, characterized in that: A sensor mounting cavity (9) is provided near the right tail section of the intermediate airway structure. The sensor group (3) is installed in the sensor mounting cavity (9) and the working end face of the sensor group (3) protrudes into the airway cavity of the intermediate airway structure.

4. The breath ketone detection instrument as described in claim 1, characterized in that: An exhaust chamber (10) is provided at the right end of the housing (1) and is connected to the exhaust pipe (5) of the variable diameter air passage assembly. An exhaust fan (11) is provided in the exhaust chamber (10), and an exhaust port (12) is provided on the housing (1) at the exhaust chamber (10).

5. The breath ketone detection instrument as described in claim 1, characterized in that: The shell (1) is composed of a front cover and a rear cover that can be detachably spliced ​​together.

6. A method for gas collection and concentration calculation in a respiratory ketone detection instrument, applied to the respiratory ketone detection instrument according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Directional collection of respiratory gases: The subject blows exhaled gas into the variable diameter airway assembly through the mouthpiece sleeve (4). The gas flows through the middle airway structure, passes through the working end face of the sensor group (3), and enters the exhaust pipe (5). It is then drawn out by the exhaust fan (11) in the exhaust chamber (10) and discharged from the exhaust port (12). The diameter of the right tail section airway chamber of the middle airway structure is smaller than that of the left section, and the opening diameter of the mouthpiece sleeve (4) is larger than that of the left section of the middle airway structure. When the gas flows through the variable diameter airway assembly, a pressure gradient is generated due to the gradual contraction of the cross-sectional area, which inhibits the reverse flow of gas in the sensor mounting cavity (9) towards the mouthpiece sleeve (4). Step 2: Quantitative acquisition and control based on airway volume: Obtain the total internal volume of the variable diameter airway assembly, obtain the inlet flow rate flowing through the back of the mouthpiece sleeve (4), and the outlet flow rate flowing through the sensor mounting cavity (9), and calculate the flow rate difference between the inlet flow rate and the outlet flow rate. Based on the ratio of the total volume to the flow rate difference, and combined with a preset safety factor, the effective blowing time is calculated. When the blowing time reaches the effective blowing time, it is determined that the gas in the sensor mounting cavity (9) has been filled and reached a stable airflow state. The acquisition window is opened, and the signal output by the sensor group (3) at this time is taken as the effective detection signal. Step 3: Real-time compensation of environmental parameters: During the gas collection process, the ambient temperature and relative humidity are obtained in real time through the temperature sensor and humidity sensor in the sensor group (3); The temperature compensation factor is calculated based on the deviation between the ambient temperature and the standard calibration temperature, combined with the preset temperature compensation coefficient. The humidity compensation factor is calculated based on the deviation between the relative humidity and the standard calibrated humidity, combined with the preset humidity compensation coefficient. Step 4: Concentration Calculation and Output: Obtain the raw concentration rough value output by the acetone gas sensor; firstly, use the preset airway volume correction coefficient to correct the structural error of the raw concentration rough value to obtain the first-level corrected concentration; then use the temperature compensation factor and humidity compensation factor obtained in step three to compensate for environmental error of the first-level corrected concentration to obtain the second-level corrected concentration; finally, use the preset standard concentration fitting equation to convert the second-level corrected concentration into the calibrated final respiratory ketone concentration and output it; wherein, the operation order of the structural error correction, environmental error compensation and standard concentration fitting in step four is executed sequentially and cannot be changed.

7. The method according to claim 6, characterized in that: In step two, when it is determined that the gas in the sensor mounting cavity (9) has been filled and reached a stable airflow state, the signal strength output by the sensor group (3) must also reach its maximum value or enter a stable plateau period.

8. The method according to claim 6, characterized in that: The temperature compensation factor and humidity compensation factor are multiplicative factors. In step four, the secondary correction concentration = primary correction concentration × temperature compensation factor × humidity compensation factor.

9. The method according to claim 6, characterized in that: The ratio of the opening diameter of the mouthpiece sleeve (4) in step one to the diameter of the left side section of the middle airway structure is in the range of 1.5:1 to 3:

1.

10. The method according to claim 6, characterized in that: The standard calibration temperature in step three is 25°C, and the standard calibration humidity is 50% relative humidity.

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