Ventilator and Method for Determining at Least One Alveolar Pressure and/or a Profile of an Alveolar Pressure in a Respiratory Tract of a Patient

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) and for determining an alveolar pressure P.sub.alv (9) and/or a profile of an alveolar pressure P.sub.alv (9) of a respiratory tract (5) of a patient. The invention also relates to a method for determining at least one alveolar pressure P.sub.alv (9) and/or a profile of an alveolar pressure P.sub.alv (9) of a respiratory tract (5) of a patient with a ventilator (1).

Claims

1. A 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 sensing a pressure P.sub.trach in the airway, and a control device for operating the ventilator; wherein the control device is configured to carry out a method comprising at least the following steps: a) defining a pressure interval in which the patient is to be ventilated for a defined time interval; b) repeatedly and alternately carrying out one inspiration process at a time with the first fluid flow Q.sub.1 by means of the gas supply device and one expiration process at a time with the second fluid flow Q.sub.2 by means of the gas discharge device within the pressure interval, c) sensing the fluid flows and the pressure which changes during step b); d) carrying out a Fourier transform for the sensed values of the pressure and forming a first frequency spectrum for the pressure and carrying out a Fourier transform for the sensed values of the fluid flows and forming a second frequency spectrum for the fluid flows; e) calculating an impedance Z.sub.aw of the airway by dividing the first frequency spectrum by the second frequency spectrum, wherein the impedance comprises a real component Real(Z.sub.aw) and an imaginary component Im(Z.sub.aw); f) modeling at least the real component by a first mathematical model and ascertaining an alveolar pressure P.sub.alv or a plot of an alveolar pressure P.sub.alv.

2. The ventilator as claimed in claim 1, wherein the first model comprises the equation Real(Z.sub.aw)=R.sub.aw+G/ω.sup.α, with R.sub.aw: airway-related resistance; G/ω.sup.α: tissue-related resistance; with G as a constant, ω as the angular frequency and a as a constant; wherein the real component describes the resistance, i.e., the resistances to be overcome during inspiration or expiration.

3. The ventilator as claimed in claim 2, wherein the alveolar pressure P.sub.alv is ascertained from the equation P.sub.alv=P.sub.trach−Q.sub.i×R.sub.aw; with Q.sub.i: the current fluid flow.

4. The ventilator as claimed in claim 2, wherein the imaginary component is also modelable in step f) by a second mathematical model, wherein the second model comprises the equation $Z_{aw} = R_{aw} + k \times j \times ω \times I_{aw} + \frac{G - j \times H}{ω^{α}}; where Im (Z_{aw}) = j \times (k \times ω \times I_{aw} + \frac{- H}{ω^{α}};$ with k: a constant; I.sub.aw: inertia of the airway; −H/ω.sup.α: resilience of the airway with H as a constant; wherein the imaginary component describes the airway reactance X.sub.a, wherein a compliance of the airway is described by $C = - \frac{1}{ω \times X_{a}} .$

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

6. The ventilator as claimed in claim 1, wherein at least steps a) to c) are carried out in different pressure intervals.

7. The ventilator as claimed in claim 1, wherein the pressure interval encompasses at most 10 mbar.

8. The ventilator as claimed in claim 1, wherein the fluid volume supplied or discharged within the pressure interval is at most 10% of a maximum volume of the airway.

9. The ventilator as claimed in claim 1, wherein at least five inspiration processes and expiration processes are carried out in step b).

10. The ventilator as claimed in claim 1, wherein values for the pressure and the fluid flow are sensed at the same time points in each case in step c) and the time points have time intervals of at most 0.1 seconds.

11. Ventilator as claimed in claim 1, wherein the ventilator is suitably designed for sole ventilation of the patient; wherein normoventilation of the patient is performable via the control device at least before step a) or after step c).

12. The ventilator as claimed in claim 1, wherein the gas discharge device comprises a suction device, so that in step b) the second fluid flow is at least partially generated by suction in at least an expiration process.

