Journal of Applied Physiology, Vol 44, Issue 2 277-283, Copyright © 1978 by American Physiological Society
Inert gas a-A differences: a direct reflection of V/Q distribution
G. R. Neufeld, J. J. Williams, P. L. Klineberg and B. E. Marshall
A computer model was developed to study the relationship between
ventilation-to-perfusion (V/Q) mismatch and the development of inert gas
arterial-to-alveolar partial pressure differences (a-A differences).
Increasing inhomogeneity of V/Q ratio is revealed directly as an increase
in the a-A difference of each gas. The quantitative relationships between
the Q vs. V/Q distribution and the fractional a-A difference solubility
plot (a-A difference plot) were studied and described. These studies
demonstrated that for log normally distributed V/Q ratios, the area under
the a-A difference plot is linearly related to the log variance of the V/Q
distribution and can be estimated directly from the values obtained from
six gases. The maximum a-A difference occurs for a gas whose solubility is
numerically equal to the mean V/Q. The effects of departure from log
normality and multimodality are discussed. We conclude from these studies
that quantitative information regarding the degree of inhomogeneity of V/Q
for log normal distribution is available from direct calculations of inert
gas retention and excretion data. Qualitative information is also available
indicating the departure from log normality and the region toward which the
distribution is skewed.
