Mechanical ventilation with automatic control of patient's work of breathing using classical feedback control
A mechanical ventilator ( 10 ) provides pressure support ventilation (PSV) to a patient ( 12 ). A power of breathing (PoB) or work of breathing (WoB) estimator ( 30 ) generates a PoB or WoB signal ( 34 ) for the patient. An error calculator ( 36 ) computes an error signal as a difference between the PoB or WoB signal and a set point PoB or WoB value ( 22 ). A controller ( 20 ) inputs a PSV control signal ( 24 ) equal to the product of the controller transfer function and the error signal to the mechanical ventilator. A patient adaptation component ( 52, 54, 56, 60 ) fits parameters of a model of a controlled mechanical ventilation system comprising the mechanical ventilator and the patient to data comprising the PoB or WoB signal and the PSV control signal generated by the operating closed loop controller, and adjusts parameters of the controller transfer function to maintain stability of the operating closed loop controller.
1. A respiratory therapy device comprising:
a mechanical ventilator configured to provide mechanical ventilation to a patient in a pressure support ventilation (PSV) or pressure support ventilation/intermittent mandatory ventilation (PSV/IMV) mode in accordance with a PSV pressure setting;
a power of breathing (PoB) or work of breathing (WoB) estimator configured to generate a PoB or WoB signal for the patient;
an error calculator configured to compute an error signal E (s) as a difference between the PoB or WoB signal and a set point PoB or WoB value; and
a controller having a controller transfer function C(s) and configured to input the PSV pressure setting equal to C(s)E(s) to the mechanical ventilator to control operation of the mechanical ventilator in providing mechanical ventilation to the patient,
wherein the mechanical ventilator, the PoB or WoB estimator, the error calculator, and the controller are operatively interconnected to form a single-input, single-output (SISO) closed loop feedback control system in which the mechanical ventilator and the PoB or WoB estimator define the controlled system whose single input is the PSV pressure setting and whose single controlled output is the PoB or WoB signal,
wherein the controlled system has a controlled system transfer function G(s) given by:
G
(
s
)
=
PoB
(
s
)
PSV
(
s
)
=
K
p
τ
s
+
1
where PoB(s) is the PoB or WoB signal, K p is a gain parameter, r is a time parameter, and PSV(s) is the PSV pressure setting, and the respiratory therapy device further comprises:
an electronic device programmed to fit K p and r to (PoB(s), PSV(s)) data generated by the operating SISO closed loop feedback control system and to adjust parameters of the controller transfer function C(s) to maintain stability of the closed loop transfer function
C
(
s
)
G
(
s
)
1
+
C
(
s
)
G
(
s
)
of the SISO closed loop feedback control system.
2. A respiratory therapy device comprising:
a mechanical ventilator configured to provide mechanical ventilation to a patient in a pressure support ventilation (PSV) or pressure support ventilation/intermittent mandatory ventilation (PSV/IMV) mode in accordance with a PSV pressure setting;
a power of breathing (PoB) or work of breathing (WoB) estimator configured to generate a PoB or WoB signal for the patient;
an error calculator configured to compute an error signal E (s) as a difference between the PoB or WoB signal and a set point PoB or WoB value; and
a controller having a controller transfer function C(s) and configured to input the PSV pressure setting equal to C(s)E(s) to the mechanical ventilator to control operation of the mechanical ventilator in providing mechanical ventilation to the patient,
wherein the mechanical ventilator, the PoB or WoB estimator, the error calculator, and the controller are operatively interconnected to form a single-input, single-output (SISO) closed loop feedback control system in which the mechanical ventilator and the PoB or WoB estimator define the controlled system whose single input is the PSV pressure setting and whose single controlled output is the PoB or WoB signal,
the respiratory therapy device further comprising an electronic device programmed to fit parameters of a model of a controlled system transfer function G(s) given by:
G
(
s
)
=
PoB
(
s
)
PSV
(
s
)
where PoB(s) is the PoB or WoB signal and PSV(s) is the PSV pressure setting to (PoB(s), PSV(s)) data generated by the operating SISO closed loop feedback control system and to adjust parameters of the controller transfer function C(s) to maintain stability of the closed loop transfer function
C
(
s
)
G
(
s
)
1
+
C
(
s
)
G
(
s
)
of the SISO closed loop feedback control system.
