Influence of adiposity on autonomic nervous system activity

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Michael S. Jarrett (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Paul Davis

Abstract: The influence of autonomic nervous system (ANS) activity on the development and progression of cardiovascular disease (CVD) is widely acknowledged, as most common CVD risk factors (e.g., hypertension, impaired glucose management, obesity, low cardiovascular fitness) affect and/or are affected by ANS activity. Increased adiposity can be viewed as an amplifier of CVD development, as it has been shown to elevate the chances of developing hypertension and diabetes mellitus. Thus, adiposity may have direct and indirect effects on CVD development. In turn, it is important to determine if similar multidirectional relations can be observed between adiposity and altered ANS activity. Therefore, this dissertation addressed two main goals. The first was to evaluate the direct and indirect influence of adiposity on ANS activity through secondary data analyses employing structural equation modeling in a large, population-based cohort. The parasympathetic and sympathetic branches of the ANS were noninvasively assessed via heart rate variability [reflected by root mean square of successive differences between normal beats (RMSSD)] and the pre-ejection period of systole [(PEP); measured via impedance cardiography], respectively. The direct effects of adiposity on ANS activity were assessed by examining the magnitude of influence of waist circumference (WC) on RMSSD and PEP. Indirect effects were assessed via the impact of WC on the latent variables of glycemic impairment (GI; fasting blood glucose and insulin concentrations, hemoglobin glycosylation percentage) and cardiac stress (CS; heart rate, diastolic blood pressure) parameters. Adiposity had both significant direct (ß = 0.208, p = 0.018) and indirect (ß = -.217, p=.041) effects on PEP through GI. Adiposity displayed no significant direct effect on RMSSD. CS displayed a significant pathway (ß = -0.524, p = 0.035) on RMSSD, but the indirect effect of WC on RMSSD through CS was not significant. These results suggest that adiposity’s relation to ANS activity is multifaceted, as increased central adiposity had opposing direct and indirect effects on markers of sympathetic activity in this population of older adults. The second goal of this dissertation was to determine if cardiovascular fitness, as determined through graded exercise testing, influenced the relation of adiposity and ANS activity beyond the role it plays in determining adiposity, per se. To accomplish this goal, ANS activity was examined in a small cohort of young males with a range of fitness and adiposity levels before and after maximal aerobic exercise. A mixed model analysis of covariance was employed to test the additional impact of cardiovascular fitness on the relations between adiposity and ANS activity at rest and following maximal exercise. Group stratification by waist circumference or body fat percentage (BF%) revealed no across-group differences in resting or post-maximal exercise HRV or PEP measurements. Accounting for weight-relative peak oxygen uptake (VO2peak) resulted in significant between-group differences in the natural logarithm SDNN (ln-SDNN), RMSSD (ln-RMSSD)], and high frequency spectral power (ln-HF) at 3- and 5-minutes post-exercise when groups were stratified by BF%. However, these differences were no longer statistically significant following adjustments for lean body weight-relative VO2peak, suggesting no effect of BF% on ANS activity. These results provide evidence that there may not be differences in resting ANS activity and post-maximal exercise ANS responsiveness across adiposity groups in apparently healthy males. Taken together, these two studies highlight the nuanced involvement of adiposity on physiological parameters that influence ANS activity. However, they do not support the notion that adiposity has a strong, independent influence on ANS activity.

Additional Information

Language: English
Date: 2022
Adiposity, ANS, Heart rate variability, HRV, Nervous system, PEP
Autonomic nervous system
Heart beat

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