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

US 20070101992A1
Filed: 11/09/2005
Published: 05/10/2007
Est. Priority Date: 11/09/2005
Status: Active Grant

First Claim

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

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

P_Ybetween a circuit pressure P_Yand a PEEP for a patient circuit used in the ventilation system;

a circuit volume estimator, operative to estimate a circuit volume VOL_CKT_—_ESTdistributed to the patient circuit based on the relationship provided by the circuit compliance estimator;

a patient volume observer, operative to provide an estimated patient volume VOL_TID_—_ESTby subtracting the estimated circuit volume from a measured machine delivered net volume VOL_NET; and

a pressure-regulated volume controller, operative to update a peak airway pressure P_SETbased on the estimated patient volume VOL_TID_—_ESTand a set tidal volume VOL_TID_—_SET.

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Abstract

A system and a method for circuit compliance compensated pressure control in a patient respiratory ventilation system, having a pressure regulated feedback servo control loop, a pressure-regulated volume controller, and a patient volume observer. The patient volume observer is operative to estimate a patient volume, that is, the volume actually delivered to the patient by accounting for volume deviation or loss caused by patient circuit leakage and valve dynamics. Based on the difference between the estimated patient volume and a set tidal volume, the pressure-regulated volume controller is operative to generate and update a circuit compliance pressure compensation factor. The pressure regulated feedback servo control loop is operative to modulate the peak airway pressure based on the circuit compliance pressure compensation factor, so as to achieve the set tidal volume while maintaining a constant inspiratory time and a constant I:E ratio.

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59 Claims

1. A circuit compliance compensated pressure regulated volume control system in a patient respiratory ventilation system, comprising:
- a circuit compliance estimator, to provide a relationship between a circuit volume V_CCand a differential pressure Δ
  
  P_Ybetween a circuit pressure P_Yand a PEEP for a patient circuit used in the ventilation system;
  
  a circuit volume estimator, operative to estimate a circuit volume VOL_CKT_—_ESTdistributed to the patient circuit based on the relationship provided by the circuit compliance estimator;
  
  a patient volume observer, operative to provide an estimated patient volume VOL_TID_—_ESTby subtracting the estimated circuit volume from a measured machine delivered net volume VOL_NET; and
  
  a pressure-regulated volume controller, operative to update a peak airway pressure P_SETbased on the estimated patient volume VOL_TID_—_ESTand a set tidal volume VOL_TID_—_SET.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
- - 2. The system of claim 1, wherein the relationship includes a linear relationship expressed as VOL_CC=CKT_CMP_SLP·
    - (P_Y−
      
      PEEP)+CKT_CMP_INTin a V_CC−
      
      Δ
      
      P_Ycoordinate, where CKT_CPM_SLPis a slope of the linear relationship and CKT_CMP_INTis an intercept of the linear relationship and a Δ
      
      P_Yaxis.
  - 3. The system of claim 1, wherein the circuit compliance estimator is operative to measure the responsive pressure differential Δ
    - P_Yat various predetermined circuit volumes V_CCbefore 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_NETis derived by integration of a net flow Q_NETdefined as a differential flow between a measured inspiratory flow Q_INSPand 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_INSPand Q_EXPto compute the net flow Q_NET.
  - 6. The system of claim 5, further comprising an integrator for integrating the flow differential Q_NETinto the machine delivered net volume VOL_NET.
  - 7. The system of claim 1, wherein machine delivered net volume VOL_NETis updated and reset at the start of the every inspiratory phase.
  - 8. The system of claim 1, wherein the estimated circuit volume VOL_CKT_—
    - _EST, the estimated patient volume VOL_TID_—_ESTare updated and the measured machine delivered net volume VOL_NETis reset at the start of an expiratory phase following an inspiratory phase during which a net flow Q_NETdefined as a difference between a measured inspiratory flow Q_INSPand a measured expiratory flow Q_EXPzero-crossing has been detected.
  - 9. The system of claim 8, wherein when the net flow Q_NETdoes not cross zero during the inspiratory phase, the estimated circuit and patient volumes VOL_CKT_—
    - _ESTand VOL_TID_—_ESTare updated and the measured machine delivered net volume VOL_NETis reset when the net flow Q_NETcrosses zero after the expiratory phase starts or when the expiratory phase has started over a predetermined period of time before the net flow Q_NETzero-crossing is detected.
  - 10. The system of claim 9, wherein the predetermined period of time is about 100 msec.
  - 11. The system of claim 1, further comprising an adder/subtractor for computing a volume error VOL_TID_—
    - _ERRby subtracting the estimated patient volume VOL_TID_—_ESTfrom the set tidal volume VOL_TID_—_SET.
  - 12. The system of claim 1, wherein the pressure-regulated volume controller further comprises:
    - an error percentage converter providing a volume error percentage VOL_PCT_—_ERRdefined as a ratio of an absolute value of a volume error to the set tidal volume VOL_TID_—_SET, wherein the volume error VOL_TID_—_ERRis a volume differential between the set tidal volume VOL_TID_—_SETand an estimated patient volume VOL_TID_—_EST;
      
