Ventilator and Method for Determining at Least the Tissue-Related Resistance in the Respiratory Tract

Abstract

The invention relates to a ventilator (1) at least comprising: a gas supply device (2) and a gas discharge device (3), for supplying a first fluid flow (4) to a respiratory tract (5) of a patient and for discharging a second fluid flow (6) from the respiratory tract (5) back into the ventilator (1) or to a surrounding area (7); a pressure sensor (8) for sensing a pressure (9) in the respiratory tract (5); and a control device (10) for operating the ventilator (1); wherein the fluid flow (4, 6) can be set to a constant value at least during an inspiration process (11) and an expiration process (12). The invention further relates to a method for determining at least a tissue-related resistance of a patient by means of a ventilator (1).

Claims

1. Ventilator, at least comprising a gas supply device and a gas discharge device, for supplying a first fluid flow to an airway of a patient and for discharging a second fluid flow from the airway back into the ventilator or to an environment, a pressure sensor for measuring a pressure in the airway, and a control device for operating the ventilator; wherein the fluid flow is adjustable to a constant value at least during an inspiration process and an expiration process; wherein the control device is configured to carry out a method comprising at least the following steps: a) carrying out an inspiration process with a constant first fluid flow by means of the gas supply device, b) stopping the first fluid flow by means of the gas supply device at a first time point, and at the same time c) determining a first pressure difference between a first pressure present at the first time point of stopping and a second pressure occurring after a time interval by means of the pressure sensor; and d) carrying out an expiration process with a constant second fluid flow by means of the gas discharge device, e) stopping the second fluid flow by means of the gas discharge device at a second time point, and at the same time f) determining a second pressure difference between a third pressure present at the second time point of stopping and a fourth pressure occurring after a time interval by means of the pressure sensor; g) defining and providing a difference between the first pressure difference and the second pressure difference as a first index which is usable for determination of at least a tissue-related resistance of the patient.

2. Ventilator as claimed in claim 1, wherein, by carrying out steps d) to f), and when the third pressure corresponds to an end-expiratory pressure, a second index is defined and provided and an airway-related resistance of the patient is thus determinable.

3. Ventilator as claimed in claim 1, wherein it is defined for step g) that the tissue-related resistance is negligible in the end-expiratory state and maximal in the end-inspiratory state and, in between, increases linearly during the inspiration process and decreases linearly during the expiration process.

4. Ventilator as claimed in claim 3, wherein a regression analysis is performable by means of the control device at least to determine the tissue-related resistance.

5. Ventilator as claimed in claim 1, wherein the pressure sensor is arranged endotracheally.

6. Ventilator as claimed in claim 1, wherein a second index is also defined and provided by means of the control device in step g), and what are thus determinable are an airway-related resistance and, by conversion to the constant fluid flow, the pressure drop in the airway during the inspiration process and the expiration process and also an alveolar pressure or plot of an alveolar pressure.

7. Ventilator as claimed in claim 1, wherein at least the second pressure or the fourth pressure is mathematically determinable.

8. Ventilator as claimed in claim 1, wherein at least the first time point is defined in a temporal second half of the inspiration process or the second time point is defined in a temporal second half of the expiration process.

9. Ventilator as claimed in claim 1, wherein, at least in step b), the first fluid flow is stopped when a defined peak inspiratory pressure has been reached or, in step e), the second fluid flow is stopped when a defined end-expiratory pressure has been reached.

10. Ventilator as claimed in claim 9, wherein, in the case of the first pressure difference, a (total) resistance arises from a sum total of an airway-related resistance and a maximum of a tissue-related resistance.

11. Ventilator as claimed in claim 9, wherein, in the case of the second pressure difference, the (total) resistance arises from the airway-related resistance.

