Ventilator control system that generates, measures, compares, and corrects flow rates

• US 5,271,389 A
• Filed: 02/12/1992
• Issued: 12/21/1993
• Est. Priority Date: 02/12/1992
• Status: Expired due to Term

• Current Assignee: Puritan Bennett Corp. (Medtronic Plc)
• Original Assignee: Puritan Bennett Corp. (Medtronic Plc)
• Inventors: Wong, Stanley Y., Isaza, Fernando J.
• Primary Examiner(s): Burr, Edgar S.
• Assistant Examiner(s): Asher, Kimberly L.
• Application Number:
  US07/836,773
• Time in Patent Office: 678 Days
• Field of Search: 128/204.21, 128/204.26, 128/204.22, 128/204.23, 128/205.23, 128/716, 128/719, 128/724, 128/725, 128/205.24, 364/413.02, 364/413.03, 364/565, 364/569, 364/224.5, 364/224.6, 364/922.2-922.4, 364/922, 364/571.02, 364/571.05
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/204 used for inhalation control
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

The present invention provides a system and method for providing an improved correction to an input flow control signal to a flow control valve in a ventilator system. The correction as derived from a sum of the error in the flow rate actually delivered as compared with the desired flow rate for each control interval in a breath with the sum of past errors corresponding to control intervals in past breaths to generate a cumulative error signal for application in the control interval in a next breath. The cumulative error signal is stored as the sum of previous sustained errors arising periodically in the system for each control interval of previous breaths, and is integrated with the current error signal for each control interval to generate an integrated correction component signal. The input flow control signal is summed with the integrated correction component to generate a corrected command flow signal to the flow control valve.

Claims

1. A ventilator control system for controlling the rate of flow of a respiratory gas supplied by a ventilation system for supporting breaths of a patient intubated on the ventilation system, said ventilator control system comprising;

means for generating an input flow control signal based upon a desired rate of flow for a control interval in a current breath;

means for measuring an actual rate of flow in the ventilation system and generating a flow rate signal representing the actual rate of flow;

means for comparing said actual rate of flow with said desired rate of flow, and generating a current error signal representing the difference between the actual rate of flow and the desired rate of flow for each said control interval in each current breath;

means for summing each current error signal for each said control interval in each current breath with a sum of previous error signals for each said control interval of previous breaths to generate a correction component signal for application in said control interval in a next breath;

means for storing said correction component signal as the sum of previous error signals of each said control interval of previous breaths;

means for integrating said current error signal and said correction component signal for each said control interval to generate an integrated correction component signal; and

means for summing said input flow control signal and said integrated correction component to generate a command flow signal for said ventilation system.

2. The system of claim 1, further including means for modifying said input flow control signal to include a predetermined valve gain feedforward component for each said control interval of each breath, and means for summing said feedforward component with said input flow control signal to generate a corrected input flow control signal for each said control interval in each current breath.

3. A method of controlling the rate of flow of a respiratory gas supplied by a ventilation system for supporting breaths of a patient intubated on the ventilation system, the method comprising the steps of:

generating an input flow control signal based upon said desired rate of flow for each control interval in a current breath;

measuring the actual rate of flow in the flow path and generating a flow rate signal representing the actual rate of flow in the ventilation system;

comparing the actual rate of flow with the desired rate of flow, and generating a current error signal representing the difference between the actual rate of flow and the desired rate of flow for each said control interval in each current breath; and

summing each said current error signal for each said control interval in each current breath with a sum of previous error signals for each said control interval of previous breaths to generate a correction component signal for application in said control interval in a next breath;

storing said correction component signal as the sum of previous error signals of each said control interval of previous breaths;

integrating said current error signal and said correction component for each said control interval to generate an integrated correction component signal; and

summing said flow control signal and said integrated correction component signal to generate a command flow signal for said ventilation system.

4. The method of claim 3, further comprising the step of modifying said input flow control signal by adding a predetermined valve gain feedforward component to said input flow control signal to generate a corrected flow control signal, for each said control interval in each current breath.

