Parasympathetic autonomic dysfunction is common in mild cognitive impairment.

Components of the central autonomic network attract the greatest neurofibrillary degeneration and related cell death during the course of Alzheimer's disease (AD). The insular cortex and brainstem are affected from the early stages of disease. Acetylcholine, the main neurotransmitter of the parasympathetic system may be deficient in mild cognitive impairment (MCI). Hence, autonomic dysfunction may be a novel biomarker of neurodegeneration. Autonomic function was examined in 97 MCI participants and 36 controls using beside cardiovascular reflex tests and heart rate variability. The association between dysautonomia and neuropsychiatric deficits was examined. This observational study was conducted in a clinical setting. MCI participants showed significant parasympathetic deficits in bedside cardiovascular reflex tests and heart rate variability compared with controls. Those with more significant autonomic dysfunction had more severe neuropsychological deficits. MCI participants were 5.60 (95% confidence interval, 1.6-27.2) times more likely than a control to have autonomic dysfunction. Autonomic dysfunction, particularly parasympathetic dysfunction is prevalent in MCI. This may be due to early neuroanatomical and neurochemical changes in the central autonomic network in Alzheimer's disease. This may accelerate cognitive decline via proinflammatory mechanisms and/or hypotension-induced cerebral hypoperfusion. This provides insight into the pathophysiological mechanisms that contribute to cognitive decline, and may lead to the development of effective therapeutic interventions.