BACKGROUND: Recently, it is thought that endothelial function is a new independent risk factor of atherosclerotic disease. However, the differences in endothelial function between Tibetan and Han nationality populations have not been fully investigated.OBJ ECTIVE: To investigate the differences in endothelial function between Tibetan and Han nationality population.DESIGN: Controlled analysis.SETTING: Department of Cardiology, General Hospital; Department of Cardiology, Tibet General Hospital of Chinese PLA.PARTICIPANTS: Totally 272 Tibetan male subjects, aged (43±9) years, were enrolled in this study to stand for Tibetan nationality populations. All of them were native residents in Lhasa city. And 580 Qinghai-Tibetan railway constructers with Han nationality, aged (42±11) years, were enrolled in this study to stand for Han nationality populations. All of them were male subjects from Sichuan province and lived in Lhasa city for at least 1 year. All the participants received regular physical examination between February and May 2006 in the General Hospital of Tibet Military Area Command of Chinese PLA. All the subjects lived in the same high-altitude area (the altitude of Lhasa is 3 658 m). Informed consents were obtained from all the participants.METHODS: ①Height, body mass, waist circumference, hip circumference, systolic blood pressure(SBP) and diastolic blood pressure (DBP) were measured. Body mass index (BMI) was measured as body mass/height2. ② Measurement of brachial artery flow-mediated dilation (FMD): All the participants, who were in the fasting state, were examined in supine position following 20-minute rest. The room temperature was about 20 ℃. In the right arm, a sphygmomanometer cuff was positioned 5 cm below the antecubital fossa. A 10-MHz transducer (Vivid 7, GE Corporation, USA) was used to image the right brachial artery. After obtaining the baseline imaging, the blood pressure cuff was inflated 50 mm Hg (1 mm Hg=0.133 kPa) above the participant's SBP to occlude the brachial artery for 4 minutes. The brachial artery was then imaged during cuff inflation and 2 minutes after cuff release. After the cuff was released and reactive hyperaemia occurred, that was, flow in the brachial artery increased to accommodate the dilated resistance vessels in the forearm. In order to ensure the reliability of the data, the cuff placement and image record were performed by two designated performers. Computer-assisted analysis software was used to calculate brachial artery diameters. The absolute and relative changes of brachial artery FMD were automatically calculated out with the attached software of Vivid 7 ultrasonic diagnosis instrument. ③Biochemical study: The biochemical parameters were obtained after an overnight fasting for 12 hours. Venous blood was sampled for the measurement of total cholesterol, triglyceride (TG), high-density lipoprotein cholesterol and low-density lipoprotein cholesterol (LDL-C). ④ Analysis of variance was used to evaluate the measurement data. Chi-square statistic was used to compare enumeration data.MAIN OUTCOME MEASURES: Comparison of change in BMI, waist-hip ratio, blood pressure, blood lipid, baseline brachial diameter and brachial diameter between 2 groups.RESULTS: Totally 272 Tibetan nationality populations and 583 Han nationality populations participated in the final analysis. ① Brachial artery FMD: The baseline brachial artery diameter of Tibetan nationality populations was significantly larger than that of Han nationality population [(4.28±0.06) mm vs. (4.03±0.04) mm, t =71.915 6, P ＜0.01]; The absolute and relative changes of brachial artery of Tibetan nationality populations were significantly smaller than those of Han nationality populations, respectively [(0.124±0.005) mm vs. (0.141±0.006) mm; (2.934±0.204)% vs.(3.587±0.152)%, t = 40.582 0,52.173 2, P ＜ 0.01]. ②Physical study results: BMI and waist-hip ratio of Tibetan nationality populations were significantly larger than those of Han nationality populations [(30.1±2.5) kg/m2 vs. (26.5±3.4) kg/m2, 0.92±0.07 vs. 0.88±0.05, t =15.595 1, 9.525 4, P ＜ 0.01]. ③TG and LDL-C levels of Tibetan nationality population were (2.31±1.31) mmol/L and (3.49±0.91) mmol/L, respectively, which were significantly higler than those of Han nationality population [(1.97±1.44) mmol/L and (3.07±0.86) mmol/L, t =3.420 0, 6.522 3, P ＜ 0.01].CONCLUSION: ① Brachial artery FMD of Tibetan nationality population is poorer than that of Han nationality population,I.e. Poor vascular reactivity. ② Tibetan nationality populations have severe abdominal obesity and higher level of blood lipid as compared with Han nationality populations.