      a gain scheduler for determining a gain K_PTID; and
      
      a pressure integrator for updating a previously computed circuit compliance pressure compensation factor PRS_TID_—_CTLby adding a product BRTH_PTID_—_CTLof the gain K_PTIDand the volume error VOL_TID_—_ERRthereto at the start of every inspiratory phase.
  - 13. The system of claim 12, wherein the gain K_PTIDdecreases and increases as the volume error percentage VOL_PCT_—
    - _ERR.
  - 14. The system of claim 12, wherein the circuit compliance pressure compensation factor PRS_TID_—
    - _CTLis initialized with a preset value INI_CKT_PRS in a first breath from which computation of the circuit compliance pressure compensation factor PRS_TID_—_CTLis started.
  - 15. The system of claim 14, wherein the circuit compliance pressure compensation factor PRS_TID_—
    - _CTLis reset to the preset value INI_CKT_PRS any time when any user preset parameter is changed.
  - 16. The system of claim 12, wherein the pressure-regulated volume controller further comprises a multiplier for computing the product BRTH_PTID_—
    - _CTLof the gain K_PTIDand the volume error VOL_TID_—_ERR.
  - 17. The system of claim 16, wherein the pressure-regulated volume controller further comprises a rate limiter for limiting the product BRTH_PTID_—
    - _CTLwithin an allowable range, such that an amount of pressure correction allowed for each breath is limited within such allowable range.
  - 18. The system of claim 17, wherein the allowable range includes a maximum value MAX_PRS_—
    - _RATEand a minimum value MIN_PRS_—_RATE, and the product BRTH_PTID_—_CTLis limited as;
      
      BRTH_PTID_—_CTL=max(KPTID*VOL_TID_—_ERR, MIN_PRS_—_RATE)
      BRTH_PTID_—_CTL=min(BRTH_PITD_—_CTL, MAX_PRS_—_RATE).
  - 19. The system of claim 18, wherein the minimum value MIN_PRS_—
    - _RATEof the product BRTH_PTID_—_CTLis equal to negative maximum value MAX_PRS_—_RATEas MIN_PRS_—=−
      
      MAX_PRS_—_RATE.
  - 20. The system of claim 12, wherein the pressure-regulated volume controller further comprises a pressure restrictor to prevent the circuit compliance pressure compensation factor PRS_TID_—
    - _CTLbeyond a range between a predetermined minimum value MAX_PRS_—_TIDand a predetermined maximum value MIN_PRS_—_TIDfrom being output.
  - 21. The system of claim 20, wherein the predetermined minimum value MIN_{PRS —}
    - _TIDis equal to negative predetermined maximum value MAX_PRS_—_TIDof the circuit compliance pressure compensation factor PRS_TID_—_CTLas;
      
      MIN_PRS_—_TID=−
      
      MAX_PRS_—_TID, and the predetermined value MAX_PRS_—_TIDis computed from an average of a user setup maximum and minimum peak airway pressures for the patient as;
      
