Journal of Applied Physiology, Vol 66, Issue 2 542-547, Copyright © 1989 by American Physiological Society
Preferential axial flow during high-frequency oscillations: effects of gas density
C. M. Alleyne, I. D. Frantz 3rd and J. J. Fredberg
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02215.
Allen et al. (J. Clin. Invest. 76: 620-629, 1985) reported that regional
phasic lung distension during high-frequency oscillations (HFO) is
substantially and systemically heterogeneous when both frequency (f) and
tidal volume (VT) are large. They hypothesized that this phenomenon was
attributable to central airway geometry and preferential axial flow induced
therein by the momentum flux of the inspiratory gas stream. According to
that hypothesis, the observed distribution of phasic lung distension would
depend on the ratio VT/VD* (where VD* is an index of anatomic dead space),
independent of gas density (rho), when f is scaled in proportion to lung
resonant frequency, fo. To test this hypothesis, we used the methods of
Allen et al. (ibid.) to study six excised dog lungs during HFO (f = 2-32
Hz; VT = 5-80 ml) using gases of different densities. Alveolar pressure
excursions (PA) were measured as rho spanned a 12-fold range using He, air,
and SF6. The apex-to-base and right-to-left ratios of PA were used as
indexes of regional heterogeneity of phasic lung distension. For each gas
at low f, distension of the lung base was favored slightly independent of
VT, but at higher f distension of the lung apex was favored when VT was
small, whereas distension of the lung base was favored when VT was large.
In addition, we observed substantial right-to-left differences in apical
lobes during oscillation at high f not seen before.(ABSTRACT TRUNCATED AT
250 WORDS)
