CONTRIBUTION FROM UPPER AND LOWER AIRWAYS TO EXHALED ENDOGENOUS NITRIC-OXIDE IN HUMANS

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.