      MAX_PRS_—_TID=(PRS_MAX−
      
      PRS_MIN)/2.
  - 22. The system of claim 12, further comprising a flow sensor operative to measure a patient flow Q_Yand an integrator for integrating the measured patient flow Q_Yinto a measured patient volume VOL_TID_—
    - _Y.
  - 23. The system of claim 22, further comprising a volume limiter operative to freeze an output of the pressure-regulated volume controller at the circuit compliance pressure compensation factor PRS_TID_—
    - _CTLcomputed in the previous breath when the measured patient volume VOL_TID_—_Yis equal to or larger than the set tidal volume VOL_TID_—_SET.
  - 24. The system of claim 23, wherein the measured machine delivered net volume VOL_NETand the measured patient volume VOL_TID_—
    - _Yare reset at the beginning at every inspiratory phase.
  - 25. The system of claim 22, wherein when a net flow Q_NETdefined as a difference between a measured inspiratory flow Q_INSPand a measured expiratory flow Q_EXPcrosses zero during an inspiratory phase, the measured machine delivered net volume VOL_NETand the measured patient volume VOL_TID_—
    - _Yare reset at the beginning of an expiratory phase following the inspiratory phase.
  - 26. The system of claim 25, wherein when a net flow Q_NEThas not been detected to cross zero during the inspiratory phase, the measured machine delivered net volume VOL_NETand the measured patient volume VOL_TID_—
    - _Yare reset at the time when the net flow Q_NETcrosses zero after an expiratory phase or at the time the expiratory phase has started over a predetermined period of time before the net flow Q_NETcrosses zero.
  - 27. The system of claim 1, further comprising:
    - an integrator for integrating a net flow Q_NETinto the measured machine delivered net volume VOL_NET, wherein the net flow Q_NETis defined as a flow differential between a measured inspiratory flow Q_INSPand a measured expiratory flow Q_EXP;
      
      a phase detector counting time t_INSPinto an inspiratory phase and determining a timing when each machine breath is cycling from an inspiratory phase to an expiratory phase.
  - 28. The system of claim 27, wherein each machine breath is cycling to the expiratory phase when the time entering the inspiratory phase t_INSPreaches a predetermined inspiratory time T_INSP_—
    - _SETas;
      
      t_INSP≧
      
      T_INSP_—_SET.

29. A circuit compliance compensated pressure regulated volume control system in a patient respiratory ventilation system, comprising:
- a patient volume provider operative to provide a measured or estimated patient volume VOL_TID_—_Yor VOL_TID_—_EST, wherein the estimated patient volume is computed based on a measured machine delivered net volume VOL_NETand a circuit compliance C_Tof a patient circuit applied to a patient; and
  
  a pressure-regulated volume controller, operative to generate a circuit compliance compensation pressure factor PRS_TID_—_CTLfor offsetting an airway peak pressure, wherein the circuit compliance compensation pressure factor PRS_TID_—_CTLis generated based on a difference between the patient volume VOL_TID_—_Yor VOL_TID_—_ESTand a set tidal volume VOL_TID_—_SET.
- View Dependent Claims (30, 31, 32, 33, 34, 35, 36)
- - 30. The system of claim 29, wherein the pressure-regulated volume controller further comprises:
    - a gain scheduler for generating a gain K_PTIDaccording to a volume error percentage VOL_PCT_—_ERRwhich is defined as a ratio between an absolute value of a volume error VOL_TID_—_ERRto the set tidal volume VOL_TID_—_SET, where the volume error VOL_TID_—_ERRis defined as a volume differential between the set tidal volume VOL_TID_—_SETand the patient volume VOL_TID_—_Yor VOL_TID_—_EST; and
      
      a pressure integrator to update the circuit compliance circuit pressure compensation factor PRS_TID_—_CTLby adding a product of the gain K_PTIDand the volume error VOL_TID_—_ERRthereon.
  - 31. The system of claim 30, wherein the gain scheduler is operative to adjust magnitude of the gain K_PTIDaccording to the volume error percentage VOL_PCT_—
    - _ERR.
  - 32. The system of claim 30, further comprising a multiplier for computing the product of the gain K_PTIDand the volume error VOL_TID_—
    - _ERR.
  - 33. The system of claim 30, further comprising a pressure correction limiter for limiting the product of the gain K_PTIDand the volume error VOL_TID_—
    - _ERRwithin a predetermined range.
  - 34. The system of claim 30, further comprising an adder to add the circuit compliance pressure compensation factor PRS_TID_—
    - _CTLto an initial set peak airway pressure P_SET_—_INIdefined as;
      
      P_SET_—_INI=(PRS_MAX+PRSM_MIN)/2
  - 35. The system of claim 29, wherein the pressure-regulated volume controller further comprises a pressure restrictor from restricting the circuit compliance pressure compensation factor PRS_TID_—
    - _CTLbeyond a range between a predetermined minimum value MIN_PRS_—_TIDand a pre-determined maximum value MAX_PRS_—_TIDfrom being output.
  - 36. The system of claim 29, wherein the patient volume provider includes either a volume integrator for integrating a patient flow Q_Yinto the measured patient volume VOL_TID_—
    - _Yor a patient volume estimator for computing the estimated patient volume VOL_TID_—_EST.

