Heart Rate Recovery and Oxygen Kinetics After Exercise in Obstructive Sleep Apnea Syndrome

Background: Patients who suffer from obstructive steep apnea (OSA) have a decreased exercise capacity and abnormal autonomic nervous function. However, the kinetics of early oxygen (O-2) 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) and without known heart disease and 10 healthy men matched for age and body mass 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 O-2 uptake (Vo(2)p), kinetics of early O-2 recovery by the first degree slope of Vo(2) during the first minute (Vo(2)/t slope), the time required for a 50% decline of Vo(2)p during recovery (T-1/2), 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] x 100). Patients with OSA had a lower Vo(2)p (28.7 +/- 4.0 vs 34.7 +/- 6.2 mL/kg/min), Vo(2)/t slope (1.04 +/- 0.3 vs 1.4 +/- 0.17 mL/kg/min(2)), and T-1/2 (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.