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

• US 20070089738A1
• Filed: 10/11/2005
• Published: 04/26/2007
• Est. Priority Date: 10/11/2005
• Status: Active Grant

• Current Assignee: Vyaire Medical 211, Inc. (Becton, Dickinson & Co)
• Original Assignee: CareFusion 207, Inc. (Becton, Dickinson & Co)
• Inventors: Duquette, Steven, Soliman, Ihab
• Granted Patent: US 7,886,739 B2
• Time in Patent Office: Days
• US Class Current: 128/202.220
• 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 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2016/0042 in the expiratory circuit
• CPC Class Codes: A61M 2205/3344 Measuring or controlling pressure at the body treatment site

Abstract

A system and a method for circuit compliance compensated volume control in a patient respiratory ventilation system having a flow regulated feedback servo control loop, a volume delivery controller, and a patient volume observer. In the flow regulated feedback servo control loop, an estimate of patient volume is used for feedback control, such that a tidal volume is achieved upon servo regulation, and the peak inspiratory flow is modulated based on volume error between the set tidal volume and the estimated patient volume. Thereby, a constant inspiratory time and a constant I:E ratio can be maintained. In the volume delivery control, the feedback volume error is normalized to a volume error percentage, and the gain of the controller is dynamically changed based on the volume error percentage, such that the controller effort can be minimized when the volume target is approached. The patient volume observer is operative to estimate the patient delivered volume based on the estimated circuit volume and the measured net delivered volume, while the measured net delivered volume includes effects of leaks and valve dynamics and is synchronously captured with true patient breathing.

Claims

1. A circuit compliance compensated volume control system in a patient respiratory ventilation system, comprising:

a circuit compliance estimator, to provide a relationship between a circuit volume V_CC and a differential pressure Δ

P_Y between a circuit pressure P_Y and a PEEP of the respiratory circuit;

a circuit volume estimator, operative to provide an estimated circuit volume VOL<sub>CKT—

EST</sub> based on the relationship between V_CC and Δ

P_Y;

a patient volume observer, operative to provide an estimated patient volume VOL<sub>TID—

EST</sub> by subtracting the estimated circuit volume VOL<sub>CKT—

EST</sub> from a machine delivered net volume as measured and denoted as VOL_NET; and

a volume delivery controller, operative to update the machine delivered net volume VOL_SYS based on the estimated patient volume VOL<sub>TID—

EST</sub> and a set tidal volume VOL<sub>TID—

SET</sub>.

2. The system of claim 1, wherein the relationship includes a linear relationship expressed as V_CC=CKT_CMP_SLP·

(P_Y−

PEEP)+CKT_CMP_INT in a V_CC−

Δ

P coordinate, where CKT_CPM_SLP is a slope of the linear relationship and CKT<sub>—

CMPINT</sub> is an intercept of the linear relationship and Δ

P_Y axis.

3. The system of claim 1, wherein the circuit compliance estimator is operative to measure the responsive pressure differential Δ

P_Y at various circuit volumes V_CC before the patient is receiving the machine ventilation, so as to estimate the relationship.

4. The system of claim 1, wherein the measured machine delivered net volume VOL_NET is derived by integration of a net flow Q_NET defined as a differential flow between a measured inspiratory flow Q_INSP and a measure expiratory flow Q_EXP.

5. The system of claim 4, further comprising an adder/subtractor for receiving the measured inspiratory and expiratory flows Q_INSP and Q_EXP to compute the net flow Q_NET.

6. The system of claim 5, further comprising an integrator for integrating the flow differential Q_NET into the measured machine delivered net volume VOL_NET.

7. The system of claim 1, wherein the measured machine delivered volume VOL_NET is updated and reset at the beginning of every inspiratory phase.

8. The system of claim 1, wherein when a measured differential flow Q_NET crosses zero during an inspiratory phase, 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 are reset at the start of the expiratory phase following the inspiratory phase.

