Devices and methods for ventilating a patient

Abstract

The present invention relates to a plurality of ventilation devices, to ventilation devices having visualization apparatuses, and to methods for operating the ventilation devices. The intent is to minimize the energy input into the at least one airway of a patient as a result of the ventilation.

Claims

1. Ventilation device for ventilating a patient, comprising: at least a fluid supply unit configured for supplying a fluid into at least one airway of a patient; a fluid discharge unit that is configured for discharging fluid from the at least one airway; a control device which, during a ventilation process for the at least one airway, during at least a one-time supply of the fluid into the at least one airway and at least a one-time discharge of the fluid from the at least one airway by operating the ventilation device, is configured to set a profile of a pressure Pin the airway and profile of a volume V of the fluid supplied to the airway and discharged from the airway according to V=f.sub.zp(P) and V=f.sub.AP(P), or according to P=f.sub.2v(V) and P=f.sub.av(V), wherein the ventilation process takes place within a pressure interval and within a volume interval; wherein the ventilation process is configured to be set by the control device such that a) over at least 60% of the pressure interval, a ratio of an absolute value of a measure of a change in a first volume that is present at a pressure P.sub.0 while supplying the fluid, i.e. df.sub.AF/d(P)(P.sub.0) and an absolute value of a measure of the change in a second volume that is present at the same pressure P.sub.0 while discharging the fluid, i.e., df.sub.ZP/d(P)(P.sub.0) or b) over at least 60% of the volume interval, a ratio of an absolute value of a measure of the change in a first pressure that is present at a volume V0 while supplying the fluid, i.e., df.sub.AV/d(V)(V.sub.0) and an absolute value of a measure of the change in a second pressure that is present at the same volume V0 while discharging the fluid, i.e. df.sub.ZV/d(V)(V.sub.o), has a value of at least 0.5 and at most 2.0.

2. Ventilation device according to claim 1, wherein the control device is configured for determining the profile of the pressure P in the airway and of the profile of the volume V of the fluid that is supplied to the airway and discharged from the airway for compliance of the patient according to one of V=fcp(P) or P=fcv(V), wherein the ventilation process is configured to be set by the control device such that a) over at least 60% of the pressure interval, a ratio of each of df.sub.AP/d(P) (P.sub.0), df.sub.ZP/d(P) (P.sub.0) and an absolute value of a measure of the change in the first volume of the compliance that is present at a pressure P.sub.0, i.e., df.sub.CP/d(P) (P.sub.0), or b) over at least 60% of the volume interval, a ratio of each of df.sub.AV/d(V) (V.sub.0), df.sub.ZV/d(V) (V.sub.0) and an absolute value of a measure of the change in the first pressure of the compliance that is present at a volume V.sub.0, i.e., df.sub.CV/d(V) (V.sub.0), has a value of at least 0.5 and at most 2.0.

3. Ventilation device according to claim 1, wherein the ventilation process is configured to be set by the control device such that over at least 60% of the pressure interval or 60% of the volume interval, the ratio has a value of at least 0.67 and at most 1.5.

4. Ventilation device according to claim 1, wherein the ventilation process is configured to be set by the control device such that over at least 60% of the pressure interval or 60% of the volume interval, the ratio is greater or lesser than 1.0.

5. Ventilation device according to claim 1, wherein the ventilation process is configured to be set by the control device such that a) while supplying the fluid, a first volume that is present at the pressure P.sub.0, and while discharging the fluid, a second volume that is present at the same pressure P.sub.0, differs at most by 30% from the volume interval that is present in the pressure interval or b) while supplying the fluid, a first pressure that is present at the volume V.sub.0 and while discharging the fluid, a second pressure that is present at the same volume V.sub.0, differs at most by 30% from the pressure interval that is present in the volume interval.

