METHOD FOR AUTOMATICALLY CONTROLLING A VENTILATION OR BREATHING SYSTEM AS WELL AS A CORRESPONDING VENTILATION OR BREATHING SYSTEM

• US 20090114224A1
• Filed: 11/05/2008
• Published: 05/07/2009
• Est. Priority Date: 11/07/2007
• Status: Active Grant

• Current Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Original Assignee: Drager Medical AG & Co KG (Dragerwerk AG)
• Inventors: RALFS, Frank, SCHUBERT, Ernst, HANDZSUJ, Thomas, EGER, Marcus
• Granted Patent: US 8,950,399 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2205/502 User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2230/42 Rate
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

A method is provided for automatically controlling a ventilation or breathing system with a ventilation unit (7), which is controlled by a control unit (5), in order to deliver an assist pressure preset by the control unit, wherein the current values of the tidal volume flow Flow(t) and those of the volume V(t) are detected in the control unit. The control unit (5) may carry out a proportionally assisting ventilation method (PAV: Proportional Assist Ventilation) by a factor for a degree of compensation (PPSp) being selected by the control unit and by the parameters for the volume assist (VA) and the flow assist (FA) being determined by:

VA=PPSp·ΔE

FA=PPSp·ΔR,

wherein ΔE is the deviation of a measured or assumed elastance (E_measured) of the patient from an ideal elastance (E_ideal) and ΔR is the deviation of a measured or assumed resistance (R_measured) of the patient from an ideal resistance (R_ideal). The assist pressure PS(t)=VA·V(t)+FA·Flow(t) is determined from this by the control unit with the flow delivery device (ventilation unit (7)) being set such as to deliver this assist pressure.

Claims

1. A method for automatically controlling a ventilation or breathing system, the method comprising the steps of:

providing a ventilation or breathing system with a ventilation unit controlled by a control unit for delivery of an assist pressure preset by said control unit;

detecting current values of the tidal volume flow (Flow(t)) and values of the volume (V(t)) are detected in said control unit;

carrying out a proportionally supporting ventilation method (PAV;

Proportional Assist Ventilation) with the control unit with a factor for a degree of compensation (PPSp) being selected by the control unit and by the parameters for the volume assist (VA) and the flow assist (FA) being determined by;

VA=PPSp·

E

FA=PPSp·

Δ

R,

wherein Δ

E is the deviation of a measured or assumed elastance (E_measured) of the patient from an ideal elastance (E_ideal) and Δ

R is the deviation of a measured or assumed resistance (R_measured) of the patient from an ideal resistance (R_ideal);

using an assist pressure (PS(t)) determined by the control unit from VA and FA wherein PS(t)=VA·

V(t)+FA·

Flow(t) is determined to set the ventilation unit such as to deliver this assist pressure.

2. A method in accordance with claim 1, further comprising:

providing the ventilation or breathing system with at least one of a user interface of said control unit and an expert system implemented in said control unit;

entering a value for a desired assist pressure (PS_desired) to be delivered by the ventilation or breathing system at the user interface or determining by the expert system implemented in said control unit according to preset dependencies on the basis of measured values for tidal volume, ventilation or breathing rate and end-tidal CO₂ concentration (etCO₂), wherein said control unit determines a new value for the degree of compensation PPSp_new from the previous value PPSp and the set point PS_desired on the basis of all implemented control function after the end of at least one breathing cycle in such a way that a representative assist pressure, which is determined as a time-averaged mean value, as a weighted mean, as a median or as a maximum of a time curve of PS(t) during inspiration over one breathing cycle or over a plurality of breathing cycles, will reach the value PS_desired within a plurality of breathing cycles exactly or as an average over a plurality of breathing cycles.

3. A method in accordance with claim 1, further comprising:

providing the ventilation or breathing system with at least one of a user interface of the control unit and an expert system implemented in said control unit;

entering a value for a desired assist pressure (PS_desired) to be delivered by the ventilation or breathing system at the user interface or determining by the expert system implemented in said control unit according to preset dependencies on the basis of measured values for the tidal volume, ventilation or breathing rate and end-tidal CO₂ concentration (etCO₂), wherein said control unit;

calculates a representative assist pressure <

PS>

, which is determined as a mean over time, as a weighted mean, as a median or as a maximum of the time curve of PS(t) during the inspiration over one breathing cycle or over a plurality of breathing cycles; and

determines a new value for the degree of compensation PPSp_new from the previous value of PPSp according to PPSp_new=PPSp+(PS_desired−

<

PS>

)/V_PPS, wherein the amplification V_PPS is an indicator of the change of the representative assist pressure <

PS>

in relation to the change of PPSp, which indicator is determined over one breathing cycle or over a plurality of consecutive breathing cycles.

