Journal of Applied Physiology, Vol 51, Issue 4 1033-1037, Copyright © 1981 by American Physiological Society
Alveolar pressure-airflow characteristics in humans breathing air, He-O2, and SF6-O2
A. S. Slutsky, J. M. Drazen, C. F. O'Cain and R. H. Ingram Jr
In a system of rigid tubes under steady flow conditions, the coefficient of
friction [CF = 2 delta P/(rho V2/A2)] (where delta P is pressure drop, rho
is density, V is flow, and A is cross-sectional area) should be a unique
function of Reynolds' number (Re). Recently it has been shown that at any
given Re, the value of CF using transpulmonary pressure (PL) was lower when
breathing He-O2 compared with air (Lisboa et al., J. Appl. Physiol.:
Respirat. Environ. Exercise Physiol. 48: 878-885, 1980). One explanation
for this discontinuity is that PL includes the pressure drop due to tissue
viscance, which is independent of V, and thus would lead to an overestimate
of CF on air compared with He-O2 at any Re. We tested this hypothesis by
measuring V related to alveolar pressure, rather than PL, in normal
subjects breathing air, He-O2, and SF6-O2. In each subject, for a given Re,
CF was greatest breathing SF6-O2 and lowest breathing He-O2, similar to
results using PL. Thus tissue viscance is not the sole cause of the
discontinuous plot of CF vs. Re, and this phenomenon must be due to other
factors, such as changing geometry or nonsteady behavior.
