Hypoxemia as a model for high altitude and cardiovascular risk reduction

Abstract

Is high-altitude living healthy? Perhaps in wealthy Aspen, Colorado. Data from China suggest that the least healthy place to live there is in Tibet [1]. Of course epidemiological surveys have to be taken with (do I dare say it?) a grain of salt. High altitude could benefit cardiovascular function. Residents of the Himalayan valleys are uniquely adapted to their hypoxic environment in terms of pulmonary vasculature. Bruno et al.[2] inspected their systemic cardiovascular function. They studied 95 high-altitude dwellers and 64 controls. Bruno et al. [2] conducted cardiac ultrasound, flow-mediated dilation (FMD) of the brachial artery, carotid geometry and stiffness, and aortic pulse wave velocity (PWV) in their subjects. Eleven high-altitude dwellers that had reduced FMD were studied after 1 h 100 % O 2 administration. High-altitude dwellers presented lower FMD and hyperemic velocity than controls, while systolic pulmonary artery pressure was higher, despite their adaptation. In multiple regression analysis performed in high-altitude dwellers, hyperemic velocity remained an independent predictor of FMD, after adjustment for baseline brachial artery diameter, room temperature and pulse pressure, explaining almost 10 % of its variance. On the contrary, in controls, brachial artery diameter remained the only independent predictor of FMD, after adjustment for confounders. The 100 % O 2 administration did not modify vascular variables.The risk factors for ischemic heart disease in Tibetan highlanders have been investigated. Fujimoto et al. [3] found that although Tibetans had remarkably high hematocrit values and a decrease of eicosapentaenoic acid in both serum total lipids and serum phospholipid possibly due to their diet, they were considered to have a low incidence of ischemic heart disease. These positive risk factors are likely counteracted by other negative risk factors that were identified. Tibetan highlanders showed a decreased level of palmitic acid and an increased level of linoleic acid in serum phospholipids, which could protect against atherosclerosis. In a study of cardiovascular risk in indigenous Argentinean children living at high altitude, there was a substantially higher prevalence of high triglycerides and low high-density lipoprotein cholesterol, compared to similar children from Buenos Aires [4]. These results are not encouraging. For hypertension, the main cardiovascular risk factor, the epidemiological data at altitude also do not inspire confidence. For instance, Mingji et al. [5] studied the relationship between altitude and the prevalence of hypertension in Tibet. In their investigation, a scatter plot of altitude against overall prevalence revealed a direct correlation. Metaregression analysis revealed a 2 % increase in the prevalence of hypertension with every 100 m increase in altitude. The locations and socioeconomic status of subjects affected the awareness and subsequent treatment and control of hypertension. Thus, an immediate argument that living at high altitude leads to cardiovascu...