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

• US 7,886,739 B2
• Filed: 10/11/2005
• Issued: 02/15/2011
• 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: Soliman, Ihab S., Duquette, Steven
• Primary Examiner(s): Bianco; Patricia M
• Assistant Examiner(s): PATEL, NIHIR B
• Application Number:
  US11/247,568
• Publication Number:
  US 20070089738A1
• Time in Patent Office: 1,953 Days
• Field of Search: 128/200.24, 128/203.12, 128/203.13, 128/204.18, 128/204.21, 128/204.22, 128/204.23, 128/204.24, 128/204.25, 128/204.26, 702/1, 702/45, 702/50, 702/55, 702/127, 702/138, 700/90, 700/213, 700/231, 700/240, 700/244, 700/281, 700/282, 700/301, 700/305, 222/1, 222/3, 222/52, 222/25
• US Class Current: 128/204.21
• 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 circuit compliance compensated volume control system in a patient respiratory ventilation system and method, including: a circuit compliance estimator, to provide a relationship between a circuit volume and a differential pressure between a circuit pressure and a positive end-expiratory pressure (PEEP) of the respiratory circuit, a circuit volume estimator, operative to provide an estimated circuit volume based on the relationship between the circuit volume and the differential pressure, a patient volume observer, operative to provide an estimated patient volume by subtracting the estimated circuit volume from a measured machine delivered net volume, and a volume delivery controller, operative to update the machine delivered net volume based on the estimated patient volume and a set tidal volume.

Claims

1. A circuit compliance compensated volume control system in a patient respiratory ventilation system, the volume control 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 positive end-expiratory pressure 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 measured machine delivered net volume VOL_NET; and

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

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

SET</sub>,

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>TID—

ERR</sub>; and

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

CTL</sub> by adding a product of the gain VOL_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, and

wherein the volume error VOL<sub>TID—

ERR</sub> is 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>.

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,

CKT_CPM_SLP is a slope of the linear relationship, and

CKT_CMP_INT 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_NETis 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_NETis 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 the volume error VOL_TID—

_ERR.

12. 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>.

13. The system of claim 12, wherein:

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

CTL</sub> is computed according to;

14. The system of claim 13, wherein the estimated inspiratory time {circumflex over (T)}_INSP—

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

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

SET</sub>.

15. The system of claim 14, 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.

16. The system of claim 15, wherein:

17. The system of claim 12, 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>.

18. The system of claim 1, 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.

19. The system of claim 1, 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.

20. The system of claim 19, 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>.

21. The system of claim 19, wherein the measured patient volume VOL_TID—

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

22. The system of claim 19, 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.

23. The system of claim 22, 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.

24. The system of claim 1, 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.

25. The system of claim 1, wherein the gain K_VTID increases and decreases with the volume error percentage VOL_PCT—

_ERR.

26. The system of claim 1, 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.

27. The system of claim 26, wherein the breathing cycles cycle from an inspiratory phase to an expiratory phase if VOL_INSP≦

VOL<sub>SET—

CTL</sub>.

28. The system of claim 1, 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—

EST</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.

29. The system of claim 28, 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>.

30. The system of claim 1, 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>.

31. The system of claim 1, wherein the virtual sensor includes a Y flow sensor for measuring the patient volume VOL_TID—

_Y from the patient circuit.

32. The system of claim 31, wherein the measured machine delivered net volume VOL_NET and the a measured patient volume VOL_TID—

_Y are reset at the beginning at every inspiratory phase.

33. The system of claim 31, 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.

34. The system of claim 33, 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.

35. A method for circuit compliance compensated volume control in a patient respiratory ventilation system, the method 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_T 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>,

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.

36. The method of claim 35, 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.

37. The method of claim 35, 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.

38. The method of claim 37, 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 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.

39. The method of claim 37, 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 of when;

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

after the expiratory has started for over a predetermined time.

40. The method of claim 35, 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> subtracting the estimated circuit volume VOL<sub>CKT—

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

41. The method of claim 35, further comprising converting the circuit compliance volume compensation factor VOL_TID—

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

CTL</sub>.

42. The method of claim 41, wherein:

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

CTL</sub> is computed according to;

43. The method of claim 41, further comprising providing an updated inspiratory flow Q_I—

_SET 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>.

44. A circuit compliance compensated volume control method used for a patient receiving a machine ventilation through a patient circuit, the method 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;

computing a volume error percentage by dividing an absolute value of the volume error over the set tidal volume;

weighing the feedback volume error by a gain defined by a function of the volume error percentage;

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.

45. The method of claim 44, further comprising a step of adjusting the gain when the error percentage varies.

46. The method of claim 44, wherein the gain is adjusted to zero when the feedback volume error is zero.

47. The method of claim 44, further comprising a step of resetting the measured machine delivered net volume at the beginning of every inspiratory phase.

48. The method of claim 44, further comprising 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.

49. The method of claim 48, further comprising, when the machined delivered net flow does not cross zero during the inspiratory phase, resetting the measured machine delivered net volume when:

the machine delivered net flow crosses zero after the expiratory phase has started, or

the expiratory phase has started over a predetermined period of time before the machine delivered net flow crosses zero.

50. The method of claim 44, further comprising converting the updated circuit compliance volume compensation factor into a circuit compliance flow compensation factor.

51. The method of claim 50, further comprising providing an updated inspiratory flow by adding the circuit compliance flow compensation factor with a predetermined peak inspiratory flow.