Closed loop control system for a high frequency oscillation ventilator

• US 20070215154A1
• Filed: 03/15/2006
• Published: 09/20/2007
• Est. Priority Date: 03/15/2006
• Status: Active Grant

• Current Assignee: Vyaire Medical 211, Inc. (Becton, Dickinson & Co)
• Original Assignee: CareFusion 207, Inc. (Becton, Dickinson & Co)
• Inventors: Borrello, Michael
• Granted Patent: US 7,861,716 B2
• Time in Patent Office: Days
• US Class Current: 128/204.210
• CPC Class Codes: A61M 16/0009 with sub-atmospheric pressure, e.g. during expiration
• CPC Class Codes: A61M 16/0057 Pumps therefor
• CPC Class Codes: A61M 16/006 Tidal volume membrane pumps
• CPC Class Codes: A61M 16/0096 High frequency jet ventilation
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 16/208 Non-controlled one-way valves, e.g. exhalation, check, pop-off non-rebreathing valves
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2205/3306 Optical measuring means
• CPC Class Codes: A61M 2205/3317 Electromagnetic, inductive or dielectric measuring means

Abstract

A control system for a high frequency oscillating ventilator (HFOV) includes and oscillator controller and a mean airway pressure (MAP) controller. The HFOV includes a reciprocating piston which is adapted to generate positive and negative pressure waves for delivery to a patient airway. The oscillator controller comprises a pair of closed loop control circuits including an oscillator pressure loop and a centering loop which are collectively adapted to regulate frequency and amplitude of piston reciprocations and centering of the piston. The MAP controller comprises a closed loop control circuit that is adapted for regulating MAP at the patient utilizing feedback in the form of patient circuit pressure. Likewise, the oscillator controller utilizes patient circuit pressure as well as piston displacement feedback in order to regulate movement of the piston.

Claims

1. A control system for a high frequency oscillating ventilator (HFOV) having a reciprocating piston and being connectable to a patient for providing airway pressure thereto, the control system comprising:

an oscillator controller comprising a pair of closed loop control circuits including an oscillator pressure loop and a centering loop collectively adapted to regulate frequency and amplitude of piston reciprocations and centering of the piston; and

a mean airway pressure (MAP) controller comprising a closed loop control circuit adapted for regulating MAP at the patient.

2. The control system of claim 1 further comprising:

a piston position sensor configured to measure the piston position and generate a piston displacement signal in response thereto for delivery to the centering loop; and

a pressure sensor configured to measure pressure at the patient and generate a measured pressure signal in response thereto for delivery to the oscillator controller;

wherein;

the oscillator pressure loop is configured to determine the difference between the measured pressure signal and a desired oscillator pressure signal and generate an oscillator pressure error signal in response thereto;

the centering loop being configured to determine the difference between the piston displacement signal and zero as the desired piston position and generate a displacement error signal in response thereto;

the oscillator pressure and piston displacement signals being combined to generate an oscillator command signal for regulating reciprocative movement of the piston.

3. The control system of claim 2 wherein the piston displacement signal and the measured pressure signal are each filtered in a manner such that the frequency bands thereof are non-overlapping.

4. The control system of claim 3 wherein:

the centering loop includes a first order low pass filter having a centering loop filter cutoff frequency;

the oscillator pressure loop including a second order band pass filter having a low cutoff frequency generally equal to the centering loop filter cutoff frequency, the band pass filter having a high cutoff frequency being such that noise propagation in the oscillator pressure loop is limited.

5. The control system of claim 4 wherein:

the band pass filter comprises a single pole high pass filter connected in series to a single pole low pass filter;

the single pole high pass filter having a -3 dB cutoff at the centering loop filter cutoff frequency;

the single pole low pass filter having a -3 dB cutoff at the high cutoff frequency.

6. The control system of claim 4 wherein each one of the centering and oscillator pressure loops includes a proportional integral (PI) controller configured to filter respective ones of the oscillator pressure error signal and displacement error signal to drive errors contained therewithin toward zero and to limit windup in integral components of the respective PI controllers.

7. The control system of claim 2 wherein the piston position sensor is configured as a displacement transducer.

8. The control system of claim 2 wherein the pressure sensor is configured as a pressure transducer.

9. The control system of claim 1 further comprising:

a pressure sensor configured to measure pressure at the patient and generate a measured pressure signal in response thereto for delivery to the MAP controller;

wherein;

the MAP controller comprises a MAP regulation loop having an exhalation valve in fluid communication with the patient and the HFOV;

the MAP regulation loop being configured to determine the difference between the measured pressure signal and a desired MAP signal and generate a MAP loop error signal in response thereto for driving the exhalation valve.

10. The control system of claim 9 wherein the MAP regulation loop includes a low pass filter configured to filter the measured pressure signal in such a manner to maximize attenuation of oscillations induced by the oscillator pressure loop and maximize the response and accuracy of the MAP regulation loop.

