Fractional Exhaled Nitric Oxide in Healthy Tibetans at High Altitude

BACKGROUND Fractional exhaled NO (FENO) is a marker of airway inflammation. For successful use of this marker it is important to have reference ranges from different healthy populations. The aim of this study was to establish these in healthy Tibetan adults who had always lived at high altitude on the Qinghai-Tibet Plateau. MATERIAL AND METHODS The study included 145 healthy Tibetan subjects, aged 18 to 75 years, who were non-smokers. FENO was measured at a flow rate of 50 mL/s using a chemiluminescence analyzer. Residential altitude was classified as: Grade 1 (3678-3800 m), Grade 2 (3800-4200 m), or Grade 3 (>4200 m). Correlations between subject characteristics (age, sex, height, and weight), altitude, and FENO were investigated. RESULTS The geometric mean FENO (95% CI) was 15.4 (7.0, 35.0) parts per billion (ppb). The 95% upper limit of the log-transformed data was 33.0 ppb, which was slightly lower than that for Han Chinese, and much lower than in the Northwest Han population. Mean FENO values were higher in males (16.8 ppb) than females (14.3 ppb) and inversely related to altitude. Multiple linear regression analysis showed that FENO was predicted by the equation Ln (FENO)=[2.844+0.161 × sex (1 for male; 0 for female) -0.111 × altitude grade]. The residual standard deviation (SD) was 0.048, and the explanatory value was 7%. CONCLUSIONS The upper limit of FENO in healthy Tibetan adults is 33 ppb. This value can be predicted on the basis of sex and altitude.