A method, system, and apparatus for measuring dead space.

Abstract

This invention provides a method, system, and device for measuring dead space. The method includes: acquiring expiratory volume data and carbon dioxide concentration data for the same respiratory cycle; plotting a volumetric carbon dioxide graph; finding points on the curve where the slope begins to be less than a set value N, starting from the origin, and the endpoint; integrating each point on the volumetric carbon dioxide graph to obtain a carbon dioxide output-volume curve; selecting data points on the carbon dioxide output-volume curve whose abscissa falls within the F and G intervals, performing regression analysis to obtain a regression equation; estimating the physiological dead space and anatomical dead space based on the principle of carbon dioxide mass conservation and the coefficients of the regression equation, and calculating the alveolar dead space. The advantages of this invention are: the dead space measurement method is simple; dead space can be measured in real time during device use; it is not affected by the user's fluctuating breathing; and accurate dead space values ​​can be obtained through continuous measurement.

Description

Technical Field

[0001] This invention belongs to the field of respiratory assistive devices, specifically relating to a method, system, and device for measuring dead space. Background Technology

[0002] Dead space, also known as ineffective space, refers to the portion of the lung that is ventilated but not involved in gas exchange. Physiological dead space consists of both anatomical dead space and alveolar dead space. Accurately monitoring the amount of dead space in a person is of significant clinical importance, but it is also a very difficult task.

[0003] Fowler proposed a method for calculating dead space, instructing subjects to inhale a deep breath of pure oxygen to total lung capacity (TLC) from their residual volume (RV) position, then exhale calmly back to their RV, and measuring the change in nitrogen concentration during exhalation. Figure 1 As shown in the diagram, during exhalation, the first gas expelled is pure oxygen, the pure oxygen remaining in the dead space at the end of inspiration. At this point, the nitrogen concentration is 0, and this stage is called stage I. Next, a mixture of nitrogen-containing alveolar gas and dead space gas is expelled, with the nitrogen concentration increasing; this stage is called stage II. When the nitrogen concentration reaches a plateau, it indicates that the expelled gas is purely alveolar gas; this stage is called stage III. In the diagram, VD represents the size of the anatomical dead space.

[0004] Existing methods for measuring dead space are complex to operate and cannot be implemented during mechanical ventilation. Furthermore, each breath is not entirely consistent, and the gas distribution within the lungs is extremely uneven; different exhalation volumes may represent entirely different areas, making it difficult to calculate dead space accurately. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies in measuring dead space, which are complex and cannot be accurately measured.

[0006] To achieve the above objectives, the present invention proposes a method for determining dead space, the method comprising:

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

[0008] Step 2: Plot a volumetric carbon dioxide graph based on expiratory volume data and carbon dioxide concentration;

[0009] Step 3: On the volumetric carbon dioxide graph, starting from the origin, find the curve where the slope begins to be less than the set value. N The point is denoted as C The endpoint of the curve in the volumetric carbon dioxide graph is denoted as... D ;

[0010] Step 4: Integrate the points on the volumetric carbon dioxide graph point by point to determine the carbon dioxide output corresponding to each expiratory volume in the expiratory phase, and obtain the carbon dioxide output-volume curve.

[0011] Step 5: Select the x-axis of the carbon dioxide emission-volume curve at which... F , G For data points within the interval, regression analysis is performed to obtain the regression equation;

[0012] Step 6: Estimate the physiological dead space and anatomical dead space based on the principle of carbon dioxide mass conservation and the coefficients of the regression equation, and calculate the alveolar dead space.

[0013] As an improvement to the above method, the volumetric carbon dioxide graph has expiratory volume on the horizontal axis and carbon dioxide concentration on the vertical axis; the carbon dioxide excretion-volume curve has expiratory volume on the horizontal axis and carbon dioxide excretion on the vertical axis.

[0014] As an improvement to the above method, the set value N The value is 10.

