Gas Exchange during Exercise in Healthy People: I. the Physiological Dead-Space Volume

Abstract

1. Physiological dead-space volume (V D) was measured in twenty-four healthy men and women aged from 20 to 71 years, at rest and at two rates of work on a treadmill, whilst breathing air and breathing oxygen. 2. The effect of correction of arterial carbon dioxide tension (Pa,CO2) to pulmonary capillary temperature on the resulting value for V D was investigated. We find that the effect is substantial and that a correction should be made. 3. Equations have been derived for the prediction of normal V D during exercise. The best prediction was given by a regression on height, age, carbon dioxide output, ventilation and respiratory frequency, with an upper 95% confidence limit of +81 ml.

Multiple breath nitrogen dead space

“…i.e., the fraction of nitrogen in the alveolar air (FAN,) multiplied by the fraction of ventilation reaching the alveoli (V,) is equal to the volume of the breath (V,) multiplied by the mixed nitrogen concentration of the exhaled gas (FEN,). The dead space is defined as the volume of exhaled gas that contains no nitrogen, exactly as CO, dead space by definition contains no CO, (Bradley et al, 1976). It is obvious that this equation can be applied to the second, third, etc., breath up to breath number n when the end-expiratory nitrogen reaches, e.g., 2%.…”

Gas Exchange during Exercise in Healthy People: II. Venous Admixture

“…Nonetheless it has been argued (Bradley et al, 1976), that the correction we have applied corresponds reasonably well with the likely difference between oral and pulmonary capillary temperature, and there can be no doubt that the uncorrected e v a l e t must be an overestimate. Mean ovalet, with the subject at rest breathing air, was 1.37% in group A and 1.50% in the corresponding group in a previous study (Harris et al, 1974).…”

“…These, including details of the subject groups A, B and C, have been described in the preceding paper (Bradley et al, 1976). During the course of the experiments the mean FOZ of the oxygen supply was found to be 0.9972, SD 0.0050.…”

“…The first of these was the subject's resting oral temperature and the second was the estimated pulmonary capillary temperature, derived according to Bradley et al (1976). The temperature correction affects Pa,oz, Pa,coz, PA,o~ (through Pa,coz) and eva/Qt (through Cc',02 and Ca,oz).…”

“…The objects were (1) to add to available information about the normal range of venous admixture during exercise, (2) to interpret the data in the light of the work of Wagner et al (1974) and Dantzker et al (1975) and (3) to assess the effect on h a l e t of correcting blood-gas tensions to pulmonary capillary temperature; in the preceding paper Bradley, Harris, Seelye & Whitlock (1976) have shown that such 335 correction materially alters estimates of dead-space volume ( VD), especially during exercise.…”