37. A ventilation system, comprising:
- a ventilator operative having an inspiratory port for supplying an inspiratory gas to a patient and an expiratory port for receiving an expiratory gas from a 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 connected to the other ends of the inspiratory and expiratory limbs and the other end connected to the patient; and
  
  a circuit compliance compensated pressure regulated volume control system, comprising a pressure-regulated volume controller operative to generate a circuit compliance pressure compensation factor based on a volume error defined as a volume differential between a set tidal volume and a volume actually delivered to the patient.
- View Dependent Claims (38, 39, 40, 41, 42, 43, 44, 45, 46, 47)
- - 38. The ventilation system of claim 37, further comprising a device for integrating a patient flow Q_Ymeasured at the patient piece of the patient circuit into a measured patient volume reflecting the volume actually delivered to the patient.
  - 39. The ventilation system of claim 37, further comprising a patient volume observer for providing an estimated patient volume reflecting the volume actually delivered to the patient, wherein the estimated patient volume is obtained based on a measured machine delivered net volume and a circuit compliance of the patient circuit.
  - 40. The ventilation system of claim 39, further comprising a circuit compliance estimator for estimating the circuit compliance as a relationship between a circuit volume and a circuit pressure.
  - 41. The ventilation system of claim 40, further comprising a circuit volume estimator for providing a circuit volume based on the relationship estimated by the circuit compliance estimator.
  - 42. The ventilation system of claim 41, wherein the patient volume observer is operative to provide the estimated patient volume by subtracting the circuit volume from the measured machine delivered net volume.
  - 43. The ventilation system of claim 37, wherein the pressure-regulated volume controller comprises:
    - an error percentage converter for providing a volume error percentage as a ratio of an absolute value of the volume error to the set tidal volume;
      
      a gain scheduler operative to provide a gain K_PTIDfor converting the volume error into an estimated pressure correction; and
      
      a pressure integrator for updating the circuit compliance pressure compensation factor by adding the estimated pressure correction thereto, wherein the circuit compliance pressure compensation factor is initialized into a preset initial value at a first breath when computation thereof is started and updated breath after breath.
  - 44. The ventilation system of claim 43, wherein the pressure-regulated volume controller further comprising a multiplier for multiplying the gain with the volume error to obtain the estimated pressure correction.
  - 45. The ventilation system of claim 43, wherein the circuit compliance pressure compensation factor is reset to the initial value when any user preset parameter is changed.
  - 46. The ventilator system of claim 37, further comprising an adder for updating a peak airway pressure by adding the circuit compliance pressure compensation factor thereto.
  - 47. The ventilation system of claim 46, further comprising a servo control subsystem for controlling the inspiratory and expiratory ports according to the updated peak airway pressure.

48. A method for circuit compliance compensated pressure regulated volume control in a patient respiratory ventilation system, comprising:
- a) measuring a patient volume VOL_TID_—_Ythrough a flow sensor installed at a patient piece of a patient circuit in the ventilation system, or estimating a patient volume VOL_TID_—_ESTbased on a machine delivered net volume VOL_NETand a circuit compliance C_Tof the patient circuit; and
  
  b) predetermining an initial value INI_CKT_PRS for a circuit compliance pressure compensation factor PRS_TID_—_CTLand updating the circuit compliance pressure compensating factor PRS_TID_—_CTLbased on a set tidal volume VOL_TID_—_SETand the patient volume VOL_TID_—_Yor VOL_TID_—_ESTfor each breath.
- View Dependent Claims (49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59)
- - 49. The method of claim 48, further comprising:
    - c) initializing the circuit compliance pressure compensation factor PRS_TID_—_CTLto the initial value INI_CKT_PRS when any user setup parameter of the ventilation system is changed
  - 50. The method of claim 48, further comprising a step of resetting and updating the measured patient volume VOL_TID_—
    - _Yand the measured machine delivered net volume VOL_NETat the beginning of every inspiratory phase.
  - 51. The method of claim 50, wherein when the estimated patient volume VOL_TID_—
    - _ESTis selected for generating the circuit compliance pressure compensation factor PRS_TID_—_CTL, step (a) further comprises;
      