4. A method in accordance with claim 3, wherein said control unit determines the value for the amplification V_PPS as a ratio of the change in the representative assist pressure <

PS>

to the change of the parameter PPSp over one or more consecutive breathing cycles according to the formula;

V_PPS=Δ

<

PS>

/Δ

PPSp.

5. A method in accordance with claim 3, wherein said control unit determines the value for the amplification V_PPS as the ratio of the change in the representative assist pressure <

PS>

to the change in the parameter PPSp over one or more consecutive breathing cycles according to the formula;

V_PPS=Δ

(PS)/(e<sup>k·

Δ

PPSp</sup>−

1).

6. A method in accordance with claim 1, wherein a value from the range of 0 to 15 mbar/L is assumed for the ideal elastance (E_ideal) and a value ranging from 0 to 5 mbar/(L/sec) is assumed for the ideal resistance (R_ideal).

7. A method in accordance with claim 1, further comprising:

measuring airway pressure (p_aw(t));

calculating with the control unit the resistance (R_measured) and elastance (E_measured) on the basis of the measured values for the airway pressure p_aw(t) and the tidal volume flow (Flow(t)).

8. A method in accordance with claim 1, further comprising:

providing the ventilation or breathing system with at least one of a user interface wherein values for the resistance (R_measured) and elastance (E_measured) of the patient are entered as numerical values at the user interface.

9. A method in accordance with claim 1, further comprising:

providing the ventilation or breathing system with at least one user interface wherein pairs of values for the resistance (R_measured) and elastance (E_measured) are selected at the user interface by means of a selector switch from a plurality of preset typified value pairs.

10. A method in accordance with claim 1, wherein said control unit automatically proposes values for the resistance (R_proposed) and elastance (E_proposed) of the patient on the basis of a determination of the time constant of the breathing mechanics (τ

_regress) and of predetermined and stored standard dependencies of the resistance and elastance, respectively, on the time constant, wherein τ

_regress is obtained by means of linear regression of the flow-vs.-volume curve during a passive expiration phase.

11. A method in accordance with claim 10, wherein the predetermined and stored standard dependencies make provisions for dividing the range of physiologically meaningful time constants into three parts, wherein two part limits (τ

₁ and τ

₂) are defined as τ

₁<

τ

₂, and an ideal resistance is assumed for τ

_regress<

τ

₁ and an ideal elastance is assumed for τ

_regress>

τ

₂, and the resistance is interpolated linearly for the part located between these limits.

12. A method in accordance with claim 10, wherein the values for the resistance (R_measured) and elastance (E_measured) of the patient are equated with the corresponding proposed values for the resistance (R_proposed) and elastance (E_proposed).

13. A method in accordance with claim 10, wherein said control unit compares proposed values for resistance (R_proposed) and elastance (E_proposed) with resistance (R_measured) and elastance (E_measured) values assumed or determined by one of:

measuring airway pressure (p_aw(t)) and calculating with the control unit the resistance (R_measured) and elastance (E_measured) on the basis of the measured values for the airway pressure p_aw(t) and the tidal volume flow (Flow(t));

providing the ventilation or breathing system with at least one of a user interface wherein values for the resistance (R_measured) and elastance (E_measured) of the patient are entered as numerical values at the user interface; and

providing the ventilation or breathing system with at least one of a user interface wherein pairs of values for the resistance (R_measured) and elastance (E_measured) are selected at the user interface by means of a selector switch from a plurality of preset typified value pairs whereby an indication is provided when the deviations between (R_proposed) and (R_measured) or between (E_proposed) and (E_measured) exceed a preset threshold.

14. A method in accordance with claim 1, further comprising:

providing resistance (R_measured) and elastance (E_measured) values assumed or determined by one of;

measuring airway pressure (p_aw(t)) and calculating with the control unit the resistance (R_measured) and elastance (E_measured) on the basis of the measured values for the airway pressure p_aw(t) and the tidal volume flow (Flow(t));

providing the ventilation or breathing system with at least one user interface wherein values for the resistance (R_measured) and elastance (E_measured) of the patient are entered as numerical values at the user interface; and

providing the ventilation or breathing system with at least one of a user interface wherein pairs of values for the resistance (R_measured) and elastance (E_measured) are selected at the user interface by means of a selector switch from a plurality of preset typified value pairs;

determining, with the control unit, a ratio R_measured/E_measured from the assumed or determined values for resistance (R_measured) and elastance (E_measured);

comparing an indicator for the time constant (τ

_R/E), where τ

_R/E=R_measured/E_measured, to an indicator obtained for the regression time constant (τ

_regress) obtained from a linear regression of the flow-vs.-volume curve during a passive expiration phase and to yield an indication when the deviation between τ

_R/E and τ

_regress exceeds a preset threshold.

