Correlating Autonomic Nervous System Aging and Cognitive Impairment
Heart rate variability is known to be a good way to assess the function of the autonomic nervous system. (That said, most of the commercially available tools for those who want to measure heart rate variability at home are quite unreliable; it is challenging for a self-experimenter to obtain results that are as useful as those provided by medical equipment used by medical staff). The autonomic nervous system, like all aspects of our biology, is negatively impacted by the progression of aging. The same mechanisms of molecular damage that drive autonomic nervous system aging will be involved in cognitive decline and neurodegenerative conditions, so it should be no great surprise to see that these forms of age-related degeneration correlate with one another.
Changes in cognitive performances and cardiovascular disorders represent a normal phenomenon of the aging process. Cardiovascular risk factors, such as smoking, obesity, diabetes mellitus, increased cholesterol, and systemic blood pressure (BP) levels, and an inadequate lifestyle may compromise also cerebral blood flow, which in turn can negatively affect cognitive performance. Moreover, the same age-related anatomical and functional cardiac changes, including also the autonomic nervous system (ANS), determine cardiac output alteration, causing cerebral blood flow modulation. This variation could interfere with microcirculation and cause cerebral ischemia, particularly in those brain sites that control the different cognitive domains.
Evidence supports the relevance of ANS study by heart rate variability (HRV) assessment as a tool for the noninvasive analysis of cardiovascular autonomic function. HRV, defined as a marker identifying the balance between sympathetic and parasympathetic tone, predicts total mortality, sudden death, cardiovascular disease risk, as well as other morbidities. It represents the measure of physiological variation in the interval between consecutive heart sinus beat or in the fluctuations between instantaneous heart rates and provides the importance that the ANS has regarding cardiovascular health and prognosis.
We assessed the relationship between long-term heart rate variability (HRV), as a measure of autonomic nervous system (ANS) functioning, and cognitive performance in elderly patients representative of outpatients in a real-life setting. 117 patients underwent anthropometric evaluation, cardiac assessment by 12-lead electrocardiogram, 24-hour electrocardiogram recording, and blood pressure (BP) measurement, as well as global cognitive evaluation. Our results show that an increased sympathetic activity, but not decreased vagal activity, is associated with better cognitive performances. These results support the sympathetic autonomic function, in that the relationship between better cognitive performances and a moderate prevalence of autonomic function appears dependent on long-term changes in heart rate, mediated by sympathetic activation.