Quantifying Human Cerebral Hemodynamics During Dynamic Exercise

人们对运动过程中大脑血流调节的机制知之甚少。无论是走路、骑自行车还是蹲着，大脑的血液流动都受到严格控制，以确保我们的脑细胞有足够的氧气和能量。了解脑血管如何在动态运动中控制血流将增加我们对脑血管如何长期适应的理解，例如运动训练计划。在运动期间，脑血流量将从开始到中等强度运动稳步上升，并将随着运动强度水平的继续增加而缓慢返回到接近基线。有几个因素会影响脑血流量，它们也会随着运动强度的变化而变化，但目前还不清楚这些因素如何共同影响运动期间的脑血流量。研究脑血管的最常用工具只提供脑血流的估计，因为它只测量血液速度。描述血流物理学或“血液动力学”的其他重要变量尚未被表征为运动背景下未描述的必要成像和分析工具。总之，这使得我们对大脑血管如何在运动过程中控制血液流动的理解不完整，存在重要的知识空白。 因此，整体研究的愿景是更好地了解人类的脑血流控制。长期目标有两个方面：1）开发成像和分析方法，用于测量和描述重要的血液动力学变量，最终帮助我们了解运动期间血流控制的机制，以及2）提高目前用于研究人类脑血流的成像工具的有效性。使用多模态成像方法（超声和磁共振成像; MRI），我们将寻求完成以下短期目标：1）开发量化人类血液动力学变量的方法，2）评估我们的大脑血管如何响应不同的MRI兼容运动（即，小肌肉群对大肌肉群）或收缩模式（即，静态的或有节奏的）。在运动生理学领域，关于女性生理学的数据很少，关于女性脑血管生理学的信息更少。因此，在短期目标3）中，我们将评估静息时脑血流动力学是否存在性别差异，以及运动时的反应是否取决于性别。 所开发的方法将为未来的神经影像学研究提供一个新的实验和分析框架，评估运动如何影响脑血流动力学。通过使用多种成像工具，研究结果将有助于验证现有的工具，这些工具可以提供的血流动力学信息有限。这项研究将提供有关脑血管如何在动态运动等自然模型中反应的新信息，这可能会为我们的大脑血管的长期适应提供见解。

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.