Hypotension is often sub divided into different categories; postural or orthostatic hypotension, Shy-Drager syndrome and neurally mediated hypotension.
Orthostatic hypotension | postural hypotension
Postural or orthostatic hypotension is a sudden drop in blood pressure, when one stand up from a sitting position or if one stand up after lying down. Ordinarily, blood pools in the legs whenever one stands, but the body compensates for this by increasing the heart rate and constricting blood vessels, thereby ensuring that enough blood returns to the brain. However, in people with postural hypotension, this compensating mechanism fails and blood pressure falls, leading to dizziness, lightheadedness, and blurred vision and even fainting.
Causes of orthostatic hypotension: Postural hypotension can occur for a variety of reasons, including dehydration, prolonged bed rest, pregnancy, diabetes, heart problems, burns, excessive heat, large varicose veins and certain neurological disorders. A number of medications can also cause it, particularly drugs used to treat high blood pressure, as well as antidepressants and drugs used to treat Parkinson's disease and erectile dysfunction.
Facts about orthostatic hypotension: Postural hypotension is especially common in older adults, with as many as 20 percent of those over age 65 experiencing it. However, postural hypotension can also affect young, otherwise healthy people who stand up suddenly after sitting with their legs crossed for long periods or after working for a time in a squatting position.
Shy-Drager syndrome - hypotension
Low blood pressure due to nervous system damage, called as Shy-Drager syndrome, this rare disorder causes progressive damage to the autonomic nervous system, which controls involuntary functions such as blood pressure, heart rate, breathing, and digestion. Although multiple system atrophy can be associated with muscle tremors, slowed movement, problems with coordination and speech, and incontinence, its main characteristic is severe orthostatic hypotension in combination with very high blood pressure when lying down. Multiple system atrophy cannot cure and usually proves fatal within seven to 10 years of diagnosis.
Low blood pressure after eating is postprandial hypotension, a problem that almost exclusively affects older adults. Just as gravity pulls blood to the feet when you stand, a large amount of blood flows to the digestive tract after eating. Ordinarily, the body counteracts this by increasing the heart rate and constricting certain blood vessels to help maintain normal blood pressure. However, in some people these mechanisms fail, leading to dizziness, faintness, and falls. Postprandial hypotension is more likely to affect people with high blood pressure or autonomic nervous system disorders such as Parkinson's disease. Lowering the dose of blood pressure drugs and eating small, low-carbohydrate meals may help reduce symptoms.
Neurally mediated hypotension
Low blood pressure from faulty brain signals is neurally mediated hypotension. Unlike orthostatic hypotension, which occurs when you stand up from a sitting or lying position, this disorder causes blood pressure to drop after standing for long periods, leading to symptoms such as dizziness, nausea and fainting. It seems to occur because of a miscommunication between the heart and the brain. When you are standing for an extended period, the blood pressure falls as the blood pool into the legs. Normally, the body makes adjustments to normalize the blood pressure. However, in people with neurally mediated hypotension, nerves in the heart's left ventricle actually signal the brain that blood pressure is too high, rather than too low, and so the brain lessens the heart rate, decreasing blood pressure even further. This causes more blood to pool in the legs and less blood to reach the brain, leading to lightheadedness and fainting.