Submaximal exercise in patients with severe obstructive sleep apnea

Several studies have used the cardiopulmonary exercise test to assess patients with obstructive sleep apnea (OSA). However, no report has investigated the use of the 6-min walk test (6MWT) in this group of patients. We studied consecutive, newly diagnosed, OSA patients (aged > 18 years). The control group was composed of matched healthy subjects with no clinical history indicative of sleep breathing disorders. The study population was divided into three groups: an OSA group, a control obese group, and a control lean group. The obese controls were gender-, age- (+/- 2 years), height- (+/- 5 cm), and weight- (+/- 2 kg) matched to the OSA patients, while the lean controls were matched in gender, age, and height, but not weight. All patients underwent sleep study at our Sleep Disorders Center. Each subject underwent a single 6MWT within 1 week of the sleep study. A total of 55 patients were recruited to the OSA group (age 36.7 +/- 7.9 years, body mass index 38.7 +/- 8.6 kg/m(2), and apnea hypopnea index 66.6 +/- 34.8/h), 32 subjects to the control obese group, and 30 to the control lean group. There was no difference in distance walked (6-min walk distance (6MWD)) between the OSA group (389 +/- 70 m) and the obese group (408 +/- 66 m). In the OSA group, the 6MWD results did not correlate with patient age, apnea hypopnea index, or other polysomnographic variables. At the end of the test, heart rate, systolic and diastolic blood pressure, and dyspnea perception were significantly increased in the OSA group compared with healthy subjects. The 6MWT is easy to perform and well tolerated by patients with OSA. There were no correlations between the 6MWD and the severity of OSA or other polysomnographic parameters. However, patients with OSA exhibited abnormal hemodynamic responses to submaximal exercise.