A dead space calculation method, system, and device supporting dead space calculation

Abstract

The present invention provides a dead space calculation method, system, and device supporting dead space calculation, the method comprising: obtaining expiratory volume data and carbon dioxide concentration data for the same respiratory cycle; drawing a volumetric capnography diagram based on the expiratory volume data and carbon dioxide concentration; finding a point on the volumetric capnography curve with the origin as the starting point where the average slope on the right side begins to be less than a set ratio N of the slope on the left side, denoted as C; denoting the end point of the curve in the volumetric capnography diagram as D; selecting data points whose abscissas are within the interval F and G on the volumetric capnography diagram, performing regression analysis to obtain a regression equation; estimating physiological dead space and anatomical dead space based on the carbon dioxide mass conservation principle and the coefficient of the regression equation, and calculating alveolar dead space. The advantages of the present invention are: the dead space calculation method is simple, the dead space can be calculated in real time during use of the device; it is not affected by the user's irregular breathing, and accurate dead space values can be obtained through continuous dead space calculation.

Description

Technical Field

[0001] The present invention belongs to the field of respiratory assistance equipment, and in particular relates to a dead space calculation method, system and device supporting dead space calculation. Background Art

[0002] Dead space, also known as ineffective space, refers to the area of the lung that undergoes ventilation but does not participate in gas exchange during respiration. Physiological dead space is composed of both anatomical and alveolar dead space. Accurately monitoring the amount of dead space in humans is clinically important, but also very difficult.

[0003] Fowler proposed a dead space calculation method, which requires the subject to take a deep breath of pure oxygen to the total lung capacity (TLC) position at the residual volume (RV) position, then exhale calmly to the RV, and measure the change in nitrogen concentration in the exhaled air, such as Figure 1 As shown. When exhaling, the first thing discharged is pure oxygen, that is, the pure oxygen remaining in the dead space at the end of inspiration. At this time, the nitrogen concentration is 0, and this stage is called stage I; then the mixed gas of nitrogen-containing alveolar gas and dead space gas is discharged, and the nitrogen concentration increases. This stage is called stage II; when the nitrogen concentration reaches a plateau, it indicates that the discharged gas is pure alveolar gas, and this stage is called stage III. D It is the size of the anatomical dead space.

[0004] Existing methods for measuring dead space are complex and cannot be implemented during mechanical ventilation. Furthermore, each breath is not completely constant, and the distribution of gas within the lungs is extremely uneven. Different exhaled volumes may represent completely different locations, making dead space difficult to accurately calculate. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art in that the dead space measurement process is complicated and cannot be accurately measured.

[0006] In order to achieve the above object, the present invention proposes a dead space calculation method, which includes:

[0007] Step 1: Obtain expiratory volume data and carbon dioxide concentration data for the same respiratory cycle;

[0008] Step 2: Create a volumetric capnogram based on the expiratory volume data and carbon dioxide concentration;

[0009] Step 3: Starting from the origin of the volumetric capnography, find the point on the curve where the average slope on the right side begins to be less than the set ratio N of the slope on the left side. This point is marked as C. The end point of the curve in the volumetric capnography is marked as D.

[0010] Step 4: Select the data points whose abscissas are within the intervals F and G on the volumetric capnography and perform regression analysis to obtain the regression equation;

[0011] Step 5: Estimate physiological dead space and anatomical dead space based on the carbon dioxide mass conservation principle and regression equation coefficients, and calculate alveolar dead space.

[0012] As an improvement to the above method, the abscissa of the volumetric carbon dioxide graph is the expiratory volume, and the ordinate is the carbon dioxide concentration.

[0013] As an improvement to the above method, the set ratio N is set to 1 / 3.

