System and method for circuit compliance compensated volume assured pressure control in a patient respiratory ventilator

• US 20070157930A1
• Filed: 01/10/2006
• Published: 07/12/2007
• Est. Priority Date: 01/10/2006
• Status: Active Grant

• Current Assignee: Vyaire Medical 211, Inc. (Becton, Dickinson & Co)
• Original Assignee: Viasys Manufacturing
• Inventors: Soliman, Ihab, Duquette, Steven
• Granted Patent: US 8,474,455 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2016/0042 in the expiratory circuit

Abstract

A system for circuit compliance compensated volume assurance pressure control in a patient respiratory ventilation circuit, having a patient circuit volume estimator for estimating a patient circuit compliance, a patient circuit volume estimator to estimate a circuit volume VOL_CKT—EST based on the patient circuit compliance, a patient volume observer, for estimating a patient volume VOL_TID—EST based on a measure delivered net volume VOL_NET and the patient circuit compliance, a volume assurance controller for generating a circuit compliance volume compensation factor VOL_TID—CTL based on a preset assured volume VOL_ASS—SET and the estimated patient volume VOL_TID—EST, and a decelerating inspiratory flow controller, operative to generate a decelerating inspiratory peak flow based on a preset inspiratory time T_INSP and the volume compensation factor VOL_TID—CTL.

Claims

1. A circuit compliance compensated volume assured pressure control system, comprising:

a circuit compliance estimator, operative to estimate a patient circuit compliance;

a patient circuit volume estimator, operative to estimate a circuit volume VOL<sub>CKT—

EST</sub> based on the patient circuit compliance;

a patient volume observer, operative to estimate a patient volume VOL<sub>TID—

EST</sub> based on a measure delivered net volume VOL_NET and the patient circuit compliance;

a volume assurance controller, operative to generate a circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> based on a preset assured volume VOL<sub>ASS—

SET</sub> and the estimated patient volume VOL<sub>TID—

EST</sub>; and

a decelerating inspiratory flow corrector, operative to generate a decelerating inspiratory flow command based on a preset inspiratory time T_INSP, the volume compensation factor VOL<sub>TID—

CTL</sub> and a preset assured volume VOL<sub>ASS—

SET</sub>

2. The system of claim 1, further comprising a sensor processor to generate and output the machine delivered net volume VOL_NET by integrating a net flow Q_NET defined as a difference between a measured inspiratory flow Q_INSP and a measured expiratory flow Q_EXP.

3. The system of claim 2, wherein machine delivered net volume VOL_NET is updated and reset at the start of the every inspiratory phase.

4. The system of claim 2, wherein the estimated circuit volume VOL_CKT—

_EST, the estimated patient volume VOL<sub>TID—

EST</sub> are updated and the measured machine delivered net volume VOL_NET is reset at the start of an expiratory phase following an inspiratory phase during which a net flow Q_NET defined as a difference between a measured inspiratory flow Q_INSP and a measured expiratory flow Q_EXP zero-crossing has been detected.

5. The system of claim 4, wherein when the net flow Q_NET does not cross zero during the inspiratory phase, the estimated circuit and patient volumes VOL_CKT—

_EST and VOL<sub>TID—

EST</sub> are updated and the measured machine delivered net volume VOL_NET is reset when the net flow Q_NET crosses zero after the expiratory phase starts or when the expiratory phase has started over a predetermined period of time before the net flow Q_NET zero-crossing is detected

6. The system of claim 1, wherein the volume assurance controller further comprises a gain scheduler operative to provide a dynamic gain K_VTID for weighting a volume error VOL_TID—

_ERR between the preset assured volume VOL<sub>ASS—

SET</sub> and the estimated patient volume VOL<sub>TID—

EST</sub>, so as to generate the volume compensation factor VOL<sub>TID—

CTL</sub> by adding the weighted volume error K_VTID*VOL<sub>TID—

ERR</sub> thereto breath after breath.

