PRODUCTION OF NITRIC-OXIDE (NO) IN INTRATHORACIC AIRWAYS OF NORMAL HUMANS

To gain insight into the source of exhaled nitric oxide (NO) in normal humans, we examined the effects of respiratory pattern on the concent ration of NO in exhaled air while subjects were wearing a noseclip and then under endotracheal intubation, using a specially designed gas sa mpling system to separate exhaled air into two fractions: the initiall y exhaled 200 ml (Fraction 1; F-1), and the remainder (Fraction 2; F-2 ) We also examined the effect of hypoxic gas inhalation (FIo2 = 0.1, 3 min) on the concentration of exhaled NO. The concentration of exhaled NO measured with a chemiluminescence NO analyzer was significantly lo wer with intubation, by 59.2 +/- 10.6% (mean +/- SD) (F-1) and 54.4 +/ - 8.0% (F-2), than without intubation. The concentration of NO in F-1 was consistently higher than that in F-2 with or without intubation. W ith breath holding, the concentration of NO increased markedly only in F-1. In contrast, prolongation of the expiratory phase slightly but s ignificantly increased the concentration of NO only in F-2. Inhalation of hypoxic gas did not cause any significant change in NO concentrati on in either fraction. These data indicate that in normal humans weari ng a noseclip, about 40 to 45% of NO in exhaled air originates from th e lungs, particularly from intrathoracic airways. The concentration of exhaled NO collected from subjects wearing a noseclip is not affected by hypoxic gas inhalation.