[0014] As an improvement to the above method, step 4 is specifically as follows:

[0015] The F and G values are obtained according to the following formula:

[0016] F=k1×X C

[0017] G=k2×X D

[0018] Among them, X C Indicates the horizontal coordinate value of point C; X D Indicates the horizontal coordinate value of point D; k1 is selected from a value between 0.8 and 1.2, and k2 is selected from a value between 0.6 and 1;

[0019] The regression equation is expressed as:

[0020] FCO2=k*VE+b

[0021] Where FCO2 represents the carbon dioxide concentration; k and b represent the regression equation coefficients; VE represents the expiratory volume. As an improvement to the above method, the formula for estimating physiological dead space is:

[0022] VD phy =X D *F A CO2-F e CO2) / F A CO2

[0023] Among them, VD phy Indicates physiological dead space;

[0024] F A CO2 represents the carbon dioxide concentration in alveolar gas, F A CO2=k3*Y C +k4*Y D , Y C Indicates the vertical coordinate value of point C; Y D Indicates the vertical coordinate value of point D; k3 and k4 are selected from values between 0.2 and 0.8 respectively;

[0025] F eCO2 represents the average concentration of carbon dioxide in exhaled gas:

[0026]

[0027] Wherein, FCO2 represents the carbon dioxide concentration obtained in step 1; represents expiratory flow; t represents time.

[0028] As an improvement to the above method, the formula for estimating anatomical dead space is:

[0029]

[0030] Among them, VD aw Indicates anatomical dead space;

[0031] FCO2 k5 =k*k5*X D +b; k5 is a value between 0.5 and 1; k and b represent the coefficients of the regression equation; X D Indicates the horizontal coordinate value of point D.

[0032] As an improvement to the above method, the alveolar dead space calculation formula is:

[0033] VD alv =VD phy -VD aw

[0034] Among them, VD alv Indicates alveolar dead space.

[0035] The present invention further provides a dead space calculation system, comprising:

[0036] Data acquisition module: used to obtain expiratory volume data and carbon dioxide concentration data of the same respiratory cycle;

[0037] A volumetric carbon dioxide graph drawing module, for drawing a volumetric carbon dioxide graph based on expiratory volume data and carbon dioxide concentration;

[0038] The key point selection module is used to find the point on the volumetric capnography curve where the average slope on the right side begins to be less than the set ratio N of the slope on the left side, starting from the origin on the volumetric capnography graph. The point is marked as C; the end point of the curve in the volumetric capnography graph is marked as D;

[0039] A regression analysis module is used to select data points whose horizontal coordinates are within the F and G intervals on the volumetric carbon dioxide graph and perform regression analysis to obtain a regression equation; and

[0040] The alveolar dead space calculation module is used to estimate physiological dead space and anatomical dead space based on the principle of carbon dioxide mass conservation and regression equation coefficients, and calculate alveolar dead space.

[0041] The present invention also provides a device for supporting dead space calculation, wherein the device includes the dead space calculation system.

[0042] As an improvement to the above device, the device is a ventilator or an anesthesia machine.

[0043] Compared with the prior art, the advantages of the present invention are:

[0044] 1. The dead space calculation method implemented by the present invention is simple and can calculate the dead space in real time during the use of the equipment;

[0045] 2. The dead space calculation method of the present invention is not affected by the user's irregular breathing, and an accurate dead space value can be obtained by continuously calculating the dead space. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Shown is a schematic diagram of Fowler's dead space determination method;

[0047] Figure 2 Shown is a flow chart of the dead space calculation method of the present invention;

[0048] Figure 3 Shown is a volumetric capnogram. DETAILED DESCRIPTION

[0049] The present invention proposes a dead space calculation method and system based on volumetric carbon dioxide diagram and a device supporting dead space calculation. The method can monitor the user's physiological dead space, anatomical dead space and alveolar dead space during the use of devices such as ventilators and anesthesia machines.

[0050] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0051] Using the principle of CO2 mass conservation, the dead space calculation formula is as follows:

[0052] F e CO2=V T =F A CO2×V A (1)

[0053] V D =V T ×(F A CO2-F e CO2) / F A CO2 (2)

[0054] Where V T represents expiratory tidal volume, V A Indicates the effective alveolar gas volume exhaled, V D =VT -V A This is the dead space volume. FeCO2 represents the average CO2 concentration in the exhaled gas and is calculated using the following formula. A CO2 refers to the CO2 concentration in alveolar gas.

