ROLE OF REACTION RESISTANCE IN LIMITING CARBON-MONOXIDE UPTAKE IN RABBIT LUNGS

The contribution of reaction resistance to overall resistance to pulmo nary carbon monoxide (CO) uptake [DLCO(Theta(CO).Vc), where DLCO is lu ng CO diffusing capacity, Theta(CO) is CO uptake conductance of erythr ocytes, and Vc is pulmonary capillary blood volume] was determined in 10 anesthetized, paralyzed, and artificially ventilated rabbits. On th e basis of the classical double-reciprocal equation off. G. W. Roughto n and R. E. Forster (J. Appl. Physiol. 11: 290-302, 1957), DLCO/(Theta (CO).Vc) was obtained by solving the relation DLCO/(Theta(CO).Vc) = 1 - 2/(DLNO/ DLCO), where DLNO/DLCO represents the ratio between the res pective single-breath diffusing capacities (DL) of nitric oxide (NO) a nd CO pulmonary capillary blood. The lungs of eight rabbits were infla ted, starting from residual volume, by using 55 ml of indicator gas mi xture (0.2% CO and 0.05% NO in nitrogen). DL values were calculated by taking the end-tidal partial pressures of CO and NO as analyzed by us ing a respiratory mass spectrometer. The overall value was DLCO/ (Thet a(CO).Vc) = 0.4 +/- 0.025 (mean +/- SD). Because of the use of O-2-fre e indicator gas mixtures, the end-tidal O-2 partial pressures were sim ilar to 21 Torr. In one other rabbit, the application of 0.2% CO and 0 .001% NO yielded DLCO/(Theta(CO).Vc) = 0.39; in the tenth rabbit, howe ver, inspiratory volume was varied, and an identical value was found a t functional residual capacity. We conclude that the contribution of r eaction resistance to overall resistance to pulmonary CO uptake is ind ependent of the inspiratory NO concentration used, including, with res pect to the pertinent literature, the conclusion that in rabbits, dogs , and humans this contribution amounts to 40% when determined at funct ional residual capacity.