13. The ventilator as claimed in claim 1, wherein the fluid flow is adjustable to a constant value at least during an inspiration process and an expiration process; wherein the first fluid flow Q.sub.1 and the second fluid flow Q.sub.2 are both constant during step b).

14. The ventilator as claimed in claim 13, wherein the fluid flows are of equal size.

15. A method for determining at least an alveolar pressure P.sub.alv or a plot of an alveolar pressure P.sub.alv of a patient by means of a ventilator, wherein the ventilator at least comprises 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 sensing a pressure P.sub.trach in the airway, and a control device for operating the ventilator; wherein the control device is configured to carry out the method comprising at least the following steps: a) defining a pressure interval in which the patient is to be ventilated for a defined time interval; b) repeatedly and alternately carrying out one inspiration process at a time with a first fluid flow Q.sub.1 by means of the gas supply device and one expiration process at a time with a second fluid flow Q.sub.2 by means of the gas discharge device within the pressure interval, c) sensing the fluid flows and the pressure which changes during step b); d) carrying out a Fourier transform for the sensed values of the pressure and forming a first frequency spectrum for the pressure and carrying out a Fourier transform for the sensed values of the fluid flows and forming a second frequency spectrum for the fluid flows; e) calculating an impedance Z.sub.aw of the airway by dividing the first frequency spectrum by the second frequency spectrum, wherein the impedance comprises a real component Real(Z.sub.aw) and an imaginary component Im(Z.sub.aw); f) modeling at least the real component by a first mathematical model and ascertaining an alveolar pressure P.sub.alv or a plot of an alveolar pressure P.sub.alv.

16. The method as claimed in claim 15, wherein the ventilator is suitably designed for sole ventilation of the patient; wherein normoventilation of the patient is carried out via the control device at least before step a).

17. The method as claimed in claim 15, wherein the gas discharge device comprises a suction device, so that in step b) the second fluid flow is at least partially generated by suction in at least an expiration process.

18. The method as claimed in claim 15, wherein the fluid flow has been adjusted to a constant value at least during an inspiration process and an expiration process; wherein the first fluid flow Q.sub.1 and the second fluid flow Q.sub.2 are both constant during step b).

19. A control device for a ventilator that is equipped, configured or programmed to carry out the method as claimed in claim 15.

Description

[0122] 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:

[0123] FIG. 1: shows a ventilator in operation;

[0124] FIG. 2: shows a diagram containing a plot of a pressure during a ventilation process;

[0125] FIG. 3: shows a diagram containing a plot of a fluid flow during the ventilation process according to FIG. 2;

[0126] FIG. 4: shows a diagram containing frequency spectra of the ventilation process according to FIGS. 2 and 3;

[0127] FIG. 5: shows a diagram containing the components of the complex impedance of the frequency spectra according to FIG. 4; and

[0128] FIG. 6: shows a diagram containing the plot of a pressure while carrying out the method.

[0129] 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 sensing a pressure 9 in the airway 5, and a control device 10 for operating the ventilator 1. The fluid flow 4, 6 can be adjusted to a constant value during an inspiration process 13 and an expiration process 14. The control device 10 is suitably designed to operate the ventilator 1 and to carry out the measurement method.

[0130] 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.

[0131] The ventilator 1 also comprises a visualization device 24 (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 22 and/or the plot of alveolar pressure 9 and volume 23 (as a pressure-volume curve) are depictable.

[0132] FIG. 2 shows a diagram containing a plot of a pressure 9 during a ventilation process. FIG. 3 shows a diagram containing a plot of a fluid flow 4, 6 during the ventilation process according to FIG. 2. FIGS. 2 and 3 will be described together in what follows. Reference is made to the discussions relating to FIG. 1.

[0133] Pressure 9 in [mbar] is plotted on the vertical axis of the diagram according to FIG. 2. Fluid flows 4, 6 in [liters/second] are plotted on the vertical axis of the diagram according to FIG. 3. Time 22 is plotted on the horizontal axes of the diagrams.

