Cardiac sympathovagal modulation evaluated by short-term heart interval variability is subtly impaired in Alzheimer's disease

Aim: Alzheimer's disease affects several nervous structures involved with the autonomic nervous system. Therefore, the still scarce evaluation of the cardiac autonomic function in this disease is of great functional, clinical, prognostic and therapeutic relevance. Methods: Time- and frequency-domain variability of 5-min R-R interval series in supine and standing positions was comparatively evaluated in 22 Alzheimer's disease subjects, aged 60-87 years (mean +/- standard error of the mean, 79.6 +/- 1.4) with variable cognitive impairment, and 24 healthy individuals, aged 60-91 years (68.6 +/- 1.6). The Student's t-test was used to compare the variability indices between the groups and logistic regression excluded the effects on these indices in the Alzheimer's group of confounding variables different from the control group (age, physical activity and caffeinated intake), at a significance level of P <= 0.05. Results: No difference was observed between the groups (P=0.12-0.72) for each time-domain mean indices and for the frequency-do main indices of overall and absolute sympathetic modulation in both positions (P=0.21-0.78). Absolute parasympathetic modulation showed borderline decrease in supine position (P=0.07) and was reduced in the standing (P=0.05). The sympathovagal balance was altered (P=0.05) toward relative parasympathetic borderline depression (P=0.07) and sympathetic exacerbation (P=0.04) only in the supine posture. Conclusion: Data indicate that Alzheimer's disease subjects with mild-to-severe cognitive dysfunction showed subtle, absolute and relative parasympathetic depression and relative sympathetic exacerbation, which may even so contribute to distinctive functional and cognitive disturbances.