Oxygen saturation in adult cystic fibrosis patients during exercise at high altitude

The objective of this study was to determine the frequency and severity of decreased arterial oxy-hemoglobin saturation during exercise in adults with cystic fibrosis at 1,500 m above sea level. A convenience sample of 50 adults with cystic fibrosis who did not have hypoxemia (oxygen saturation, < 90%) at rest were evaluated. Spirometry was performed according to American Thoracic Society standards, and maximal exercise tests were performed on an electronically braked cycle ergometer using a ramp protocol individualized for each patient. Pulse oximetry was measured every 2 min. When exercising at high altitude, 45 of 50 patients had a decrease in arterial oxy-hemoglobin saturation from baseline to some degree. In 29 patients, oxy-hemoglobin saturation fell below 90%; in 14 patients, it fell below 85%; and in 4 patients, it fell below 80%. Oxy-hemoglobin saturation decreased to < 90% in 12 of 14 patients with severe pulmonary disease (FEV₁ < 40% predicted), in 15 of 26 patients with moderate disease (40% less than or equal to FEV₁ < 70% predicted), in 2 of 6 patients with mild disease (70% less than or equal to FEV₁ < 90% predicted), and in 0 of 4 with normal pulmonary function (FEV₁ greater than or equal to 90%). Percent predicted FEV₁ (r=0.57; P<0.0001) and FEV₁/FVC ratio (r=0.52; P<0.0001) most highly correlated with arterial oxy-hemoglobin saturation at peak exercise. We conclude that at 1,500 m above sea level, adult CF patients with obstructive airways disease are at significant risk for decreased arterial oxy-hemoglobin saturation during exercise. A supervised exercise test should be considered prior to recommending an exercise program for such patients.