A method and system for measuring the flow rate of anesthesia machines based on gas composition compensation

Abstract

This invention relates to the field of flow measurement and gas composition compensation, and specifically to a method and system for measuring the flow rate of an anesthesia machine based on gas composition compensation. The method includes: Step S0. Calibrating a differential pressure flow sensor using pure oxygen; Step S1. Measuring the flow rate of the anesthesia machine using the differential pressure flow sensor; Step S2. Obtaining compensation coefficients based on the concentrations of various gases in the anesthesia machine, and using these compensation coefficients to correct the flow rate value measured by the differential pressure flow sensor, thereby obtaining a corrected flow rate value. The compensation coefficients of this invention do not fully compensate according to concentration percentages and relative molecular masses of the gases; instead, correction coefficients are used, which improve the accuracy of the compensation coefficients.

Description

Technical Field

[0001] This invention relates to the fields of flow measurement and gas composition compensation, and specifically to a method and system for measuring the flow of an anesthesia machine based on gas composition compensation. Background Technology

[0002] Flow measurement is one of the most basic functions of anesthesia machines. By measuring the inhaled and exhaled ventilation flow in real time, the true tidal volume of mechanical ventilation is obtained and adjusted according to the target tidal volume setting. Precise tidal volume measurement and control are crucial for anesthesia machines to effectively support the patient's life.

[0003] Currently, the main method for measuring flow in anesthesia machines is to install flow sensors at the inspiratory and expiratory ports of the ventilation circuit, using two flow sensors to measure the flow. The mainstream flow sensor types currently available on the market include differential pressure flow sensors and thermal flow sensors. Due to the specific application of anesthesia machines, mainstream products have gradually adopted differential pressure flow sensors for flow measurement.

[0004] When using a differential pressure flow sensor for flow testing, sensor calibration is required first. This involves connecting a third-party high-precision flow sensor in series with the anesthesia machine's flow sensor, performing ventilation, adjusting the flow rate, and recording the flow rate values ​​of the third-party flow sensor and the voltage values ​​of the anesthesia machine's flow sensor at various flow rates. These values ​​are then stored as a flow-voltage curve table, which serves as the basis for the anesthesia machine to convert the output voltage of the differential pressure flow sensor into flow rate. However, this calibration and flow calculation method has certain drawbacks in the specific application scenarios of anesthesia machines.

[0005] The different calibration and usage scenarios can affect the flow measurement results when using calibration data for conversion. Because the gas used for calibration differs from the gas actually used in the anesthesia machine, related research shows that different gases of the same volume, under the same flow rate conditions, produce different differential pressure inputs to differential pressure flow sensors, ultimately leading to some errors in the converted flow rate value. Summary of the Invention

[0006] To compensate for the errors caused by the problems described in the background art, the present invention provides a method for measuring the flow rate of anesthesia machines based on gas composition compensation.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution.

[0008] This invention proposes a method for measuring the flow rate of an anesthesia machine based on gas composition compensation, the method comprising:

[0009] Step S1. Measure the flow rate of the anesthesia machine using a differential pressure flow sensor;

[0010] Step S2. Obtain the compensation coefficient based on the concentration of various gases in the anesthesia machine, and use the compensation coefficient to correct the flow rate value of the anesthesia machine measured by the differential pressure flow sensor to obtain the corrected flow rate value.

[0011] In step S1, a differential pressure flow sensor is used to collect the pressure difference generated by the flow velocity and convert it into a voltage value. The corresponding flow rate value is calculated using a lookup table method, and compensation is performed using the compensation coefficient of this patent.

[0012] In step S2, after discovering that the problem of not being able to fully compensate based on the percentage of gas components is discovered, experiments with multiple gas components are conducted using a third-party calibrated measuring device as the standard.

[0013] As an improvement to the above technical solution, the method further includes the following step before step S1:

[0014] Step S0. Calibrate the differential pressure flow sensor using pure oxygen.

[0015] As an improvement to the above technical solution, in step S2, the various gases in the anesthesia machine include: oxygen, carbon dioxide, nitrous oxide and nitrogen.

[0016] As an improvement to the above technical solution, step S2, obtaining the concentrations of various gases in the anesthesia machine, includes the following steps:

[0017] The gas monitoring module built into the anesthesia machine was used to monitor the concentrations of the corresponding gases, and the concentrations of oxygen, carbon dioxide and nitrous oxide were obtained respectively.

[0018] The nitrogen concentration is calculated based on the obtained oxygen, carbon dioxide, and nitrous oxide concentrations.

[0019] As one of the improvements to the above technical solution, the nitrogen concentration T N2 The formula for calculation is:

[0020] T N2 =1-(T) o2 +T CO2 +T N2O )

[0021] Among them, T o2 T represents the oxygen concentration. CO2 T represents the carbon dioxide concentration. N2O This represents the concentration of nitrous oxide.