6. Ventilation device according to claim 1, wherein a) the ventilation process is configured to be set over at least 60% of the pressure interval in such a way that while supplying the fluid, a first volume that is present at the pressure P.sub.0, and while discharging the fluid, a second volume that is present at the same pressure P.sub.0, differs at least by 1% from the volume interval that is present in the pressure interval or b) the ventilation process is configured to be set over at least 60% of the volume interval in such a way that while supplying the fluid, a first pressure that is present at the volume V.sub.0, and while discharging the fluid, a second pressure that is present at the same volume V.sub.0, differs at least by 1% from the pressure interval that is present in the volume interval.

7. Ventilation device according to claim 1, wherein the control device is configured to a) determine integrals of f.sub.ZP(P) and f.sub.AP(P) in the pressure interval and determine a difference between ∫f.sub.ZP(P) dP and ∫f.sub.AP(P) dP in the pressure interval or b) for determining integrals of f.sub.ZV(V) and f.sub.AV(V) in the volume interval and for determining a difference between ∫f.sub.ZV(V) dV and ∫f.sub.AV(V) dV in the volume interval.

8. Ventilation device according to claim 7, wherein the control device is configured to carry out multiple ventilation processes, in which the difference between a) ∫f.sub.ZP(P) dP and ∫f.sub.AP(P) dP in the pressure interval or b) ∫f.sub.ZV(V) dV and ∫f.sub.AV(V) dV in the volume interval is configured to be controlled, wherein a ratio of the difference to a critical difference that is established for a given patient is settable.

9. Method for operating a ventilation device provided for ventilating a patient, the ventilation device comprising: at least a fluid supply unit configured to supply a fluid into at least one airway; a fluid discharge unit configured to discharge the fluid from the at least one airway; and a control device, wherein the method comprises at least the following steps: a) carryout a ventilation process, including delivering at least a one-time supply of a fluid into the at least one airway and discharging at least a one-time discharge of the fluid from the airway by operating the ventilation device; wherein the ventilation process takes place within a pressure interval and within a volume interval; b) determining or setting a profile of at least one volume-pressure curve in a volume-pressure diagram by the control device during the ventilation process; wherein the curve has a first curve section V=f.sub.ZP(P) or P=f.sub.ZV(V), and a second curve section, V=f.sub.AP(P) or P=f.sub.AV(V), wherein the first curve section represents the profile of the supplied volume V and of the pressure P while supplying the fluid into the at least on airway, and the second curve section represents the profile of the discharged volume V and of the pressure P while discharging the fluid from the at least one airway wherein by use of the control device the ventilation process is configured to 1) over at least 60% of the pressure interval, a ratio of an absolute value of a first slope of the first curve section at a pressure P.sub.0, i.e. df.sub.ZP/d(P)(P.sub.0), and an absolute value of a second slope of the second curve section, at the pressure P.sub.0 has a value of at least 0.5 and at more 2.0, or 2) over at least 60% of the volume interval, a ratio of an absolute value of a first slope of the first curve section at a volume V.sub.0, i.e. df.sub.AV/d(V)(V.sub.0), and an absolute value of a second slope of the second curve section, i.e., df.sub.AV/d(V)(V.sub.0), at volume V.sub.0 has a value of at least 0.5 and at most 2.0.

10. Method according to claim 9, wherein the control device determines the profile of the volume-pressure curve in the volume pressure diagram during the ventilation process for compliance of the airway according to one of V=f.sub.CP(P) or P=f.sub.CV(V); wherein the ventilation process in steps a) and b) is configured such that that over at least 60% of the pressure interval or over at least 60% of the volume interval, a ratio of each of df.sub.AP/d(P) (P.sub.0), df.sub.ZP/d(P) (P.sub.0) and an absolute value of a measure of the change in the first volume of the compliance that is present at a pressure P.sub.0, i.e., dfc/d(P) (P.sub.0), or a ratio of each of df.sub.AV/d(V) (V.sub.0), df.sub.ZV/d(V) (V.sub.0) and an absolute value of a measure of the change in the first pressure of the compliance that is present at a volume V.sub.0, i.e., dfc/d(V) (V.sub.0), has a value of at least 0.5 and at most 2.0.

