Journal of Applied Physiology, Vol 51, Issue 6 1463-1470, Copyright © 1981 by American Physiological Society
Distribution of ventilation and diffusing capacity in the normal and diseased lung
S. M. Lewis, D. Z. Rubin and C. Mittman
Conventional tests of diffusing capacity (DL) consider the lung to be a
uniform structure with regard to both ventilation and diffusion. These
assumptions are incorrect even in normal subjects. We present a method for
determining the distribution of both specific ventilation (SV) and DL from
the washin and washout of C18O and simultaneous washout of argon. Both
end-tidal and mixed-expired data are fit to a two-compartment lung model;
parameters that define SV and DL are assigned to each compartment. From
data generated by a model, the parameters recovered were found to be
relatively insensitive to realistic levels of noise. Measurements in one
subject were highly repeatable. We examined 15 normal subjects and 16
subjects with varying degrees of obstructive lung disease. In both groups
the better ventilated spaces generally showed a higher DL. The sum of the
total two-compartmental DL's correlated with, but was found to exceed, the
value obtained using the steady-state method and generally exceeded the
single-breath result. We conclude that this method has potential advantages
over conventional methods and is worthy of further study.
