SINGLE-BREATH DIFFUSING-CAPACITY OF NO INDEPENDENT OF INSPIRATORY NO CONCENTRATION IN RABBITS

Pulmonary diffusing capacity of NO (DLNO) was determined by performing single-breath experiments on six anesthetized paralyzed supine rabbit s, applying inspiratory concentrations of NO (FINO) within a range of 10 parts per million (ppm) less than or equal to FINO less than or equ al to 800 ppm Starting from residual volume, the rabbit lungs were inf lated by 50 mi of a NO-nitrogen-containing indicator gas mixture. Brea th-holding time was set at 0.1, 1, 3, 5, and 7 s. Alveolar partial pre ssure of NO was determined by analyzing the end-tidal portion from exp irates, with the use of respiratory mass spectrometry. In the six anim als, 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 foun d 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 dependenc e of DLNO On the respective duration of the single-breath maneuvers. I n addition, the time course of NO removal from alveolar space was inde pendent of applied FINO levels. These results suggest that DLNO determ inations are neither affected by chemical reactions of NO in alveolar gas phase as well as in lung tissue nor biased by endogenous release o f NO from pulmonary tissue. It is our conclusion that the single-breat h diffusing capacity of NO is able to provide a measure of alveolar-ca pillary gas conductance that is not influenced by the biochemical reac tions of NO.