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Doctor of Philosophy / Department of Kinesiology / Craig A. Harms / The overall aim of this dissertation is to further understand sex differences in the cardiopulmonary responses during exercise in younger and older individuals. Emphasis is directed towards the influence of sex in modulating respiratory muscle blood flow and the inspiratory muscle metaboreflex. The first investigation of this dissertation (Chapter 2) demonstrated that sex differences do not alter respiratory muscle blood flow at rest or during exercise. The second investigation (Chapter 3) demonstrated that sex differences exist in the cardiovascular consequences of the inspiratory muscle metaboreflex. Specifically, premenopausal women, compared to age-matched men, exhibited attenuated increases in mean arterial pressure and limb vascular resistance as well as decreases in limb blood flow during inspiratory muscle metaboreflex activation. In Chapter 4, we demonstrated that postmenopausal, compared to pre-menopausal, women exhibit greater increases in mean arterial pressure and limb vascular resistance and decreases in limb blood flow during activation of the inspiratory muscle metaboreflex. Furthermore, no differences in the cardiovascular consequences were present between older men and women or younger and older men with activation of the inspiratory muscle metaboreflex. These data suggest that the tonically active inspiratory muscle metaboreflex present during maximal exercise will result in less blood flow redistribution away from the locomotor muscles in pre-menopausal women compared to postmenopausal women, as well as younger and older men. In conclusion, sex differences in young adults incur a major impact in the cardiovascular consequences during inspiratory muscle metaboreflex activation, while not modifying respiratory muscle blood flow.

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Background: Exercise is widely recognized as the cornerstone of management of type II diabetes (T2D). However, it is also known that people with T2D have poor adherence to exercise regimens, which is largely thought to be because of poor exercise tolerance. Recent studies have suggested that this exercise intolerance may be caused by a reduction in exercising muscle blood flow. One physiological mechanism which could potentially contribute is the muscle metaboreflex (MMR). This mechanism is thought to be a pressure-based flow-improving mechanism, but as a result of reduced efficacy of vasodilators and sympatholytic agents, might in fact be restraining the flow-improvement in persons with T2D. Hypothesis: Persons with T2D would not improve exercising muscle blood flow upon MMR activation. This absence of flow-improvement will be due to an augmented vasoconstriction in the exercising muscle. Methods: T2D (n=7) and CTL (n=6) participants performed rhythmic forearm handgrip exercise at an intensity equivalent to 20% MVC for 9 minutes with and without the application of ischemic plantar flexion (IPF). Forearm blood flow (FBF), mean arterial pressure (MAP), cardiac output (CO), heart rate (HR), total peripheral resistance (TPR) and forearm vascular conductance (FVK) were quantified for the last thirty seconds of each of four time points during the protocol. Plasma norepinephrine was measured via deep venous and arterialized venous blood sampling. Results: Steady state exercising FBF was increased in CTL but not in T2D during MMR activation (mean ± SE mL/min: CTLControl 161.16 ± 5.95, CTLMMR 212.72 ± 9.49, T2DControl 156.71 ± 13.08, T2DMMR 144.22 ± 10.55). This occurred despite similar increases in MAP, CO, HR, and TPR (across groups and treatment conditions, NS). FVK increased in CTL during the MMR protocol compared to the Control protocol, but decreased in the T2D group using the same comparison (mean ± SE mL/min/100 mm Hg: CTLControl 144.74 ± 5.63, CTLMMR 176.76 ± 11.99, T2DControl 143.29 ± 13.44, T2DMMR 103.53 ± 8.44). Conclusions: In the exercise model utilized, persons with T2D do not demonstrate the MMR-induced flow improvement seen in CTL. This impaired muscle blood flow in T2D is the result of MMR induced exercising limb vasoconstriction. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2012-01-31 09:30:42.604

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