[0022] As one improvement to the above technical solution, in step S2, the expression for the compensation coefficient α is:

[0023]

[0024] Among them, T o2 T represents the oxygen concentration. CO2 T represents the carbon dioxide concentration. N2O T represents the concentration of nitrous oxide. N2 δ represents the nitrogen concentration, and δ is the gas composition correction factor.

[0025] As one improvement to the above technical solution, the formula for calculating the gas composition correction coefficient δ is:

[0026]

[0027] Where p1 is standard atmospheric pressure, t1 is standard temperature, p is actual gas pressure, t is current temperature, 101.325 kPa is standard gas pressure parameter, and 273.15 is absolute zero temperature.

[0028] As one of the improvements to the above technical solution, the gas composition correction coefficient δ is designed for use at flow rates below 120 L / min, with a specific value of 0.96.

[0029] As an improvement to the above technical solution, in step S2, the formula for calculating the corrected flow rate value f is:

[0030] f = f m *α

[0031] Among them, f m The flow rate of the anesthesia machine is measured by a differential pressure flow sensor.

[0032] This invention also proposes a flow measurement system for anesthesia machines based on gas composition compensation, the system comprising: a flow acquisition module and a flow correction module; wherein,

[0033] The flow acquisition module is used to acquire the flow value of the anesthesia machine measured using a differential pressure flow sensor;

[0034] The flow correction module is used to obtain a compensation coefficient based on the concentration of various gases in the anesthesia machine, and to use the compensation coefficient to correct the flow rate value of the anesthesia machine measured by the differential pressure flow sensor to obtain the corrected flow rate value.

[0035] The advantages of this invention compared to the prior art are:

[0036] 1. This invention compensates for the flow rate measured by the flow sensor by using the concentration of gases such as air, oxygen, nitrous oxide, and carbon dioxide that may flow through the throttling device when the anesthesia machine is working normally, thereby correcting the flow rate measured by the flow sensor.

[0037] 2. The compensation coefficient of this invention does not fully compensate according to the concentration percentage and the relative molecular mass of the gas. A correction coefficient is used for correction, which improves the accuracy of the compensation coefficient.

[0038] 3. Before measurement, the present invention uses pure oxygen to calibrate the flow sensor, which greatly reduces the error of the flow sensor's flow value. Attached Figure Description

[0039] Figure 1 This is a flowchart of a method according to an embodiment of the present invention. Detailed Implementation

[0040] The technical solutions provided by the present invention will be further described below with reference to the embodiments and accompanying drawings.

[0041] Differential pressure flow sensors measure flow rate based on Bernoulli's equation and the fluid continuity equation. When gas flows through a throttling device, including a standard orifice plate, standard nozzle, or variable diameter probe, a pressure difference is generated before and after it. This pressure difference is proportional to the square of the flow rate. This can be expressed by the following commonly used standard formula:

[0042]

[0043] In the formula, q v ρ1 is the volumetric flow rate, ρ1 is the density of the gas being measured, and Δp is the pressure difference of the gas before and after the throttling device. The pressure difference is directly input into the differential pressure flow sensor to measure the gas flow rate. The other variables are irrelevant to the analysis and are not explained.

[0044] As can be seen from the formula above, gases with different compositions will produce different pressure differences at the same volume flow rate.

[0045] As can be seen from the above conclusions, the gas composition affects the pressure difference. When the anesthesia machine is working normally, the gas flowing through the throttling device may be air, oxygen, nitrous oxide, carbon dioxide, etc., and the concentration of each gas is not fixed. Therefore, the use of any mixed gas during the calibration process cannot be compared with the actual use scenario.

[0046] Example 1

[0047] like Figure 1 The diagram shown is a flowchart of the method in Embodiment 1 of the present invention. To compensate for any errors, the following measures are taken:

[0048] 1) Use pure oxygen to calibrate the flow sensor. Since most of the gas used during surgery is oxygen, using oxygen as the basic standard can significantly reduce errors.

[0049] 2) Use the various gas monitoring modules built into the anesthesia machine to monitor the gas concentrations, and obtain the oxygen concentration, carbon dioxide concentration, and nitrous oxide concentration T respectively. o2 T CO2 T N2O The nitrogen concentration was calculated to be

[0050] T N2 =1-(T) o2 +T CO2 +T N2O )

[0051] 3) Compensate for the flow rate using the concentration of each gas component, setting the compensation coefficient to [value missing].

