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 assessment of inflammatory disease in the lung, We determined immediate and day-to-day reproducibility of single-breath NO measurements at different points on the exhaled test, and whether levels recorded reflect levels of NO in the lower airways, Using a rapid chemiluminescence analyser, 55 healthy control subjects pel formed three sequential tests on each of two days, NO levels were compared at the le cel corresponding with: 1) the time the mouth pressure fell below 4 cmH(2)O (MP); 2) the plateau of end-exhaled CO2 (CO2); and 3) the NO plateau (NOp), NO levels were measured directly from the lower airways of 15 lung transplant recipients and compared with NO levels from a single-breath test performed 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 recorded at the mouth from a single-breath test and in the lower airways were 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 oxide levels are a simple, reproducible and valid measure of nitric oxide production from the lower respiratory tract.