title: Left Ventricular Diastolic Function in Adolescents with Overweight and Obesity: The Moderating Influence of Physical Activity, Cardiorespiratory Fitness, and Metabolic Health
Creators: name: Burden, Samuel
Publisher: name: Oxford Brookes University
Year: 2023

description: Lifelong preservation of left ventricular diastolic function (LVDF) is an important goal for reducing the burden of diastolic heart failure and related adverse health outcomes. LVDF is strongly linked with obesity. The global obesity pandemic has already increased the burden of diastolic heart failure in adults, but the prevalence of overweight and obesity is rising fastest in children, potentially setting them on a course to early heart disease. Public health measures designed to tackle the problem of adolescent obesity have focused on lifestyle interventions, such as exercise promotion and dietary improvements, with uncertain impact on LVDF. This thesis aimed to investigate how obesity, physical activity (PA) and innate cardiorespiratory fitness (CRF) influence LVDF in adolescents. From these data, it was also aimed to identify a PA target that might be sufficient to prevent adolescent impaired LVDF. To demonstrate the need for a focus on LVDF in this age group, Study 1 was a meta-analysis of the relationship of obesity with LVDF in adolescents. The results indicated that those with obesity were likely to have impaired LVDF and that such impairments were best demonstrated by septal tissue-Doppler imaging (TDI) methods of echocardiography (z-score difference=0.91; 95% CI=0.46, 1.37). This study also identified preliminary evidence for links of insulin resistance (IR) and CRF with LVDF, but there were no studies to address the relationship between PA and LVDF. Therefore, Study 2 leveraged data from 99 adolescents with either overweight/obesity or normal-weight and high PA (≥75th percentile) or low PA (≤25th percentile) to address this question. Vigorous physical activity (VPA) was the only PA intensity associated with LVDF, with the strongest links to septal TDI. Mediation analyses revealed that higher VPA had a direct benefit on LVDF as well as an indirect effect through decreased adiposity. This study also confirmed the link of IR and CRF with LVDF, independently from adiposity. As CRF was linked with LVDF and is a good measure of general cardiovascular health, Study 3 aimed to understand the intensity and duration of PA that are best associated with CRF in a large population of adolescents (n=339). Only VPA was associated with CRF, with relationships plateauing at around 20 minutes. This short duration of daily VPA contrasts with the World Health Organization’s moderate-to-vigorous PA guidelines, which can be satisfied by only undertaking moderate PA, with no apparent independent benefit on LVDF or CRF, suggesting that specific VPA guidelines for adolescent cardiovascular health are needed. This thesis provides novel insights into the effects of obesity and PA on LVDF in adolescents. A targeted approach, not simply focused on weight loss, has been identified, in theory, to prevent or reverse this adverse early phenotype and provides a roadmap for the duration of routine VPA that might be tested in a randomised, controlled clinical trial as a means to normalise LVDF.