[0055]

[0056] Where FCO2 represents the CO2 concentration (monitored by the mouth CO2 sensor) that changes with expiratory volume (or time), Indicates the exhaled air flow rate (monitored by the flow sensor). FeCO2 can be easily calculated by combining the CO2 sensor value at the mouth end and the flow sensor value.

[0057] Currently, the exhaled gas volume is collected using a Douglas bag and the CO2 concentration mixed therein is measured as FeCO2. A CO2, so the maximum CO2 partial pressure of each exhalation is used instead.

[0058] The steps of the dead space calculation method provided by the present invention are as follows:

[0059] Step 1: Obtain the expiratory volume data and carbon dioxide concentration data of the same respiratory cycle, which are recorded as VE and FCO2 respectively.

[0060] The sensor can directly obtain the exhaled volume data and carbon dioxide concentration data.

[0061] Step 2: Draw a volumetric capnography diagram based on VE and FCO2, as shown in Figure 3.

[0062] Draw a volumetric carbon dioxide diagram with VE as the horizontal axis and FCO2 as the vertical axis.

[0063] Step 3: Based on the slope, find the point on the volumetric capnography graph where the average slope on the right side begins to be less than 1 / 3 of the slope on the left side, and record it as C; the end point of the curve in the volumetric capnography graph is recorded as D. The coordinates of the two points are recorded as C(X C ,Y C )、D(X D ,Y D ).

[0064] Step 4: Select the horizontal coordinate at [k1*X C ,k2*X D ], and perform linear regression on the (VE, FCO2) data points within the interval to obtain the regression equation:

[0065] FCO2=k*VE+b (4)

[0066] like Figure 3 The straight line FG is shown in the figure. k1 is a value between 0.8 and 1.2, and k2 is a value between 0.6 and 1. k and b are the coefficients of the regression equation.

[0067] Step 5: Estimate physiological dead space:

[0068] Calculate the physiological dead space VD using formulas (5) and (6) phy :

[0069] VD phy =V T ×(F A CO2-F e CO2 / F A CO2 (5)

[0070] Where V T =X D , F A CO2=k3*Y C +k4*Y D , k3 and k4 are selected from values between 0.2 and 0.8 respectively;

[0071]

[0072] Step 6: Estimate anatomical dead space VD aw :

[0073]

[0074] Among them, FCO2 k5 =k*k5*V T +b, k5 selects a value between 0.5 and 1.

[0075] Step 7: Calculate alveolar dead space VD alv :

[0076] VD alv =VD phy -VD aw (8)

[0077] The present invention further provides a dead space calculation system, comprising:

[0078] Data acquisition module: used to obtain expiratory volume data and carbon dioxide concentration data of the same respiratory cycle;

[0079] A volumetric carbon dioxide graph drawing module, for drawing a volumetric carbon dioxide graph based on expiratory volume data and carbon dioxide concentration;

[0080] The key point selection module is used to find the point on the volumetric capnography curve where the average slope on the right side begins to be less than the set ratio N of the slope on the left side, starting from the origin on the volumetric capnography graph. The point is marked as C; the end point of the curve in the volumetric capnography graph is marked as D;

[0081] A regression analysis module is used to select data points whose horizontal coordinates are within the F and G intervals on the volumetric carbon dioxide graph and perform regression analysis to obtain a regression equation; and

[0082] The alveolar dead space calculation module is used to estimate physiological dead space and anatomical dead space based on the principle of carbon dioxide mass conservation and regression equation coefficients, and calculate alveolar dead space.

[0083] The present invention also provides a device for supporting dead space calculation, wherein the device comprises the above-mentioned dead space calculation system, and the device is a ventilator or an anesthesia machine.