7. The system of claim 6, wherein the volume assurance controller further comprises a volume error percentage converter for converting the volume error VOL_TID—

_ERR into an error percentage

8. The system of claim 7, wherein the volume assurance controller further comprises a multiplier for multiplying the dynamic gain K_VTID with the preset assured volume VOL_ASS—

_SET.

9. The system of claim 8, wherein the volume assurance controller further comprises an integrator operative to provide the volume compensation factor for a current breath by adding an output of the multiplier K_VTID*VOL_ASS—

_SET with the volume compensation factor VOL<sub>TID—

CTL</sub> obtained from a previous breath.

10. The system of claim 9, wherein the integrator is operative to receive an initialized value INI_CKT—

_VOL of the volume compensation factor VOL<sub>TID—

CTL</sub> for a first breath of ventilation.

11. The system of claim 6, wherein the volume assurance controller further comprises a volume restrictor operative to prevent the volume compensation factor VOL_TID—

_CTL exceeding a safety range from being output.

12. The system of claim 1, further comprising a volume limiter operative to limit the volume compensation factor VOL_TID—

_CTL output from the volume assurance controller according to a patient volume VOL<sub>TID—

Y</sub> measured from a Y flow sensor.

13. The system of claim 12, wherein before the measured patient volume VOL_TID—

_Y reaches the preset assured volume VOL<sub>ASS—

SET</sub> and the circuit compliance compensation is disabled, the volume limiter is operative to control the volume assurance controller to output the volume compensation factor by;

a) computing a volume error VOL<sub>TID—

ERR</sub> by a difference between the assured volume VOL<sub>ASS—

SET</sub> preset for a current breath and the patient volume VOL<sub>TID—

EST</sub> estimated from a previous breath;

b) computing the volume compensation factor of the current breath by adding the volume error VOL<sub>TID—

ERR</sub> to the volume compensator factor obtained from the previous breath; and

c) limiting the volume compensation factor of the current breath between a maximum and minimum value.

14. The system of claim 13, wherein when the measured patient volume VOL_TID—

_Y reaches the preset assured volume VOL<sub>ASS—

SET</sub>, the volume assurance controller is operative to output the volume compensation factor VOL<sub>TID—

CTL</sub> obtained from the previous breath.

15. The system of claim 1, wherein the decelerating inspiratory flow corrector is operative to compute a maximum inspiratory peak flow Q_INSP—

_PEAK by;

16. The system of claim 15, wherein the decelerating inspiratory flow corrector is operative to compute a modulated decelerating inspiratory flow Q_INSP—

_SET by;

17. A system for circuit compliance compensated volume assured pressure control in a patient ventilation circuit, comprising:

a volume assurance controller operative to provide an estimated circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> based on an estimated or measured patient volume, VOL<sub>TID—

EST</sub> or VOL<sub>TID—

Y</sub>, and a preset assured volume VOL<sub>ASS—

SET</sub>; and

a decelerating inspiratory flow corrector operative to modulate an inspiratory flow Q<sub>INSP—

SET</sub> based on a preset waveform, a preset inspiratory time T<sub>INSP—

SET</sub>, a preset assured volume VOL<sub>ASS—

SET</sub> and the volume compensation factor VOL<sub>TID—

CTL</sub> output from the volume assurance controller.

18. The system of claim 17, further comprising a patient volume observer operative to provide the estimated patient volume VOL_TID—

_EST from a measured machine delivered net volume VOL_NET.

19. The system of claim 18, wherein the measured machine delivered net volume VOL_NET is integrated from a net flow Q_NET defined as a flow difference between a measure inspiratory flow Q_INSP and a measured expiratory flow Q_EXP.

20. The system of claim 18, further comprising a circuit volume estimator operative to provide an estimated circuit volume VOL_CKT—

_EST according to an estimated circuit compliance.

21. The system of claim 20, wherein the patient volume estimator is operative to subtract the estimated circuit volume VOL_CKT—

_EST from the measured machine delivered net volume VOL_NET as the estimated patient volume VOL<sub>TID—

EST</sub> and output the estimated patient volume VOL<sub>TID—

EST</sub> to the volume assurance controller.

