Association of a decrease in dynamic compliance with a change in gas distribution.

Abstract

The relationship between a decrease in dynamic compliance (Cdyn) and a change in the N2 washout of the lungs was tested by comparing simultaneously measured Cdyn and the N2 washout with constant tidal volume at slow and rapid respiratory rates. Five normal subjects and 5 patients with mild obstructive airway disease were studied. N2-washout curves of the log end-tidal N2 for each breath versus cumulative expired volume show a greater separation between curves at the 2 rates (less efficient washout at the rapid rate) in those subjects in whom there was the greatest fall in Cdyn with the rapid rate. These data support the mechanical time-constant theory as a factor in changing gas distribution with respiratory frequency.