Heart rate recovery and oxygen kinetics after exercise in obstructive sleep apnea syndrome

Abstract

Background: Patients who suffer from obstructive sleep apnea (OSA) have a decreased exercise capacity and abnormal autonomic nervous function. However, the kinetics of early oxygen (O2) and heart rate recovery (HRR) have not been described. Materials and Methods: We evaluated 21 men with moderate to severe OSA (mean age: 48 ± 11 yrs, mean apnea-hypopnea index [AHI]: 55 ± 13) andwithout known heart disease and 10 healthymen matched for age and bodymass index (BMI; controls). Men with OSA underwent overnight polysomnography, and both groups underwent symptom-limited incremental cardiopulmonary exercise testing (CPET). We recorded the CPET parameters including peak O2 uptake (VO2p), kinetics of early O 2 recovery by the first degree slope of VO2 during the first minute (VO2/t slope), the time required for a 50% decline of VO2p during recovery (T1/2), and early heart rate recovery (HRR=HR at maximal exercise-HR at 1 min of recovery), as well as the chronotropic reserve to exercise ([CR]=[peak HR-resting HR/220-age-resting HR]x100). Patients with OSA had a lower VO2p (28.7 ± 4.0 vs 34.7 ± 6.2mL/kg/min), VO2/t slope (1.04 ± 0.3 vs 1.4 ± 0.17 mL/kg/min2), and T1/2 (74 ± 10 vs 56 ± 6 sec) compared to controls (all P < 0.001). In addition, both HRR and CR were lower in the OSA group(22.0 ± 7.0 vs 31.0 ± 6.0 bpm, P:0.003, and 79.0% ± 15%vs 99.0% ± 13.0%, P:0.01, respectively). Conclusions: Patients with OSA demonstrate reduced exercise capacity, delayed oxygen kinetics, and reduced HRR. These data point to abnormal oxygen delivery and/or oxidative function of the peripheral muscles and impaired autonomic nervous activity in OSA patients. © 2010 Wiley Periodicals, Inc.