THE IMPACT OF CARDIORESPIRATORY FITNESS ON PERIPHERAL VASCULAR FUNCTION IN OLDER ADULTS

Abstract

Optimal regulation of peripheral vascular function ensures adequate blood flow to tissues and the maintenance of vascular homeostasis. This is achieved via endothelium-derived vasodilator and vasoconstrictor chemicals, as well as sympathetic neural inputs. A higher aerobic fitness confers better cardiovascular health. Vascular function and aerobic fitness generally worsen with age. The purpose of this thesis was to investigate the impact of aerobic fitness on peripheral vascular function in older adults. Relative peak oxygen consumption (V̇O2peak, indirect calorimetry) using a maximal cycle ergometer protocol was assessed in all four studies. Low-flow-mediated constriction (L-FMC) and flow-mediated dilation (FMD) represent endothelial-dependent vasoconstrictor and vasodilator function, respectively. For Studies 1-3, L-FMC and FMD were measured using high-resolution ultrasound and quantified as the percent change in baseline diameter during distal cuff occlusion and the subsequent reactive hyperemia, respectively. I demonstrated that higher aerobic fitness was associated with larger L-FMC (more negative) and FMD (more positive) responses in the brachial artery of older adults (Study 1). However, the brachial artery is not typically the site of peripheral vascular disease development. I then documented that brachial artery endothelial function was not correlated to that in the popliteal artery. However, aerobic fitness was still associated with better endothelial function in the popliteal artery (Study 2). Building off these cross-sectional studies, a 6-week training study was conducted in which I observed that high-intensity-interval-training (HIIT) and moderate-intensity-continuous-training (MICT) similarly increased brachial FMD, but only HIIT improved brachial L-FMC. Both HIIT and MICT similarly enhanced popliteal FMD and L-FMC responses. Whole-body resistance training did not impact endothelial function in either artery (Study 3). Vascular function is also influenced by sympathetic activity directed towards resistance vessels within skeletal muscle beds. Peroneal muscle sympathetic nerve activity (MSNA; via microneurography) and arterial pressure (finger photoplethysmography) were recorded during ≥10-min of rest in healthy older adults. Lower aerobic fitness was associated with lower MSNA burst incidence and higher neurohemodynamic transduction, along with greater blood pressure variability in older adults (Study 4). The studies conducted provide support for the favorable impact of maintaining or increasing aerobic fitness in healthy older adults on peripheral vascular function.