Breath-by-Breath Measurement of Respiratory Gas Exchange Using On-Line Analog Computation

Abstract

Study of transient changes in pulmonary oxygen uptake (Vo₂) and carbon dioxide elimination (Vco₂,) is becoming increasingly important in attempts to explore the dynamic behavior of the overall gas exchange system in response to physiological stimuli such as exercise. A method is described for accurate on-line computation and recording of breath-by-breath Vo₂, Vco₂ and respiratory exchange ratio (R) using fast-response transducers for expiratory flow, O₂ and CO₂ concentrations in conjunction with an analog computer. Special procedures for time alignment of flow and concentration signals, treatment of inspired-expired PH₂O differences in respired gas, and computation of true R are described. The accuracy of the method was studied under steady and non-steady state exercise conditions, Vo₂ and Vco₂ values being in good agreement with those obtained by the conventional Douglas bag technique.

Key Words:

• Biomedical engineering
• carbon dioxide
• exertion
• kinetics
• metabolism
• oxygen consumption
• respiration