During increased neuronal activity, early changes of regional CBF are more localized than later changes at time points when increased blood flow reaches the area of the draining veins. Deoxyhemoglobin concentration is larger in the venous compartment. Therefore, imaging techniques based on deoxyhemoglobin changes during the phase of hyperoxygenation are more affected by the draining vein effect than techniques using early oxyhemoglobin or regional CBF changes for brain mapping. However, as long as the mechanisms and mediators of neurovascular coupling are not known in detail, the question remains whether the area of increased blood flow exactly matches neuronally active areas of the brain or whether cerebral blood flow is controlled on a more coarse spatial scale.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.