IntroductionEndothelial function at high altitude has been measured only in populations that are genetically adapted to chronic hypoxia. The objective of this study was to evaluate endothelial dysfunction (ED) in a nongenetically adapted high-altitude population of the Andes mountains, in Huancayo, Peru (3,250 meters above sea level).MethodsParticipants included 61 patients: 28 cases and 33 controls. The cases were subjects with hypertension, diabetes mellitus, obesity, or a history of stroke or coronary artery disease. Flow-mediated vasodilation (FMD) of the brachial artery was measured in the supine position, at noon, after 5 minutes of resting. The brachial artery was identified above the elbow. Its basal diameter was measured during diastole, and FMD was tested after 5 minutes of forearm ischemia. Intima–media complex in the right carotid artery was also determined. An increase in the artery’s baseline diameter <10% indicated a positive test. Endothelium-independent vasodilation was evaluated with sublingual nitrate administration. The intima–media complex in the right carotid artery was also measured.Results100% of diabetics had ED; ED was also found in 68.8% of obese individuals, 55% of hypertensive patients, and 46.5% of controls. Age, height, body mass index, and waist diameter were higher in the cases as compared with the controls. A total of 57.9% (n=11) of the cases and 45.2% (n=19) of the controls presented ED. Patients without ED had a mean increase in brachial artery diameter of 23.16%, while in those with ED it was only 3.84%. Individuals with diabetes or hypertension had a greater thickness of the carotid artery intima media layer (1.092 versus 0.664 cm) (p=0.037). A positive test for ED was associated with a greater basal diameter of the brachial artery (4.66±0.62 versus 4.23±0.59 cm) (p=0.02). A total of 7 patients presented paradoxical response, developing posthyperemia vasoconstriction.DiscussionThe proportion of ED was high among controls and among patients with risk factors. Controls showed better FMD profiles than subjects studied in Tibet and the Himalayas.