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If you stand up too quickly and start to feel light headed, it's caused by a drop in blood pressure in your head and upper body. It's the same reason fighter pilots black out in high G turns, and ...
Orthostatic hypotension (or postural hypotension) is a drop in blood pressure upon standing. One definition (AAFP) calls for a systolic blood pressure decrease of at least 20 mm Hg or a diastolic blood pressure decrease of at least 10 mm Hg within 3 minutes of standing. [31]
Orthostatic intolerance occurs in humans because standing upright is a fundamental stressor, so requires rapid and effective circulatory and neurologic compensations to maintain blood pressure, cerebral blood flow, and consciousness. When a human stands, about 750 ml of thoracic blood are abruptly translocated
Blood is red due to the presence of hemoglobin; deoxygenated blood (in veins) has a deep red color, and oxygenated blood (in arteries) has a light cherry-red color. Veins below the skin can appear blue or green due to subsurface scattering of light through the skin, and aspects of human color perception.
Carotid sinus syncope is due to pressure on the carotid sinus in the neck. [2] The underlying mechanism involves the nervous system slowing the heart rate and dilating blood vessels, resulting in low blood pressure and thus not enough blood flow to the brain. [2] Diagnosis is based on the symptoms after ruling out other possible causes. [3]
High diastolic blood pressure measured while standing in a person who stood up shortly after waking up. When it affects an individual's ability to remain upright, orthostatic hypertension is considered as a form of orthostatic intolerance. The body's inability to regulate blood pressure can be a type of dysautonomia.
Pressure drops gradually as blood flows from the major arteries, through the arterioles, the capillaries until blood is pushed up back into the heart via the venules, the veins through the vena cava with the help of the muscles. At any given pressure drop, the flow rate is determined by the resistance to the blood flow.
When blood pressure rises, the carotid and aortic sinuses are distended further, resulting in increased stretch and, therefore, a greater degree of activation of the baroreceptors. At normal resting blood pressures, many baroreceptors are actively reporting blood pressure information and the baroreflex is actively modulating autonomic activity.