Cardiopulmonary Function in Obstructive Sleep Apnea Patients After Short-term Nasal CPAP Therapy

Abstract

Obstructive Sleep Apnea (OSA) is characterized by repetitive episodes of airway occlusion that result in hypoxia, hypercapnia, and disrupted sleep. These events increase daytime sympathetic outflow and likely contribute to the development of hypertension. Clinical exercise testing has been used to identify patients with abnormal blood pressure (BP) responses and evaluate therapeutic applications, but such responses have not been studied extensively in OSA. PURPOSE: To examine the effects of short-term (12 wk) nasal continuous airway pressure (CPAP) treatment on cardiopulmonary function in patients with diagnosed OSA. METHODS: Twenty-two OSA patients (mean age+SD = 46.2+10.6yr; BMI = 33.6+6.8 kg/m2; Apnea Hypopnea Index (AHI) = 24.4+14.1 events/hr) and 9 overweight controls without OSA (age = 41.7+9.8 yr; BMI = 28.5+5.9 kg/m2; AHI = 4.9+0.1) completed a maximal cycle ergometer ramp exercise test, including measures of oxygen consumption (VO2), heart rate (HR), and BP at baseline, 6 wk, and 12 wk. RESULTS: To better evaluate the effects of treatment, OSA patients were classified as CPAP compliant (CPC) or non-compliant (CPN). Age, BMI, resting HR and BP, and VO2pk were not different between OSA subjects and CTL at baseline (p>0.05). OSA patients reported more daytime sleepiness (Epworth Sleepiness Scale) at baseline compared to CTL (p<0.01), which significantly improved (>20%; p<0.05) by 12 wk in both the CPC and CPN groups. Both OSA and CTL exhibited prehypertension at baseline which continued throughout treatment. Submaximal exercise systolic BP significantly improved in the CPC group (∼16 mmHg ↓; p=0.02) compared to CPN and CTL. At baseline, peak systolic and diastolic BP were higher, and submaximal and peak exercise HR were lower for the overall OSA group compared to CTL, and this persisted throughout treatment and regardless of compliance (p<0.05). Otherwise, responses of the CPC patients, including VO2pk, were not different over time compared to CPN or CTL (P<0.05). CONCLUSION: Middle-aged OSA patients display exaggerated BP and blunted HR to graded exercise that suggests impaired sympathetic autonomic function which may be partially responsive to short-term CPAP. Supported by a grant from ResMed Sleep Disordered Breathing Foundation, Poway, CA.