12. Method for determining at least a tissue-related resistance of a patient by means of a ventilator, wherein the ventilator at least a gas supply device and a gas discharge device, for supplying a first fluid flow to an airway of a patient and for discharging a second fluid flow from the airway back into the ventilator or to an environment, a pressure sensor for measuring a pressure in the airway, and a control device for operating the ventilator; wherein the fluid flow is adjustable to a constant value at least during an inspiration process and an expiration process; wherein the control device is suitably designed to carry out a method comprising at least the following steps: a) carrying out an inspiration process with a constant first fluid flow by means of the gas supply device, b) stopping the first fluid flow by means of the gas supply device at a first time point, and at the same time c) determining a first pressure difference between a first pressure present at the first time point of stopping and a second pressure occurring after a time interval by means of the pressure sensor; and d) carrying out an expiration process with a constant second fluid flow by means of the gas discharge device, e) stopping the second fluid flow by means of the gas discharge device at a second time point, and at the same time f) determining a second pressure difference between a third pressure present at the second time point of stopping and a fourth pressure occurring after a time interval by means of the pressure sensor; g) defining and providing a difference between the first pressure difference and the second pressure difference as a first index and determining at least a tissue-related resistance of the patient.

13. Method as claimed in claim 12, wherein, by carrying out steps d) to f), and when the third pressure corresponds to an end-expiratory pressure, a second index is defined and provided and an airway-related resistance of the patient is thus determined.

14. Method as claimed in claim 12, wherein at least steps a) to c) during an inspiration process or steps d) to f) during an expiration process are in each case carried out multiple times together with step g).

15. Method as claimed in claim 12, wherein it is defined for step g) that the tissue-related resistance is negligible in the end-expiratory state and maximal in the end-inspiratory state and, in between, increases linearly during the inspiration process and decreases linearly during the expiration process.

16. Control device for a ventilator that is equipped, configured or programmed to carry out the method as claimed in claim 12.

Description

[0131] The invention and the technical environment will be more particularly elucidated below with reference to the accompanying figures. It should be noted that the invention is not to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts elucidated in the figures and to combine them with other parts and findings from the present description. In particular, it should be noted that the figures and in particular the proportions depicted are only schematic. In the figures:

[0132] FIG. 1: shows a ventilator in operation;

[0133] FIG. 2: shows a first variant of the method;

[0134] FIG. 3: shows a second variant of the method; and

[0135] FIG. 4: shows a pressure-volume diagram.

[0136] FIG. 1 shows a ventilator 1 in operation. The ventilator 1 comprises a gas supply device 2 and a gas discharge device 3, for supplying an (inspiratory) first fluid flow 4 to an airway 5 of a patient and for discharging an (expiratory) second fluid flow 6 from the airway 5 back into the ventilator 1 or into the environment 7, a pressure sensor 8 for measuring a pressure 9 in the airway 5, and a control device 10 for operating the ventilator 1. The fluid flow 4, 6 is adjustable to a constant value during an inspiration process 11 and an expiration process 12. The control device 10 is suitably designed to operate the ventilator 1 and to carry out the measurement method.

[0137] The pressure sensor 8 is arranged endotracheally. The pressure sensor 8 is located at the distal end of a ventilation catheter, which is arranged in the airway 5 of the patient as part of the ventilator 1.

[0138] The ventilator 1 also comprises a visualization device 30 (e.g., a display) on which the (total) resistance, airway-related resistance and tissue-related resistance, but especially also the current alveolar pressure 9 over time 28 and/or the plot 24 of alveolar pressure 9 and volume 29 (as a pressure-volume curve) are depictable.

[0139] FIG. 2 shows a first variant of the method. Multiple ventilation cycles are depicted in FIG. 2. The upper part of FIG. 2 depicts a graph in which pressure 9 is plotted on the vertical axis. Time 28 is plotted on the horizontal axis. The lower part of FIG. 2 depicts a graph in which fluid flow 4, 6 is plotted on the vertical axis. Time 28 is plotted on the horizontal axis.

[0140] The first ventilation cycle (far left) depicts a normal FCV cycle having a stable fluid flow 4, 6 that is equal (in absolute value) during inspiration and expiration and thus having a 1:1 ratio of inspiration process 11 to expiration process 12. The second ventilation cycle (second from the left) and the third ventilation cycle (second from the right) are measurement cycles: in the case of the second ventilation cycle, the first fluid flow 4 stops when the set peak inspiratory pressure 25 (first pressure 15) is reached. The pressure 9 then falls in the time interval 16 to an end-inspiratory (plateau) pressure, the second pressure 17. The thus ascertainable first pressure difference 14 in relation to the inspiratory first fluid flow 4 gives the (total) resistance (i.e., the sum total of airway-related and tissue-related resistance). In the case of the third ventilation cycle, the expiratory second fluid flow 6 stops when the set end-expiratory pressure 26 (third pressure 20) is reached. The pressure 9 then rises to a slightly higher end-expiratory (plateau) pressure, the fourth pressure 21. The thus ascertainable second pressure difference 19 in relation to the expiratory second fluid flow 6 gives the airway-related resistance. The tissue-related resistance is the difference between the pressure differences 14, 19 in relation to the inspiratory and expiratory fluid flow 4, 6, respectively. The fourth ventilation cycle (far right) is again a normal FCV cycle having a slightly shortened inspiration process 11 owing to the preceding measurement and the thus slightly increased starting pressure.

