Getting to the Heart of the Problem: Exercise and Cardiac Function in Diabetic Youth

Abstract

Adolescents with type 1 diabetes have lower exercise capacity than non-diabetic adolescents. Recent studies have shown that signs of cardiac and vascular dysfunction already present in type 1 diabetic adolescents at rest might contribute to the reduced exercise capacity. Exercise training has a positive effect on the cardiovascular function of healthy individual by improving left ventricular function and blood flow to tissues. However, the impact of exercise training in the left ventricular and vascular function of type 1 adolescents is unknown. Therefore, the purpose of this study was to use the gold standard magnetic resonance imaging technology to determine the role of left ventricular function and femoral artery blood flow on the reduced exercise capacity of type 1 diabetic patients. Moreover, this study aimed to determine the effect of 20 weeks of exercise training in the left ventricle and vessels of adolescents. Cardiac and femoral artery blood flow scans were performed at rest, during submaximal leg exercise in 53 adolescents with type 1 diabetes and 22 healthy controls aged between 14 and 20 years. They were matched for body composition and reported physical activity level. Maximal exercise capacity by cycling to exertion, blood tests and body composition performed using dual energy X-ray absorptiometry scan were also determined in all participants. At baseline, maximal exercise capacity was reduced in adolescents with type 1 diabetes compared to non-diabetic controls. Resting and sub-maximal exercise femoral artery blood flows were similar between type 1 diabetic and non-diabetic adolescents, while stroke volume and left ventricular filling capacity (end-diastolic volume) were significantly reduced. Twenty weeks of exercise training increased maximal exercise capacity by 10 %. Although no changes were seen with exercise training in femoral artery blood flow, stroke volume increased. Both resting and sub-maximal stroke volumes increased due to improvements in myocardial contractility (reduced end-systolic volume and increased ejection fraction). Exercise training was ineffective in improving left ventricular filling capacity (end-diastolic volume) in diabetic adolescents. Thus, while diabetes is already limiting the exercise capacity and cardiac function in adolescents, exercise training minimises, to some extent, these limitations.