3. A respiratory therapy device comprising:
a mechanical ventilator configured to provide mechanical ventilation to a patient in a pressure support ventilation (PSV) or pressure support ventilation/intermittent mandatory ventilation (PSV/IMV) mode in accordance with a PSV pressure setting;
a power of breathing (PoB) or work of breathing (WoB) estimator configured to generate a PoB or WoB signal for the patient;
an error calculator configured to compute an error signal E(s) as a difference between the PoB or WoB signal and a set point PoB or WoB value; and
a controller having a controller transfer function C(s) and configured to input the PSV pressure setting equal to C(s)E(s) to the mechanical ventilator to control operation of the mechanical ventilator in providing mechanical ventilation to the patient,
wherein the mechanical ventilator, the PoB or WoB estimator, the error calculator, and the controller are operatively interconnected to form a single-input, single-output (SISO) closed loop feedback control system in which the mechanical ventilator and the PoB or WoB estimator define the controlled system whose single input is the PSV pressure setting and whose single controlled output is the PoB or WoB signal;
wherein the controller transfer function C(s) is given by:
C
(
s
)
=
-
K
s
(
s
+
P
)
where K is a controller gain having a positive value, P is a noise-suppressing pole having a positive value and where s is a complex frequency.
4. The respiratory therapy device of claim 3 wherein C(s) includes a pole at zero and a pole with a positive value P.
5. The respiratory therapy device of claim 3 wherein P≤200 sec −1 .
6. A single input, single output (SISO) closed-loop controller for controlling a mechanical ventilator) configured to provide mechanical ventilation to a patient in a pressure support ventilation (PSV) or pressure support ventilation/intermittent mandatory ventilation (PSV/IMV) mode in accordance with a PSV pressure setting, the closed-loop controller comprising:
a power of breathing (PoB) or work of breathing (WoB) estimator) configured to generate a signal representing PoB or WoB of the patient;
an error calculator configured to compute an error signal E (s) as a difference between the signal representing PoB or WoB of the patient and a set point value; and
a controller having a controller transfer function C(s) and configured to generate the PSV pressure setting as the product C(s)E(s) to control operation of the mechanical ventilator in providing mechanical ventilation to the patient; and
an electronic device programmed to fit parameters of a model of a controlled system transfer function G (s), given by
G
(
s
)
=
PoB
(
s
)
PSV
(
s
)
of the mechanical ventilator providing ventilation to the patient under control of the SISO closed-loop controller to PoB (s) and PSV (s) data generated by the operating SISO closed loop controller, where PoB (s) are signal data representing the PoB or WoB of the patient and PSV (s) are PSV pressure setting data, and to adjust parameters of the controller transfer function C(s) to maintain stability of the closed loop transfer function
C
(
s
)
G
(
s
)
1
+
C
(
s
)
G
(
s
)
.
7. The SISO closed-loop controller of claim 6 further comprising:
an electronic device programmed to fit parameters of a model of the controlled system transfer function of the mechanical ventilator providing ventilation to the patient under control of the operating SISO close-loop controller to PoB (s) and PSV (s) data generated by the operating SISO closed loop controller, where PoB (s) are signal data representing the PoB or WoB of the patient and PSV (s) are PSV pressure setting data, and to adjust parameters of the controller transfer function C(s) to maintain stability of the operating SISO closed-loop controller.
8. The SISO closed-loop controller of claim 6 wherein the controller has programmed upper and lower limits for the PSV pressure setting.
9. The SISO closed-loop controller of claim 6 wherein the controller transfer function C(s) is given by:
C
(
s
)
=
-
K
s
(
s
+
P
)
where K is a controller gain having a positive value, P is a noise-suppressing pole having a positive value and where s is a complex frequency.
10. The SISO closed-loop controller of claim 9 wherein C(s) includes a pole at zero and a pole with a positive value P.
11. The SISO closed-loop controller of claim 9 wherein P≤200 sec −1 .
12. The SISO closed-loop controller of claim 6 wherein the electronic device is programmed to adjust parameters of the controller transfer function C(s) including at least one non-zero and positive pole of the controller transfer function C(s) to maintain stability of the operating closed-loop controller.