The Integrative Effect of Changes in Intrathoracic Pressure on Cardiac and Cerebrovascular Function.

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Changes in pressures within the chest cavity (intrathoracic pressure) made during breathing can alter how the heart fills and empties by placing different challenges to the right and left sides of the heart. As the lungs, heart and brain circulation are all in series, changes in intrathoracic pressure will not only influence blood flow in the heart and lungs but may also alter brain blood flow through changes in arterial inflow, pressure within the skull and venous outflow. To our knowledge, this important interaction between three intrinsically linked systems has never been studied and changes in intrathoracic pressure could have significant implications beyond the lungs and heart, especially during challenges to the body's natural physiological balance (homeostasis). The aim of this program of research is to simultaneously measure intrathoracic pressure, heart filling and emptying, brain blood flow as well as blood flow into and out of the brain and examine how changes in intrathoracic pressure simultaneously alter these systems. Additionally, we will alter homeostasis with a variety of challenges including blood volume loading and changes in oxygen and carbon dioxide levels within the blood. As such, there is considerable novelty alone in investigating how all three of these systems interact during any physiological stimulus. To date there have been few studies that have investigated how changes in intrathoracic pressure affect cardiac function especially when the body is fluid loaded or there are changes to blood gases i.e. low oxygen and high carbon dioxide levels. Additionally, no study has systematically investigated how intrathoracic pressure effects brain blood flow. Therefore, the combination of the three systems approach will add considerably to our present knowledge in this important area of mechanical factors that affect blood flow regulation in humans.