[0052]

[0053] Among them, the numerical constants are the relative molecular masses of the gas, and δ is the gas composition correction coefficient. In practical applications, the compensation coefficient is related to the gas composition, but it cannot be fully compensated according to the concentration percentage and the relative molecular mass of the gas. A correction coefficient is needed for correction. This correction coefficient was obtained through multiple sets of experiments and is suitable for use at flow rates below 120 L / min. The specific value is 0.96.

[0054] Correction factor:

[0055]

[0056] Where p1 is standard atmospheric pressure, t1 is standard temperature 20 degrees Celsius, p is actual gas pressure, t is current temperature, 101.325 kPa and 20 degrees Celsius are standard gas parameters, and 273.15 is absolute zero temperature.

[0057] 4) Perform flow correction f = f m *α, finally yielding the corrected flow rate value.

[0058] In practical use, the applicant discovered that the influence of gas composition on flow rate is not solely determined by percentage. In tests where only percentage correction was applied, the output flow rate value still differed from the measured value by standard measuring equipment. After multiple flow rate measurement experiments, it was found that the flow rate deviation was linearly proportional to the flow rate compensation values ​​of other gas components, and this proportional relationship had different values ​​at different temperatures. It was 0.96 at the typical operating room temperature of 20 degrees Celsius and 0.92 at human body temperature. The correction could be calculated based on the actual measured circuit gas temperature.

[0059] Example 2

[0060] This invention also proposes a flow measurement system for anesthesia machines based on gas composition compensation, the system comprising: a flow acquisition module and a flow correction module; wherein,

[0061] The flow acquisition module is used to acquire the flow value of the anesthesia machine measured using a differential pressure flow sensor;

[0062] The flow correction module is used to obtain a compensation coefficient based on the concentration of various gases in the anesthesia machine, and to use the compensation coefficient to correct the flow rate value of the anesthesia machine measured by the differential pressure flow sensor to obtain the corrected flow rate value.

[0063] As can be seen from the above detailed description of the present invention, the gas composition compensation-based anesthesia machine flow measurement method of the present invention greatly reduces measurement error.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the flow rate of an anesthesia machine based on gas composition compensation, the method comprising: Step S1. Measure the flow rate of the anesthesia machine using a differential pressure flow sensor; Step S2. Obtain compensation coefficients based on the concentrations of various gases in the anesthesia machine, and use the compensation coefficients to correct the flow rate value of the anesthesia machine measured by the differential pressure flow sensor to obtain the corrected flow rate value; the various gases include: oxygen, carbon dioxide, nitrous oxide and nitrogen; The compensation coefficient The expression is: in, Oxygen concentration, This refers to the concentration of carbon dioxide. This refers to the concentration of nitrous oxide. Nitrogen concentration, This is a correction factor for gas composition; The gas composition correction coefficient The formula for calculation is: Where p1 is standard atmospheric pressure, t1 is standard temperature, p is actual gas pressure, t is current temperature, 101.325 kPa is standard gas pressure, and 273.15 is absolute zero temperature.

2. The anesthesia machine flow measurement method based on gas composition compensation according to claim 1, characterized in that, The method further includes the following steps prior to step S1: Step S0. Calibrate the differential pressure flow sensor using pure oxygen.

3. The anesthesia machine flow measurement method based on gas composition compensation according to claim 1, characterized in that, In step S2, obtaining the concentrations of various gases in the anesthesia machine includes the following steps: The gas monitoring module built into the anesthesia machine was used to monitor the concentrations of the corresponding gases, and the concentrations of oxygen, carbon dioxide and nitrous oxide were obtained respectively. The nitrogen concentration is calculated based on the obtained oxygen, carbon dioxide, and nitrous oxide concentrations.

4. The anesthesia machine flow measurement method based on gas composition compensation according to claim 3, characterized in that, The nitrogen concentration The formula for calculation is: in, Oxygen concentration, This refers to the concentration of carbon dioxide. This represents the concentration of nitrous oxide.

5. The anesthesia machine flow measurement method based on gas composition compensation according to claim 1, characterized in that, The gas composition correction coefficient It is suitable for use at flow rates below 120L / min, with a specific value of 0.

96.

6. The anesthesia machine flow measurement method based on gas composition compensation according to claim 1, characterized in that, In step S2, the corrected flow rate value f The formula for calculation is: in, The flow rate of the anesthesia machine is measured by a differential pressure flow sensor.

7. A system for measuring the flow rate of an anesthesia machine based on the gas composition compensation method as described in claim 1, characterized in that, The system includes: a traffic acquisition module and a traffic correction module; wherein... The flow acquisition module is used to acquire the flow value of the anesthesia machine measured using a differential pressure flow sensor; The flow correction module is used to obtain a compensation coefficient based on the concentration of various gases in the anesthesia machine, and to use the compensation coefficient to correct the flow rate value of the anesthesia machine measured by the differential pressure flow sensor to obtain the corrected flow rate value.

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