Journal of Applied Physiology, Vol 68, Issue 2 792-795, Copyright © 1990 by American Physiological Society
Tracheal dead space influences regional ventilation measurement in dogs
L. Delaunois, R. Boileau and R. R. Martin
Meakins-Christie Laboratories, McGill University, Royal Victoria Hospital, Montreal, Quebec, Canada.
The lung volume at which airway closure begins during expiration (closing
volume, CV) can be measured 1) with a radioactive bolus inspired at
residual volume (RV) and 2) with the single-breath N2 elimination test. In
previous studies in dogs, we observed that N2 CV was systematically larger
than 133Xe bolus CV (Xe CV) [N2 CV %vital capacity (VC) = 35 +/- 2.3 (SE)
vs. Xe CV %VC = 24 +/- 2.2, P less than 0.01]. Because the regional RV in
the dog is evenly distributed throughout the lung and all airways closed at
RV, N2 CV is related to the regional distribution of the tracheal N2;
differences between N2 and Xe CV could then be related to the size of the
inhaled dead space. Simultaneous measurements of Xe and N2 CV were
performed at various sites of Xe bolus injection while the regional
distribution of the bolus was measured. Injections at the level of the
carina increased Xe CV to a value (30 +/- 1.4%VC) near simultaneous N2 CV
(32 +/- 1.5%VC) and increased the unevenness of regional distribution of
the Xe bolus. The difference between N2 and Xe CV is then the result of the
size of the inspired tracheal dead space. Moreover, comparisons between
different values of Xe CV require injections of the boluses at the same
distance from the carina.