11. Method according to claim 9, wherein the ventilation process is configured such that that over at least 60% of the pressure interval or 60% of the volume interval, the ratio has a value of at least 0.67 and at most 1.5.

12. Method according to claim 9, wherein in step b) or in a further step c) the control device carries out a determination or a setting of an area; wherein this area in the volume-pressure diagram is enclosed by the first curve section and the second curve section of the one ventilation process.

13. Method according to claim 12, wherein in the at least one ventilation process, a ratio of the area to a critical area that is established for a given patient is set.

14. Method according to claim 9, wherein the ventilation device includes a visualization apparatus, wherein at least one of the following parameters is visually discernibly displayed via the visualization apparatus: a) a measure for a size of the area; or b) a measure for a change in the area over multiple ventilation processes; or c) a measure for a ratio of the area to a critical area that is established for a given patient; or d) a measure for a change in the ratio of the area to a critical area that is established for a given patient over multiple ventilation processes.

Description

(1) The invention and the technical field are explained in greater detail below with reference to the figures. It is pointed out that the figures show one particularly preferred embodiment variant of the invention, to which the invention, however, is not restricted. Identical components are denoted by the same reference numerals in the figures. In the figures, in each case schematically:

(2) FIG. 1: shows a ventilation device and a patient;

(3) FIG. 2: shows a profile of a compliance curve;

(4) FIG. 3: shows a first illustration of a ventilation process in a volume-pressure diagram;

(5) FIG. 4: shows a second illustration of a ventilation process in a volume-pressure diagram;

(6) FIG. 5: shows a first diagram in which a volumetric flow rate is plotted with respect to time;

(7) FIG. 6: shows a second diagram in which a volumetric flow rate is plotted with respect to time;

(8) FIG. 7: shows a third diagram in which the square of a speed is plotted with respect to time; and

(9) FIG. 8: shows a fourth diagram in which the square of a speed is plotted with respect to time.

(10) FIG. 1 shows a ventilation device 1 and a patient with at least one airway 5, i.e., a lung. The ventilation device 1 comprises a fluid supply unit 2 and a fluid discharge unit 3 that are suitable for respectively supplying a fluid 4 into an airway 5, i.e., into a lung part or into the lung, of a patient and for discharging the fluid 4 from this airway 5. The ventilation device 1 further comprises a control device 6 which, during a ventilation of the at least one airway 5 of the patient, i.e., supplying a fluid 4 into the at least one airway 5 and/or discharging the fluid 4 from the at least one airway 5 by operating the ventilation device 1, is suitable for setting a profile of a pressure P7 in the airway 5 and a profile of a volume V8 of the fluid 4 that is supplied to the airway 5 and discharged from the airway 5 according to V=f.sub.ZP(P) and V=f.sub.AP(P). The ventilation device 1 is connected to the airway 5 of the patient via a catheter 40 of the lumen, with a lumen cross section 41 through which the fluid 4 can flow. The ventilation thus takes place, for example, via a single lumen, in particular using a gas flow reversing device.

(11) The ventilation device 1 has a visualization apparatus 17, wherein at least one of the following parameters may be visually discernibly displayed via the visualization apparatus 17: a measure for a size of the area 20; or a measure for a change in the area 20 over multiple ventilation processes; or a measure for a ratio of the area 20 to a critical area 21 that is established for a given patient; or a measure for a change in the ratio of the area 20 to a critical area 21 that is established for a given patient over multiple ventilation processes.

(12) A pressure sensor 39 is situated on the catheter 40 inside the airway 5. The airway 5 has a compliance C25.

(13) FIG. 2 shows a profile of a compliance curve 35 in a pressure-volume diagram. The pressure 7 is plotted on the horizontal axis, and the volume 8 is plotted on the vertical axis. The profile of the compliance curve 35 is to be determined individually for each patient. In addition, the profile 7 may also change during a ventilation.

