Closed loop control in a piston ventilator

• US 6,321,748 B1
• Filed: 03/10/1998
• Issued: 11/27/2001
• Est. Priority Date: 03/10/1998
• Status: Expired due to Term

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: NELLCOR PURITAN BENNETT
• Inventors: OʼMahoney, John
• Primary Examiner(s): Lewis, Aaron J.
• Application Number:
  US09/037,385
• Time in Patent Office: 1,358 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23, 128/205.18
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/0072 Tidal volume piston pumps
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/107 in the inspiratory path
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/1025 the O2 concentration

Abstract

A piston ventilator (10) includes a control circuit (80) for controlling the pressure to a patient circuit and thereby to the patient during patient inspiration. The control circuit (80) determines an error between the gas pressure and a set point pressure and in response, sends motor control signals to the motor (24) controlling the piston (22) to change the gas flow therefrom by the amount necessary so that the gas pressure substantially conforms to the set point pressure. More particularly, the motor control signals are a function of a proportion of the error, an integration of the error and the amount of leakage in the patient circuit at the current gas pressure. The set point is one of a plurality of set points on a pressure trajectory between a beginning pressure and a final target pressure during patient inspiration.

Claims

1. In a piston ventilator having a piston motor for driving a piston to deliver gas at a gas pressure and flow to a patient circuit, a control circuit comprising:

a pressure sensor coupled with the patient circuit and operable for sensing the gas pressure therein and for producing sensor signals representative thereof;

a motor controller coupled with the piston motor for receiving motor control signals and for operating the piston motor in accordance therewith; and

a digital processor under computer program control coupled with said motor controller and coupled with said pressure sensor for receiving and processing said pressure signals for determining the gas flow amount from said piston necessary so that said gas pressure substantially conforms to a predetermined set point pressure, and for producing motor control signals representative of said gas flow amount and delivering said motor control signals to said motor controller for driving said piston to produce said gas flow amount, said digital processor being programmed to determine said set point pressure as one of a plurality of sequential set point pressures on a pressure trajectory determined as a function of a predetermined rate of rise between a beginning pressure and a target pressure wherein said beginning pressure is the pressure in the patient circuit at the beginning of patient inspiration.

2. The control circuit as set forth in claim 1, said digital processor being programmed to determine an error as the difference between said set point pressure and said gas pressure and for producing said motor control signals as a function of a proportion constant times said error.

3. The control circuit as set forth in claim 1, said digital processor being programmed to determine an error as the difference between said set point pressure and said gas pressure, and for producing said motor control signals as a function of an integration constant times said error over time.

4. The control circuit as set forth in claim 1, said digital processor being programmed to determine an error as the difference between said set point pressure and said gas pressure, and for producing said motor control signals as a function of the sum of a proportion constant times said error and integration constant times said error over time.

5. The control circuit as set forth in claim 4, the patient circuit being subject to gas leakage proportional to the gas pressure, said sum further including a leak constant times a gas pressure.

6. The control circuit as set forth in claim 1, said digital processor including a microprocessor.