Rate of nitric oxide release in the lung and factors influencing the concentration of exhaled nitric oxide.

The level of nitric oxide (NO) in exhaled air fluctuates in normal individuals depending on the physiological conditions. We evaluated the effects of duration of exhalation and breath-holding on the exhaled concentrations of NO in 16 normal human volunteers. Exhaled gas corresponding to vital capacity was collected in 6-liter Tedlar bags and analyzed by chemiluminescence. The NO concentration in exhaled gas increased significantly in proportion to the duration of exhalation [P = 0.009 +/- 0.011 (SD)] and was increased after breath-holding. There was no significant difference in the exhaled NO concentration among 10-s phases of a 30-s exhalation, as determined from multiple breath collections. The NO released from the airways is presumably unaffected by fluctuation of exhalation speed. The NO release rate, calculated from a single regression analysis between the NO concentration and the duration of exhalation, was 39 +/- 29 pmol/s, a value which was about fourfold greater in nine patients with bronchial asthma.