Quantifying Human Cerebral Hemodynamics During Dynamic Exercise

人类运动时脑血流量调节的机制尚不清楚。无论是走路、骑自行车还是蹲着，脑部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。了解在动态运动中脑血管是如何控制血液流动的，将增加我们对脑血管如何长期适应的理解，比如运动训练计划。在运动过程中，从开始到中等强度运动，脑血流量稳定上升，随着运动强度水平的继续增加，脑血流量缓慢恢复到接近基线水平。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是如何共同影响运动时的脑血流量的。研究脑血管最常用的工具只能提供脑血流量的估计，因为它只测量血流速度。其他描述血流物理或“血流动力学”的重要变量尚未被描述为必要的成像和分析工具，在运动的背景下没有描述。总之，这使得我们对运动时脑血管如何控制血液流动的理解不完整，存在重要的知识空白。因此，总体的研究愿景是更好地理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来测量和描述重要的血流动力学变量，最终帮助我们了解运动过程中血流控制的机制；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对不同MRI兼容运动（即小肌群与大肌群）或收缩模式（即静态或节律性）的反应。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就更少了。因此，在短期目标3中，我们将评估休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依赖于性别。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，以评估运动如何影响脑血流动力学。通过使用多种成像工具，这些发现将有助于验证现有工具所能提供的血流动力学信息的局限性。这项研究将提供关于脑血管在动态运动等自然模式下如何反应的新信息，这可能为我们的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.