Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. Robert J. Petrella


Metabolic syndrome (MetS) is a clustering of risk factors for cardiovascular disease (CVD) and type 2 diabetes (T2D) – two major causes of morbidity and mortality worldwide. Heart rate variability (HRV) is a non-invasive measure of cardiac autonomic regulation that predicts mortality and morbidity. Additionally, HRV is reduced in CVD, T2D and MetS. As such, HRV has potential to be a novel cardiometabolic risk factor to be included in clinical risk assessment. Therefore, the purpose of this thesis was to examine the relationships between MetS and HRV. A systematic review of cross-sectional studies examining relationships between HRV and MetS was completed to consolidate existing evidence and to guide future studies. This was followed by a cross-sectional investigation of time and frequency domain and nonlinear HRV in a population with MetS risk factors to determine which MetS risk factors were associated with HRV parameters. A pilot study was then conducted to study the feasibility of conducting a mobile health (mHealth) and exercise intervention in a rural population, which was followed by a 24-week randomized clinical trial to examine the effects of the interactive mHealth exercise intervention compared to standard of care exercise in participants with MetS risk factors. Overall, HRV was reduced in women with MetS compared to those without, though there were no differences in men. Waist circumference and lipid profiles were most commonly related to HRV parameters when studied cross-sectionally. The changes in waist circumference and fasting plasma glucose were associated with the change in HRV parameters when studied longitudinally. Following the intervention period, waist circumference and blood pressure were improved with no other changes in MetS risk factors. HRV parameters indicative of vagal activity were reduced over the intervention period, but there were no changes in other HRV parameters. There were no differences in changes between the intervention and control groups. In conclusion, MetS and HRV are associated in women but not men. However, there were no clear associations between MetS and HRV to suggest that HRV would be a valuable clinical risk factor.