Influence of inhaled nitric oxide on gas exchange during normoxic and hypoxic exercise in highly trained cyclists

This study tested the effects of inhaled nitric oxide [NO; 20 parts per mil lion (ppm)] during normoxic and hypoxic (fraction of inspired O-2 = 14%) ex ercise on gas exchange in athletes with exercise-induced hypoxemia. Trained male cyclists (n = 7) performed two cycle tests to exhaustion to determine maximal O-2 consumption ((V)o(2 max)) and arterial oxyhemoglobin saturatio n (Sa(O2), Ohmeda Biox ear oximeter) under normoxic ((V)o(2 max) = 4.88 +/- 0.43 l/min and SaO(2) = 90.2 +/- 0.9, means +/- SD) and hypoxic ((V) over dot(2 max) = 4.24 +/- 0.49 l/min and Sa(O2) = 75.5 +/- 4.5) conditions. On a third occasion, subjects performed four 5-min cycle tests, each separated by Ih at their respective (V) over dot o(2 max), under randomly assigned c onditions: normoxia (N), normoxia + NO (N/NO), hypoxia (H), and hypoxia + N O (H/NO). Gas exchange, heart rate, and metabolic parameters were determine d during each condition. Arterial blood was drawn at rest and at each minut e of the 5-min test. Arterial Po-2 (Pa-O2), arterial PCO2, and Sa(O2) were determined, and the alveolar-arterial difference for Po-2 (A-aDo(2)) was ca lculated. Measurements of Pa-O2 and Sa(O2) were significantly lower and A-a Do(2) was widened during exercise compared with rest for all conditions (P < 0.05). No significant differences were detected between N and N/NO or bet ween H and H/NO for Pa-O2, Sa(O2) and A-aDo(2) (P > 0.05). We conclude that inhalation df 20 ppm NO during normoxic and hypoxic exercise has no effect on gas exchange in highly trained cyclists.