System and method for circuit compliance compensated volume assured pressure control in a patient respiratory ventilator
View Patent ↗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 .
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 CKT — EST based on the patient circuit compliance and a patient estimated pressure P y ;
a patient volume observer, operative to estimate a patient volume VOL TID — EST 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 TID — CTL based on a preset assured volume VOL ASS — SET and the estimated patient volume VOL TID — EST , 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 TID — CTL and a preset assured volume VOL ASS — SET .
2. The system of claim 1 , further comprising:
a sensor processor operative to generate and to output the machine delivered net volume VOL NET ;
a netflow Q NET integrator operative to integrate a net flow Q NET value defined as by finding a difference between a measured inspiratory flow Q INSP and a measured expiratory flow Q EXP .
3. The system of claim 2 , wherein said 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 , and the estimated patient volume VOL TID — EST 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 crosses zero;
wherein the system further comprises:
a netflow Q NET zero crossing detector operative to detect a zero-crossing; and
a Q NET finder operative to find Q NET by taking a difference between a measured inspiratory flow Q INSP and a measured expiratory flow Q EXP after said 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 TID — EST 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:
wherein the assurance controller is operative to
generate a dynamic gain K VTID for weighting a volume error VOL TID — ERR between the preset assured volume VOL ASS — SET and the estimated patient volume VOL TID — EST ; and
add the volume compensation factor VOL TID — CTL to the weighted volume error KVTID multiplied with the VOL TID ERR after each 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
VOL
PCT_ERR
by
VOL
PCT_ERR
=
VOL
TID_ERR
VOL
ASS_SET
×
100
%
,
so as to compute the dynamic gain K VTID as a function thereto.
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 product of K VTID and VOL ASS — SET with the volume compensation factor VOL TID — CTL 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 TID — CTL 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 TID — Y 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 ASS — SET and the circuit compliance compensation is disabled, the volume limiter is operative to control the volume assurance controller to output the volume compensation factor using:
a) a volume error computer operative for computing a volume error VOL TID — ERR by a difference between the assured volume VOL ASS — SET preset for a current breath and the patient volume VOL TID — EST estimated from a previous breath;
b) a volume compensation factor computer operative for computing the volume compensation factor of the current breath by adding the volume error VOL TID — ERR to the volume compensator factor obtained from the previous breath; and
c) a volume compensation factor limiter operative for 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 ASS SET , the volume assurance controller is operative to output the volume compensation factor VOL TID — CTL 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:
Q
INSP_PEAK
=
4
/
3
*
(
VOL
ASS_SETk
+
VOL
TID_CTLk
)
*
60
T
INSP_SETk
.
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:
Q
INSP_SET
=
Q
INSP_PEAK
-
T
INSPk
*
Q
INSP_PEAK
2
*
T
INSP_SETk
.
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 TID — CTL based on a patient estimated pressure P y , an estimated or measured patient volume, VOL TID — EST or VOL TID — Y , and a preset assured volume VOL ASS — SET ; and
a decelerating inspiratory flow corrector operative to modulate an inspiratory flow Q INSP — SET based on a preset waveform, a preset inspiratory time T INSP — SET , a preset assured volume VOL ASS — SET and the volume compensation factor VOL TID — CTL 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 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 TID — EST and output the estimated patient volume VOL TID — EST 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 ; and
a measured patient volume integrator operative to integrate the measured patient volume producing a patient flow Q y .
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 PCT — ERR is defined as an absolute value of a volume error VOL TID — EST between a preset assured volume VOL ASS — SET and the estimated or measured patient volume VOL TID — EST or VOL TID — Y divided by the preset assured volume VOL ASS — SET .
24. The system of claim 23 , wherein the volume compensation factor VOL TID — CTL is initialized with an initial value INI CKT — VOL 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:
Q
INSP_PEAK
=
4
/
3
*
(
VOL
ASS_SETk
+
VOL
TID_CTLk
)
*
60
T
INSP_SETk
.
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:
Q
INSP_SETk
=
Q
INSP_PEAKk
-
T
INSPk
*
Q
INSP_PEAKk
2
*
T
INSP_SETk
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 TID — CTL based on an estimated or measured patient volume, VOL TID — EST or VOL TID — Y , and a preset assured volume VOL ASS — SET , and
a decelerating inspiratory flow corrector operative to modulate an inspiratory flow Q INSP — SET based on a preset waveform, a preset inspiratory time T INSP — SET , a preset assured volume VOL ASS — SET , and the volume compensation factor VOL TID — CTL 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 INSP — SET , and the larger amount between the inspiratory flow Q INSP — SET modulated by the decelerating inspiratory flow corrector and an inspiratory pressure controller flow Q INSP — PRSCTL .
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 TID — EST and output the estimated patient volume VOL TID — EST 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 PCT — ERR is defined as an absolute value of a volume error VOL TID — ERR between a preset assured volume VOL ASS — SET and the estimated or measured patient volume VOL TID — EST or VOL TID — Y divided by the preset assured volume VOL ASS — SET .
