Association between heart rate recovery and severity of obstructive sleep apnea syndrome

Background: Obstructive sleep apnea syndrome (OSAS) is associated with autonomic dysfunction and metabolic abnormalities including obesity, dyslipidemia, and insulin resistance. Heart rate recovery at 1 min after exercise termination (HRR-1) is a marker of vagal tone. We hypothesized that patients with more severe OSAS would have a lower HRR-1, either due to the co-existing metabolic abnormalities or OSAS. Methods: Sixty-three patients with untreated OSAS (49.2 ± 9.8 years) without glucose- or lipid-lowering or negatively chronotropic drugs underwent cardiopulmonary exercise testing including HRR-1 measurement and assessment of several metabolic parameters. Patients with severe OSAS (apnea–hypopnea index [AHI] > 30 h 1 ; n = 32) were compared to patients with mild to moderate OSAS (AHI 5–30 h 1 ; n = 31). Results: Patients with severe OSAS were more likely to be male (25 vs. 3%; p = 0.01) and to have hypertension (72 vs. 39%; p = 0.01); they also had higher fasting glucose (5.4 ± 0.5 vs. 5.1 ± 0.4 mmol/l; p = 0.016) and C-peptide [905 (651–1353) vs. 749 (597–919) pmol/l; p = 0.028] levels compared to patients with mild to moderate OSAS. The groups did not differ with respect to peak heart rate (p = 0.2) or peak oxygen consumption (p = 0.9), but HRR-1 was significantly lower in patients with severe OSAS compared to patients with mild and moderate OSAS [20 (15–25) vs. 24 (18–34) bpm; p = 0.022]. Higher AHI (p = 0.01) and lower peak heart rate (p = 0.02), but not body mass index or insulin resistance, were independently associated with lower HRR-1. Conclusions: The severity of OSAS expressed as higher AHI is independently associated with lower HRR-1, a measure of autonomic dysfunction.