Journal of Applied Physiology, Vol 51, Issue 5 1331-1337, Copyright © 1981 by American Physiological Society
Steady expiratory flow in dog lungs: an isovolume preparation
S. L. Sneddon and J. D. Brain
By supplying air and other gases through discs glued to the pleural
surface, we studied steady expiratory flow at constant volume. Dog lungs
were studied at constant PA - Ppl (alveolar minus pleural pressure) of 7 to
10 cmH2O, as increasing flow was achieved by increasing driving pressure
[Ppl - Pao (airway opening pressure)]. Flow became limited (independent of
further increases in Ppl - Pao) at between 3.5 and 5.5 l/s.
Isovolume-pressure-flow (IVPF) curves constructed from forced expirations
at graded efforts yielded similar maximal flows. When the airways were made
rigid by drying, flow limitation was abolished. When various gases were
passed through the dried lung Moody plots of normalized pressure drop (CD)
vs. Reynolds number (Re) showed that all of the data could be plotted on a
single curve. Although variable among animals, all Moody plots showed a
laminar flow region at Re below 100 and an inertial region at Re above
10,000, with a distinct transition.
