The role of exercise in modulating vascular function in childhood and adolescent obesity

Purpose: Overweight children and adolescents have increased aortic stiffness conferring an increased risk of future cardiovascular events. This thesis evaluated exercise training as a means to modify aortic stiffness in obese youth. An institutional treadmill protocol (British Columbia Children’s Hospital, BCCH) for assessing metabolic gas exchange parameters (minute ventilation, tidal volume, breathing frequency, oxygen consumption, carbon dioxide production) was validated using a healthy cohort (study 1, Chapter 3). This protocol was used to test obese children and adolescents before and after an exercise intervention. Echocardiography was used to study changes to vascular properties pre- and post- training (study 2, Chapter 4). Pulmonary function tests were used to assess lung function pre- and post- training (study 3, Chapter 5). Study 1: A scaled institutional (BCCH) protocol was validated using 70 healthy boys and girls. This validated protocol was used in the subsequent training study to individually adjust intensity to V̇O2 capacity, in keeping with exercise intervention recommendations. Study 2: Ten to 18 year old children and adolescents (BMI ≥ 97th percentile for age) were recruited to undergo a 12-week exercise program in a randomized cross-over study. Standard echocardiographic dimensions and measures of systolic and diastolic cardiac function were recorded before and after both a 12-week exercise intervention and 12-week control phase. Biophysical properties of the aorta including pulsewave velocity were calculated using an echocardiographic-Doppler method. Treadmill exercise tests were also performed before and after each study phase. Study 3: The same participants that underwent the exercise training in study 2 were measured for resting pulmonary function and exercise spirometry as per the protocol described in the second study. Results: The institutional treadmill protocol produced similar peak exercises responses compared to the traditional protocol and was validated as an alternate for pediatric exercise testing. Ten participants completed the exercise intervention (age 14.3+3.2 yrs). Training showed a significant reduction in PWV (p=0.003), a modest reduction in body mass (p=0.0135), and exercise tolerance improved (METs, p=0.003; total exercise time, p=0.015). A reduction of aortic pulsewave velocity can be achieved with exercise training in obese children and adolescents and cardiovascular fitness can be modestly improved.