Contribution from upper and lower airways to exhaled endogenous nitric oxide in humans

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Abstract
Endogenous nitric oxide (NO) is thought to regulate many biological functions, including pulmonary circulation and bronchomotion, and it has been found in exhaled air. Our aim was to study the excretion of NO in different parts of the respiratory system. Exhaled concentrations of NO were measured by chemiluminescence in chronic tracheostomy outpatients (group 1), in patients admitted for minor abdominal surgery (group 2), and in patients with acute respiratory failure (ARF) during mechanical ventilation (group 3). In awake volunteers (group 4), 0.57 L/min gas was aspirated through the nasal cavity into the chemiluminescence device. In group 1 (tracheostomy, n=5) we detected 16±2 (mean±s.c. mean) parts per billion (ppb) NO when exhaling through the mouth, and a lower (PP90%) to exhaled air. The physiological implications of an upper airway source of NO remain to be defined.