Ap. Pietropaoli et al., Simultaneous measurement of nitric oxide production by conducting and alveolar airways of humans, J APP PHYSL, 87(4), 1999, pp. 1532-1542
Human airways produce nitric oxide (NO), and exhaled NO increases as expira
tory flow rates fall. We show that mixing during exhalation between the NO
produced by the lower, alveolar airways ((V) over dot (LNO)) and the upper
conducting airways ((V) over dot (UNO)) explains this phenomenon and permit
s measurement of (V) over dot (LNO), (V) over dot (UNO) and the NO diffusin
g capacity of the conducting airways (D-UNO) After breath holding for 10-15
s the partial pressure of alveolar NO (PA) becomes constant, and during a
subsequent exhalation at a constant expiratory flow rate the alveoli will d
eliver a stable amount of NO to the conducting airways. The conducting airw
ays secrete NO into the lumen ((V) over dot (UNO)), which mixes with PA dur
ing exhalation, resulting in the observed expiratory concentration of NO (P
E). At fast exhalations, PA makes a large contribution to PE, and, at slow
exhalations, NO from the conducting airways predominates. Simple equations
describing this mixing, combined with measurements of PE at several differe
nt expiratory flow rates, permit calculation of PA, (V) over dot (UNO), and
DUNO. (V) over dot (LNO) is the product of PA and the alveolar airway diff
usion capacity for NO. In seven normal subjects, PA = 1.6 +/- 0.7 x 10(-6)
(SD) Torr, (V) over dot (LNO) = 0.19 +/- 0.07 mu l/min, (V) over dot (UNO)
= 0.08 +/- 0.05 mu l/min, and DUNO = 0.4 +/- 0.4 ml.min(-1).Torr(-1). These
quantitative measurements of (V) over dot (LNO) and (V) over dot (UNO) are
suitable for exploring alterations in NO production at these sites by dise
ases and physiological stresses.