Comparative Analysis of Autonomic Function Across Aging Populations

Thesis Abstract

This study addresses the rising prevalence of autonomic dysfunction across aging populations and its differential manifestation across diverse demographic groups, with the aim of elucidating how aging modulates autonomic regulation and its downstream health implications. The objective is to (1) compare autonomic function across younger, middle-aged, and older adult cohorts using standardized autonomic and cardiovascular assessments, (2) examine the influence of sex, ethnicity, and comorbid conditions (e.g., hypertension, diabetes) on autonomic indices, and (3) test theoretical propositions from the Neurovisceral Integration Model and the Polyvagal Theory to explain patterns of autonomic flexibility with aging. A cross-sectional, multi-site design will be employed, enrolling 360 participants stratified into three age bands 20–35 (n=120), 50–64 (n=120), and 75–89 (n=120). Within each age band, equal representation of sexes and diverse ethnic backgrounds will be pursued. Data collection will comprise (a) autonomic function tests including heart rate variability (HRV) in time and frequency domains, baroreflex sensitivity, and pupillometry; (b) cardiovascular measures such as resting blood pressure, orthostatic hypotension assessment, and carotid-femoral pulse wave velocity; (c) functional assessments of daily living activities and perceived stress using validated scales; and (d) clinical data including body mass index, glycemic status, lipid profile, and medication use extracted from medical records. Physiological data will be captured under standardized laboratory conditions to minimize environmental confounds. Validity and reliability will be ensured through calibration of equipment, standardized protocols, and inter-rater reliability checks for observational components. Data analysis will proceed in stages descriptive statistics to characterize cohorts, multivariate analysis of covariance (MANCOVA) to compare autonomic indices across age groups while controlling for covariates, and hierarchical linear modeling to assess interaction effects of age with sex and ethnicity. Regression analyses will identify predictors of autonomic flexibility, while Bonferroni-corrected post hoc tests will delineate group differences. Mediation analyses will explore whether stress and cardiovascular risk factors mediate the relationship between age and autonomic function. A theoretical framework integrating the Neurovisceral Integration Model and the Polyvagal Theory will guide interpretation of autonomic patterns, particularly the balance between sympathetic and parasympathetic activity and the influence of vagal tone on cognitive-emotional regulation. Anticipated findings include a progressive decline in HRV with advancing age, attenuated baroreflex sensitivity in older groups, and differential autonomic profiles by sex and ethnicity, with potential compensatory vagal adaptations in certain subgroups. The study will contribute to knowledge by delineating nuanced age-related trajectories of autonomic function in a diverse population, informing identification of high-risk subgroups for autonomic disorders, and providing empirical support for theoretical models of autonomic regulation in aging. Clinically, findings may guide tailored interventions—such as exercise prescriptions, stress reduction techniques, and pharmacological considerations—that optimize autonomic balance and reduce cardiovascular risk in older adults. Policy implications include informing screening recommendations for autonomic dysfunction in aging populations and emphasizing the integration of autonomic assessment into geriatric care pathways. The conclusion will synthesize how aging interacts with demographic and Health-related factors to shape autonomic control, and recommendations will emphasize longitudinal studies to track causal pathways, interventional trials targeting autonomic rehabilitation, and the incorporation of autonomic metrics into routine geriatric assessments.