Rate of nitric oxide production by lower alveolar airways of human lungs

This report describes methods for measuring nitric oxide production by the lungs' lower alveolar airways ((V) over dot NO), defined as those alveoli a nd bronchioles well perfused by the pulmonary circulation. Breath holding o r vigorous rebreathing for 15-20 s minimizes removal of NO from the lower a irways and results in a constant partial pressure of NO in the lower airway s (PL). Then the amount of NO diffusing into the perfusing blood will be th e pulmonary diffusing capacity for NO (DNO) multiplied by PL and by mass ba lance equals (V) over dot NO, or (V) over dot NO = DNO(PL). To measure PL, 10 normal subjects breath held for 20 s followed by exhalation at a constan t flow rate of 0.83 +/- 0.14 (SD) l/s or rebreathed at 59 +/- 15 l/min for 20 s while NO was continuously measured at the mouth. DNO was estimated to equal five times the single-breath carbon monoxide diffusing capacity. By u sing breath holding, PL equaled 2.9 +/- 0.8 mmHg x 10(-6) and (V) over dot NO equaled 0.39 +/- 0.12 mu l/min. During rebreathing PL equaled 2.3 +/- 0. 6 mmHg x 10(-6) and (V) over dot NO equaled 0.29 +/- 0.11 mu l/min. Measure ments of NO at the mouth during rapid, constant exhalation after breath hol ding for 20 s or during rebreathing provide reproducible methods for measur ing (V) over dot NO in humans.