Cardiac vs. Peripheral Vascular Dependency of Cardiovascular Circuit Flow in Exercise

点击翻译按钮获取中文摘要

Being physically active protects quality of life and well-being as we age. Understanding what determines exercise tolerance provides key guidance for enabling a physically active lifestyle. Therefore, my research investigates how the cardiovascular system functions to meet exercising muscle demand for oxygen in humans, because fatigue of muscle and feelings of discomfort in exercise that limit exercise tolerance are highly sensitive to the adequacy of oxygen delivery. Current Research Problem: Exercising muscle has a tremendous capacity to increase its demand for oxygen. This poses a considerable challenge to the cardiovascular system's ability to increase the circuit blood flow (cardiac output to muscle blood flow to venous return to cardiac output) while maintaining arterial blood pressure. While much has been learned about 1) mechanisms that dilate blood vessels in exercising muscle to achieve higher blood flow, 2) neural mechanisms that activate the heart to increase the rate and strength of its contractions, and 3) neural mechanisms that oppose exercising muscle blood vessel dilation; the way these mechanisms act and interact has been interpreted from the point of view that increasing muscle blood flow is a potential threat to arterial blood pressure if it is allowed to exceed the cardiac output. It reflects a construct of the circulation where the response of the heart determines how quickly and how much the cardiovascular circuit flow can increase with exercise. This current explanation ignores accumulating evidence that the heart pumps whatever blood flow it receives from exercising muscle and therefore cannot be exceeded by that flow unless the limits of its pumping capacity are reached. The Problem: I propose that the "cardiac-limited and driven" view of cardiovascular circuit flow may be flawed and requires renewed scrutiny.   Overall objectives of this proposal are: 1) to challenge the current explanation for sympathetic restraint of exercising muscle blood flow, 2) to determine the extent to which cardiovascular circuit flow in exercise is driven/limited by exercising muscle blood flow vs. cardiac output. Anticipated Outcomes: Challenging currently accepted views of cardiovascular control in exercise provides a research environment in which HQP's will develop the blueprint for creating research programs that apply innovative thinking, experimental creativity and the willingness to continually rethink currently accepted paradigms. In other words, develop the capacity for paradigm-shifting research. Second, demonstrating a peripheral origin of driving cardiovascular circuit flow with a heart that simply responds to transfer volume back over to the arterial circulation fundamentally changes the paradigm of understanding cardiovascular control in exercise. This has critical implications for guiding targeted approaches to improving cardiovascular function in exercise when it declines due to aging, inactivity or disease.