Effect of the Level of Expiration on Body Density Measurement

This experiment was designed to test the reproducibility of body density measurements following maximum and approximately one-half maximum expiration. A total of 26 adult males were tested. Duplicate density measurements were made at each level of expiration. The average lung volume following maximum expiration was 1.66 liters. The average density following maximum expiration (d = 1.0559 gm/cc) was 0.0017 density units lower than that determined following one-half maximum expiration. This difference was significant (P < 0.01). Each technique was consistent within itself; the standard deviation of the maximum expiration replicates being 0.0018, and the one-half maximum expiration replicates 0.0024. The latter differences were not significant. Note: with the technical assistance of R. S. Isenstein and W. C. Roemer. Submitted on September 23, 1957