Cardiovascular autonomic functions in Alzheimer's disease.

We investigated cardiovascular autonomic functions in 23 patients with Alzheimer's disease (AD) and 23 age-matched control subjects. The vagal parasympathetic function was assessed with R-R interval variation (RRIV), and sympathetic function with sympathetic skin response (SSR) and orthostatic cardiovascular reflexes. Compared with controls, the AD patients had significantly depressed RRIV during rest (6.4 +/- 1.3% vs. 7.5 +/- 1.6%, p < 0.02) and deep breathing (12.6 +/- 4.6% vs. 17.0 +/- 5.1%, p < 0.006), but all AD patients had normal SSR. After standing for 3 minutes from supine, the changes of blood pressure and heart rate from baseline in AD patients did not differ from those in controls. The AD patients had a lower systolic blood pressure than controls in both supine (130.7 +/- 17.4 vs. 145.4 +/- 20.7 mmHg, p < 0.02) and standing (129.2 +/- 20.1 vs. 146.6 +/- 21.1 mmHg, p < 0.008) positions, especially in those patients with more severe dementia. We conclude that AD patients have mildly impaired autonomic functions, mainly in vagal parasympathetic functions. The pathogenesis and clinical significance of low blood pressure in AD needs further study.