36. The circuit of claim 35 , wherein the volume compensation factor VOL TID — CTL is initialized with an initial value INI CKT — VOL 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:
Q
INSP_PEAKK
=
4
/
3
*
(
VOL
ASS_SETk
+
VOL
TID_CTLk
)
*
60
T
INSP_SETk
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:
Q
INSP_SETk
=
Q
INSP_PEAKk
-
T
INSPk
*
(
Q
INSP_PEAKk
2
*
T
INSP_SETk
)
.
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 INSP — PRSCTL computed based on an error between a preset inspiratory pressure PRS INSP — SET captured at the beginning of every breath and a measured patient pressure P y ,
a comparator operative to output a final inspiratory flow Q INSP — DES from the larger amount between the modulated decelerating inspiratory flow Q INSP — SET and the inspiratory pressure controller flow Q INSP — PRSCTL ;
an inspiratory flow servo controller operative to receive the final inspiratory flow Q INSP — DES and a preset maximum allowable inspiratory flow Q INSP — MAX to generate a flow control valve signal FCVDIA according to the final inspiratory flow Q INSP — DES restricted under the preset maximum allowable inspiratory flow Q INSP — MAX ; 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 .
43. The method of claim 42 , further comprising:
d) initializing the circuit compliance pressure compensation factor VOL TID — CTL to the initial value INI CKT — VOL when any user setup parameter of the ventilation system is changed.
44. The method of claim 43 , wherein when the estimated patient volume VOL TID — EST is selected for generating the volume compensation factor VOL TID — CTL , step (a) further comprises:
a1) providing a machine delivered net flow Q NET by computing a flow differential of a measured inspiratory flow Q IWSP 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 .
45. The method of claim 44 , 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 TID — EST are updated, and the measured machine delivered net volume VOL NET is reset.
46. A method for circuit compliance compensated volume assurance pressure control in a patient respiratory ventilation system, comprising:
a) measuring a patient volume VOL TID — Y through a flow sensor installed at a patient piece of a patient circuit in the ventilation system, or estimating a patient volume VOL TID — EST based on a machine delivered net volume VOL NET and a circuit compliance CT of the patient circuit; and
b) predetermining an initial value INI CKT — VOL for a circuit compliance volume compensation factor VOL TID — CTL and updating the volume compensation factor VOL TID — CTL based on a preset assured volume VOL ASS — SET and the patient volume VOL TID — Y or VOL TID — EST for each breath; and
c) generating an inspiratory flow Q INSP — SET according to a predetermined waveform, a preset inspiratory time T INSP , a preset assured volume VOL ASS — SET , and the volume compensation factor VOL TID — CTL .
47. The method of claim 46 , 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.
48. The method of claim 47 , 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 CKT — EST from the relationship by providing a measured patient circuit P y ; and
a5) subtracting the estimated circuit volume VOL CKT — EST from the measured machine delivered net volume VOL NET to obtain the estimated patient volume VOL TID — EST .
49. The method of claim 48 , 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 TID — EST 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 49 , wherein step (b2) further comprising multiplying the gain K VTID with the volume error VOL TID — ERR to obtain the volume correction.
51. The method of claim 50 , wherein step (b) further comprising:
b4) limiting the updated circuit compliance volume compensation factor between a predetermined allowable range.
52. The method of claim 46 , wherein step (b) further comprises:
b1) computing a volume error percentage VOL PCT — ERR defined as a ratio of an absolute value of a volume error VOL TID — ERR to a preset assured volume VOL ASS — SET , wherein the volume error VOL TID — ERR is a volume differential between the preset assured volume VOL ASS — SET and the patient volume VOL TID — Y or VOL TID — EST ;
b2) determining a gain K VTID as a function of the volume error percentage VOL PCT ERR , so as convert the volume error VOL TID ERR into a volume correction for the circuit compliance volume compensation factor VOL TID — CTL ; and
b3) updating the circuit compliance volume compensation factor VOL TID — CTL by adding the volume correction thereto.
53. The method of claim 46 , wherein step (c) further comprises:
c1) computing a maximum peak flow Q INSP PEAK by:
Q
INSP_PEAKK
=
4
/
3
*
(
VOL
ASS_SETk
+
VOL
TID_CTLk
)
*
60
T
INSP_SETk
;
and
c2) computing a modulated decelerating inspiratory flow by:
Q
INSP_SETk
=
Q
INSP_PEAKk
-
T
INSPk
*
Q
INSP_PEAKk
2
*
T
INSP_SETk
54. The method of claim 46 , further comprising:
d1) capturing a preset inspiratory pressure PRS INSP — SET at the beginning of every breath;
d2) generating an inspiratory pressure controller flow Q INSP — PRSCTL based on an error between the preset inspiratory pressure PRS INSP — SET and a measured patient pressure P y ;
d3) selecting a larger amount between the inspiratory pressure controller flow QINSP — PRSCTL and the modulated decelerating inspiratory flow Q INSP — SET to determine a flow control valve command FCV DIA .
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.