[0084] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art 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 are intended to be encompassed by the claims of the present invention.

Claims

1. A dead space calculation method, comprising: Step 1: Obtain expiratory volume data and carbon dioxide concentration data for the same respiratory cycle; Step 2: Create a volumetric capnogram based on the expiratory volume data and carbon dioxide concentration; Step 3: Starting from the origin of the volumetric capnography, find the point on the curve where the average slope on the right side begins to be less than the set ratio N of the slope on the left side. This point is marked as C. The end point of the curve in the volumetric capnography is marked as D. Step 4: Select the data points whose abscissas are within the intervals F and G on the volumetric capnography and perform regression analysis to obtain the regression equation; Step 5: Estimate physiological and anatomical dead space based on the carbon dioxide mass conservation principle and regression equation coefficients, and calculate alveolar dead space; The formula for estimating physiological dead space is: VD phy =X D *(F A CO2-F e CO2) / F A CO2 Among them, VD phy Indicates physiological dead space; F A CO2 represents the carbon dioxide concentration in alveolar gas, F A CO2=k3*Y C +k4*Y D , Y C Indicates the vertical coordinate value of point C; Y D Indicates the vertical coordinate value of point D; k3 and k4 are selected from values between 0.2 and 0.8 respectively; F e CO2 represents the average concentration of carbon dioxide in exhaled gas: Wherein, FCO2 represents the carbon dioxide concentration obtained in step 1; represents expiratory flow; t represents time; The formula for estimating anatomical dead space is: Among them, VD aw Indicates anatomical dead space; FCO2 k5 =k*k5*X D +b; k5 is a value between 0.5 and 1; k and b represent the coefficients of the regression equation; X D Indicates the horizontal coordinate value of point D.

2. The dead space calculation method according to claim 1, characterized in that: The abscissa of the volumetric capnography is the expiratory volume, and the ordinate is the carbon dioxide concentration.

3. The dead space calculation method according to claim 1, characterized in that: The set ratio N is set to 1 / 3.

4. The dead space calculation method according to claim 1, characterized in that: The step 4 is specifically as follows: The F and G values are obtained according to the following formula: F=k1×X C G=k2×X D Among them, X C Indicates the horizontal coordinate value of point C; X D Indicates the horizontal coordinate value of point D; k1 is selected from a value between 0.8 and 1.2, and k2 is selected from a value between 0.6 and 1; The regression equation is expressed as: FCO2=k*VE+b Where FCO2 represents the carbon dioxide concentration; k and b represent the regression equation coefficients; VE represents the expiratory volume.

5. The dead space calculation method according to claim 1, characterized in that: The formula for calculating alveolar dead space is: VD alv =VD phy -VD aw Among them, VD alv Indicates alveolar dead space.

6. A dead space calculation system, implemented based on the method according to any one of claims 1 to 5, characterized in that: The system comprises: Data acquisition module: used to obtain expiratory volume data and carbon dioxide concentration data of the same respiratory cycle; A volumetric carbon dioxide graph drawing module, for drawing a volumetric carbon dioxide graph based on expiratory volume data and carbon dioxide concentration; The key point selection module is used to find the point on the volumetric capnography curve where the average slope on the right side begins to be less than the set ratio N of the slope on the left side, starting from the origin on the volumetric capnography graph. The point is marked as C; the end point of the curve in the volumetric capnography graph is marked as D; A regression analysis module is used to select data points whose horizontal coordinates are within the F and G intervals on the volumetric carbon dioxide graph and perform regression analysis to obtain a regression equation; and The alveolar dead space calculation module is used to estimate physiological dead space and anatomical dead space based on the principle of carbon dioxide mass conservation and regression equation coefficients, and calculate alveolar dead space.

7. A device for supporting dead space calculation, characterized in that: The device comprises the dead space calculation system according to claim 6.

8. The device for supporting dead space calculation according to claim 7, characterized in that: The device is a ventilator or an anesthesia machine.

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