[0134] According to step a) of the method, what takes place is defining a pressure interval 11 in which the patient is to be ventilated for a defined time interval 12 (not defined here). According to step b), what takes place is repeatedly and alternately carrying out one inspiration process 13 at a time with a first fluid flow Q.sub.1 4 by means of the gas supply device 2 and one expiration process 14 at a time with a second fluid flow Q.sub.2 6 by means of the gas discharge device 3 within the pressure interval 11. According to step c), what takes place is sensing the fluid flows 4, 6 and the pressure 9 which changes during step b).

[0135] Ventilation is done continuously (i.e., without any relevant pauses) with fluid flows 4, 6 which are stable or constant and are equal in absolute value during inspiration and expiration (and thus an I:E ratio of typically 1:1), preferably in the region of optimal or maximal compliance. The fluid flow 4, 6 is just high enough to achieve normoventilation or the desired degree of carbon dioxide elimination or exhalation in the patient.

[0136] It can be seen that there is a ventilation frequency of approx. 0.167 Hz, i.e., five ventilation processes are carried out in 30 seconds.

[0137] FIG. 4 shows a diagram containing frequency spectra 15, 16 of the ventilation process according to FIGS. 2 and 3. FIG. 5 shows a diagram containing the components 17, 18 of the complex impedance of the frequency spectra 15, 16 according to FIG. 4. Reference is made to the discussions relating to FIGS. 1 to 3.

[0138] According to step d), what takes place is carrying out a Fourier transform for the sensed values of the pressure 9 and forming a first frequency spectrum 15 for the pressure 9 and carrying out a Fourier transform for the sensed values of the fluid flows 4, 6 and forming a second frequency spectrum 16 for the fluid flows 4, 6. It can be seen that the frequency spectra 15, 16 have clearly recognizable local maxima, for example at the ventilation frequency 19, i.e., at 0.167 Hz, and at multiples of the ventilation frequency 19, i.e., at 3×ventilation frequency 19, at 5×ventilation frequency, at 7×ventilation frequency 19, at 9×ventilation frequency 19, etc.

[0139] According to step e), what takes place is calculating an impedance Z.sub.aw of the airway 5 by dividing the first frequency spectrum 15 by the second frequency spectrum 16, wherein the impedance comprises a real component Real(Z.sub.aw) 17 and an imaginary component Im(Z.sub.aw) 18.

[0140] The impedance is respectively ascertained for the frequencies 19 that generate the local maxima. FIG. 5 depicts the values of the individual components 17, 18 for the respective frequency 19. The thus ascertained individual values of the components 17, 18 of the impedance, or points in the diagram, can then be approximated or modeled according to step f) by a curve, i.e., by a first mathematical model.

[0141] According to step f), what thus takes place is modeling at least the real component 17 by a first mathematical model and ascertaining an alveolar pressure 9 or a plot of an alveolar pressure 9.

[0142] In particular, the first model comprises the equation Real(Z.sub.aw)=R.sub.aw+G/ω.sup.α, with

[0143] R.sub.aw: airway-related resistance;

[0144] G/ω.sup.α: tissue-related resistance; with G as a constant, w as the angular frequency (i.e., 2×π×frequency of ventilation) and a as a constant; wherein the real component 17 describes the resistance, i.e., the resistances of the airway 5 to be overcome during inspiration or expiration.

[0145] The alveolar pressure 9 P.sub.aiv or the plot thereof is ascertained from the equation P.sub.alv=P.sub.trach−Q.sub.i×R.sub.aw, with

[0146] Q.sub.i: the current fluid flow 4, 6 during step b) (see FIG. 3).

[0147] The measured or determined pressure 9 P.sub.trach is the pressure 9 in the airway 5 that changes over time 22 (see FIG. 2). The plot of the pressure 9 P.sub.alv over time 22 thus arises as a function of the pressure 9 P.sub.trach that changes over time 22.

