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

Obstructive sleep apnea syndrome (OSAS) is associated with autonomic dysfunction and metabolic abnormalities including obesity, dyslipidemia, and insulin resistance. Heart rate recovery at 1min 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.

Sixty-three patients with untreated OSAS (49.2+/-9.8years) 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]>30h(-1); n=32) were compared to patients with mild to moderate OSAS (AHI 5-30h(-1); n=31).

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+/-0.4mmol/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.

The severity of OSAS expressed as higher AHI is independently associated with lower HRR-1, a measure of autonomic dysfunction.