Assessment of sympathetic neural activity in chronic insomnia: evidence for elevated cardiovascular risk

Study Objectives: Chronic insomnia affects up to 15 per cent of adults. Recent cross-sectional and prospective epidemiological studies report an association between insomnia and hypertension, including incident hypertension, yet mechanisms underlying the association remain unknown. We hypothesized that participants with chronic insomnia would have elevated sympathetic neural outflow, blunted baroreflex sensitivity, and augmented sympathetic neural and cardiovascular reactivity to stress when compared with good-sleeper controls. Methods: Twelve participants with chronic insomnia (11 women, 1 man) and 12 controls (8 women, 4 men) underwent one night of laboratory polysomnography, two weeks of at-home wrist actigraphy, and one night of controlled laboratory sleep prior to a comprehensive morning autonomic function test. The autonomic function test consisted of simultaneous recordings of muscle sympathetic nerve activity (MSNA; microneurography), beat-to-beat blood pressure (finger plethysmography), and heart rate (electrocardiogram) during a 10 min supine baseline and a 2 min cold pressor test. Results: Baseline blood pressure, heart rate, and MSNA were not different between groups, but sympathetic baroreflex sensitivity was significantly blunted in participants with insomnia (-2.1 +/- 1.0 vs. -4.3 +/- 1.3 bursts/100 heartbeats/mm Hg; p < 0.001). During the cold pressor test, systolic arterial pressure reactivity (-21 +/- 11 vs. -14 +/- 8 mm Hg; time x group = 0.04) and total MSNA reactivity (Delta 127%, 54%-208% vs Delta 52%, 30%-81%; time x group = 0.02) were augmented in chronic insomnia. Conclusions: Participants with chronic insomnia demonstrated impaired sympathetic baroreflex function and augmented neural cardiovascular responsiveness to stress, when compared with controls. These findings support growing evidence of cardiovascular risk and physiological hyperarousal in chronic insomnia.