Journal of Applied Physiology, Vol 56, Issue 2 343-354, Copyright © 1984 by American Physiological Society
Intra-airway gas mixing during high-frequency ventilation
J. Solway, N. Gavriely, R. D. Kamm, J. M. Drazen, R. H. Ingram Jr, M. C. Khoo, R. Brown and A. S. Slutsky
We examined the intra-airway gas transport mediated by high-frequency
oscillations (HFO) in 10 nonintubated healthy volunteers using a method
based on comparisons of single-breath N2-washout curves obtained after
various durations of breath hold or high-frequency oscillations. With a
mathematical analysis based on Fick's law of diffusion we computed the
local transport parameter, effective diffusivity, during oscillations of
frequency 2-24 Hz and tidal volume 10-120 ml and during breath hold alone.
Local effective diffusivity increased with both oscillatory frequency and
tidal volume at all levels in the tracheobronchial tree; the enhancing
effect of tidal volume on local effective diffusivity was more pronounced
than that of frequency so that effective diffusivity was greater with
larger tidal volume at fixed frequency-tidal volume product (f . VT). The
greatest enhancement of gas mixing within the lung during HFO (over breath
hold) was seen in the central airways. In previous studies examining CO2
removal rate during HFO (J. Clin. Invest. 68: 1475, 1981), we found that
CO2 output was also greater with larger tidal volume at fixed f . VT, and
we attributed this to an end constraint imposed by a fresh gas bias flow.
Results of the current study, performed without a bias flow, indicate that
bias flow end constraint does not solely account for the observed
dependence of CO2 output on frequency and tidal volume.
