Doctor of Philosophy
Dr. Donald H. Paterson
Vascular impairments at both the macro- and the micro-circulatory level are known to be associated with cardiovascular disease (CVD) and may be one of the earlier signs of disease. As such, it is important to have a means of non-invasively assessing vascular reactivity, however accurate assessment remains challenging. Tests of flow-mediated dilation (FMD) have been widely used to non-invasively determine endothelium-dependent vasodilation in humans; however, the use of this technique poses some challenges. Thus, the purpose of this thesis was to explore new strategies to non-invasively determine the magnitude and dynamic adjustment of vascular responses in humans. Using near-infrared spectroscopy (NIRS)-derived measures of tissue oxygen saturation (StO2) following vascular occlusion it was demonstrated that: 1) the reperfusion rate (Slope 2 StO2) was significantly correlated to the widely used measure of vascular function, FMD (Chapter II); and 2) that the measure of Slope 2 StO2 had a strong reliability both within and between testing days (Chapter III). Allometric scaling has been proposed to address one of the challenges associated with the FMD measurement, however this allometric scaling, and the development of a new scaling calculation, to account for variability in baseline diameter between subjects did not improve the measure (Chapter IV). Additionally, the application of allometric scaling may not be necessary for homogenous groups. In Chapter V a “dose-response” like curve was constructed for the Slope 2 StO2 measurement across a range of different occlusion durations, to determine differences in vascular responsiveness, and demonstrated differences in trained versus untrained individuals. Collectively, these data suggest that the NIRS-derived measure of Slope 2 StO2 obtained directly at the microvascular level is reflective of the vascular responsiveness as measured by FMD. The strong reliability, both intra- and interday, of the NIRS-derived Slope 2 StO2 measure make this technique suitable for the assessment of vascular responsiveness, and it is particularly well-suited for determining differences between groups or before and after an intervention. Slope 2 StO2 is sensitive to different occlusion durations and changes in this sensitivity of the measure to a variety of ischemic challenges can be used to detect differences between groups. Therefore, NIRS-derived measures of StO2 show promise for assessing vascular responsiveness between groups, or for monitoring changes in vascular responses to various interventions.
McLay, Kaitlin M., "Non-invasive determination of vascular reactivity: a new approach to an important measure" (2016). Electronic Thesis and Dissertation Repository. 3968.