[0015] As an improvement to the above method, step 5 specifically includes:

[0016] According to the following formula, we obtain... F , G The possible values ​​are:

[0017]

[0018]

[0019] in, express C x-coordinate of the point; express D x-coordinate of the point; c1 Select a value between 0.8 and 1.2. c2 Select a value between 0.6 and 1;

[0020] The regression equation is expressed as:

[0021]

[0022] in, Indicates carbon dioxide emissions; , , Represents the coefficients of the regression equation; It indicates expiratory volume.

[0023] As an improvement to the above method, the formula for estimating physiological dead space is:

[0024]

[0025] in, Indicates physiological dead space;

[0026] This indicates the carbon dioxide concentration in the alveolar gases. F A CO2 = c3 * Y D ; Y D express D The ordinate value of the point; c3 Select a value between 0.5 and 1.2;

[0027] This indicates the average concentration of carbon dioxide in exhaled breath:

[0028]

[0029] in, This indicates the carbon dioxide concentration obtained in step 1; Indicates expiratory flow rate; t Indicates time.

[0030] As an improvement to the above method, the formula for estimating anatomical dead space is:

[0031]

[0032] in, Indicates the anatomical dead space. .

[0033] As an improvement to the above method, the formula for calculating alveolar dead space is:

[0034] VD alv = VD phy - VD aw

[0035] in, VD alv This indicates the dead space of the alveoli.

[0036] The present invention also provides a dead space measurement system, the system comprising:

[0037] The data acquisition module is used to acquire expiratory volume data and carbon dioxide concentration data for the same respiratory cycle;

[0038] The volumetric carbon dioxide graph plotting module is used to plot volumetric carbon dioxide graphs based on expiratory volume data and carbon dioxide concentration.

[0039] The key segment selection module is used to find the curve with a slope less than the origin on the volumetric carbon dioxide plot. N The point is denoted as C The endpoint of the curve in the volumetric carbon dioxide graph is denoted as... D ;

[0040] The carbon dioxide output-volume graph plotting module is used to integrate the points on the volumetric carbon dioxide graph point by point to determine the carbon dioxide output corresponding to each expiratory volume in the expiratory phase, and to obtain the carbon dioxide output-volume curve.

[0041] The regression analysis module is used to select the x-axis position on the carbon dioxide emission-volume curve. F , G For data points within the interval, regression analysis is performed to obtain the regression equation;

[0042] The alveolar dead space calculation module is used to estimate physiological and anatomical dead spaces based on the principle of carbon dioxide mass conservation and regression equation coefficients, and to calculate alveolar dead spaces.

[0043] The present invention also provides an apparatus for supporting dead space measurement, comprising the dead space measurement system described above.

[0044] As an improvement to the above-mentioned device, the device is a ventilator or anesthesia machine.

[0045] Compared with the prior art, the advantages of the present invention are:

[0046] 1. The dead space measurement method implemented by this invention is simple and can measure the dead space in real time during equipment use;

[0047] 2. The dead space measurement method of the present invention is not affected by the user's inconsistent breathing. Accurate dead space values ​​can be obtained by continuously measuring the dead space. Attached Figure Description

[0048] Figure 1 The diagram shown is a schematic of the Fowler dead space measurement method.

[0049] Figure 2 The diagram shown is a flowchart of the method for determining dead space according to the present invention.

[0050] Figure 3 The diagram shown is a volumetric carbon dioxide graph;

[0051] Figure 4 The figure shown is a graph of carbon dioxide emissions versus volume. Detailed Implementation

[0052] This invention proposes a method, system, and device for measuring dead space based on carbon dioxide output-volume curve. This method can monitor the physiological dead space, anatomical dead space, and alveolar dead space of users during the use of devices such as ventilators and anesthesia machines.

[0053] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0054] Based on the principle of CO2 mass conservation, the formula for calculating dead space is as follows:

[0055] (1)

[0056] (2)

[0057] In the formula V T Indicates tidal volume during exhalation. V A Indicates the effective alveolar gas volume exhaled. V D = V T - V A This is the dead space. FeCO2 The average concentration of CO2 in exhaled air is calculated using the following formula. F A CO2 This indicates the CO2 concentration in the alveolar gas.