22. The system of claim 17, further comprising a patient flow sensor operative to provide the measured patient volume VOL_TID—

_Y by integrating a patient flow Q_Y measured thereby.

23. The system of claim 17, wherein the volume assurance controller further comprises a gain scheduler operative to provide a weighting gain K_VTID as a function of a volume percentage VOL_PCT—

_ERR, wherein the volume percentage VOL<sub>PCT—

ERR</sub> is defined as an absolute value of a volume error VOL<sub>TID—

ERR</sub> between a preset assured volume VOL<sub>ASS—

SET</sub> and the estimated or measured patient volume VOL<sub>TID—

EST</sub> or VOL<sub>TID—

Y</sub> divided by the preset assured volume VOL<sub>ASS—

SET</sub>.

24. The system of claim 23, wherein the volume compensation factor VOL_TID—

_CTL is initialized with an initial value INI<sub>CKT—

VOL</sub> at a first breath of ventilation provided by the patient ventilation circuit.

25. The system of claim 24, wherein the volume assurance controller further comprises a multiplier for multiplying the weighting gain K_VTID with the volume error VOL_TID—

_ERR.

26. The system of claim 25, wherein the volume assurance controller further comprises an integrator operative to add an output of the multiplier with the volume compensation factor VOL_TID—

_CTL obtained from a previous breath.

27. The system of claim 17, wherein the decelerating inspiratory flow corrector is operative to compute a maximum peak inspiratory flow Q_INSP—

_PEAK by;

28. The system of claim 27, wherein the decelerating inspiratory flow corrector is operative to compute a modulated decelerating inspiratory flow Q_INSP—

_SET by;

29. A patient respiratory ventilation circuit, comprising:

a ventilator, operative to provide an inspiratory gas to and receive an expiratory gas from a patient via a patient circuit;

a system for circuit compliance compensated volume assured pressure control, comprising;

a volume assurance controller operative to provide an estimated circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> based on an estimated or measured patient volume, VOL<sub>TID—

EST</sub> or VOL<sub>TID—

Y</sub>, and a preset assured volume VOL<sub>ASS—

SET</sub>; and

a decelerating inspiratory flow corrector operative to modulate an inspiratory flow Q<sub>INSP—

SET</sub> based on a preset waveform, a preset inspiratory time T<sub>INSP—

SET</sub>, a preset assured volume VOL<sub>ASS—

SET</sub>, and the volume compensation factor VOL<sub>TID—

CTL</sub> output from the volume assurance controller; and

a servo control subsystem operative to control a flow control valve and an exhalation valve of the ventilator according to the preset waveform, the preset inspiratory time T<sub>INSP—

SET</sub>, and the larger amount between the inspiratory flow Q<sub>INSP—

SET</sub> modulated by the decelerating inspiratory flow corrector and an inspiratory pressure controller flow Q<sub>INSP—

PRSCTL</sub>.

30. The circuit of claim 29, wherein the volume assured pressure control system further comprises a patient volume observer operative to provide the estimated patient volume VOL_TID—

_EST from a measured machine delivered net volume VOL_NET.

31. The circuit of claim 30, wherein the measured machine delivered net volume VOL_NET is integrated from a net flow Q_NET defined as a flow difference between a measure inspiratory flow Q_INSP and a measured expiratory flow Q_EXP.

32. The circuit of claim 31, wherein the volume assured pressure control system further comprises a circuit volume estimator operative to provide an estimated circuit volume VOL_CKT—

_EST according to an estimated circuit compliance.

33. The circuit of claim 32, wherein the patient volume estimator is operative to subtract the estimated circuit volume VOL_CKT—

_EST from the measured machine delivered net volume VOL_NET as the estimated patient volume VOL<sub>TID—

EST</sub> and output the estimated patient volume VOL<sub>TID—

EST</sub> to the volume assurance controller.

