Method for controlling mixing and delivery of respiratory gas

• US 5,299,568 A
• Filed: 01/11/1993
• Issued: 04/05/1994
• Est. Priority Date: 06/22/1989
• Status: Expired due to Term

• Current Assignee: Puritan Bennett Corp. (Medtronic Plc)
• Original Assignee: Puritan Bennett Corp. (Medtronic Plc)
• Inventors: Forare, Lester, Gagne, Roger, Fennema, Paul
• Primary Examiner(s): Wiecking, David A.
• Assistant Examiner(s): Asher, Kimberly L.
• Application Number:
  US08/002,690
• Time in Patent Office: 449 Days
• Field of Search: 128/204.21, 128/204.22, 128/205.11, 128/205.13-205.17, 128/204.28, 128/205.24
• US Class Current: 128/205.11
• CPC Class Codes: A61M 16/107 in the inspiratory path
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 16/202 electrically actuated
• CPC Class Codes: A61M 16/204 used for inhalation control
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 16/209 Relief valves
• CPC Class Codes: A61M 2016/0027 pressure meter

Abstract

The ventilator control method for delivery of respiratory gas to a patient involves an apparatus which includes a pressure sensor for measuring the pressure within a gas containment vessel, the control of the flow of respiratory gas into the containment vessel responsive to pressure within the containment vessel, and the control of the outflow of respiratory gas responsive to changes in pressure in the containment vessel. Both the inflow of gas to a receiver tank and outflow of respiratory gas are responsive to modes of breathing being provided to a patient.

Claims

1. A method for delivering respiratory gas to a patient from a respirator providing a rigid, fixed wall pressure containment vessel having first and second inlet ports, each of said inlet ports connecting the vessel in fluid communication with first and second separate sources of respective first and second component gases to be combined in said vessel in a desired ratio to form said respiratory gas, said respiratory gas in said vessel having an initial known ratio of said component gases;

said respirator providing outlet means to connect the vessel in fluid communication with the patient;

said respirator providing sensor means to sense the pressure of said respiratory gas in the containment vessel;

said respirator providing means to sequentially control the flow of said component gases through said inlet ports; and

said respirator providing output flow control means to control the flow of said respiratory gas through said outlet means, the method further comprising the steps of;

a) measuring the pressure of gas within said vessel following inhalation by the patient;

b) determining pressure increase values for said first and second component gases in said vessel corresponding to the number of molecules of each said component gas required to fill said vessel with said desired ratio of said component gases to a desired fill pressure based upon the total pressure and said initial known ratio of component gases in said vessel;

c) sequentially filling said vessel with said component gases to said corresponding pressure increase values while measuring pressure in said containment vessel, by introducing said first component gas into said vessel through said first inlet port while said second inlet port is closed, and said second component gas through said second inlet port while said first inlet is closed according to said pressure change values until said fill pressure of gas in said vessel is reached;

d) measuring an actual pressure increase in said containment vessel for each said component gas introduced into said vessel;

e) determining the ratio of said component gases in said containment vessel based upon said initial known ratio of component gases in said vessel, said total pressure and said actual pressure changes for each said component gas introduced into said vessel;

f) withdrawing said respiratory gas from said vessel for a predetermined period of time according to a withdrawal flow command;

g) measuring an outflow change in the pressure of gas in the vessel over time;

(h) subtracting said measured outflow change in pressure from a desired pressure change to obtain a gas pressure change error in the amount of gas delivered in a gas delivery;

(i) integrating said gas pressure change error for each said delivery to determine an integral error in the amount of gas delivered;

(j) setting said withdrawal flow command for the next withdrawal to said desired pressure change plus an amount proportional to the above integral error;

(k) controlling said withdrawing of gas from said vessel in a predetermined manner responsive to changes in the pressure of gas sensed in said containment vessel; and

(l) repeating steps h)-j) for a subsequent delivery of a volume of gas.