(14) At least one value of the compliance 25 is initially determined within the scope of the method, i.e., by the ventilation device 1, where the following applies for the compliance C25: C=delta volume V8/delta P7 in milliliter/millibar. In the subregion of the compliance curve 35 shown here, the absolute value of the compliance 25 is at a maximum. By determining or estimating the profile of the compliance curve 25, the position of a pressure interval 9 with the pressures P1 36 and P2 37 may now be determined in which a tidal volume V.sub.T 38 of the fluid 4 can be supplied to the at least one airway 5. These pressures P1 36 and P2 37 are set on the ventilation device 1, so that at least one ventilation process, i.e., an inhalation and/or an exhalation, takes place in each case with a tidal volume V.sub.T 38 between these pressures P1 36 and P2 37.

(15) FIG. 3 shows a first illustration of a ventilation process in a volume-pressure diagram. The pressure 7 is plotted on the horizontal axis, and the volume 8 is plotted on the vertical axis. The illustrated volume-pressure curve shows the profile of the pressure P 7 in the airway 5 while the volume V8 in the airway 5 changes by the tidal volume V.sub.T 38, i.e., on the one hand by the supplied volume V8 of fluid 4, and on the other hand by the discharged volume V8 of fluid 4. The curve has a first curve section 18 V=f.sub.ZP(P) (the bottom curve extending from a lowest pressure 7 and a smallest volume 8 to a highest pressure 7 and a largest volume 8), and a second curve section 19 V=f.sub.AP(P) (the top curve extending next to the first curve section 18, from a highest pressure 7 and a largest volume 8 to a lowest pressure 7 and a smallest volume 8), wherein the first curve section 18 represents the profile of the supplied volume V8 (tidal volume V.sub.T 38) and of the pressure P7 while supplying the fluid 4 into the at least one airway 5, and the second curve section 19 represents the profile of the discharged volume V8 (tidal volume V.sub.T 38) and of the pressure P7 while discharging the fluid 4 from the at least one airway 5.

(16) The measure of the change in the first volume 12 that is present at a pressure P.sub.0 11 is, for example, the first slope 23 of the volume-pressure curve, in the present case, of the first curve section 18, in a volume-pressure diagram. The slope (first slope 23 and second slope 24) is determined by the first derivative of the respective function V=f.sub.ZP(P) and V=f.sub.AP(P), i.e., df.sub.AP/d(P) (P.sub.0) and df.sub.ZP/d(P) (P.sub.0).

(17) It has been found that the first slope 23 of a first curve section 18 at a pressure P.sub.0 11 of a volume-pressure curve, representable in a volume-pressure diagram, and the second slope 24 of a second curve section 19 (i.e., the absolute value of a measure of the change in a second volume 13, present at the same pressure P.sub.0 11, while discharging the fluid 4), at the same pressure P.sub.0 11 in each case (the pressure P.sub.0 11 lies within the pressure interval 9), should have approximately the same value in a largest possible range of the pressure interval 9.

(18) The control device 6 on the one hand controls and monitors the pressure profile and volume profile while fluid 4 is supplied into the at least one airway 5. On the other hand, the discharge of the fluid 4 from the airway 5 is now also controlled and monitored as a function of the profile of this first curve section 18. In particular, no passive exhalation (see FIG. 3), which typically would produce a second curve section 19 that differed greatly from the first curve section 18, and thus a large area 20, is allowed here. In contrast, it is proposed for the control device 6 to also actively monitor and control the discharge of the fluid 4, wherein the second curve section 19 approximates the profile of the first curve section 18 (see FIG. 4).

(19) Initial tests with these types of ventilation devices and methods have shown that damage to the at least one airway 5 (ventilator-induced lung injury (VILI)) may be at least reduced or even effectively prevented by such control of the ventilation.

(20) The control device 6 is suitable for determining integrals f.sub.ZP(P) and f.sub.AP(P) in the pressure interval 9, and for determining a difference between ∫f.sub.ZP(P) dP and ∫f.sub.AP(P) dP in the pressure interval 9.

(21) The control device 6 is suitable for carrying out multiple ventilation processes in which the difference between ∫f.sub.ZP(P) dP and ∫f.sub.AP(P) dP in the pressure interval 9 is controllable, wherein a ratio of the difference to a critical difference that is established for a given patient may be set.

