Dynamic cardio-respiratory-cerebrovascular interactions

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Our ability to adapt to the challenges of daily life depends on blood flow supply to the working skeletal muscles and to the brain. We plan to explore two topics that highlight the important role of oxygen delivery to working muscles and develop methods that explicitly measure brain blood flow. Our first experiments will explore the impact of ischemic preconditioning to enhance muscle function. Ischemic preconditioning is accomplished by restricting blood flow for short periods of time before a larger challenge to blood flow. Recently we showed that stopping blood flow to a muscle then allowing a brief recovery prior to exercise delayed adaptation of muscle metabolism. We anticipate that ischemic preconditioning will prepare the muscle for the challenge of longer arrest of blood flow allowing the muscle to cope well with exercise. We will add magnetic resonance spectroscopy to our existing techniques to monitor intramuscular metabolic events. Manipulation of oxygen supply to the muscle by changing inspired gas concentrations and arterial blood pressure will allow us to test hypotheses showing the importance of oxygen in regulation of muscle metabolism at the onset of physical activity. Our second series of experiments will examine blood flow to the brain under several conditions. We will compare estimates from brain blood flow velocity through the middle cerebral artery to absolute blood flow in the internal carotid artery in the neck. In preliminary research, we determined that the estimates from the middle cerebral artery velocity are incorrect in many circumstances. We will investigate the effects of different drugs that affect blood pressure, changes in blood levels of carbon dioxide and changes in posture to show that velocity does not accurately reflect brain blood flow. Our final objective is to consider how changes in brain blood flow affect the regulation of breathing and impact the ability to tolerate an upright posture. Through this research, students will gain critical knowledge about the integrative cardiovascular and brain blood flow mechanisms that contribute to human physiological responses to physical activity and upright posture in our everyday lives.