2. A method for delivering respiratory gas having a known ratio of component gases to a patient from a respirator providing a rigid, fixed wall pressure containment vessel having a plurality of inlet ports, with each inlet port connecting the vessel in fluid communication with separate sources of different component gases for forming said respiratory gas;

said respirator providing outlet means to connect the vessel in fluid communication with the patient;

said respirator providing sensor means for sensing the pressure of respiratory gas in the containment vessel;

said respirator providing means to sequentially control the flow of said component gases through each of said inlet ports while the remainder of said inlet ports are closed; and

said respirator providing output flow control means to control the flow of respiratory gas through said outlet means, the method further comprising the steps of;

measuring the volume of the flow in said outlet means based upon changes in the pressure of said gas in said containment vessel following inhalation by the patient;

comparing said volume of flow in said outlet means with a predetermined outlet lower threshold level and with a predetermined outlet upper threshold level;

initiating outflow of said gas through said outlet means when said outlet flow volume falls below said lower threshold level;

stopping outflow of said gas through said outlet means when said volume of outlet flow rises above said predetermined upper threshold level;

measuring the pressure of gas within said vessel following inhalation by the patient;

determining pressure increase values for said first and second component gases in said vessel corresponding to the number of molecules of each said component gas required to fill said vessel with said desired ratio of said component gases to a desired fill pressure based upon the total pressure and said initial known ratio of component gases in said vessel;

filling said vessel with said component gases through each of said inlet ports in desired proportions while the remainder of said inlet ports in desired proportions while the remainder of said inlet ports are closed until a total predetermined pressure in said vessel is reached;

measuring the pressure of gas in said containment vessel and determining an actual pressure increase in said containment vessel for each said, component gas introduced into said vessel; and

determining the ratio of said component gases in said containment vessel based upon said initial known ratio of component gases in said vessel, said total pressure and said actual pressure changes for each said component gas introduced into said vessel.

3. A method for delivering respiratory gas to a patient from a respirator by providing a rigid, fixed wall pressure containment vessel having first and second inlet ports, each of said inlet ports connecting the vessel in fluid communication with first and second separate sources of respective first and second component gases to be combined in said vessel in a desired ratio to form said respiratory gas, said respiratory gas in said vessel having an initial known ratio of said component gases;

providing outlet means to connect the vessel in fluid communication with the patient;

providing sensor means to sense the pressure of said respiratory gas in the containment vessel;

providing means to sequentially control the flow of said component gases through said inlet ports; and

providing output flow control means to control the flow of said respiratory gas through said outlet means, the method further comprising the steps of;

a) measuring the pressure of gas within said vessel following inhalation by the patient;

b) determining pressure increase values for said first and second component gases in said vessel corresponding to the number of molecules of each said component gas required to fill said vessel with said desired ratio of said component gases to a desired fill pressure based upon a total pressure and said initial known ratio of component gases in said vessel;

c) sequentially filling said vessel with said component gases to said corresponding pressure increase values while measuring pressure in said containment vessel, by introducing said first component gas into said vessel through said first inlet port while said second inlet port is closed, and said second component gas through said second inlet port while said first inlet is closed according to said pressure increase values until said fill pressure of gas in said vessel is reached;

d) measuring an actual pressure increase in said containment vessel for each said component gas introduced into said vessel;

e) determining the ratio of said component gases in said containment vessel based upon said initial known ratio of component gases in said vessel, said total pressure and aid actual pressure changes for each said component gas introduced into said vessel;

f) withdrawing said gas from said vessel through said outlet means according to a withdrawal flow command;

g) measuring an outflow change in the pressure of gas in the vessel over time;

h) subtracting said measured outflow change in pressure from a desired pressure change to obtain a gas pressure change error in the amount of gas delivered in a gas delivery;

i) integrating said gas pressure change error for each said delivery to determine an integral error in the amount of gas delivered;

j) setting said withdrawal flow command for a next withdrawal to said desired pressure change plus an amount proportional to the above integral error;

k) controlling said withdrawing of gas from said vessel in a predetermined manner responsive to changes in the pressure of gas sensed in said containment vessel; and

l) repeating steps a)-k) for a subsequent delivery of a volume of gas.

4. The method of claim 3, further including the steps of:

determining a predicted pressure in said vessel after a predicted next inhalation by the patient based upon a predicted rate of change in pressure in said vessel over a predetermined period of time;

comparing the predicted pressure with a predetermined threshold pressure value; and

filling said vessel with said gas when the predicted pressure falls below the predetermined threshold pressure value.