34. The circuit of claim 29, wherein the volume assured pressure control system further comprises a patient flow sensor operative to provide the measured patient volume VOL_TID—

_Y by integrating a patient flow Q_Y measured thereby.

35. The circuit of claim 29, wherein the volume assurance controller further comprises a gain scheduler operative to provide a weighting gain K_VTID as a function of a volume percentage VOL_PCT—

_ERR, wherein the volume percentage VOL<sub>PCT—

ERR</sub> is defined as an absolute value of a volume error VOL<sub>TID—

ERR</sub> between a preset assured volume VOL<sub>ASS—

SET</sub> and the estimated or measured patient volume VOL<sub>TID—

EST</sub> or VOL<sub>TID—

Y</sub> divided by the preset assured volume VOL<sub>ASS—

SET</sub>.

36. The circuit of claim 35, wherein the volume compensation factor VOL_TID—

_CTL is initialized with an initial value INI<sub>CKT—

VOL</sub> at a first breath of ventilation provided by the patient ventilation circuit.

37. The circuit of claim 36, wherein the volume assurance controller further comprises a multiplier for multiplying the weighting gain K_VTID with the volume error VOL_TID—

_ERR.

38. The circuit of claim 37, wherein the volume assurance controller further comprises an integrator operative to add an output of the multiplier with the volume compensation factor VOL_TID—

_CTL obtained from a previous breath.

39. The circuit of claim 29, wherein the decelerating inspiratory flow corrector is operative to compute a maximum peak inspiratory flow Q_INSP—

_PEAK by;

40. The circuit of claim 29, wherein the decelerating inspiratory flow corrector is operative to compute an a modulated decelerating inspiratory flow Q_INSP—

_SET by;

41. The circuit of claim 29, wherein the servo control subsystem further comprises:

an inspiratory pressure servo controller operative to output an inspiratory pressure controller flow Q<sub>INSP—

PRSCTL</sub> computed based on an error between a preset inspiratory pressure PRS<sub>INSP—

SET</sub> captured at the beginning of every breath and a measured patient pressure P_Y;

a comparator operative to output a final inspiratory flow Q<sub>INSP—

DES</sub> from the larger amount between the modulated decelerating inspiratory flow Q<sub>INSP—

SET</sub> and the inspiratory pressure controller flow Q<sub>INSP—

PRSCTL</sub>;

an inspiratory flow servo controller operative to receive the final inspiratory flow Q<sub>INSP—

DES</sub> and a preset maximum allowable inspiratory flow Q<sub>INSP—

MAX</sub> to generate a flow control valve signal FCV_D/A according to the final inspiratory flow Q<sub>INSP—

DES</sub> restricted under the preset maximum allowable inspiratory flow Q<sub>INSP—

MAX</sub>; and

an exhalation pressure servo controller operative to open or close the exhalation valve of the ventilator.

42. The circuit of claim 41, wherein the exhalation pressure servo controller is operative to open or close the exhalation valve according to an exhalation valve pressure command PRS_EXH—

_DES.

44. The method of claim 42, further comprising:

d) initializing the circuit compliance pressure compensation factor VOL<sub>TID—

CTL</sub> to the initial value INI<sub>CKT—

VOL</sub> when any user setup parameter of the ventilation system is changed.

46. The method of claim 44, wherein when the estimated patient volume VOL_TID—

_EST is selected for generating the volume compensation factor VOL<sub>TID—

CTL</sub>, step (a) further comprises;

a1) providing a machine delivered net flow Q_NET by computing a flow differential of a measured inspiratory flow Q_INSP and a measured expiratory flows Q_EXP; and

a2) integrating the machine delivery net flow Q_NET into the machine delivered net volume VOL_NET.

48. The method of claim 46, wherein when the net flow Q_NET is detected to cross zero during an inspiratory phase, at the start of an expiratory phase following the inspiratory phase, the estimated circuit volume VOL_CKT—

_EST and the estimated patient volume VOL<sub>TID—

EST</sub> are updated, and the measured machine delivered net volume VOL_NET is reset.

