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 (VNO) in exhaled air. Young human subjects (n = 8) of varying fitness levels having peak O2 consumption (VO2) 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. VNO rose significantly in most subjects from a mean resting value of 12.3 +/- 3.5 nmol/min. VNO correlated linearly and significantly with ventilation (VE) and CO2 output in 6 of 8 subjects, with VO2 in 4 of 8 subjects, and with heart rate in 5 of 8 subjects. Increases of VNO per unit increase of VE were significantly higher in subjects having higher peak VO2 levels. Voluntary hyperventilation (two-fold of the control VE) for 1 min in 6 subjects decreased expired [NO] from 9.5 (+/- 2.5) to 4.8 (+/- 2.8) ppb and VNO was unchanged, while hyperventilation at 3 x control VE increased VNO by 50% and [NO] decreased to 4.7 +/- 1.8 ppb. VNO appeared to be related to VO2 during hyperventilation. The results suggest that VNO can be correlated with ventilation and heart rate during exercise and with VO2 during both exercise and hyperventilation. [NO] is influenced by the flow rate of the expired air whereas VNO is influenced by NO clearance at the alveolus.