Quantifying Human Cerebral Hemodynamics During Dynamic Exercise

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The mechanisms underpinning the regulation of brain blood flow during exercise in humans are poorly understood. Whether one is walking, cycling or squatting, brain blood flow is tightly controlled to ensure our brain cells have enough oxygen and energy. Understanding how brain blood vessels control blood flow during dynamic movement will increase our understanding of how brain blood vessels adapt in the long-term, such as to an exercise training plan. During exercise, brain blood flow will steadily rise from onset to moderate intensity exercise and will slowly return to near baseline as exercise intensity level continues to increase. Several factors affect brain blood flow, and they too change with exercise intensity, yet it is unclear how these factors work together to affect brain blood flow during exercise. The most common tool for studying brain blood vessels provides only an estimate of brain blood flow, as it only measures blood velocity. Other important variables that describe the physics of blood flow, or "hemodynamics", have yet to be characterized as the necessary imaging and analytical tools are not described in the context of exercise. Together, this leaves our understanding of how our brain blood vessels control blood flow during exercise incomplete with important knowledge gaps. Thus, the overall research vision is to better our understanding of brain blood flow control in humans. The long-term objectives are two-fold: 1) to develop imaging and analytical methods for measuring and describing important hemodynamic variables that ultimately help us understand mechanisms underlying blood flow control during exercise, and 2) to increase the validity of current imaging tools used to study brain blood flow in humans. Using a multi-modality imaging approach (ultrasound and magnetic resonance imaging; MRI), we will seek to complete the following short-term objectives: 1) develop means to quantify hemodynamic variables in humans, 2) assess how our brain's blood vessels respond to different MRI-compatible exercises (i.e., small versus larger muscle groups) or patterns of contraction (i.e., static or rhythmic). There is a paucity of data on female physiology in the field of exercise physiology, with even less information available on female brain blood vessel physiology. Thus, in short-term objective 3) we will assess whether sex-differences exist in brain hemodynamics at rest and whether responses during exercise are dependent upon sex. The developed methods will provide a novel experimental and analytical framework for future neuroimaging studies assessing how exercise affects brain hemodynamics. By using multiple imaging tools, findings will help validate existing tools that are limited in the hemodynamic information they can provide. This research will provide novel information on how brain blood vessels respond in a naturalistic model such as dynamic exercise, which may provide insight on long-term adaptations to our brain's vessels.