Combining optical neuromonitoring with a respiratory gas system to assess neurovascular function

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The sudden loss of consciousness when blood flow to the brain is reduced is a dramatic demonstration of the brain’s reliance on flow for a continuous supply of oxygen and energy substrates. This reliance is not surprising considering the brain consumes 20% of the total energy used by the body, yet only accounts for 2% of body mass. Eighty percent of its energy use goes to supporting neuronal (brain) activity and, consequently, control of blood flow in different regions of the brain must meet local energy demands. Continual adjustments to brain blood vessels are also performed to maintain adequate blood flow when there are changes in arterial blood pressure and levels of oxygen and carbon dioxide in the blood. Given its importance, understanding flow regulation is critical to our overall understanding of the mechanisms controlling brain function. The equipment asked for in this proposal includes light-based devices for monitoring brain blood flow and oxygenation, a computer-controlled breathing system for precise control of arterial oxygen and carbon dioxide levels, and a noninvasive device for continuous monitoring of arterial blood pressure. Combining these non-invasive and safe technologies will provide a unique platform for studying blood flow regulation in the brain, specifically at the level of smallest blood vessels, which is the most critical because it is at this level that oxygen is delivered to tissue. Our aim is to investigate how the brain's blood vessels respond to changes in arterial pressure and blood gas levels, which are related to vascular compliance (i.e., the ability of vessels to stretch) and resistance (i.e. the effort required to push blood through vessels). These are key indicators of the proper functioning of the brain's circulatory system and our research team is ultimately interested in understanding how these indicators are affected by factors such as age and life-style practices including regular exercise. This application will also provide a highly competitive training environment for the next generation of Canadian researchers as it combines three established research groups with expertise in optical methods for noninvasive monitoring of brain function, cerebral and systemic physiology, and mathematical modelling of blood flow control and function. Our vision is that this combined expertise coupled with the proposed equipment will give trainees ranging from undergraduate students to postdoctorate fellows with the tools to tackle fundamental issues relating to how blood flow is regulated in the human brain and what factors are possibly harmful or beneficial to this regulation. Considering the growing prevalence of diseases, such as dementia, as the population ages, a better understanding of flow regulation in the brain should be beneficially to all Canadians.