[0148] In particular, the imaginary component 18 (see FIG. 5) is also modelable in step f) by a second mathematical model, wherein the second model comprises the equation

[00003] $Z_{aw} = R_{aw} + k \times j \times ω \times I_{aw} + \frac{G - j \times H}{ω^{α}}; where Im (Z_{aw}) = j \times (k \times ω \times I_{aw} + \frac{- H}{ω^{α}};$

with

[0149] k: a constant;

[0150] I.sub.aw: inertia of the airway 5;

[0151] −H/ω.sup.α: resilience of the airway 5 with H as a constant;

[0152] wherein the imaginary component 18 describes the airway reactance X.sub.a, wherein a compliance of the airway 5 is described by

[00004] $C = - \frac{1}{ω \times X_{a}} .$

[0153] The imaginary component 18 should in particular not be ascertained for the determination of the alveolar pressure 9 or the plot thereof. However, other parameters that may be considered relevant can be derived from the imaginary component 18, for example airway reactance and compliance of the airway 5.

[0154] FIG. 6 shows a diagram containing the plot of a pressure 9 while carrying out the method. Pressure 9 in [mbar] is plotted on the vertical axis of the diagram. Time 22 is plotted on the horizontal axis. Reference is made to the discussions relating to FIGS. 1 to 5.

[0155] It is preferred that the pressure interval 11 is reduced at least for a time interval 12, the method being carried out within said time interval 12.

[0156] Steps a) to c) are carried out repeatedly here, i.e., multiple different pressure intervals 11 are defined one after the other and values for pressure 9 and fluid flows 4, 6 are then sensed in said pressure intervals 11 according to step c). Said values from different pressure intervals 11 are then further processed in steps d) to f).

[0157] In each step b), five inspiration processes 13 and expiration processes 14 (cf. FIG. 2) are carried out.

[0158] Each pressure interval 11 is associated with an average pressure 9, with the pressure interval 11 being limited by a pressure 9 PEEP (positive end-expiratory pressure) in an end-expiratory state 20 and by a pressure 9 PIP (peak inspiratory pressure) in an end-inspiratory state 21.

[0159] The pressure interval 11 encompasses, for example, at most 5 mbar, with only a small volume 23 of the fluid being supplied or discharged with each ventilation process. For example, the volume 23 of the fluid supplied and/or discharged within the pressure interval 11 and within one ventilation process is at most 10% of a maximum volume of the airway 5.

[0160] Here, five pressure intervals 11 are defined one after the other, the patient being ventilated with the ventilator 1 and the different pressure intervals being applied to the airway 5 in direct succession.

LIST OF REFERENCE SIGNS

[0161] 1 Ventilator [0162] 2 Gas supply device [0163] 3 Gas discharge device [0164] 4 First fluid flow [0165] 5 Airway [0166] 6 Second fluid flow [0167] 7 Environment [0168] 8 Pressure sensor [0169] 9 Pressure [0170] 10 Control device [0171] 11 Pressure interval [0172] 12 Time interval [0173] 13 Inspiration process [0174] 14 Expiration process [0175] 15 First frequency spectrum [0176] 16 Second frequency spectrum [0177] 17 Real component [0178] 18 Imaginary component [0179] 19 Frequency [0180] 20 End-expiratory state [0181] 21 End-inspiratory state [0182] 22 Time [0183] 23 Volume [0184] 24 Visualization device

Ventilator and Method for Determining at Least One Alveolar Pressure and/or a Profile of an Alveolar Pressure in a Respiratory Tract of a Patient

Inventors

Cpc classification

Classification Explorer

A61M2205/3344

HUMAN NECESSITIES

Classification Explorer

A61M16/024

HUMAN NECESSITIES

Classification Explorer

A61M16/0045

HUMAN NECESSITIES

Classification Explorer

A61M2230/42

HUMAN NECESSITIES

Classification Explorer

A61M16/026

HUMAN NECESSITIES

Classification Explorer

A61M2016/0027

HUMAN NECESSITIES

Classification Explorer

A61M2230/46

HUMAN NECESSITIES

International classification

Classification Explorer

A61M16/00

HUMAN NECESSITIES

Abstract

Claims

Description