Effect of graded exercise on nitric oxide in expired air in humans

This study was performed to determine the influence of graded dynamic exercise and of voluntary hyperventilation on both the concentration ([NO]) and the amount of nitric oxide per unit time (V̇_NO) in exhaled air. Young human subjects (n = 8) of varying fitness levels having peak O₂ consumption (V̇_O2) values ranging between 25.7 and 50.9 ml/min/kg were studied during graded levels of treadmill exercise. Expired [NO] determined by chemiluminescence was 26.3 ± 6.7 SE parts per billion (ppb) at rest ranging between 11 and 66 ppb. Although variable, [NO] was maintained as work rate increased. V̇_NO rose significantly in most subjects from a mean resting value of 12.3 ± 3.5 nmol/min. V̇_NO correlated linearly and significantly with ventilation (V̇E) and CO₂ output in 6 of 8 subjects, with V̇_O2 in 4 of 8 subjects, and with heart rate in 5 of 8 subjects. Increases of V̇_NO per unit increase of V̇E were significantly higher in subjects having higher peak V̇_O2 levels. Voluntary hyperventilation (two-fold of the control V̇E) for 1 min in 6 subjects decreased expired [NO] from 9.5 (±2.5) to 4.8 (±2.8) ppb and V̇_NO was unchanged, while hyperventilation at 3 × control V̇E increased V̇_NO by 50% and [NO] decreased to 4.7 ± 1.8 ppb. V̇_NO appeared to be related to V̇_O2 during hyperventilation. The results suggest that V̇_NO can be correlated with ventilation and heart rate during exercise and with V̇_O2 during both exercise and hyperventilation. [NO] is influenced by the flow rate of the expired air whereas V̇_NO is influenced by NO clearance at the alveolus.