the brainstem is continually adjusting BP to ensure just the right perfusion pressure and blood flow. Furthermore, an increase in brainstem blood flow will result in homeostatic changes that lower BP i.e. This theory suggests that the cardio-cranial distance is a major factor determining BP. This theory explains the increase in blood pressure in humans from birth to adulthood, the higher high blood pressure in taller than shorter individuals and the progressive increase in blood pressure as the length of the Giraffe’s neck grows with aging (see Fig. It should also be recalled that the hydrostatic pressure changes by 0.77 mmHg for every 1 cm change in vertical distance. According to this theory the MAP at all times in all individuals is determined by the pressure needed to perfuse the brainstem. As first suggested by Harvey Cushing in 1901, any reduction in cerebral blood flow to the cardiovascular control centers (in the brainstem) will result in activation of these centers which will proportionally increase systemic blood pressure (BP) and return cerebral blood flow to a new homeostatic level.
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