Journal of Applied Physiology, Vol 55, Issue 6 1818-1824, Copyright © 1983 by American Physiological Society
Measurement of lung emptying patterns during slow exhalations
W. R. Scott and H. D. Van Liew
Five subjects slowly inhaled a 200-ml bolus of sulfur hexafluoride (SF6)
from residual volume (RV) followed by an O2-Ar mixture to total lung
capacity, then exhaled to RV, either slowly or as rapidly as possible.
Larger amounts of SF6 and N2 were recovered in fast than in slow
exhalations. We calculated the gas volumes of the apical and basal halves
of the parenchymal mass as functions of exhaled volume during slow
exhalations from 1) the difference between SF6 recovered in slow and fast
exhalations and 2) an estimate of the apex-to-base concentration profile of
SF6 in the lung after inspiration. The maximal volume difference, where the
apex contained 600 ml more gas than the base, occurred when 70% of the
vital capacity had been exhaled. The same calculation, but using N2 data,
gave unrealistically large volume differences. Apparently SF6 delivered as
a bolus results in an apex-to-base gradient that is large relative to
intraregional gradients, but dilution of the resident N2 by a non-N2 gas
results in sizable intraregional gradients.
