The Parallel Determination of the Respiratory Quotient and Alveolar Air of Man in the Post-Absorptive Condition

Abstract

The respiratory exchange of two human subjects was measured on 3 and 4 days for 4 consecutive 15-minute periods, and then for 9 or 10 consecutive 15-minute periods in the post-absorptive condition, in a sitting position, by means of an open-circuit respiration apparatus with mouthpiece as a breathing appliance. The alveolar air was sampled at least every 15 minutes without interrupting the measurements of the respiratory exchange, by means of an arrangement described in detail. With one trained subject the average respiratory quotient and the alveolar carbon dioxide did not change significantly in the course of a total of three and one-half hours. With one untrained subject both the respiratory quotient and the alveolar carbon dioxide varied, usually in opposite directions during the same length of time. The alveolar respiratory quotients of both subjects tended to run parallel with the respiratory quotients of the total expired air. There was a tendency to an inverse relationship between the alveolar carbon dioxide and the alveolar respiratory quotients which was more marked in the extreme values, and with the trained subject than with the untrained subject and was due either to slight variations in ventilation at the time of taking of the alveolar air samples or to variations in the sensitivity of the respiratory center. There was a marked negative correlation between the alveolar respiratory quotient and the percentage alveolar oxygen deficit.