Journal of Applied Physiology, Vol 74, Issue 5 2127-2134, Copyright © 1993 by American Physiological Society
Contribution of tissue lipid to long xenon residence times in muscle
J. A. Novotny, E. C. Parker, S. S. Survanshi, G. W. Albin and L. D. Homer
Naval Medical Research Institute, Bethesda, Maryland 20889-5055.
Experiments demonstrate that the mean residence time of an inert gas in
tissue is longer than that predicted by a single-compartment model of gas
exchange. Also the relative dispersion (RD, the standard deviation of
residence times divided by the mean) is 1 according to this model, but RDs
in real tissues are closer to 2, suggesting that a multiple-compartment
model might be more accurate. The residence time of a gas is proportional
to its solubility in the tissue. Although the noble gases in particular are
10 times more soluble in lipid than in nonlipid tissues, models of gas
exchange generally do not incorporate measurements of the lipid in tissue,
which may lead to error in the predicted gas residence times. Could a
multiple-compartment model that accounts for the lipid in tissue more
accurately predict the mean and RD of gas residence times? In this study,
we determined the mean and RD of Xe residence times in intact and
surgically isolated muscles in a canine model. We then determined the lipid
content and the perfusion heterogeneity in each tissue, and we used these
measurements with a multiple-compartment model of gas exchange to predict
the longest physiologically plausible Xe residence times. Even so, we found
the observed Xe mean residence times to be twice as long as those predicted
by the model. However, the predicted RDs were considerably larger than the
observed RDs. We conclude that lipid alone cannot account for the residence
times of Xe in tissue and that a multiple-compartment model is not an
accurate representation of inert gas exchange in tissue.(ABSTRACT TRUNCATED
AT 250 WORDS)
