Autonomic dysfunction in patients with Alzheimer’s disease

Abstract

Objective: To look for evidence of cardiac autonomic dysfunction in patients with Alzheimer's disease (AD). Rationale: Limbic structures are important components of central autonomic control, which undergo degeneration in AD. Acetylcholine is a major neurotransmitter of parasympathetic system and there is cholinergic depletion in AD. Methods: It is a prospective two group comparative study. 25 clinically probable Alzheimer's patients were compared with 25 age and gender matched healthy controls. Short term heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) were assessed. Comparison between the groups was done using Mann-Whitney and Wilcoxon test. Spearman's correlation co-efficient was used to assess correlation between the disease severity and study parameters. Results: In Alzheimer's group, among frequency domain parameters of HRV, high frequency power in normalized units (HF nu) was significantly low (p<0.05): low frequency power in normalized units (LF nu) and LF/HF ratio was significantly high (p<0.05). There was a negative correlation between HF nu and disease severity and a positive correlation between LF nu and LF/HF ratio and disease severity. Discussion: There is a significant reduction in parasympathetic activity with sympathyovagal imbalance with sympathetic dominance in AD. This may be due to central autonomic dysfunction as well as cholinergic depletion. In addition, cardiac autonomic dysfunction and disease severity are positively correlated. Conclusion: There is statistically significant abnormality suggestive of sympathetic predominance and suppression of parasympathetic activity in AD group as compared to control group.