Objective: Heart rate variability, a quantitative measure of mainly parasympathetic activity, has been applied in evaluating many types of psychiatric and neurological disorders, including dementia (or neurocognitive disorders). However, although dementia patients often showed significantly lower heart rate variability (various indices) than healthy controls, and different types of dementia had distinct heart rate variability features, the results were not identical across studies. We designed a systematic review and meta-analysis for incorporating data from different studies.
Methods: We gathered studies comparing heart rate variability in patients with dementia and in healthy controls. Heart rate variability was analysed in several ways: parasympathetic function in hierarchical order (main analysis), total variability, comparison of heart rate variability between different subtypes of dementia, specific indices of heart rate variability and heart rate variability reactivity.
Results: In the initial search, we found 3425 relevant articles, from which 24 studies with a total of 1107 dementia patients and 1017 control participants finally entered the main meta-analysis. The dementia patients had a significantly lower resting heart rate variability for parasympathetic function (Hedges' g = -0.3596, p = 0.0002) and total variability (Hedges' g = -0.3059, p = 0.0002) than the controls. For diagnostic subgroup analysis relative to the controls, heart rate variability was significantly lower in patients with mild cognitive impairment (Hedges' g = -0.3060) and in patients with dementia with Lewy bodies (Hedges' g = -1.4154, p < 0.0001). Relative to patients with Alzheimer's disease, heart rate variability in patients with dementia with Lewy bodies was significantly lower (Hedges' g = -1.5465, p = 0.0381). Meta-regression revealed that gender proportion was significantly associated with effect size.
Conclusion: Our results show that dementia patients (especially those with dementia with Lewy bodies and mild cognitive impairment) have lower parasympathetic activity than healthy people. The influence of gender on the results should be carefully interpreted.
Keywords: Heart rate variability; dementia; dementia with Lewy bodies; mild cognitive impairment; neurocognitive disorders; parasympathetic activity.