Resp Care
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Comparative Study
A comparison of the oxygen cost of breathing between a continuous-flow CPAP system and a demand-flow CPAP system.
We undertook a study to measure the difference in work of breathing, as reflected by oxygen uptake (VO2) and carbon dioxide production (VCO2), between that on a continuous-flow CPAP system (Emerson IMV) and that on a demand-flow CPAP system (Bennett MA-2). A specially designed valve permitted the isolation and collection of expired gases from the Emerson IMV/CPAP ventilator. Ten patients receiving CPAP therapy were selected for study. ⋯ Analyses of VO2, VCO2, respiratory quotient, minute ventilation, tidal volume (VT), respiratory rate, and FIO2 were made serially at approximately 45-second intervals for 8 minutes. A comparison between the Emerson continuous-flow CPAP system and the MA-2 demand-flow CPAP system revealed that with the MA-2 the mean values for VO2, VCO2, and VT were, respectively, 16.3%, 12.6%, and 6.4% higher, a statistically significant difference. We believe that this difference was probably due to the additional effort required of the patient on the MA-2 to open and close the demand valve.