      a1) providing a machine delivered net flow Q_NETcomputing a flow differential of a measured inspiratory flow Q_INSPand a measured expiratory flows Q_EXP; and
      
      a2) integrating the machine delivery net flow Q_NETinto the machine delivered net volume VOL_NET.
  - 52. The method of claim 51, wherein step (a) further comprising:
    - a3) deriving a relationship between circuit pressure P_Yand circuit volume V_CCfrom the circuit compliance C_T;
      
      a4) estimating a circuit volume VOL_CKT_—_ESTfrom the relationship by providing a measured patient circuit P_Y; and
      
      a5) subtracting the estimated circuit volume VOL_CKT_—_ESTfrom the measured machine delivered net volume VOL_NETto obtain the estimated patient volume VOL_TID_—_EST.
  - 53. The method of claim 52, wherein when the net flow Q_NETis 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_—
    - _ESTand the estimated patient volume VOL_TID_—_ESTare updated, and the measured machine delivered net volume VOL_NETis reset.
  - 54. The method of claim 52, wherein when the net flow Q_NETdoes not cross zero during an inspiratory phase, the estimated circuit volume VOL_CKT_—
    - _ESTand the estimated patient volume VOL_TID_—_ESTare updated, and the measured machine delivered net volume VOL_NETis reset at the earlier when the net flow Q_NETcrosses zero during the expiratory phase starts or when the expiratory phase has started over a predetermined period of time before the net flow Q_NEThas crossed zero.
  - 55. The method of claim 48, wherein step (b) further comprises:
    - b1) computing a volume error percentage VOL_PCT_—_ERRdefined as a ratio of an absolute value of a volume error VOL_TID_—_ERRto the set tidal volume VOL_TID_—_SET, wherein the volume error VOL_TID_—_ERRis a volume differential between the set tidal volume VOL_TID_—_SETand the patient volume VOL_TID_—_Yor VOL_TID_—_EST;
      
      b2) determining a gain K_PTIDas a function of the volume error percentage VOL_PCT_—_ERR, so as convert the volume error VOL_TID_—_ERRinto a pressure correction for the circuit compliance compensation factor PRS_TID_—_CTL; and
      
      b3) updating the circuit compliance pressure compensation factor PRS_TID_—_CTLby adding the pressure correction thereto.
  - 56. The method of claim 50, wherein step (b2) further comprising multiplying the gain K_PTIDwith the volume error VOL_TID_—
    - _ERRto obtain the pressure correction.
  - 57. The method of claim 56, wherein step (b2) further comprising limiting the pressure correction between a predetermined maximum value and a predetermined minimum value.
  - 58. The method of claim 55, wherein step (b) further comprising:
    - b4) limiting the updated circuit compliance pressure compensation factor between a predetermined allowable range.
  - 59. The method of claim 55, further comprising the step of:
    - d) providing a set peak airway pressure P_SETby adding the updated circuit compliance pressure compensation factor PRS_TID_—_CTLto an initial set peak airway pressureas;
      
      P_SET=PRS_TID_—_CTL+P_SET_—_INI

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Current Assignee
Vyaire Medical 211, Inc. (Becton, Dickinson & Co)
Original Assignee
Viasys Manufacturing
Inventors
Soliman, Ihab, Duquette, Steven

Granted Patent

US 7,918,223 B2
Time in Patent Office

Days
Field of Search
US Class Current

128/204.210
CPC Class Codes

A61M 16/0051   with alarm devices

A61M 16/026   specially adapted for predi...

A61M 2016/0021   with a proportional output ...

A61M 2016/0039   in the inspiratory circuit

A61M 2016/0042   in the expiratory circuit

A61M 2205/3344   Measuring or controlling pr...

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

First Claim

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

First Claim

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Abstract

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59 Claims

Specification

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