Cardiopulmonary performance analyzer having dynamic transit time compensation

• US 5,398,695 A
• Filed: 03/24/1994
• Issued: 03/21/1995
• Est. Priority Date: 03/24/1994
• Status: Expired due to Term

• Current Assignee: Medical Graphics Corporation (Niterra Co., Ltd.)
• Original Assignee: Medical Graphics Corporation (Niterra Co., Ltd.)
• Inventors: Anderson, David M., McCutcheon, Shawn
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): GREEN, BRIAN
• Application Number:
  US08/217,231
• Time in Patent Office: 362 Days
• Field of Search: 128/716, 128/719, 128/725, 128/205.27
• US Class Current: 600/532
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/097 Devices for facilitating collection of breath or for directing breath into or through measuring devices

Abstract

The gas sample line in a cardlopulmonary performance analyzing system is designed to include a flow sensor for measuring the rate of flow of the gas sample being drawn and is used to adjust the initial transit time value measured at the time of system calibration for a known value of flow in arriving at a new or current transit time value at the time that a test is actually being performed on a patient. This dynamically compensates the transit time for variations in the sample flow rate, thus providing a system with accuracy that is not dependent upon maintaining constant sample flow rates.

Claims

1. For use in microprocessor-based cardiopulmonary performance analyzing system of the type including a flow meter for measuring inspiratory and expiratory flow and a gas sample line having a plurality of gas sensors therealong for measuring the concentration of respiratory gases in an expired sample volume of such respiratory gases, said gas sensors having a known, fixed response time, a method for time-wise aligning the concentration measurements of the respiratory gases with the flow measurements of said expired sample comprising the steps of:

(a) sensing at a predetermined calibration time the gas transit time through said sample line for a known flow rate and producing first signals proportional thereto;

(b) digitizing and storing said first signals in a memory of a microprocessor;

(c) measuring a sample flow during the course of a cardiopulmonary test on a patient and producing a second digitized signal proportional thereto;

(d) calculating from said stored first signal and said second digitized signal the present gas transit time in said sample line to each of said plurality of gas sensors

(d) (e) adding the calculated present gas transit time to said known, fixed response time of said gas sensors to obtain the phase delay between the expiratory flow and said concentration measurement.

2. In a cardiopulmonary performance analyzer of the type having a sample line leading to at least one respiratory gas analyzer, said gas analyzer adapted to measure the percentage concentration of a particular gas present in the sample line, means for drawing a sample of respiratory gas through said sample line, and a flow meter for measuring the volume rate of flow of inspired and expired respiratory gases by a patient, the improvement comprise apparatus for compensating for transit time delays between the time a gas sample is drawn into said sample line and the time that said at least one gas analyzer produces a predetermined output response comprising:

(a) microprocessor means operative at an initial calibration time for computing and storing digital values proportional to the transit time of an initial gas sample drawn into said sample line to reach said at least one gas analyzer and for storing a calibration flow rate for said initial gas sample;

(b) sample flow measuring means in said sample line for producing a signal proportional to a rate of flow of a subsequent gas sample later drawn through said sample line during the course of a cardiopulmonary test on a patient;

(c) means for digitizing said signal proportional to the rate of flow of the subsequent gas sample;

(d) computing means including said microprocessor means for receiving said digitized signal and the stored values for said transit time and sample flow rate of said initial gas sample stored at the calibration time for computing a present gas transit time;

(e) means in said microprocessor means responsive to the computed transit time value for time-wise aligning said measured percentage concentration of said particular gas with said measured volume rate of flow of inspired and expired respiratory gases.