EXHALED SINGLE-BREATH NITRIC-OXIDE MEASUREMENTS ARE REPRODUCIBLE, REPEATABLE AND REFLECT LEVELS OF NITRIC-OXIDE FOUND IN THE LOWER AIRWAYS

Measurement of exhaled nitric oxide (NO) may allow noninvasive assessm ent of inflammatory disease in the lung, We determined immediate and d ay-to-day reproducibility of single-breath NO measurements at differen t points on the exhaled test, and whether levels recorded reflect leve ls of NO in the lower airways, Using a rapid chemiluminescence analyse r, 55 healthy control subjects pel formed three sequential tests on ea ch of two days, NO levels were compared at the le cel corresponding wi th: 1) the time the mouth pressure fell below 4 cmH(2)O (MP); 2) the p lateau of end-exhaled CO2 (CO2); and 3) the NO plateau (NOp), NO level s were measured directly from the lower airways of 15 lung transplant recipients and compared with NO levels from a single-breath test perfo rmed in the same cohort, For measurements performed at MP, CO2 and NOp , the mean+/-SD, differences between the two closest levels pel formed on the same day were 0.11+/-0.18, 0.095+/-0.16 and 0.094+/-0.13 parts per billion (ppb, respectively, and between days were 0.18+/-0.76, 0. 19+/-0.78 and 0.17+/-0.8 ppb, respectively, End-expiratory levels reco rded at the mouth from a single-breath test and in the lower airways w ere highly correlated (mouth versus trachea r(2)=0.95, p<0.0001, mouth versus bronchus r(2)=0.92, p<0.0001), Single-breath exhaled nitric ox ide levels are a simple, reproducible and valid measure of nitric oxid e production from the lower respiratory tract.