(22) The area below the first curve section 18 and the area below the second curve section 19 is respectively determined by the integral of ∫f.sub.ZP(P) and f.sub.AP(P), i.e., ∫f.sub.ZP(P) dP and ∫f.sub.AP(P) dP, in the pressure interval 9. A difference between the integrals f.sub.ZP(P) and f.sub.AP(P) in the pressure interval 9 thus denotes the area 20 that is enclosed by the first curve section 18 and the second curve section 19. The difference between the integrals f.sub.ZP(P) and f.sub.AP(P) in the pressure interval 9, and thus, the area 20 enclosed by the curve sections 18, 19, is regarded as a measure for the energy E that is absorbed by the airway 5. This difference between the integrals, i.e., this area 20, should therefore be as small as possible so that the energy E absorbed by the airway 5 is as low as possible. FIG. 4 shows a ventilation process that is set in this way.

(23) In particular, a critical difference, i.e., a critical area 21, may be determined for a patient based, for example, on empirical values or a determination of a compliance 25 of the airway 5. This critical difference or critical area 21 refers to the amount of energy E that may be supplied to the at least one airway 5 during a ventilation process without the expectation of damage (VILI) to the at least one airway 5. The critical difference may be, for example, the difference between the integrals of f.sub.ZP(P) and f.sub.AP(P) in the pressure interval 9, wherein f.sub.ZP(P), i.e., the first curve section 18 in the diagram according to FIG. 3, describes the supply of the fluid 4 with the highest possible compliance 25, and wherein f.sub.AP(P), i.e., the second curve section 19 in the diagram according to FIG. 3, describes the discharge of the fluid 4 due to passive exhalation (i.e., (only) the energy stored in the elastic tissue elements of the lung and thorax drives the exhalation). The critical difference in FIG. 3 is thus the critical area 21 between the curve sections 18, 19.

(24) FIG. 4 shows a second illustration of a ventilation process in a volume-pressure diagram. Reference is made to the description for FIG. 3.

(25) The control device 6, at least during the one shown ventilation process of the at least one airway 5, i.e., at least the one-time supply of the fluid 4 into the at least one airway 5 and the at least one-time discharge of the fluid 4 from the at least one airway 5 by operating the ventilation device 1, is configured for setting a profile of a pressure P7 in the airway 5 and a profile of a volume V8 of the fluid 4 supplied to the airway 5 and discharged from the airway 5 according to V=f.sub.ZP(P) and V=f.sub.AP(P). The ventilation process takes place within a pressure interval 9. By use of the control device 6, the ventilation process is settable in such a way that over at least 60% of the pressure interval 9, a ratio of an absolute value of a measure of the change in the first volume 12 that is present at a pressure P.sub.0 11 while supplying the fluid 4, i.e., df.sub.AP/d(P) (P.sub.0) (first slope 23 of the first curve section 18 at the pressure P.sub.0 11), and an absolute value of a measure of the change in a second volume 13 that is present at the same pressure P.sub.0 11 while discharging the fluid 4, i.e., df.sub.ZP/d(P) (P.sub.0) (second slope 24 of the second curve section 19 at the pressure P.sub.0 11), has a value of at least 0.5 and at most 2.0.

(26) The same correspondingly applies for each volume V.sub.0 14 (not shown here), wherein over at least 60% of the volume interval 10, a ratio of an absolute value of a measure of the change in the first pressure 15 that is present at a volume V.sub.0 14 while supplying the fluid 4, i.e., df.sub.AV/d(V) (V.sub.0), and an absolute value of a measure of the change in a second pressure 16 that is present at the same volume V.sub.0 14 while discharging the fluid 4, i.e., df.sub.ZV/d(V) (V.sub.0), has a value of at least 0.5 and at most 2.0.

