Effect of gravity on lung exhaled nitric oxide at rest and during exercise

Exhaled nitric oxide (NO) from the lungs (V̇(NO)) in nose-clipped subjects increases during exercise. This may be due to endothelial shear stress secondary to changes in pulmonary blood flow. We measured V̇(NO) after modifying pulmonary blood flow with head-out water immersion (WI) or increased gravity (2 Gz) at rest and during exercise. Ten sedentary males were studied during exercise performed in air and WI. Nine subjects were studied at 1 and 2 Gz. Resting NO concentrations in exhaled air ([NO]) were 16.3 ± 8.2 ppb (air), 15 ± 8.2 ppb (WI) and 17.4 ± 5 ppb (2 Gz). V̇(NO) (ppb/min) was calculated as [NO]V̇(E) and was unchanged at rest by either WI or 2 Gz. V̇(NO) increased linearly with V̇(O₂),V̇E and fH during exercise in air, WI and at 2 Gz. These relationships did not differ among the experimental conditions. Therefore, changes in pulmonary blood flow failed to alter the output of NO exhaled from the lungs at rest or during exercise.