9. The system of claim 8, wherein when the differential flow Q_NET does not cross zero during the inspiratory phase, the estimated circuit volume and the estimated patient volume VOL_TID—

_EST are updated, and the measured machine delivered net volume VOL_NET is reset when the differential flow Q_NET crosses zero after the expiratory phase starts, or when the expiratory phase has started for a predetermined period of time before the differential flow Q_NET has been detected to cross zero.

10. The system of claim 9, wherein the predetermined period is about 100 msec.

11. The system of claim 1, further comprising an adder/subtractor for computing a volume error VOL_TID—

_ERR defined as the volume differential between the set tidal volume VOL<sub>TID—

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

EST</sub>.

12. The system of claim 11, wherein the volume delivery controller further comprises:

an error percentage converter for providing a volume error percentage VOL<sub>PCT—

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

ERR</sub> to the set tidal volume VOL<sub>TID—

SET</sub>;

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

ERR</sub>; and

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

CTLK</sub> by adding a product of the gain K_VTID and the volume error VOL<sub>TID—

ERR</sub> thereto, wherein the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> is updated at the beginning of every inspiratory phase.

13. The system of claim 12, wherein the volume delivery controller further comprises a volume restrictor to prevent the circuit compliance volume compensation factor VOL_TID—

_CTL that is lower than a minimum value from being output.

14. The system of claim 12, further comprising:

a flow sensor operative to measure a patient flow Q_Y; and

an integrator operative to provide a measured patient volume VOL<sub>TID—

Y</sub> by integrating the measured patient flow Q_Y.

15. The system of claim 14, further comprising a volume limiter operative to freeze computation of an output VOL_TID—

_CTL of the volume delivery controller when the measured patient volume VOL<sub>TID—

Y</sub> is larger than or equal to the set tidal volume VOL<sub>TID—

SET</sub>.

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

_Y and VOL_NET are reset at the beginning at every inspiratory phase.

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

_Y and the measured machine delivered net volume VOL_NET are reset at the beginning of an expiratory phase when differential flow Q_NET between a measured inspiratory flow Q_INSP and a measured expiratory flow Q_EXP crosses zero in an inspiratory phase followed by the expiratory phase.

18. The system of claim 17, wherein when the differential flow Q_NET does not crosses zero during the inspiratory phase, the measured patient volume VOL_TID—

_Y and the measured machine delivered net volume VOL_NET are reset at the time the differential flow Q_NET crosses zero after the expiratory phase starts or when the expiratory phase has started for a predetermined period of time before the differential flow Q_NET crosses zero.

19. The system of claim 12, wherein the circuit compliance volume compensation factor VOL_TID—

_CTL is reset to INI_CKT_VOL whenever any user setting of the system is changed.

20. The system of claim 12, wherein the gain K_VTID increases and decreases with the volume error percentage VOL_PCT—

_ERR.

21. The system of claim 12, further comprising:

an adder/subtractor operative to add the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> with the set tidal volume VOL<sub>TID—

SET</sub> into the desired machine delivered net volume VOL<sub>SET—

CTL</sub>;

an integrator for integrating the measured inspiratory flow Q_INSP into an actual inspiratory volume VOL_INSP; and

a phase detector for determining the current breathing phase by comparing the desired machine delivered net volume VOL<sub>SET—

CTL</sub> and the actual inspiratory volume VOL_INSP.

22. The system of claim 21, wherein the breathing cycles is cycling from an inspiratory phase to an expiratory phase if VOL_INSP≧

VOL<sub>SET—

CTL</sub>.

23. The system of claim 11, further comprising a volume-to-flow converter to convert the circuit compliance compensation factor VOL_TID—

_CTL into a circuit compliance flow compensation factor Q<sub>TID—

CTL</sub>.