(27) In this case, by use of the control device 6 the ventilation process is set in such a way that over at least a portion of the pressure interval 9, a ratio of an absolute value of a first slope of the first curve section 18 at a pressure P.sub.0 11, i.e., df.sub.AP/d(P) (P.sub.0), and an absolute value of a second slope 24 of the second curve section 19, i.e., df.sub.ZP/d(P) (P.sub.0), at the same pressure P.sub.0 11, has a value of at least 0.5 and at most 2.0. The absolute value of the result of the equation [df.sub.AP/d(P) (P.sub.0)]/[df.sub.ZP/d(P) (P.sub.0)] should thus be at least 0.5 and at most 2.0. The pressure P.sub.0 11 is thus any pressure 7 within the pressure interval 9 or within a portion of the pressure interval 9.

(28) The ventilation process is further set here in such a way that while supplying the fluid 4 a first volume 12 that is present at the pressure P.sub.0 11, and while discharging the fluid 4 a second volume 13 that is present at the same pressure P.sub.0 11, differ at most by 20% of the supplied or discharged volume 8 in the pressure interval 9.

(29) The ventilation process is further set here in such a way that while supplying the fluid 4 a first volume 12 that is present at the pressure P.sub.0 11, and while discharging the fluid 4 a second volume 13 that is present at the same pressure P.sub.0 11, differ at least by 1% of the (overall) supplied or discharged volume 8 (the tidal volume V.sub.T 38 in this case) in the pressure interval.

(30) At least one or some of the following parameters, for example, may be visually displayed via the visualization apparatus 17: a measure for a size of the area 20; a measure for a change in the area 20 over multiple ventilation processes; a measure for a ratio of the area 20 to a critical area 21 that is established for a given patient (i.e., the critical difference of the integrals); a measure for a change in the ratio of the area 20 to a critical area 21 that is established for a given patient (i.e., the critical difference of the integrals) over multiple ventilation processes. In addition, by use of the visualization apparatus 17 and based on the display, for example, of a ventilation process in a volume-pressure diagram according to FIG. 3 or FIG. 4, the slopes 23, 24 of the curve sections 18, 19 may be set or changed, either via the control device 6 or by an operator of the ventilation device 1.

(31) FIG. 4 also shows that the control device 6 is configured for determining a profile of the pressure P7 in the airway 5 and a profile of a volume V8 of the fluid 4 that is supplied to the airway 5 and discharged from the airway 5 for a compliance 25 of the patient according to one of V=f.sub.CP(P) or P=f.sub.CV(V). The first curve section 18 corresponds to the compliance 25 here. The ventilation process may be set by the control device 6 in such a way that over at least 60% of the pressure interval 9, a ratio of each of df.sub.AP/d(P) (P.sub.0) (in this case, the second slope 24 of the second curve section 19), df.sub.ZP/d(P) (P.sub.0) (in this case, the first slope 23 of the first curve section 18) and an absolute value of a measure of the change in the first volume 12 of the compliance 25 that is present at a pressure P.sub.0 11, i.e., df.sub.CP/d(P) (P.sub.0), has a value of at least 0.5 and at most 2.0.

(32) FIG. 5 shows a first diagram in which a volumetric flow rate 26 is depicted over time 44. FIG. 6 shows a second diagram in which a volumetric flow rate 26 is depicted over time 44. FIGS. 5 and 6 are described together in the following discussion.

