AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 6 2055-R2058, Copyright © 1997 by American Physiological Society
Single-breath diffusing capacity of NO independent of inspiratory NO concentration in rabbits
H. Heller and K. D. Schuster
Department of Physiology, University of Bonn, Germany.
Pulmonary diffusing capacity of NO (DLNO) was determined by performing
single-breath experiments on six anesthetized paralyzed supine rabbits,
applying inspiratory concentrations of NO (FINO) within a range of 10 parts
per million (ppm) < or = FINO < or = 800 ppm. Starting from residual
volume, the rabbit lungs were inflated by 50 ml of a NO-nitrogen-containing
indicator gas mixture. Breath-holding time was set at 0.1, 1, 3, 5, and 7
s. Alveolar partial pressure of NO was determined by analyzing the
end-tidal portion from expirates, with the use of respiratory mass
spectrometry. In the six animals, pulmonary diffusing capacity of NO
averaged DLNO = 1.92 +/- 0.21 ml.mmHg-1.min-1 (mean +/- SD value). Despite
extreme variations in FINO, we found very similar DLNO values, and in three
rabbits we found identical values even at such different FINO levels of 80
ppm or 500, 20, or 200 ppm as well as 10 or 800 ppm. There was also no
dependence of DLNO on the respective duration of the single-breath
maneuvers. In addition, the time course of NO removal from alveolar space
was independent of applied FINO levels. These results suggest that DLNO
determinations are neither affected by chemical reactions of NO in alveolar
gas phase as well as in lung tissue nor biased by endogenous release of NO
from pulmonary tissue. It is our conclusion that the single-breath
diffusing capacity of NO is able to provide a measure of alveolar-capillary
gas conductance that is not influenced by the biochemical reactions of NO.