24. The system of claim 23 the circuit compliance flow compensation factor Q_TID—

_CTL is computed as;

25. The system of claim 24, wherein the estimated inspiratory time {circumflex over (T)}_INSP—

_EST is determined based on a predetermined peak inspiratory flow Q<sub>PEAK—

SET</sub> and the set tidal volume VOL<sub>TID—

SET</sub>.

26. The system of claim 25, wherein the predetermined peak inspiratory flow Q_PEAK—

_SET equals to a preset peak inspiratory flow constant Q<sub>PEAK—

USER</sub> for a square waveform or a function of the preset peak inspiratory flow constant Q<sub>PEAK—

USER</sub> and time t into an inspiratory phase for a decelerating waveform.

27. The system of claim 26, wherein:

28. The system of claim 23, further comprising an adder/subtractor to add the predetermined peak inspiratory flow Q_PEAK—

_SET with the circuit compliance flow compensation factor Q<sub>TID—

CTL</sub> into a required inspiratory flow Q<sub>I—

SET</sub>.

29. A circuit compliance compensated volume control system in a patient respiratory ventilation system, comprising:

a virtual sensor operative to provide a measured patient volume VOL<sub>TID—

Y</sub> or to estimate a patient volume VOL<sub>TID—

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

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

CTL</sub> based on the measure patient volume VOL<sub>TID—

Y</sub> or the estimated patient volume VOL<sub>TID—

EST</sub> and a set tidal volume VOL<sub>TID—

SET</sub>.

30. The system of claim 29, wherein the volume delivery controller comprises:

a gain scheduler for weighing a volume error VOL<sub>TID—

ERR</sub> according to a ratio of an absolute value of the volume error VOL<sub>TID—

ERR</sub> to the set tidal volume VOL<sub>TID—

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

ERR</sub> is defined as a volume differential between the measured patient volume VOL<sub>TID—

Y</sub> or the estimated patient volume VOL<sub>TID—

EST</sub> and the set tidal volume VOL<sub>TID—

SET</sub>; and

a volume integrator to update the circuit compliance circuit volume compensation factor VOL<sub>TID—

CTL</sub> with the volume error VOL<sub>TID—

ERR</sub> weighed by the gain scheduler.

31. The system of claim 30, wherein the gain scheduler is operative to provide a gain that increases and decreases with the ratio of the volume error VOL_TID—

_ERR to the set tidal volume VOL<sub>TID—

SET</sub>.

32. The system of claim 29, further comprising a volume-to-flow converter to convert the circuit compliance volume compensation factor VOL_TID—

_CTL into a circuit compliance volume flow compensation factor Q<sub>TID—

CTL</sub>, so as to provide a desired inspiratory flow Q<sub>I—

SET</sub>.

33. The system of claim 29, wherein the virtual sensor includes a Y flow sensor for measuring the patient volume VOL_TID—

_Y from the patient circuit.

34. The system of claim 29, wherein the measured machine delivered net volume VOL_NET and the measured patient volume VOL_TID—

_Y are reset at the beginning at every inspiratory phase.

35. The system of claim 29, wherein the measured machine delivered net volume VOL_NET and the measured patient volume VOL_TID—

_Y are reset at the time an expiratory starts when a differential flow Q_NET measured to compute the measured machine delivered net volume VOL_NET crosses zero during an inspiratory phase followed by the expiratory phase.

36. The system of claim 35, wherein when the differential flow Q_NET does not cross zero during the inspiratory phase, the measured machine delivered net volume VOL_NET and the measured patient volume VOL_TID—

_Y are reset when the differential flow Q_NET crosses zero after the expiratory starts or when the expiratory phase has started for a predetermined period of time before the flow differential Q_NET crosses zero.

