Cardiopulmonary responses to exercise in moderate-to-severe obstructive sleep apnea

Information regarding the safety of maximal cardiopulmonary exercise testing (CPET) or the mechanisms of exercise limitation in obstructive sleep apnea (OSA) patients is fairly limited. In the present study, we addressed the problem of exercise capacity in moderate-to-severe OSA patients. Nineteen non-consecutive patients (three female, 16 male) with moderate-to-severe OSA and 11 age and body mass index matched control subjects (four female, seven male) underwent respiratory function tests during pre-exercise resting period and volitionally limited cardiopulmonary exercise testing on an electronically braked cycle ergometer. All participants completed CPET without any complication. Control subjects were exercise limited due to deconditioning. None of the patients revealed mechanical ventilatory limitation to exercise or had evidence of cardiac ischaemia. Five patients had no limitation to exercise. Six patients had low VO2peak, low anaerobic treshold (AT), and low peak O2 pulse, a pattern consistent with ventricular dysfunction. Six patients had low VO2peak, low AT, and peak heart rate less than 85% predicted. This pattern is consistent with exercise limitation due to peripheral vascular disease. Two patients had low VO2peak, low AT without peak oxygen pulse and peak heart rate abnormalities consistent with deconditioning. We concluded that moderate-to-severe OSA patients have impaired exercise capacity. Exercise limitation seems to originate from cardiovascular reasons namely left ventricular dysfunction and/or peripheral vascular impairment; and finally, maximal CPET can be tolerated by these patient group without serious complications.