11. The control system of claim 10 wherein the MAP regulation loop low pass filter is configured as a high order filter having a steep cutoff relative to the desired MAP signal.

12. The control system of claim 1 wherein the MAP regulation loop further includes an integral controller configured to receive the MAP loop error signal, drive the error therein toward zero, and limit integral action thereof between voltage saturation limits of the exhalation valve.

13. The control system of claim 1 wherein the HFOV comprises:

a housing assembly;

a linear actuator fixedly mounted within the housing assembly;

a linear coil coaxially disposed within the linear actuator and having a pushrod extending axially therethrough for slidably supporting the linear coil on the linear actuator;

a piston mounted on the pushrod;

a diaphragm operatively engageable to the piston and sealingly dividing the housing assembly into first and second sides, the linear coil and actuator being disposed on the first side, the diaphragm having a deep radius groove formed about a periphery thereof and being configured to be non-inverting during piston reciprocation; and

an opening formed on the second side and being fluidly connected to the patient for delivering gas thereto;

wherein;

the linear coil and linear actuator cooperate to effectuate reciprocation of the diaphragm in a manner to alternately produce positive and negative pressure waves in the gas at the patient.

14. A closed loop method of regulating piston movement and mean airway pressure (MAP) in a patient ventilator system having an exhalation valve, the method comprising the steps of:

measuring a pressure at the patient and generating a measured pressure signal in response thereto;

comparing a desired oscillator pressure signal to the measured pressure signal and generating a pressure output signal in response thereto;

measuring piston displacement and generating a piston displacement signal in response thereto;

subtracting the piston displacement signal from zero as a desired piston position and generating a displacement output signal in response thereto;

combining the pressure output signal with the displacement output signal and generating an oscillator command signal in response thereto for regulating the piston movement; and

comparing a desired MAP signal to the measured pressure and generating an exhalation valve command signal in response thereto for regulating MAP at the patient.

15. The method of claim 14 further comprising the step of filtering the measured pressure signal and the displacement output signal such that the frequency bands thereof are non-overlapping.

16. A method of regulating movement of an oscillator piston of a patient ventilator using an oscillator controller comprising an oscillator pressure loop and a centering loop, the method comprising the steps of:

in the oscillator pressure loop;

measuring a pressure at the patient and generating a measured pressure signal representative thereof;

filtering the measured pressure signal to limit bandwidth thereof to between a predetermined transition frequency and a noise-limiting frequency and generating a filtered pressure signal in response thereto;

receiving a desired oscillator pressure signal;

summing the filtered pressure signal and the desired oscillator pressure signal and generating an oscillator pressure error signal in response thereto; and

filtering the oscillator pressure error signal through an oscillator pressure loop proportional integral (PI_p) controller and generating a pressure output signal in response thereto; and

in the centering loop;

measuring a piston position and generating a piston displacement signal representative thereof;

filtering the piston displacement signal to limit bandwidth thereof to between static and the predetermined transition frequency and generating a filtered displacement signal in response thereto;

subtracting the filtered displacement signal from zero as a desired piston position and generating a displacement error signal in response thereto;

filtering the displacement error signal through a centering loop proportional integral (PI_x) controller and generating a displacement output signal in response thereto;

summing the pressure and displacement output signals and generating the oscillator command signal in response thereto for driving the piston movement.

17. The method of claim 16 wherein the measured piston displacement signal is filtered using a first order low pass filter with −

3 dB rolloff at the transition frequency.

18. The method of claim 16 wherein the measured pressure signal is filtered using a second order band pass filter having a low cutoff frequency generally equal to the centering loop low pass filter cutoff frequency, the band pass filter having a high cutoff frequency being such that noise propagation in the oscillator pressure loop is limited.

19. The method of claim 16 further comprising the steps of:

inducing a change in at least one of frequency, amplitude, and duty cycle settings of the desired oscillator pressure signal;

filtering the change in the settings of the desired oscillator pressure signal in such a manner as to slow the rate of change from a previous setting.

20. The method of claim 16 wherein the patient ventilator includes an exhalation valve for regulating MAP thereat using a MAP regulation loop, the method further comprising the steps of:

receiving the measured pressure signal at the MAP regulation loop;

filtering the measured pressure signal in such a manner as to maximize attenuation of oscillations induced by the oscillator pressure loop and maximize the response of the MAP regulation loop and generating a filtered pressure signal in response thereto;

receiving a desired MAP signal at the MAP regulation loop;

subtracting the filtered pressure signal from the desired MAP signal and generating an MAP pressure error signal in response thereto;

filtering the MAP pressure error signal through an integral controller and generating an exhalation valve command signal in response thereto for driving the exhalation valve.

21. The method of claim 20 wherein the measured pressure signal is filtered using a high order low pass filter with a steep cutoff frequency.