Endothelium-dependent vasodilation is an important marker of vascular function. Brachial artery flow-mediated dilation (FMD) is a noninvasive assessment of peripheral artery endothelial function that is associated with coronary artery endothelial function and is an index of cardiovascular health. This thesis sought to investigate factors that may influence the brachial artery FMD response in humans, particularly the sex hormone estrogen and low-volume sprint interval training (SIT). We first demonstrated the intra-individual consistency of the FMD response pattern in healthy young adults and introduced visual data screening as a tool for improving data accuracy. Having established best practices for FMD data analysis, we investigated the brachial artery FMD response in adults with different estrogen profiles: men, premenopausal women with a natural menstrual cycle (NAT), and premenopausal women using combined oral contraceptive pills (OCP). Our findings suggest that estrogen does not augment FMD during high-estrogen phases of a NAT or OCP cycle compared to low-estrogen phases or to men. We also investigated the acute and chronic brachial artery FMD response to a 3x20-s low-volume SIT model. Following a single SIT session, FMD was unchanged in men or women. These findings demonstrate that estrogen does not influence endothelium-dependent dilation at rest or following intense intermittent exercise, but also suggest that low-volume SIT may be an insufficient stimulus for eliciting changes in endothelial function. This stimulus magnitude postulation was further supported by a 12-wk exercise training study, whereby vascular changes were evident following moderate-intensity continuous training but not SIT. Taken together, this work suggests that controlling for menstrual cycle phase and/or OCP use in premenopausal women may not be necessary, making it more feasible to include women as research participants, and highlights the need for future characterization of the minimum low-volume interval stimulus that evokes improvements in endothelial function in healthy young adults. / Thesis / Doctor of Philosophy (PhD) / The endothelium is the inner lining of an artery that separates it from the flowing blood. A healthy endothelium responds to increases in blood flow by producing substances that enable an artery to widen. The projects in this thesis examined whether the responsiveness, and overall function, of the endothelium in healthy young adults is enhanced by the sex hormone estrogen or by “all-out” cycling sprints, an exercise protocol that has gained appeal for its time-efficiency. We demonstrated that estrogen does not enhance endothelial function in women, compared to men, at any phase of a menstrual or birth control pill cycle. A single session or 12-weeks of the intense but brief interval exercise also does not enhance endothelial function. This work suggests it may be easier to include women in future research assessing this measure and that this particular interval exercise protocol may not enhance endothelial function in healthy adults.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/23031 |
| Date | 14 June 2018 |
| Creators | Shenouda, Ninette |
| Contributors | MacDonald, Maureen, Kinesiology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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