15. A method in accordance with claim 2, wherein a ramp time constant, which sets a minimum of the duration of the pressure rise at the beginning of inspiration, is entered via the user interface of said control unit.

16. A method in accordance with claim 3, wherein a ramp time constant, which sets a minimum of the duration of the pressure rise at the beginning of inspiration, is entered via the user interface of said control unit.

17. A method in accordance with claim 2, wherein the assist pressure PS(t) is limited to a pressure limit value that is related to the desired assist pressure PS_desired.

18. A method in accordance with claim 4, wherein the assist pressure PS(t) is limited to a pressure limit value that is related to the desired assist pressure PS_desired.

19. A method in accordance with claim 18, wherein the pressure limit value is selected in proportion to the desired assist pressure PS_desired or additively thereto.

20. A ventilation or breathing system for automatically controlled ventilation or breathing, the ventilation or breathing system comprising:

a ventilation unit for delivering an assist pressure;

a control unit detecting current values of the tidal volume, flow (Flow(t)) and volume (V(t)) and receiving and storing assumed or measured values for a resistance (R_measured) and an elastance (E_measured) of the patient as well as for an ideal resistance (R_ideal) and an ideal elastance (E_ideal), wherein said control unit carries out a proportionally assisting ventilation method (PAV;

Proportional Assist Ventilation) by a factor for a degree of compensation (PPSp) selected in said control unit and by parameters for the volume assist (VA) and the flow assist (FA) being determined by said control unit according to;

VA=PPSp·

E

FA=PPSp·

Δ

R

wherein Δ

E is the deviation of the measured or assumed elastance (E_measured) of the patient from the ideal elastance E_ideal and Δ

R is the deviation of a measured or assumed resistance (R_measured) of the patient from an ideal resistance (R_ideal), and by the assist pressure PS(t)=VA·

V(t)+FA·

Flow(t) being determined from this, and controlling said ventilation unit to deliver said assist pressure.

21. A ventilation or breathing system in accordance with claim 20, further comprising:

one of a user interface, via which a value for the desired assist pressure (PS_desired) to be delivered by the ventilation or breathing system can be entered in said control unit, and an expert system implemented in said control unit for determining PS_desired according to preset dependencies on the basis of measured values for the tidal volume, ventilation or breathing rate and end-tidal CO₂ concentration (etCO₂), wherein said control unit determines a new value for the degree of compensation (PPSp_new) from the previous value PPSp and determines PS_desired on the basis of an implemented control function after the end of at least one breathing cycle in such a way that a representative assist pressure (<

PS>

), which is determined as a mean over time, as a weighted mean, as a median or as a maximum of the time curve of PS(t) during inspiration over one breathing cycle or over a plurality of breathing cycles, is reached exactly or as an average over several breathing cycles.

22. A ventilation or breathing system in accordance with claim 20, further comprising:

one of a user interface, via which a value for the desired assist pressure (PS_desired) to be delivered by the ventilation or breathing system can be entered in said control unit, and an expert system implemented in said control unit for determining PS_desired according to preset dependencies on the basis of measured values for the tidal volume, ventilation or breathing rate and end-tidal CO₂ concentration (etCO₂), wherein said control unit calculates a representative assist pressure (<

PS>

), which is determined as a mean value over time, as a weighted mean, as a median or as a maximum of the time curve of PS(t) during the inspiration over one breathing cycle or over a plurality of breathing cycles, and determines a new value for the degree of compensation (PPSp_new) from the previous value of PPSp according to PPSp_new=PPSp+(PS_desired−

<

PS>

)V_PPS, wherein the amplification V_PPS is an indicator of the change in <

PS>

in relation to the change in PPSp, which indicator is determined over one breathing cycle or over a plurality of consecutive breathing cycles.

23. A ventilation or breathing system in accordance with claim 20, wherein said control unit determines V_PPS as a ratio of the change in the representative assist pressure (<

P_S>

) to the change in the parameter PPSp over one or more consecutive breathing cycles according to the formula;

V_PPS=Δ

<

PS>

/Δ

PPSp.

24. A ventilation or breathing system in accordance with claim 20, wherein said control unit determines V_PPS as a ratio of the change in the representative assist pressure (<

P_S>

) to the change in the parameter PPSp over one or more consecutive breathing cycles according to the formula V_PPS=Δ

(PS)/(e<sup>k·

Δ

PPSp</sup>−

1).

