Daily Variations of Vital Capacity, Residual Air, and Expiratory Reserve Including a Study of the Residual Air Method

Abstract

Daily measurements were made of the vital capacities of 17 individuals over a 2- to 3-month period. The avg. of the standard deviations was 2.36% of their vital capacity volume. No seasonal correlations could be established. Daily measurements of the residual air by a N dilution method on 5 subjects over a period of 2 months gave an avg. standard deviation of 5.5% of the residual air volume. The expiratory reserve and the vital capacities of these same individuals had an avg. standard deviation of 7.9% and 1.9%, respectively, for their particular volumes. Reasons for the modification of the Lundsgaard-Van Slyke method for the detn. of the residual air are discussed. A method of calculating the N percentage for instantaneous mixing is given and it is shown that the value so obtained is approx. equal to the N percentage after the 3d expiration. The latter value is therefore used in practice for the calculation of the residual air.