COMPARISON OF EXHALED NITRIC-OXIDE AND CARDIORESPIRATORY INDEXES BETWEEN NASAL AND ORAL BREATHING DURING SUBMAXIMAL EXERCISE IN HUMANS

In order to examine the origin and role of nitric oxide (NO) in exhale d air during exercise, exhaled NO outputs of 8 healthy human subjects were compared using different breathing methods, through the mouth or nose, at two intensities of bicycle exercise. The concentration of NO in the exhaled air and ventilatory gas exchange variables were measure d by a chemiluminescence analyzer and a mixing chamber method, respect ively. The concentration and total output of NO in the expired air was significantly higher under nasal breathing than under oral breathing for both exercise intensities, whereas no significant difference was o bserved in cardiorespiratory variables between them. NO output increas ed significantly when exercise intensity was increased from unloaded ( 0 W) to 60 W under nasal breathing, but not under oral breathing. A ne gative correlation among subjects was found between NO output and minu te ventilation in both breathing methods only for unloaded exercise. D ata indicate that nasal airways have a large contribution, at least 50 % of total NO output in the exhaled air during nasal breathing, but th is nasal NO may have no further modulation on respiratory function dur ing submaximal exercise by healthy humans.