37. A ventilation system, comprising:

a ventilator having an inspiratory port for supplying an inspiratory gas to a patient and an expiratory port for receiving an expiratory gas from the patient;

a patient circuit having an inspiratory limb having one end connected to the inspiratory port, an expiratory limb having one end connected to the expiratory port, and a patient piece having one end merging the other ends of the inspiratory and expiratory limbs and the other end connected to the patient; and

a circuit compliance compensated volume control system, comprising;

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

EST</sub> based on a measured machine delivered net volume VOL_NET and a circuit compliance of the patient circuit, or to provide a patient volume VOL<sub>TID—

Y</sub> measured at the patient piece of the patient circuit; and

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

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

EST</sub> or VOL<sub>TID—

Y</sub> and a set tidal volume VOL<sub>TID—

SET</sub>, so as to update an inspiratory flow Q<sub>INSP—

SET</sub>.

38. The ventilation system of claim 37, wherein the circuit compliance compensated volume control system further comprising a circuit compliance estimator operative to compute a circuit volume VOL_CKT—

_EST based on a relationship between the circuit compliance and a pressure measured at the patient piece of the patient circuit.

39. The ventilation system of claim 38, wherein the patient volume observer is operative to estimate the patient volume by subtracting the estimated circuit volume VOL_CKT—

_EST from the measured machine delivered net volume VOL_NET.

40. The ventilation system of claim 38, wherein the circuit compliance compensated volume control system further comprises a volume-to-flow converter for converting the circuit compliance volume compensation factor VOL_TID—

_CTL into a circuit compliance flow compensation factor Q<sub>TID—

CTL</sub>.

41. The ventilation system of claim 37, further comprising an adder/subtactor for updating the inspiratory flow Q_INSP—

_SET by adding the circuit compliance flow compensation factor Q<sub>TID—

CTL</sub> thereto.

42. The ventilation system of claim 37, wherein the volume delivery controller further comprises:

an error percentage converter for providing an error percentage defined by a ratio of an absolute value of a feedback volume error VOL<sub>TID—

ERR</sub> to the set tidal volume VOL<sub>TID—

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

ERR</sub> is defined as a volume differential between the measured patient volume VOL<sub>TID—

Y</sub> or the estimated patient volume VOL<sub>TID—

EST</sub> and the set tidal volume VOL<sub>TID—

SET</sub>;

a gain scheduler operative to provide a gain K_VTID for weighing the feedback volume error VOL<sub>TID—

ERR</sub> according to the error percentage; and

a volume integrator for updating the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> by adding the weighed volume error thereto.

43. The system of claim 37, further comprising a servo control subsystem for controlling the inspiratory and expiratory ports according to the updated inspiratory flow Q_INSP—

_SET and an inspiratory time estimated based on the set tidal volume VOL<sub>TID—

SET</sub> and a predetermined peak inspiratory flow Q<sub>PEAK—

SET</sub>.

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

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

EST</sub> based on a machine delivered net volume and a circuit compliance of a patient circuit of the patient respiratory ventilation system, or measuring a patient volume VOL<sub>TID—

Y</sub> via a flow sensor located at a patient piece of the patient circuit; and

b) updating a circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> based on a set tidal volume VOL<sub>TID—

SET</sub> and a feedback volume error VOL<sub>TID—

ERR</sub>, wherein the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> has an initial setup value INI_CKT_VOL and the feedback volume VOL<sub>TID—

ERR</sub> is defined as a volume differential between the patient volume VOL<sub>TID—

EST</sub> or VOL<sub>TID—

Y</sub> and the set tidal volume VOL<sub>TID—

SET</sub>.

45. The method of claim 44, wherein the machine delivered net volume VOL_NET and the measured patient volume VOL_TID—

_Y are reset and updated at the start of every inspiratory phase.

46. The method of claim 44, wherein when the patient volume is estimated, step (a) further comprises:

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

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

47. The method of claim 46, wherein 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 and the measured patient volume VOL<sub>TID—

Y</sub> are reset at the start of an expiratory phase if the machine delivered net flow Q_NET has been detected to cross zero during the inspiratory phase.

