Partitional Respirometry in Human Subjects

¹ From the Department of Preventive Medicine and Industrial Health, University of Cincinnati College of Medicine, Cincinnati, Ohio

The technique of partitional respirometry has been critically evaluated in experiments on 38 healthy men aged 20–67 and 12 healthy women aged 21–55. After lung mixing, the decrease of ether uptake conformed closely to a simple exponential curve, but acetylene saturation of visceral tissues was rapid and several terms were required to describe gas uptake. Extrapolation of the early part of the acetylene curve gave the correct uptake at ‘zero time,’ but the 15–20 minute period recommended by previous authors yielded erroneously low results. Ether did not give acceptable dead-space values owing to difficulties of sampling a rapidly absorbed gas and the inclusion of ‘parallel’ dead-space. The mean nitrogen meter dead-space was 178.7 ml in the male subjects and 97.7 ml in the females. The efficiency of alveolar ventilation varied with tidal volume, sex and height, averaging 93.1% in the male subjects and 91.8% in the female. The effective pulmonary blood flow varied with blood/air contact time, tidal volume and body surface, but was usually close to the total cardiac output, the average value of 5.5 l/m²/min. actually exceeding ballistocardiographic estimates. Despite the efficiency of blood flow, there was some impairment of helium mixing in these subjects, implying that poorly ventilated areas of lung were also poorly perfused. The effective diffusing capacity was related to body surface area, age and blood flow, the average of 34.8 ml/mm Hg/min. being larger than most published steady-state figures.