Excessive daytime sleepiness does not correlate with sympathetic nervous system activation and arterial stiffening in patients with mild-to-moderate obstructive sleep apnoea: A proof-of-principle study

Background Increased arterial stiffness and sympathetic nervous system activity, independent markers of cardiovascular risk, are common in patients with severe obstructive sleep apnoea, who have excessive daytime sleepiness. Among patients with mild-to-moderate obstructive sleep apnoea, however, it remains unknown whether arterial stiffness and/or increased sympathetic nervous system activity correlate with excessive daytime sleepiness. Methods We measured heart rate variability, as an index of autonomic nervous system activity, and arterial stiffness index, as a marker of vascular damage and cardiovascular risk, in 56 men aged 18 to 75 years, with mild-to-moderate obstructive sleep apnoea, and matched into two groups, “sleepy” (Epworth Sleepiness Scale ≥ 10) and “non-sleepy” (Epworth Sleepiness Scale < 10). Results We found no association of excessive daytime sleepiness with sympathetic nervous system activation (very low frequency power 18,947 ± 11,207 ms2 vs 15,893 ± 8,272 ms2, p = 0.28; low frequency (LH) power 17,753 ± 8,441 ms2 vs 15,414 ± 5,666 ms2, p = 0.26; high frequency (HF) power 7,527 ± 1,979 ms2 vs 8,257 ± 3,416 ms2, p = 0.36; LF/HF ratio 3.04 ± 1.37 vs 2.55 ± 1.01, p = 0.15) and mean arterial stiffness index (6.97 ± 0.83 vs 7.26 ± 0.66, p = 0.18) in mild-to-moderate obstructive sleep apnoea patients. Conclusions Symptoms of excessive daytime sleepiness are not associated with sympathetic nervous system activation and arterial stiffness in male subjects with mild-to-moderate obstructive sleep apnoea.