[0141] In accordance with step a) of the method or measurement method, an inspiration process 11 with a constant first fluid flow 4 is carried out in the second ventilation cycle. In accordance with step b), the first fluid flow 4 is stopped at a first time point 13, and at the same time, in accordance with step c), a first pressure difference 14 is measured or determined between a first pressure 15 present at the first time point 13 of stopping and a second pressure 17 occurring after a time interval 16. An expiration process 12 is then carried out. In the subsequent third ventilation cycle, an inspiration process 11 is first carried out, followed by carrying out, in accordance with step d), an expiration process 12 with a constant second fluid flow 6. In accordance with step e), the second fluid flow 6 is stopped at a second time point 18, and at the same time, in accordance with step f), a second pressure difference 19 is measured or determined between a third pressure 20 present at the second time point 18 of stopping and a fourth pressure 21 occurring after a time interval 16. In accordance with step g), the difference between the first pressure difference 14 and the second pressure difference 19 is formed and at least a tissue-related resistance of the patient is determined.

[0142] FIG. 2 corresponds to the 1st calculation example, in which the first pressure difference 14 is measured in the end-inspiratory state 23 and the second pressure difference 19 is measured in the end-expiratory state 22. In the end-inspiratory state 23, the measured (total) resistance is thus composed of a maximum of the tissue-related resistance and of the (especially constant) airway-related resistance. In the end-expiratory state 22, the measured (total) resistance comprises especially only the airway-related resistance, since the tissue-related resistance is disregarded.

[0143] FIG. 3 shows a second variant of the method. Reference is made to the discussions relating to FIG. 2.

[0144] Multiple ventilation cycles are depicted in FIG. 3. The upper part of FIG. 3 depicts a graph in which pressure 9 is plotted on the vertical axis. Time 28 is plotted on the horizontal axis. The lower part of FIG. 3 depicts a graph in which fluid flow 4, 6 is plotted on the vertical axis. Time 28 is plotted on the horizontal axis.

[0145] The second ventilation cycle (second from the left) and the fourth ventilation cycle (far right) are normal FCV cycles having a stable fluid flow 4, 6 that is equal (in absolute value) during inspiration and expiration and thus having a 1:1 ratio of inspiration process 11 to expiration process 12. The first ventilation cycle (far left) and fourth ventilation cycle are measurement cycles: in the case of the first ventilation cycle, the (inspiratory) first fluid flow 4 stops temporarily at a first pressure 15 before the set peak inspiratory pressure 25 is reached. The pressure 9 then falls to an (intermediate) inspiratory (plateau) pressure, the second pressure 17. The first pressure difference 14 in relation to the inspiratory first fluid flow 4 gives the (total) resistance (i.e., the sum total of airway-related and tissue-related resistance) at this first time point 13. In the case of the third ventilation cycle (second from the right), the (expiratory) second fluid flow 6 stops temporarily at a third pressure 20 before the set end-expiratory pressure 26 is reached. The pressure 9 then rises to a slightly higher (intermediate) expiratory (plateau) pressure, the fourth pressure 21. The second pressure difference 19 in relation to the expiratory second fluid flow 6 gives the airway-related (total) resistance (i.e., the sum total of airway-related and tissue-related resistance) at this second time point 18. The tissue-related resistance via the pressure difference 14, 19 when the fluid flow 4, 6 is temporarily stopped during inspiration and expiration is the difference between the first pressure difference 14 and the second pressure difference 19 in relation to the inspiratory and expiratory fluid flow 4, 6, respectively.

