Hypoxemia and hypercapnia during exercise and sleep in patients with cystic fibrosis

Background: In patients with cystic fibrosis (CF), it has been proposed that hypoxemia and hypercapnia occur during episodes of stress, such as exercise and sleep, and that respiratory muscle weakness because of malnutrition may be responsible. Methods: Pulmonary function, respiratory muscle strength, and nutrition were assessed and correlated with the degree of hypoxemia and hypercapnia during exercise and sleep in 14 patients with CF and 8 control subjects. Results: Despite no differences in maximum static inspiratory pressure (PImax) between the two groups, the CF group developed more severe hypoxemia (minimum oxyhemoglobin saturation [SpO(2)], 89 +/- 5% vs 98 +/- 2%; p < 0.001) and hypercapnia (maximum transcutaneous CO, tension [PtcCO(2)], 43 +/- 6 vs 33 +/- 7 mm Hg; p < 0.01) during exercise, Similarly, during sleep, the CF group developed greater hypoxemia (minimum SpO(2), 82 +/- 8% vs 91 +/- 2%; p < 0.005), although CO, levels were not significantly different (maximum PtcCO(2), 48 +/- 7 vs 50 +/- 2 mm Hg), Within the CF group, exercise-related hypoxemia and hypercapnia did not correlate with FEV,, residual volume/total lung capacity ratio (RV/TLC), PImax, or body mass index (BMI), Hypoxemia and hypercapnia during sleep correlated with markers of gas trapping (RV vs minimum arterial oxygen saturation [r = -0.654; p < 0.05]), RV vs maximum PtcCO(2) (r = 0.878; p < 0.001), and RV/TLC vs maximum PtcCO(2), (r = 0.790; p < 0.01) but not with PImax or BMI. Conclusion: Patients with moderately severe CF develop hypoxemia and hypercapnia during exercise and sleep to a greater extent than healthy subjects with similar respiratory muscle strength and nutritional status, Neither respiratory muscle weakness nor malnutrition are necessary to develop hypoxemia or hypercapnia during exercise or sleep.