(33) The control device 6, as described above, is configured for setting a profile of a pressure P7 in the airway 5 and a profile of a volume V8 of the fluid 4 that is supplied to the airway 5 and discharged from the airway 5 according to V=f.sub.ZP(P) and V=f.sub.AP(P) or according to P=f.sub.ZV(V) and P=f.sub.AV(V), wherein the ventilation process takes place within a pressure interval 9 and within a volume interval 10. FIG. 5 shows the volumetric flow rate F(t) 26 of the ventilation process according to FIG. 3. FIG. 6 shows the volumetric flow rate F(t) 26 of the ventilation process according to FIG. 4. By use of the control device 6, the ventilation process is now settable (see FIG. 6) in such a way that while supplying the fluid 4 and while discharging the fluid 4, a volumetric flow rate F(t) 26 [L/min] (shown here with different algebraic signs and thus depicted as 0 L/min with respect to the zero line) varies at most by 50% with respect to an average volumetric flow rate FD 42 in the ventilation process, at least for 80% of a duration of the ventilation process. It is apparent that the volumetric flow rate F(t) 26 varies over time 44, wherein in particular a (preferably) constant volumetric flow rate F(t) 26 (based on the absolute value) should be set. The average volumetric flow rate FD 43 is determined by dividing the sum of the supplied and the discharged fluid 4 (i.e., always a positive value) by the duration of the ventilation process (i.e., the time 43 between the origin in the diagram and the vertical line). For setting and controlling the volumetric flow rate F(t) 26, the average volumetric flow rate FD 43 may also be determined based on the prior ventilation processes or based on the preset parameters (for example, frequency and tidal volume 38).

(34) FIG. 7 shows a third diagram in which the square of a speed over time 44 is illustrated. FIG. 8 shows a fourth diagram in which the square of a speed over time 44 is illustrated. FIGS. 7 and 8 are described together in the following discussion.

(35) The control device 6, as described above, is configured for setting a profile of a pressure P7 in the airway 5 and a profile of a volume V8 of the fluid 4 that is supplied to the airway 5 and discharged from the airway 5 according to V=f.sub.ZP(P) and V=f.sub.AP(P) or according to P=f.sub.ZV(V) and P=f.sub.AV(V), wherein the ventilation process takes place within a pressure interval 9 and within a volume interval 10. FIG. 7 shows the square of a speed 32, i.e., (s(t)).sup.2, of the ventilation process according to FIG. 3. FIG. 8 shows the square of a speed 32, i.e., (s(t)).sup.2, of the ventilation process according to FIG. 4. By use of the control device 6, the ventilation process is settable in such a way that the square of a speed (s(t)).sup.2 32 of the profile of the pressure P7 and of the volume V8 while supplying the fluid 4 and while discharging the fluid 4, i.e., (s(t)).sup.2=(dP/dt).sup.2+(dV/dt).sup.2, varies at most by 300% with respect to an average square of a speed sD.sup.2 43 during the ventilation process, at least for 80% of a duration of the ventilation process. It is apparent that in FIG. 7 a single maximum is present, and in FIG. 8 the square of the speed 32 has a more uniform profile. The units are not illustrated here. However, it has been found that in the ventilation technique described herein, a significantly reduced power loss 28 and thus a significantly lower energy loss 29 may be achieved during the ventilation process (time 44). The power loss PW(t) 28 corresponds to the profile of the square of a speed (s(t)).sup.2 32.

LIST OF REFERENCE NUMERALS

(36) 1 ventilation device

(37) 2 fluid supply unit

(38) 3 fluid discharge unit

(39) 4 fluid

(40) 5 airway

(41) 6 control device

(42) 7 pressure P

(43) 8 volume V

(44) 9 pressure interval

(45) 10 volume interval

(46) 11 pressure P.sub.0

(47) 12 first volume

(48) 13 second volume

(49) 14 volume V.sub.0

(50) 15 first pressure

(51) 16 second pressure

(52) 17 visualization apparatus

(53) 18 first curve section

(54) 19 second curve section

(55) 20 area

(56) 21 critical area

(57) 22 intervention limit

(58) 23 first slope

(59) 24 second slope

(60) 25 compliance C

(61) 26 volumetric flow rate F(t)

(62) 27 airway resistance

(63) 28 power loss PW(t)

(64) 29 energy loss E

(65) 30 critical power loss

(66) 31 critical energy loss

(67) 32 speed squared (s(t).sup.2

(68) 33 critical speed squared

(69) 34 variable

(70) 35 compliance curve

(71) 36 pressure P1

(72) 37 pressure P2

(73) 38 tidal volume V.sub.T

(74) 39 pressure sensor

(75) 40 catheter

(76) 41 cross section

(77) 42 average volumetric flow rate

(78) 43 average square of a speed

(79) 44 time t