[0146] Assuming an airway-related resistance that remains largely the same during the inspiration process 11 and expiration process 12 and a tissue-related resistance that gradually increases (approximately) linearly during the inspiration process 11 and gradually decreases (approximately) linearly again during the expiration process 12 (which appears permissible in the case of ventilation in the region of optimal or maximal compliance and under the prerequisite of slow and even changes in pressure 9 and volume 29 over time 28), it is possible to derive the (global) alveolar pressure 9 or plot 24 of alveolar pressure 9.

[0147] To this end, what must be ascertained, by converting the airway-related resistance to the respective (current) fluid flow 4, 6, is the pressure drop that is responsible for the gas flow from trachea to alveoli (i.e., from the windpipe in the direction of the alveoli) during inspiration or for the gas flow from alveoli to trachea (i.e., from the alveoli in the direction of the windpipe) during expiration.

[0148] A regression analysis, especially a linear regression analysis, is performable by means of the control device 10 at least to determine the tissue-related resistance. Use is made of a linear function to describe the change in tissue-related resistance between the end-inspiratory state 23 and the end-expiratory state 22.

[0149] The control device 10 is suitably designed especially to carry out the regression analysis.

[0150] At least the tissue-related resistance can thus be ascertained from a measurement of the pressure differences 14, 19 during the inspiration process 11 (and not only when the peak inspiratory pressure 25 has been reached) and/or the expiration process 12 (and not only when the end-expiratory pressure 26 has been reached). In particular, the position of the time points 13, 18 in relation to the position of the end-inspiratory state 23 and the end-expiratory state 22 is taken into account and the proportion of the tissue-related resistance present at this time point 13, 18 is determined, for example on the basis of a regression analysis. In this connection, reference is made to the 2nd calculation example mentioned above.

[0151] FIG. 4 shows a pressure-volume diagram. Volume 29 (in ml) is plotted on the vertical axis. Pressure 9 (in mbar) is plotted on the horizontal axis. Reference is made to the discussions relating to FIGS. 1 to 3.

[0152] FIG. 4 is based on a pressure-volume curve of an optimally ventilated patient. The (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9 can be estimated quite well just on the basis of the inspiratory (total) resistance. To this end, use is made of the second half 27 of the inspiratory pressure-volume curve and the second half 27 of the expiratory pressure-volume curve, since fluid flow conditions are (very) stable here in FCV and the effects (e.g., mass inertia effects and resultant shear effects) relevant in the first halves (especially at the start of the inspiration process 11 and expiration process 12 or when changing from inspiration process 11 to expiration process 12 and inspiration process 11 again) are hardly significant.

[0153] In this example, the inspiratory and expiratory fluid flow 4, 6 is 11 I/min (=0.183 I/s) in each case. The inspiratory (total) resistance is 5.7 mbar/I/s or 1.05 mbar/0.183 I/s (based on the fluid flow 4, 6). The width of the pressure-volume curve in the middle (along the dashed line intersecting the curve) is 2.1 mbar. The (maximal) inspiratory pressure drop from trachea to alveoli estimated at 1.05 mbar or the plot 24 thereof is drawn in as a dashed parallel line in relation to the straight second half 27 of the inspiratory pressure-volume curve (traced here in black), i.e., of the inspiration process 11. The expiratory pressure drop from alveoli to trachea estimated at the same level or the plot 24 thereof is accordingly drawn in as a solid parallel line in relation to the straight second half 27 of the expiratory pressure-volume curve (likewise traced here in black), i.e., of the expiration process 12.

[0154] Together, the dashed parallel line and the solid parallel line reproduce quite well the (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9 during this ventilation cycle.

[0155] It is noticeable that the two parallel lines together do not form a straight line, but are slightly tilted against each other. This represents (in greatly simplified form) the central region of an S-shapedly curved dynamic compliance curve. The inflection point 31 formed by the two parallel lines correctly indicates the inflection (change in the direction of curvature). In the method described here for estimating the (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9, it is inevitably ascertained somewhat too high, especially in early inspiration, since the higher (total) resistance measured end-inspiratorily is used to this end, and not the lower end-expiratory (mainly airway-related) resistance. However, this is only relevant if a measurable tissue-related resistance builds up during the inspiration process 11, which then decreases during the expiration process 12 and (almost) disappears again at the end of the expiration process 12.

