Flowmeter for providing synchronized flow data and respiratory gas samples to a medical mass spectrometer

• US 4,178,919 A
• Filed: 04/03/1978
• Issued: 12/18/1979
• Est. Priority Date: 04/03/1978
• Status: Expired due to Term

• Current Assignee: Marquette Gas Analysis Corporation
• Original Assignee: Perkinelmer Incorporated
• Inventors: Hall, Lawrence G.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US05/893,033
• Time in Patent Office: 624 Days
• Field of Search: 128/2.07, 128/2.08, 128/2 C, 73/421.5 R, 23/232 R, 23/232 E, 422/83, 422/84, 250/294
• US Class Current: 600/532
• CPC Class Codes: A61B 5/0813 Measurement of pulmonary parameters by tracers, e.g. radioactive tracers
• CPC Class Codes: G01F 1/36 the pressure or differential pressure being created by the use of flow constriction
• CPC Class Codes: H01J 49/0422 for gaseous samples interfaces to gas chromatographs G01N30/7206

Abstract

Respiratory gas flow data is synchronously provided along with continuous samples of the gases for analysis by a medical mass spectrometer. The gas flow data is determined by use of the differential pressure across a resistive core in a sampling flowmeter and the flow value at any instant is registered by proportionately admitting a non-toxic gas that is foreign to the normal respiratory gases into the sampling inlet in a quantity controlled by the differential pressure. The quantity of foreign gas therefore represents flow and is drawn through the inlet tube in exact synchronism with its corresponding respiratory gas sample for analysis by the spectrometer. The generated signal representing the amount of foreign gas, hence the flow, may then be used with the signals representing concentration of the various gases in the corresponding respiratory gas sample to calculate various medical parameters, such as oxygen uptake, where the exact synchronism of these signals is important.

Claims

1. A flowmeter for providing synchronized gas flow data concurrently with gas samples to a mass spectrometer comprising:

a mass spectrometer having an input port,

a tubular flowmeter element for a gas flow to be sampled and having a first end, a second end, and a flow restricting means interposed between said first and second ends;

a gas transmission tube connecting the first end of said flowmeter element to said input port of said mass spectrometer;

first means for introducing a second gas into the second end of said flowmeter element, said second gas being foreign to the gases to be sampled;

conduit means coupled between said second end and said gas transmission tube, one end of said conduit means positioned in said second end to withdraw only said second gas, the other end of said conduit means being connected into said transmission tube at a point where a sample of gas will combine with said second gas withdrawn at substantially the same instant as said sample; and

second means within said mass spectrometer for measuring the quantity of second gas in the combined sample transmitted to said mass spectrometer, said quantity being proportional to the pressure difference across said flow restricting means and indicative of the gas flow through said flowmeter.

2. The flowmeter claimed in claim 1 comprising a gas collector cup opened to said second end of said flowmeter element for receiving said second gas from said first means, and said one end of said conduit means opens into said cup to withdraw only said second gas at the pressure of said second end.

3. The flowmeter claimed in claim 2 wherein said second gas is helium and said gas collector cup is inverted to collect said helium.

4. The flowmeter claimed in claim 2 wherein said conduit means and said transmission tube are capillary tubes.

5. The flowmeter claimed in claim 4 comprising a patient'"'"'s mouthpiece and wherein said flowmeter element is a pneumotachograph flowmeter in which said first end is coupled to said patient'"'"'s mouthpiece.

6. A method for transmitting pressure data of a flowing gas simultaneously with samples of said gas comprising the steps of:

providing a sampling element through which said gas flows, said element having a first end coupled to a pressure varying source of said gas, a second end, and a flow-restricting means within said element and interposed between said first and said second ends for creating a pressure difference between said first and second ends that is proportional to the gas flow through said restricting means;

withdrawing samples of said gas with a sampling tube positioned within said first end of said element;

admitting into the second end of said element a second gas that is distinguishable from said sampled gas;

positioning a withdrawing tube within said second end and proximate the location where said second gas is admitted, withdrawing samples of only said second gas with said withdrawing tube and at the pressure existing in said second end;

interconnecting said gas sampling tube and said second gas withdrawing tube at a location near said sampling element and at locations in said tubes where a sample of said sampled gas will arrive and combine with a sample of said second gas that was withdrawn from said sampling element at substantially the same instant; and

determining the quantity of second gas in the combined sampled gas and second gas, said quantity being proportional to the pressure difference existing between said first and said second ends of said sampling element at the instant said sampled gas was withdrawn.