43. A method for circuit compliance compensated volume assurance pressure control in a patient respiratory ventilation system, comprising:

a) measuring a patient volume VOL<sub>TID—

Y</sub> through a flow sensor installed at a patient piece of a patient circuit in the ventilation system, or estimating a patient volume VOL<sub>TID—

EST</sub> based on a machine delivered net volume VOL_NET and a circuit compliance C_T of the patient circuit; and

b) predetermining an initial value INI<sub>CKT—

VOL</sub> for a circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> and updating the volume compensation factor VOL<sub>TID—

CTL</sub> based on a preset assured volume VOL<sub>ASS—

SET</sub> and the patient volume VOL<sub>TID—

Y</sub> or VOL<sub>TID—

EST</sub> for each breath; and

c) generating an inspiratory flow Q<sub>INSP—

SET</sub> according to a predetermined waveform, a preset inspiratory time T_INSP, a preset assured volume VOL<sub>ASS—

SET</sub>, and the volume compensation factor VOL<sub>TID—

CTL</sub>.

45. The method of claim 43, further comprising a step of resetting and updating the measured patient volume VOL_TID—

_Y and/or the measured machine delivered net volume VOL_NET at the beginning of every inspiratory phase.

47. The method of claim 45, wherein step (a) further comprising:

a3) deriving a relationship between circuit pressure P_Y and circuit volume V_CC from the circuit compliance C_T;

a4) estimating a circuit volume VOL<sub>CKT—

EST</sub> from the relationship by providing a measured patient circuit P_Y; and

a5) subtracting the estimated circuit volume VOL<sub>CKT—

EST</sub> from the measured machine delivered net volume VOL_NET to obtain the estimated patient volume VOL<sub>TID—

EST</sub>.

49. The method of claim 47, wherein when the net flow Q_NET does not cross zero during an inspiratory phase, the estimated circuit volume VOL_CKT—

_EST and the estimated patient volume VOL<sub>TID—

EST</sub> are updated, and the measured machine delivered net volume VOL_NET is reset at the earlier when the net flow Q_NET crosses zero after the expiratory phase starts or when the expiratory phase has started over a predetermined period of time before the net flow Q_NET has crossed zero.

50. The method of claim 43, wherein step (b) further comprises:

b1) computing a volume error percentage VOL<sub>PCT—

ERR</sub> defined as a ratio of an absolute value of a volume error VOL<sub>TID—

ERR</sub> to a preset assured volume VOL<sub>ASS—

SET</sub>, wherein the volume error VOL<sub>TID—

ERR</sub> is a volume differential between the preset assured volume VOL<sub>ASS—

SET</sub> and the patient volume VOL<sub>TID—

Y</sub> or VOL<sub>TID—

EST</sub>;

b2) determining a gain K_VTID as a function of the volume error percentage VOL<sub>PCT—

ERR</sub>, so as convert the volume error VOL<sub>TID—

ERR</sub> into a volume correction for the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub>; and

b3) updating the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> by adding the volume correction thereto.

51. The method of claim 49, wherein step (b2) further comprising multiplying the gain K_VTID with the volume error VOL_TID—

_ERR to obtain the volume correction.

52. The method of claim 51, wherein step (b) further comprising:

b4) limiting the updated circuit compliance volume compensation factor between a predetermined allowable range.

53. The method of claim 43, wherein step (c) further comprises:

c1) computing a maximum peak flow Q<sub>INSP—

PEAK</sub> by;

$Q_{\mathrm{INSP\_PEAK}}=\frac{4/3*\left({\mathrm{VOL}}_{\mathrm{ASS\_SET}}+{\mathrm{VOL}}_{\mathrm{TID\_CTL}}\right)*60}{T_{\mathrm{INSP\_SET}}};<br><br>$

c2) computing a modulated decelerating inspiratory flow by;

54.

55. The method of claim 54, further comprising a step of generating an exhalation valve command to control open/close status of an exhalation valve.

56. The method of claim 55, further comprising a step of closing the exhalation valve during an inspiratory phase.