Journal of Applied Physiology, Vol 51, Issue 6 1581-1593, Copyright © 1981 by American Physiological Society
Time-constant histograms from the forced expired volume signal
R. L. Pimmel, T. K. Miller 3rd, J. M. Fouke and J. G. Eyles
The forced expired volume signal was analyzed using a parallel compartment
model in which each compartment emptied exponentially. With this model the
forced expired volume signal was represented by a histogram showing the
fraction of the vital capacity as a functional of compartmental time
constants. We developed an algorithm to compute this histogram from the
volume signal. The algorithm used the least-squares criterion function with
both smoothness and nonnegativity constraints. In a stimulation study
reasonable histograms were obtained even in the presence of realistic
random error. Three dependent forced expired volume signals from 16
subjects were analyzed, and the histograms were reproducible. Most
histograms were bimodal with fast time constants of 0.12-0.55 s and slow
time constants of 1.3-2.7 s. In all normal subjects and patients with
restrictive disease more than 75% of the vital capacity was in the fast
time-constant mode. Subjects with obstructive disease had more than 40% of
the vital capacity in the slow time-constant mode.
