Published online before print August 25, 2003, doi: 10.1161/01.CIR.0000087432.63671.2E
(Circulation. 2003;108:1202.)
© 2003 American Heart Association, Inc.
Clinical Investigation and Reports |
Influence of Altitude Exposure on Coronary Flow Reserve
From the Department of Cardiology, Nuclear Cardiology Unit (C.A.W., P.K., G.F., P.A.K.), University Hospital, and the Institute of Physiology (M.S., C.S.), University of Zurich, Zurich, Switzerland.
Correspondence to P.A. Kaufmann, MD, Head, Nuclear Cardiology, Cardiovascular Center, Cardiology C NUK 32, University Hospital, Raemistrasse 100, CH-8091 Zurich, Switzerland. E-mail pak{at}usz.ch
Received October 7, 2002; de novo received April 8, 2003; revision received June 17, 2003; accepted June 18, 2003.
Background— Although no data exist on the effect of altitude exposure on coronary flow reserve (CFR), patients with coronary artery disease (CAD) are advised not to exceed moderate altitudes of 
2500 m above sea level. We studied the influence of altitude on myocardial blood flow (MBF) in controls and CAD patients.
Methods and Results— In 10 healthy controls and 8 patients with CAD, MBF was measured by positron emission tomography and 15O-labeled water at rest, during adenosine stress, and after supine bicycle exercise. This protocol was repeated during inhalation of a hypoxic gas mixture corresponding to an altitude of 4500 m (controls) and 2500 m (CAD). Workload was targeted to comparable heart rate–blood pressure products at normoxia and hypoxia. Resting MBF increased significantly in controls at 4500 m (+24%, P<0.01) and in CAD patients at 2500 m (+24%, P<0.05). Altitude had no influence on adenosine-induced hyperemia and CFR. Exercise-induced hyperemia increased significantly in controls (+38%, P<0.01) at 4500 m (despite a reduction in workload, -28%, P<0.0001) but not in CAD patients at 2500 m (moderate decrease in workload, -11%, P<0.05). Exercise-induced reserve was preserved in controls (+10%, P=NS) but decreased in CAD patients (-18%, P<0.005).
Conclusions— At 2500 m altitude, there is a significant decrease in exercise-induced reserve in CAD patients, indicating that compensatory mechanisms might be exhausted even at moderate altitudes, whereas healthy controls have preserved reserve up to 4500 m. Thus, patients with CAD and impaired CFR should be cautious when performing physical exercise even at moderate altitude.
Key Words: blood flow • hypoxia • exercise • coronary disease • tomography
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