System for protecting sample line in respiratory gas analyzer

• US 5,676,131 A
• Filed: 07/11/1996
• Issued: 10/14/1997
• Est. Priority Date: 07/11/1996
• Status: Expired due to Fees

• Current Assignee: Medical Graphics Corporation (Niterra Co., Ltd.)
• Original Assignee: Medical Graphics Corporation (Niterra Co., Ltd.)
• Inventors: Anderson, David M., Larson, Thor A., James, Steven D.
• Primary Examiner(s): Millin, Vincent
• Assistant Examiner(s): WIELAND, ROBERT N
• Application Number:
  US08/678,347
• Time in Patent Office: 460 Days
• Field of Search: 128/202.22, 128/204.22, 128/204.23, 364/413.01, 364/413.02, 364/413.03
• US Class Current: 128/204.22
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61M 16/085 Gas sampling
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2230/43 Composition of exhalation
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/435 partial O2 pressure (P-O2)

Abstract

A method and apparatus is described for preventing contamination of a gas analyzer of respiratory gas exchange analyzing equipment due to a patient'"'"'s saliva. The method involves determining a resistance value of the inspired respiratory gas flow in a sample line leading to the gas analyzer. This is determined by calculating the absolute pressure in the line at the gas analyzer. The pressure difference from atmospheric pressure is then divided by the sample flow rate to obtain a resistance value. A microprocessor in the equipment compares the calculated resistance of the flow with a previously stored reference threshold resistance. If the calculated resistance exceeds the predetermined threshold, the microprocessor sends a signal to a vacuum pump used to draw the respiratory gases through the gas analyzer. The vacuum pump is immediately shut down when the calculated resistance exceeds the predetermined resistance threshold and, hence, any saliva in the sample line is not drawn into the gas analyzer.

Claims

1. In a respiratory gas exchange system of the type including a patient mouthpiece having a sampling port coupled by a sample line in circuit with a gas analyzer and a vacuum pump, the vacuum pump drawing respiratory gases from said mouthpiece through said sample line and into said gas analyzer, a method for precluding a patient'"'"'s saliva from reaching the gas analyzer, said method comprising the steps of:

a) measuring the rate of flow of respiratory gases in the sample line;

b) measuring the pressure in said sample line;

d) comparing the computed flow resistance value with a predetermined reference threshold;

e) repeating steps a)-d) until said computed flow resistance value exceeds said predetermined reference threshold; and

f) shutting off the vacuum pump when the computed flow resistance value exceeds the predetermined reference threshold.

2. The method of claim 1 and further comprising the steps of repeating steps a-e until said resistance exceeds said threshold resistance value and automatically shutting down said pump when said resistance value exceeds said threshold resistance value.

3. In a gas exchange system analyzer of the type having a microprocessor based waveform analyzer including a memory for storing a program of instructions and operands, a sample line extending from a mouthpiece to a respiratory gas analyzer, a flow meter located in said sample line and coupled to said waveform analyzer for providing input thereto proportional to the volume rate of sample flow of respiratory gases in the sample line, a pressure sensor located adjacent said gas analyzer for sensing pressure of said sample flow in said gas analyzer and a pump for drawing said respiratory gases through said sample line and said respiratory gas analyzer, a method for determining the presence of saliva in the sample line, said method comprising the steps of:

a. entering into said memory a reference threshold sample resistance value;

b. sensing a first pressure value at the pressure sensor;

c. storing said first pressure in said memory;

d. computing a resistance value of said sample flow, using a value of atmospheric pressure, said first pressure and said volume rate of flow of said respiratory gases by using the formula;

##EQU3## and e. comparing said resistance value with said threshold resistance value.

4. An apparatus for protecting a sample line and a respiratory gas analyzer from saliva build up in a respiratory gas exchange system, said apparatus comprising:

a. a pneumotach mouthpiece;

b. a sample line circuit having a first end and a second end, said sample line coupled at said first end to said pneumatach mouthpiece;

c. a gas analyzer coupled to said sample line circuit;

d. a flow meter coupled to said sample line circuit, said flow meter measuring flow of respiratory gases flowing in said sample line;

e. a pressure sensor located adjacent said gas analyzer, said pressure sensor sensing the pressure of the sample line at said gas analyzer;

f. a vacuum pump coupled to said second end of said sample line, said vacuum pump drawing said respiratory gases through said sample line and said gas analyzer; and

g. a controller for determining saliva build up in said sample line by analyzing inputs from said pressure sensor at said gas analyzer and said flow meter, said controller programmed to shut down said vacuum pump when a pre-determined saliva build up threshold is met.