48. The method of claim 46, wherein when the net flow Q_NET does not cross zero during the inspiratory phase, the estimated circuit volume VOL_CKT—

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

EST</sub> are updated, and the machine delivered net flow VOL_NET and the measured patient volume VOL<sub>TID—

Y</sub> are reset at the earlier when;

the net flow Q_NET crosses zero after the expiratory phase starts; and

after the expiratory has started for over a predetermined time.

49. The method of claim 44, wherein step (a) further comprises:

a3) providing a relationship between a patient circuit pressure P_Y and a circuit volume V_CC of the respiratory circuit;

a2) providing an estimated circuit volume VOL<sub>CKT—

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

a3) providing the estimated patient volume VOL<sub>TID—

EST</sub> by subtracting the estimated circuit volume VOL<sub>CKT—

EST</sub> from a machine delivered net volume VOL_NET.

50. The method of claim 44, wherein step (b) further comprises:

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

ERR</sub> by dividing an absolute value of the volume error VOL<sub>TID—

ERR</sub> over the set tidal volume VOL<sub>TID—

SET</sub>;

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

ERR</sub>; and

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

CTL</sub> by adding a product of the gain K_VTID and the volume error VOL<sub>TID—

ERR</sub> thereto.

51. The method of claim 44, further comprising the step of:

c) converting the circuit compliance volume compensation factor VOL<sub>TID—

CTL</sub> into a circuit compliance flow compensation factor Q<sub>TID—

CTL</sub>.

52. The method of claim 51, wherein the circuit compliance flow compensation factor Q_TID—

_CTL is computed by;

Q<sub>TID—

CTL</sub>=60·

(VOL<sub>TID—

CTL</sub>/{circumflex over (T)}<sub>INSP—

EST</sub>), where {circumflex over (T)}<sub>INSP—

EST</sub> is an inspiratory time estimated based on the set tidal volume VOL<sub>TID—

SET</sub>, a preset inspiratory peak flow Q<sub>PEAK—

USER</sub>, and a pre-selected waveform.

53. The method of claim 51, further comprising the step of:

d) providing an updated inspiratory flow Q<sub>I—

SET</sub> by adding the circuit compliance flow compensation factor flow Q<sub>TID—

CTL</sub> with a predetermined peak inspiratory flow Q<sub>PEAK—

SET</sub>.

54. A circuit compliance compensated volume control method used for a patient receiving a machine ventilation through a patient circuit, comprising:

providing a measured patient volume or an estimated patient volume by subtracting a circuit volume estimated based on a circuit compliance of the patient circuit from a measured machine delivered net volume;

estimating a feedback volume error by computing a volume differential between the patient volume and a set tidal volume;

weighing the feedback volume error by a gain defined by a ratio between an absolute value of the feedback volume error and the set tidal volume;

presetting an initial value of a circuit compliance volume compensation factor; and

updating the circuit compliance volume compensation factor based on the feedback volume error weighed by the gain.

55. The method of claim 54, further comprising a step of adjusting the gain when the error percentage varies.

56. The method of claim 54, wherein the gain is adjusted to zero when the feedback volume error is zero.

57. The method of claim 54, further comprising a step of resetting the measured machine delivered net volume at the beginning of every inspiratory phase.

58. The method of claim 54, further comprising a step of resetting the measured machine delivered net volume at the beginning of an expiratory phase only when a measured machine delivered net flow crosses zero during an inspiratory phase followed by the expiratory phase.

59. The method of claim 58, when the machined delivered net flow does not cross zero during the inspiratory phase, further comprising resetting the measured machine delivered net volume when the machine delivered net flow crosses zero after the expiratory phase has started, or when the expiratory phase has started over a predetermined period of time before the machine delivered net flow crosses zero.

60. The method of claim 54, further comprising a step of converting the updated circuit compliance volume compensation factor into a circuit compliance flow compensation factor.

61. The method of claim 60, further comprising a step of providing an updated inspiratory flow by adding the circuit compliance flow compensation factor with a predetermined peak inspiratory flow.