5. A method of controlling the rate of flow of a respiratory gas supplied by a ventilation system for supporting breaths of a patient intubated on the ventilation system, the method comprising the steps of:

generating an input flow control signal based upon said desired rate of flow for each control interval in a current breath;

measuring the actual rate of flow in the flow path and generating a flow rate signal representing the actual rate of flow in the ventilation system;

comparing the actual rate of flow with the desired rate of flow, and generating a current error signal representing the difference between the actual rate of flow and the desired rate of flow for each said control interval in each current breath; and

summing each said current error signal for each said control interval in each current breath with a sum of previous error signals for each said control interval of previous breaths to generate a correction component signal for application in said control interval in a next breath.

6. A ventilator control system for controlling the rate of flow a respiratory gas supplied by a ventilation system for supporting breaths of a patient intubated on the ventilation system, comprising a source of respiratory gas, a flow path between said source of respiratory gas and in fluid communication with a patient, a flow control valve for controlling the rate of flow in said flow path, control means for generating a control signal for operating said flow control valve at least once in a predetermined control interval in a breath to deliver a desired rate of flow in said flow path for each said control interval in that breath, and a flow sensor in said flow path connected to said control means for measuring the actual rate of flow in said flow path, said ventilator control system further comprising;

means for generating an input flow control signal based upon said desired rate of flow for each control interval in a current breath;

means for measuring the actual rate of flow in the flow path and generating a flow rate signal representing the actual rate of flow in the flow path;

means for comparing said rate of flow in said flow path with said desired rate of flow, and generating a current error signal representing the difference between the actual rate of flow and the desired rate of flow for each said control interval in that breath;

means for summing each said current error signal for each said control interval in said breath with a sum of previous error signals for each said control interval of the previous breaths to generate a correction component signal for application in said control interval in a next breath;

means for storing said correction component signal as the sum of previous error signals of each said control interval of those previous breaths;

means for integrating said current error signal and said correction component signal for each said control interval to generate an integrated correction component signal; and

means for summing said input flow control signal and said integrated correction component signal to generate a command flow signal for said flow control valve.

7. The system of claim 6, further including means for modifying said input flow control signal to include a predetermined valve gain feedforward component for each said control interval of each breath, and means for summing said feedforward component with said input flow control signal to generate a corrected input flow control signal for each said control interval in that breath, said means for modifying overcoming initial flow resistances inherent in the ventilator system.

8. A method of controlling the rate of flow of respiratory gas supplied by a ventilation system for supporting breaths of a patient intubated on the ventilation system, comprising providing a ventilation system including a source of respiratory gas, a flow path for said respiratory gas in fluid communication with a patient, a flow control valve for controlling the rate of flow in said flow path, control means for generating a control signal for operating said flow control valve at least once in a predetermined control interval in a breath to deliver a desired rate of flow in said flow path for each said control interval in that breath, and means for measuring the rate of flow in said flow path connected to said control means for generating a flow rate signal representing the actual rate of flow in said flow path, and further comprising the steps of:

generating an input flow control signal based upon said desired rate of flow for each control interval in a current breath;

measuring the actual rate of flow in the flow path and generating a flow rate signal representing the actual rate of flow in the flow path;

comparing the rate of flow in said flow path with the desired rate of flow in said flow path, and generating a current error signal representing the difference between the actual rate of flow and the desired rate of flow for each said control interval in said breath;

summing each said current error signal for each said control interval in said breath with a sum of previous error signals for each said control interval of previous breaths to generate a correction component signal for application in said control interval in a next breath;

storing said correction component signal as the sum of previous error signals of each said control interval of the previous breaths;

integrating said current error signal and said correction component for each said control interval to generate an integrated correction component signal; and

summing said flow control signal and said integrated correction component signal to generate a command flow signal for said control valve.

9. The method of claim 8, further comprising the steps of modifying said input flow control signal by adding a predetermined valve gain feedforward component to said input flow control signal to generate a corrected flow control signal, for each said control interval in that breath and thereby correcting for initial flow resistances within said system.