Effects of early-onset type 2 diabetes on cardiac and respiratory function at rest and during exercise and responses to high intensity interval training

Abstract

This thesis examined people with early-onset type 2 diabetes (EOT2D) and a matched group without diabetes. It is well known that EOT2D presents a more aggressive phenotype when compared to later-onset type 2 diabetes (T2D) and that micro- and macrovascular complications are common, but there is very limited evidence about whether these changes affect cardiac function and fitness early in the course of the disease, and if so, whether these are amenable to exercise training. The few studies that have been conducted have demonstrated differing conclusions as to whether moderate-intensity or high-intensity interval exercise training (HIIT) are effective in improving fitness or metabolic control.

Hence, the aims of this thesis were to: 1. compare cardiac and respiratory function at rest in participants with EOT2D and a control group without diabetes, matched for the important confounders of age, sex and body mass index (BMI); 2. compare cardiac, metabolic and respiratory function during submaximal and maximal exercise and peak exercise capacity in participants with EOT2D and matched controls without diabetes and 3. investigate the impact of HIIT in people with EOT2D.

The joint primary outcome measures included VO2peak, glycaemic control (HbA1c) and cardiac (diastolic) function. We found that despite our group with EOT2D being in good metabolic control and of recent diagnosis, they evidenced subclinical changes at rest in cardiac function and in the diffusing capacity of the lung compared to controls without diabetes.

We found people with EOT2D had lower oxygen extraction during submaximal exercise, and lower cardiorespiratory fitness measured by VO2peak. We also conducted an RCT that investigated the cardiorespiratory and cardiac effects of exercise and HIIT among a group with EOT2D who had been recently diagnosed with diabetes. We found HIIT safely improved cardiovascular fitness (VO2peak).

HIIT may be an important therapeutic tool in this population.