[0058] (3)

[0059] In the formula FCO2 CO2 concentration as a function of expiratory volume (or time) (monitored by an oral CO2 sensor), This represents the expiratory flow rate (monitored by a flow sensor). The combined readings from the oral CO2 sensor and the flow sensor can be easily calculated. FeCO2 .

[0060] Currently, the common practice is to use a Douglas bag to collect the amount of gas expelled and measure the concentration of CO2 mixed inside as the basis for measurement. FeCO2 Because it is difficult to measure alveolar CO2 concentration in actual operation. F A CO2 Therefore, the maximum partial pressure of CO2 per exhalation is used instead.

[0061] The dead space measurement method provided by this invention has the following steps:

[0062] Step 1: Obtain expiratory volume data and carbon dioxide concentration data for the same respiratory cycle, and record them as follows: VE and FCO2 .

[0063] Sensors can be used to directly obtain data on expiratory volume and carbon dioxide concentration.

[0064] Step 2: Based on VE and FCO2 Plot a volumetric carbon dioxide diagram, such as... Figure 3 As shown.

[0065] by VE The x-axis is... FCO2 Use the vertical axis to plot the volumetric carbon dioxide graph.

[0066] Step 3: Based on the slope, find the point on the volumetric carbon dioxide chart where the slope begins to be less than 10, starting from the origin, and denot it as... C The endpoint of the curve in the volumetric carbon dioxide graph is denoted as... D . C , D The coordinates of the two points are denoted as follows: C ( X C , Y C ), D ( X D , Y D ).

[0067] Step 4: Integrate point by point on the volumetric carbon dioxide graph according to formula (4) to determine the expiratory volume for each phase. vt Corresponding CO2 emissions This leads to the carbon dioxide emission-volume curve, such as... Figure 4 As shown, the horizontal axis represents expiratory volume, and the vertical axis represents carbon dioxide excretion.

[0068] (4)

[0069] Step 5: Select the x-coordinate located at [ c1 * X C , c2 * X D Within the interval ( VE , VCO2 Data points, i.e. Figure 3 middle FG The regression equation was obtained by performing regression analysis on the segment curve:

[0070] (5)

[0071] in,c1 Select a value between 0.8 and 1.2. c2 Choose a value between 0.6 and 1. , , These are the coefficients of the regression equation.

[0072] Step 6: Estimate the physiological dead space: Calculate the physiological dead space using formulas (6) and (7). VD phy ,in, V T = X D , F A CO2 = c3 * Y D , c3 Choose a value between 0.5 and 1.2.

[0073] (6)

[0074] (7)

[0075] Step 7: Estimate the anatomical dead space: .

[0076] Step 8: Calculate alveolar dead space: VD alv = VD phy - VD aw .

[0077] The present invention also provides a dead space measurement system, the system comprising:

[0078] The data acquisition module is used to acquire expiratory volume data and carbon dioxide concentration data for the same respiratory cycle;

[0079] The volumetric carbon dioxide graph plotting module is used to plot volumetric carbon dioxide graphs based on expiratory volume data and carbon dioxide concentration.

[0080] The key segment selection module is used to find the curve with a slope less than the origin on the volumetric carbon dioxide plot. N The point is denoted as C The endpoint of the curve in the volumetric carbon dioxide graph is denoted as... D ;

[0081] The carbon dioxide output-volume graph plotting module is used to integrate the points on the volumetric carbon dioxide graph point by point to determine the carbon dioxide output corresponding to each expiratory volume in the expiratory phase, and to obtain the carbon dioxide output-volume curve.

[0082] The regression analysis module is used to select the x-axis position on the carbon dioxide emission-volume curve. F , G For data points within the interval, regression analysis is performed to obtain the regression equation;

[0083] The alveolar dead space calculation module is used to estimate physiological and anatomical dead spaces based on the principle of carbon dioxide mass conservation and regression equation coefficients, and to calculate alveolar dead spaces.

