NITRIC-OXIDE IN SINGLE-BREATH EXHALATION IN HUMANS

This study was performed to test the hypothesis that the amount of nit ric oxide (NO) in exhaled air (VNO) is the net result of both NO forma tion in the conducting airway and its clearance by diffusion in the al veoli. It's so difficult to collect the gas in the alveoli in voluntee rs that we made the following consideration from the profile of CO2 fr action (FECO2): the late fraction of exhaled air coming mainly from th e alveoli while the early fraction representing mixed gas from both th e conducting airway and/or the transition zone, and the alveoli. We co mpared the FECO2, NO concentration, and VNO in the early and late frac tions of exhaled air after subjects inspiring either NO-free gas or NO -containing gas (510 ppb) using a single-breath technique (n=5). After inspiring both the NO-free and NO-containing gases, NO appeared in a significantly lower concentration and amount in the late fraction of e xhaled air than those in the early fraction. If NO was not cleared by diffusion in the alveoli or the transition zone, exhaled NO in the lat e fraction should not differ significantly from that in the early frac tion. The results suggest that: 1) NO is constantly formed in the cond ucting airway and/or the transition zone, and is acquired by both inha led and exhaled air; and 2) NO is cleared by diffusion in the alveoli.