U. Schedin et al., CONTRIBUTION FROM UPPER AND LOWER AIRWAYS TO EXHALED ENDOGENOUS NITRIC-OXIDE IN HUMANS, Acta anaesthesiologica Scandinavica, 39(3), 1995, pp. 327-332
Endogenous nitric oxide (NO) is thought to regulate many biological fu
nctions, including pulmonary circulation and bronchomotion, and it has
been found in exhaled air. Our aim was to study the excretion of NO i
n different parts of the respiratory system. Exhaled concentrations of
NO were measured by chemiluminescence in chronic tracheostomy outpati
ents (group 1), in patients admitted for minor abdominal surgery (grou
p 2), and in patients with acute respiratory failure (ARF) during mech
anical ventilation (group 3). In awake volunteers (group dr), 0.57 L/m
in gas was aspirated through the nasal cavity into the chemiluminescen
ce device. In group 1 (tracheostomy, n=5) we detected 16+/-2 (mean+/-s
.e. mean) parts per billion (ppb) NO when exhaling through the mouth,
and a lower (P<0.05) value of 4.6+/-0.8 ppb NO when exhaling through t
he tracheostomy. Before anaesthesia, group 2 (n=11) exhibited 13+/-2.4
ppb NO in orally exhaled gas, increasing considerably during exhalati
on through the nose. Upon endotracheal intubation exhaled NO concentra
tion dropped to 1.3+/-0.2 ppb (P<0.05). In group 3 (ARF, n=7) tracheal
NO concentrations were 0.8+/-0.2 ppb. In group 4 (volunteers, n=6) 39
4+/-23 ppb NO was recorded in air from the nasal cavity. In both healt
hy subjects and patients with respiratory failure a significant NO exc
retion occurs in the lower airways and lungs. The upper airways, expec
ially the nose, contribute the largest amount of NO (>90%) to exhaled
air. The physiological implications of an upper airway source of NO re
main to be defined.