The acute and chronic effects of isometric exercise on haemodynamic, autonomic and cardiac function in a pre-hypertensive population

Raised blood pressure (BP) remains the leading modifiable risk factor for cardiovascular disease morbidity and mortality globally. As such, primary prevention strategies are required to improve risk factors to prevent the development of hypertension (HTN).

Isometric exercise training (IET) is becoming an established intervention for reducing resting BP. However, few studies have investigated the effects of IET in a population at increased risk of developing HTN. Therefore, this thesis examined the effects of IET, using a novel home-based wall squat intervention, in a pre-hypertensive male population. Specifically, the thesis aimed to explore the potential mechanism/s responsible for improved BP control using an acute isometric exercise (IE) stimuli and a four-week IET intervention.

Firstly, acute IE was shown to elicit a step-wise increase in BP, heart rate and cardiac output and associated increase in sympathetic activity. In the immediate recovery period, there was a hypotensiveresponse, which was associated with parasympathetic activation, increased baroreceptor reflex control and reduced peripheral vascular resistance. The hypotensive response was also associated with improved indices of cardiac function,
including a reduced estimated filling pressure. Four weeks of IET was shown to significantly reduce resting and ambulatory BP. Improved autonomic cardiovascular control, with increased parasympathetic over sympathetic activity, greater baroreceptor reflex sensitivity and reduced peripheral vascular resistance potentially mediated the decreased BP. A reduction in plasma interleukin-6 and asymmetric dimethylarginine suggests an anti-inflammatory response and improved vascular function, respectively,
following IET.

Finally, improved myocardial diastolic function suggests positive cardiac adaptations in response to BP reductions. Collectively, the findings of this thesis highlight potential mechanistic pathways for improved BP control in a prehypertensive population and demonstrates wider cardiovascular benefits of IET beyond BP reductions, which are important observations for risk reduction in this population.