Background: Obstructive sleep apnea (OSA) is often accompanied by the metabolic syndrome. Because both conditions are associated with depressed heart rate variability (HRV) separately, our aim was to study whether co-morbid OSA is associated with more reduced HRV in male patients with the metabolic syndrome.
Methods: In this cross-sectional study, 35 men (age, 57±11 years) with the metabolic syndrome (according to International Diabetes Federation criteria) were included. OSA severity was defined by the apnea-hypopnea index (AHI). HRV was assessed by 24-hr ambulatory electrocardiographic monitoring. Standard deviation of all normal-to-normal RR intervals (SDNN), the high frequency power (HFP), and the ratio of low- to high-frequency power (LF/HF) were measured.
Results: There were 14, 6, and 8 cases of severe (AHI ≥30/hr), moderate (15/hr≤AHI <30/hr), and mild (5/hr ≤AHI <15/hr) OSA, respectively. Seven patients had no OSA. Patients with mild-moderate or severe OSA had reduced SDNN and HFP values compared to those without OSA. Increasing OSA severity was associated significantly with lower daytime LF/HF ratio [standardized β regression coefficient (β)=-0.362, P=0.043] and higher night/day LF/HF ratio (β=0.377, P=0.023) after controlling for age, duration of diabetes, and severity of metabolic syndrome.
Conclusions: Co-morbid OSA is associated with decreased overall HRV, parasympathetic loss, and impaired diurnal pattern of sympathovagal balance that may further increase the cardiovascular vulnerability of male patients with the metabolic syndrome. The role of the HRV analysis in the risk assessment of these patients warrants further studies.