25. A ventilation or breathing system in accordance with claim 20, further comprising measuring means for measuring the airway pressure (P_aw(t)), wherein said control unit is prepared to calculate the resistance (R_measured) and elastance (E_measured) on the basis of the measured values for the airway pressure (p_aw(t)) and the tidal volume flow (Flow(t)).

26. A ventilation or breathing system in accordance with claim 20, further comprising a selector switch for selecting values for the resistance (R_measured) and elastance (E_measured) from a plurality of preset typified combinations of values for (E_measured) and (R_measured).

27. A ventilation or breathing system in accordance with claim 20, wherein the control unit proposes or presents automatic values for the resistance (R_proposed) and elastance (E_proposed) of the patient on the basis of a determination of the time constant of the mechanics of breathing (τ

_regress) and predetermined and stored standard dependencies of the elastance, on the one hand, and of the resistance, on the other hand, on the time constant, wherein the time constant (τ

_regress) is obtained by means of linear regression of the flow-vs.-volume curve during a passive expiration phase.

28. A ventilation or breathing system in accordance with claim 27, wherein said control unit is prepared such that the predetermined and stored standard dependencies of the elastance, on the one hand, and of the resistance, on the other hand, on the time constant make provisions for dividing the range of physiologically meaningful time constants into three parts, wherein two part limits, namely, τ

₁ and τ

₂, are defined by τ

₁<

τ

₂, and an ideal resistance is assumed for τ

_regress<

τ

₁ and an ideal elastance is assumed for τ

_regress>

τ

₂, and the resistance is interpolated linearly for the part located between these limits.

29. A ventilation or breathing system in accordance with claim 27, wherein said control unit is prepared such that the values for the resistance (R_proposed) and elastance (E_measured) of the patient are equated with the corresponding proposed values for the resistance (R_proposed) and elastance (E_proposed).

30. A ventilation or breathing system in accordance with claim 27, wherein said control unit compares proposed values for the resistance (R_proposed) and elastance (E_proposed) with the values assumed or determined by one of:

measuring means for measuring the airway pressure (P_aw(t)), and a selector switch for selecting values for the resistance (R_measured) and elastance (E_measured) from a plurality of preset typified combinations of values for (E_measured) and (R_measured), said control unit sending an indication when the deviations between (R_proposed) and (R_measured) or between E_proposed and (E_measured) exceed a preset threshold.

31. A ventilation or breathing system in accordance with claim 28, wherein said control unit compares proposed values for the resistance (R_proposed) and elastance (E_proposed) with the values assumed or determined by one of:

measuring means for measuring the airway pressure (P_aw(t)), and a selector switch for selecting values for the resistance (R_measured) and elastance (E_measured) from a plurality of preset typified combinations of values for (E_measured) and (R_measured), said control unit sending an indication when the deviations between (R_proposed) and (R_measured) or between (E_proposed) and (E_measured) exceed a preset threshold.

32. A ventilation or breathing system in accordance with claim 25, wherein said control unit determines a ratio R_measured/E_measured from a hypothetical or determined values for the resistance R_measured and elastance E_measured and compares this indicator for the time constant τ

_R/E=R_measured/E_measured to the indicator obtained for the time constant τ

_regress obtained from a linear regression of the flow-vs.-volume curve during a passive expiration phase and to send an indication when the deviation between τ

_R/E and τ

_regress exceeds a preset threshold.

33. A ventilation or breathing system in accordance with claim 26, wherein said control unit determines a ratio R_measured/E_measured from a hypothetical value or determined values for the resistance (R_measured) and elastance (E_measured) and compares this indicator for the time constant τ

_R/E=R_measured/E_measured to the indicator obtained for the time constant τ

_regress obtained from a linear regression of the flow-vs.-volume curve during a passive expiration phase and to send an indication when the deviation between τ

_R/E and τ

_regress exceeds a preset threshold.

34. A ventilation or breathing system in accordance with claim 20, wherein said control unit has a user interface, which permits a ramp time constant, which sets a minimum of the duration of the pressure rise at the beginning of inspiration, to be entered.

35. A ventilation or breathing system in accordance with claim 21, wherein said control unit limits the assist pressure (PS(t)) to a pressure value that is related to a desired assist pressure (PS_desired).

36. A ventilation or breathing system in accordance with claim 22, wherein said control unit limits the assist pressure (PS(t)) to a pressure value that is related to a desired assist pressure (PS_desired).