Daytime baroreflex sensitivity in patients with primary insomnia.

Insomnia has been linked to cardiovascular disease and among these especially hypertension and changes in autonomic function. One marker for cardiovascular risk is baroreflex sensitivity (BRS). We investigate daytime BRS in patients with primary insomnia in order to assess cardiovascular risk. Twenty-one patients (18 females/3 males) with primary insomnia according to DSM-IV were recruited. Careful investigations excluded confounding sleep disorders such as sleep-disordered breathing and periodic limb movements. An age-matched control group with 21 healthy subjects (18 females/3 males) underwent the same investigations. To assess BRS, an experimental protocol with paced breathing during daytime was performed. ECG and continuous non-invasive blood pressure were recorded to obtain spontaneous BRS by calculating the α index (BRS-α) and also by transfer function analysis (TF-BRS). There were no differences at daytime between insomnia patients and controls neither in BRS-α (8.1 ms/mmHg, range 5.8-14.7 vs. 9.6 ms/mmHg, range 6.9-15.8) nor in TF-BRS (5.8 ms/mmHg, range 2.4-16.8 vs. 5.4 ms/mmHg, range 2.3-11.4). Also there were no differences in absolute, low or high frequency bands of heart rate or blood pressure variability between the two groups. We could show that primary insomnia may be not associated with daytime parameters of autonomic imbalance (e.g., baroreflex sensitivity) which are known as non-classical risk markers of cardiovascular disease.