Increased myocardial blood flow during acute exposure to simulated altitudes

Background. Although only poor data er;ist on changes in myocardial blood f low (MBF) under acute hypoxia, patients with known coronary artery disease are advised not to exceed a moderate altitude exposure of about 2000 m abov e sea level. Methods and Results, We measured MBF with positron emission tomography usin g O15-labeled water in 8 healthy human volunteers (aged 26 +/- 3 years [mea n +/- SDI) at baseline (450 m above sea level, Zurich, Switzerland) and dur ing acute hypoxic hypoxemia induced by inhalation of 2 hypoxic gas mixtures corresponding to altitudes of 2000 and 4500 m, MBF remained unchanged at 2 000 m (increase of 10%, not significant) hut increased significantly at 450 0 m (628, P < ,001), exceeding the relative increase in rate pressure produ ct, Conclusions. Our results may explain why exposure to an altitude of 2000 m (corresponding to the cabin pressure in most airplanes during flight) is cl inically well tolerated, even by patients with reduced coronary flow reserv e, such as those dth coronary artery disease. However, at an altitude of 45 00 m, MBF increases significantly, supporting the recommendation that patie nts with impaired flow reserve avoid exposure to higher altitudes,