Our aim was to investigate the sympathetic hyperactivity of systemic sclerosis that may lead to greater morbidity and mortality from cardiovascular events. We analysed the sympathetic (low-frequency) and vagal (high-frequency) components of heart rate variability, in supine and upright positions, in 10 patients with systemic sclerosis, 12 patients with primary Raynaud's phenomenon and 14 controls. We also analysed lung function in order to evaluate a possible link between heart rate variability and ventilation parameters. Heart rate variability was reduced in the supine position in subjects with systemic sclerosis both in comparison with primary Raynaud's phenomenon (total power: 1103±156 versus 3302±486 ;ms2, P< 0.004) and control subjects (3148±422 ;ms2, P< 0.002). Low-frequency power was higher in patients with systemic sclerosis than in the controls (54.5±4.5 versus 42.5±3.5 normalized units, P< 0.01). During tilt, the change in heart rate was +44% in controls, +24% in subjects with primary Raynaud's phenomenon, and only +17% in the patients with systemic sclerosis (P< 0.01 versus controls). In patients with systemic sclerosis we found a significant correlation between high-frequency power and the indices of lung function (residual volume: r2 = 0.5143, P< 0.01; total lung capacity: r2 = 0.5142, P< 0.01, vital capacity: r2 = 0.3789, P< 0.05). Heart rate variability was reduced and sympathetic output increased in patients with systemic sclerosis. Subjects with primary Raynaud's phenomenon were characterized by normal heart rate variability and by some degree of sympathetic hyperactivity. During tilting, subjects with systemic sclerosis maintained an unmodified heart rate variability, thus suggesting an impaired baroceptor modulation of the autonomic control. The negative correlation between high-frequency power and indices of respiratory insufficiency in patients with systemic sclerosis suggests that the pulmonary structure plays an important role in the modulation of heart rate variability.

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