Journal of Applied Physiology, Vol 49, Issue 4 684-692, Copyright © 1980 by American Physiological Society
A comparison of continuous and discrete foreign gas VA/Q distributions
R. Teplick, M. T. Snider and J. P. Gilbert
Estimates of ventilation-perfusion ratio (VA/Q) distributions from foreign
gas infusions have utilized a discrete lung model that constrains all
alveoli to have 1 of 50 specified VA/Q. In contrast, distribution estimates
based on a continuous model allow alveoli to have any VA/Q and can be
derived directly from foreign gas data or by transforming distributions
derived using the discrete model. We have compared analytically and
empirically the properties of distributions based on these two models.
Unlike the discrete model, the shape of distributions obtained from the
continuous model are insensitive to changes in the VA/Q used in their
calculation. Perfusion distributions found from the discrete model using
VA/Q values evenly spaced on a logarithmic scale resemble ventilation
distributions derived from the continuous model. In contrast, by use of
VA/Q evenly spaced on a linear scale, perfusion distributions derived from
either model have a similar shape. We concluded that physiological
inferences derived from distribution shapes may vary according to the model
employed. However, those based upon cumulative perfusion or distribution
moments are invariant.
