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 ind ividuals depending on the physiological conditions. We evaluated the e ffects of duration of exhalation and breath-holding on the exhaled con centrations of NO in 16 normal human volunteers. Exhaled gas correspon ding to vital capacity was collected in 6-liter Tedlar bags and analyz ed 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 s ignificant difference in the exhaled NO concentration among 10-s phase s of a 30-s exhalation, as determined from multiple breath collections . The NO released from the airways is presumably unaffected by fluctua tion of exhalation speed. The NO release rate, calculated from a singl e regression analysis between the NO concentration and the duration of exhalation, was 39 +/- 29 pmol/s, a value which was about fourfold gr eater in nine patients with bronchial asthma.