Relative compliances of well and poorly ventilated spaces in the normal human lung

¹ Biophysics Laboratory, Department of Medicine, University of Sydney, Sydney, Australia

A series of experiments was performed in each of which the subject inspired a .25-liter bolus of argon in a large breath consisting otherwise of air. The slope of the argon plateau in the subsequent expiration was found to depend upon the lung volume at which the bolus was administered. When inspiring from residual volume to total lung capacity, bolus injection at a low lung volume led to a rising plateau; injection at medium volume led to a flat plateau; and at a high lung volume to a steeply falling plateau. From measurements of the different plateau slopes produced it was possible to deduce the ratio of the effective compliances shown at any lung volume by the "well" and "poorly" ventilated alveolar populations. In four normal subjects this ratio rose from about 0.5 at residual volume to about 4 near total lung capacity. The qualitative behavior of the two populations resembled that of the upper and lower zones of the erect lung, as indicated by the nature of the cardiac oscillations on the expired gas plateaus.

Submitted on January 20, 1964