System and method for circuit compliance compensated volume control in a patient respiratory ventilator
View Patent ↗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.
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 ΔP 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 CKT — EST based on the relationship between V CC and ΔP Y ;
a patient volume observer, operative to provide an estimated patient volume VOL TID — EST by subtracting the estimated circuit volume VOL CKT — EST 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 TID — EST and a set tidal volume VOL TID — SET ,
wherein the volume delivery controller further comprises:
an error percentage converter for providing a volume error percentage VOL PCT — ERR defined by a ratio of an absolute value of the volume error VOL TID — ERR to the set tidal volume VOL TID — SET ;
a gain scheduler for determining a gain K VTID of the volume error as a function of the volume error percentage VOL TID — ERR ; and
a volume integrator for updating a circuit compliance volume compensation factor VOL TID — CTL by adding a product of the gain VOL VTID and the volume error VOL TID — ERR thereto,
wherein the circuit compliance volume compensation factor VOL TID — CTL is updated at the beginning of every inspiratory phase, and
wherein the volume error VOL TID — ERR is defined as the volume differential between the set tidal volume VOL TID — SET and the estimated patient volume VOL TID — EST .
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 −ΔP coordinate,
CKT_CPM SLP is a slope of the linear relationship, and
CKT_CMP INT is an intercept of the linear relationship and ΔP Y axis.
3. The system of claim 1 , wherein the circuit compliance estimator is operative to measure the responsive pressure differential ΔP 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 TID — EST 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 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 TID — CTL .
13. The system of claim 12 , wherein:
the circuit compliance flow compensation factor Q TID — CTL is computed according to:
Q
TID_CTL
=
60
·
(
VOL
TID_CTL
T
^
INSP_EST
)
,
where
T
^
INSP_EST
is an estimated inspiratory time.
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 PEAK — SET and the set tidal volume VOL TID — SET .
15. The system of claim 14 , wherein the predetermined peak inspiratory flow Q PEAK — SET equals to a preset peak inspiratory flow constant Q PEAK — USER for a square waveform or a function of the preset peak inspiratory flow constant Q PEAK — USER and time t into an inspiratory phase for a decelerating waveform.
16. The system of claim 15 , wherein:
T
^
INSP_EST
=
{
VOL
TID_SET
(
Q
PEAK_USER
/
60
)
for
square
waveform
(
4
/
3
)
·
VOL
TID_SET
(
Q
PEAK_USER
/
60
)
for
decelerating
waveform
.
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 TID — CTL into a required inspiratory flow Q I — SET .
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 TID — Y 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 TID — Y is larger than or equal to the set tidal volume VOL TID — SET .
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 TID — CTL with the set tidal volume VOL TID — SET into the desired machine delivered net volume VOL SET — CTL ;
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 SET — CTL 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 SET — CTL .
28. The system of claim 1 , wherein the volume delivery controller comprises:
a gain scheduler for weighing a volume error VOL TID — ERR according to a ratio of an absolute value of the volume error VOL TID — ERR to the set tidal volume VOL TID — SET , wherein the volume error VOL TID — ERR is defined as a volume differential between the measured patient volume VOL TID — EST or the estimated patient volume VOL TID — EST and the set tidal volume VOL TID — SET ; and
a volume integrator to update the circuit compliance circuit volume compensation factor VOL TID — CTL with the volume error VOL TID — ERR 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 TID — SET .
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 TID — CTL , so as to provide a desired inspiratory flow Q I — SET .
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 TID — EST 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 TID — Y via a flow sensor located at a patient piece of the patient circuit; and
b) updating a circuit compliance volume compensation factor VOL TID — CTL based on a set tidal volume VOL TID — SET and a feedback volume error VOL TID — ERR ,
wherein the circuit compliance volume compensation factor VOL TID — CTL has an initial setup value INI_CKT_VOL T and the feedback volume VOL TID — ERR is defined as a volume differential between the patient volume VOL TID — EST or VOL TID — Y and the set tidal volume VOL TID — SET ,
wherein step (b) further comprises:
b1) computing a volume error percentage VOL PCT — ERR by dividing an absolute value of the volume error VOL TID — ERR over the set tidal volume VOL TID — SET ;
b2) determining a gain K VTID as a function of the volume error percentage VOL PCT — ERR ; and
b3) updating the circuit compliance volume compensation factor VOL TID — CTL by adding a product of the gain K VTID and the volume error VOL TID — ERR 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 TID — EST are updated, and the measured machine delivered net volume VOL NET and the measured patient volume VOL TID — Y 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 TID — EST are updated, and the machine delivered net flow VOL NET and the measured patient volume VOL TID — Y 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 CKT — EST from a measured patient circuit pressure P Y and the relationship; and
a3) providing the estimated patient volume VOL TID — EST subtracting the estimated circuit volume VOL CKT — EST 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 TID — CTL .
42. The method of claim 41 , wherein:
the circuit compliance flow compensation factor Q TID — CTL is computed according to:
Q
TID_CTL
=
60
·
(
VOL
TID_CTL
T
^
INSP_ESP
)
,
and
T
^
INSP_ESP
is an inspiratory time estimated based on the set tidal volume VOL TID — SET , a preset inspiratory peak flow Q PEAK — USER , and a pre-selected waveform.
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 TID — CTL , with a predetermined peak inspiratory flow Q PEAK — SET .
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.