Increased sympathetic and decreased parasympathetic cardiac innervation in patients with Alzheimer's disease.

To assess whether Alzheimer's disease affects the sympathetic and parasympathetic influences on the heart rate, we used power spectrum analysis of heart rate variability derived from simple body-surface electrocardiography. We calculated the energy ratio of low- to high-frequency bands. This ratio was significantly higher in patients with Alzheimer's disease than in normal controls (upright posture, 0.41 +/- 0.21 vs 0.23 +/- 0.08). The parasympathetically mediated baroreceptor activity reflected by the energy ratio of medium- to low- and high-frequency bands was significantly depressed in patients with Alzheimer's disease (upright posture, 0.12 +/- 0.02 vs 0.07 +/- 0.03; supine posture, 0.11 +/- 0.02 vs 0.085 +/- 0.025). Compared with normal volunteer controls, patients with Alzheimer's disease manifested a relatively hypersympathetic, hypoparasympathetic state.