[0084] The present invention also provides an apparatus for supporting dead space measurement, the apparatus comprising the dead space measurement system described above.

[0085] The device that supports dead space measurement is a ventilator or anesthesia machine.

[0086] 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 determining dead space, the method comprising: Step 1: Obtain expiratory volume data and carbon dioxide concentration data for the same respiratory cycle; Step 2: Plot a volumetric carbon dioxide graph based on expiratory volume data and carbon dioxide concentration; Step 3: On the volumetric carbon dioxide graph, starting from the origin, find the curve where the slope begins to be less than the set value. N The point is denoted as C The endpoint of the curve in the volumetric carbon dioxide graph is denoted as... D ; Step 4: Integrate the points on the volumetric carbon dioxide graph point by point to determine the carbon dioxide output corresponding to each expiratory volume in the expiratory phase, and obtain the carbon dioxide output-volume curve. Step 5: Select the x-axis of the carbon dioxide emission-volume curve at which... F , G For data points within the interval, regression analysis is performed to obtain the regression equation; Step 6: Estimate the physiological dead space and anatomical dead space based on the principle of carbon dioxide conservation and the coefficients of the regression equation, and calculate the alveolar dead space; Step 5 specifically involves: According to the following formula, we obtain... F , G The value can be: ； ； in, express C x-coordinate of the point; express D x-coordinate of the point; c1 Select a value between 0.8 and 1.

2. c2 Select a value between 0.6 and 1; The regression equation is expressed as: ； in, Indicates carbon dioxide emissions; , , Represents the coefficients of the regression equation; Indicates expiratory volume; The formula for estimating physiological dead space is: ； in, Indicates physiological dead space; This indicates the carbon dioxide concentration in the alveolar gases. F A CO2 = c3 * Y D ; Y D express D The ordinate value of the point; c3 Select a value between 0.5 and 1.2; This indicates the average concentration of carbon dioxide in exhaled breath: ； in, This indicates the carbon dioxide concentration obtained in step 1; Indicates expiratory flow rate; t Indicates time; The formula for estimating anatomical dead space is: ； in, Indicates the anatomical dead space. ; The formula for calculating alveolar dead space is: VD alv = VD phy - VD aw ； in, VD alv This indicates the dead space of the alveoli.

2. The dead space measurement method according to claim 1, characterized in that, The volumetric carbon dioxide graph has expiratory volume on the horizontal axis and carbon dioxide concentration on the vertical axis; the carbon dioxide excretion-volume curve has expiratory volume on the horizontal axis and carbon dioxide excretion on the vertical axis.

3. The method for determining dead space according to claim 1, characterized in that, The set value N The value is 10.

4. A dead space measurement system, implemented based on the method described in any one of claims 1-3, characterized in that, The system includes: The data acquisition module is used to acquire expiratory volume data and carbon dioxide concentration data for the same respiratory cycle; The volumetric carbon dioxide graph plotting module is used to plot volumetric carbon dioxide graphs based on expiratory volume data and carbon dioxide concentration. The key segment selection module is used to find the curve with a slope less than the origin on the volumetric carbon dioxide plot. N The point is denoted as C The endpoint of the curve in the volumetric carbon dioxide graph is denoted as... D ; The carbon dioxide output-volume graph plotting module is used to integrate the points on the volumetric carbon dioxide graph point by point to determine the carbon dioxide output corresponding to each expiratory volume in the expiratory phase, and to obtain the carbon dioxide output-volume curve. The regression analysis module is used to select the x-axis position on the carbon dioxide emission-volume curve. F , G For data points within the interval, regression analysis is performed to obtain the regression equation; The alveolar dead space calculation module is used to estimate physiological and anatomical dead spaces based on the principle of carbon dioxide mass conservation and regression equation coefficients, and to calculate alveolar dead spaces.

5. A device for supporting dead space measurement, characterized in that, The device comprises the dead space measurement system of claim 4.

6. The device for supporting dead space measurement according to claim 5, characterized in that, The device is a ventilator or anesthesia machine.

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