[0156] In particular, the (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9 is thus calculated on the basis of the second half 27 of the inspiration process 11 and the second half 27 of the expiration process 12, since the first fluid flow 4 from the ventilator 1 to the airway 5 and the second fluid flow 6 from the airway 5 back into the ventilator 1 or into the environment 7 are then both very stable (in terms of absolute value) and mass inertia effects, which occur especially in inhomogeneous lungs at the start of the inspiration process 11 and expiration process 12 or when changing from the inspiration process 11 to the expiration process 12 and from the expiration process 12 to the inspiration process 11, and resultant shear effects are hardly relevant.

[0157] By means of the ventilator 1 or by means of the method for differentiated measurement of the airway-related and tissue-related resistance and for ascertainment of the (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9, it is possible to ascertain and optionally output the airway-related and tissue-related resistance on the basis of the described pressure measurements according to steps c) and f) and of the respective (known) inspiratory and expiratory fluid flow 4, 6.

[0158] From the airway-related resistance and the respective (known) inspiratory and expiratory fluid flow 4, 6, it is then possible to calculate the inspiratory and expiratory pressure drop (even during ventilation) and to optionally output it (e.g., on the display of the ventilator 1). Lastly, the (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9 can be calculated and optionally output (e.g., on the display of the ventilator 1).

[0159] By means of the ventilator 1 and/or the described method, it is possible to determine and differentiate the airway-related and tissue-related resistance even over sections of (optimal, i.e., maximal) compliance especially by means of temporary stopping of the fluid flow 4, 6 during the inspiration process 11 and expiration process 12 (see, for example, FIG. 3, first ventilation cycle (far left), and FIG. 3, third ventilation cycle (second from right)).

[0160] The combination of a measurement after the set peak inspiratory pressure 25 has been reached at the first time point 13 (see, for example, FIG. 2, second ventilation cycle (second from left), with the first pressure difference 14 occurring in the subsequent time interval 16) with an interim measurement before the set end-expiratory pressure 26 has been reached at the second time point 18 (see, for example, FIG. 3, third ventilation cycle (second from the right), with the second pressure difference 19 occurring in the subsequent time interval 16) makes it possible in particular to determine and differentiate the airway-related and tissue-related resistance even more precisely and to accordingly also calculate the (global) alveolar pressure 9 or the plot 24 of the alveolar pressure 9 even more precisely.

[0161] The same is also achieved by the combination of an interim measurement at the first time point 13 before the set peak inspiratory peak 25 has been reached (see FIG. 3, first ventilation cycle (far left), with the first pressure difference 14 occurring in the subsequent time interval 16) with a measurement at the second time point 18 after the set end-expiratory pressure 26 has been reached (see, for example, FIG. 2, third ventilation cycle (second from the right), with the second pressure difference 19 occurring in the subsequent time interval 16).

[0162] Especially in the case of interim measurements, i.e., during the inspiration process 11 and before the peak inspiratory pressure 25 has been reached or during the expiration process 12 and before the end-expiratory pressure 26 has been reached, it should be borne in mind that, in the case of FCV, fluid flow conditions are (very) stable or constant especially in the second half 27 of the inspiration process 11 and in the second half 27 of the expiration process 12 and measurement conditions are therefore then particularly advantageous.

LIST OF REFERENCE SIGNS

[0163] 1 Ventilator

[0164] 2 Gas supply device

[0165] 3 Gas discharge device

[0166] 4 First fluid flow

[0167] 5 Airway

[0168] 6 Second fluid flow

[0169] 7 Environment

[0170] 8 Pressure sensor

[0171] 9 Pressure

[0172] 10 Control device

[0173] 11 Inspiration process

[0174] 12 Expiration process

[0175] 13 First time point

[0176] 14 First pressure difference

[0177] 15 First pressure

[0178] 16 Time interval

[0179] 17 Second pressure

[0180] 18 Second time point

[0181] 19 Second pressure difference

[0182] 20 Third pressure

[0183] 21 Fourth pressure

[0184] 22 End-expiratory state

[0185] 23 End-inspiratory state

[0186] 24 Plot

[0187] 25 Peak inspiratory pressure

[0188] 26 End-expiratory pressure

[0189] 27 Second half

[0190] 28 Time

[0191] 29 Volume

[0192] 30 Visualization device

[0193] 31 Inflection point