Nighttime cardiac sympathetic hyper-activation in young primary insomniacs.

Objective: A growing literature supports the association between insomnia and cardiovascular risk. Since only few studies have provided empirical evidence of hyper-activation of the cardiovascular system in insomniacs, the aim of the present study was to analyze cardiac autonomic responses in primary insomnia.

Methods: Impedance cardiography and heart rate variability (HRV) measures were assessed in 9 insomniacs and 9 good sleepers during a night of polysomnographic recording.

Results: Insomniacs were found to be characterized by a constant sympathetic hyper-activation which was maintained all night, as suggested by a faster pre-ejection period (PEP) compared to good sleepers. In addition, only insomniacs showed a strong reduction in heart rate in the transition from wake to sleep. Both groups exhibited a reduction in cardiac output and sympathovagal balance, i.e., reductions in low-frequency/high-frequency ratio and increases in high-frequency normalized units of HRV, across the night. In addition, in our sample, a high physiological sympathetic activation (fast PEP) at night was found to be directly associated with low quality of sleep.

Conclusions: These preliminary findings suggest that a constant cardiac sympathetic hyper-activation throughout the night is a main feature of primary insomnia. Our evidences support the association between insomnia and increased risk for cardiovascular diseases.