Effects of simulated altitude-induced hypoxia on exercise capacity in patients with chronic heart failure

Patients with stable heart failure often wish to spend time at altitudes above those of their residence. However, it is not known whether they can safely tolerate ascent to high altitudes or what its effects on work capacity may be.

We studied 14 normal subjects and 38 patients with clinically stable heart failure, 12 of whom had normal workload [peak exercise oxygen consumption (VO(2)) greater than 20 mL/min/kg], 14 of whom had slightly diminished workload (peak VO(2) 20 to 15 mL/min/kg), and 12 of whom had markedly diminished workload (peak VO(2) less than 15 mL/min/kg) at baseline. All performed cardiopulmonary exercise tests with inspired oxygen fractions equal to those at 92, 1,000, 1,500, 2,000, and 3,000 m, and maximum achieved work rates (mean +/- SD) were measured.

All subjects completed the trial; no test was interrupted because of arrhythmia, angina, or ischemia. Maximum work rate decreased in parallel with increasing simulated altitude. The percentage decrease was greater for patients with heart failure and was most marked among those with the lowest workload at baseline. Maximum achieved work rate declined by 3% +/- 4% per 1,000 m in normal subjects, by 5% +/- 3% (P <0.01) in patients with heart failure with normal workload, by 5% +/- 4% (P <0.01) in patients with slightly diminished workload, and by 11% +/- 5% (P <0.01 vs normal subjects and vs the other patients with heart failure) in patients with markedly reduced workload.

Patients with stable heart failure who ascend to higher altitudes should expect to have a reduction in maximum physical activity in proportion to their exercise capacity at sea level.