In
Physiology and
Medicine , refers to an abnormally low
Blood Pressure . This is best understood as a physiologic state, rather than a disease. It is often associated with
Shock , though not necessarily indicative of it. Hypotension is not to be confused with
Hypertension , which is high blood pressure, the opposite of hypotension. Hypotension is a fairly rare problem, hypertension is a much more common problem. Hypotension is almost never a serious problem, although in some very rare cases it can be life threatening.
Blood pressure is continuously regulated by the
Autonomic Nervous System , using an elaborate network of
Receptors ,
Nerves , and
Hormones to balance the effects of the
Sympathetic Nervous System , which tends to raise blood pressure, and the
Parasympathetic Nervous System , which lowers it. The vast and rapid compensation abilities of the autonomic nervous system allow normal individuals to maintain an acceptable blood pressure over a wide range of activities and in many disease states.
, called
Hypovolemia , is the most common mechanism producing hypotension. This can result from
Hemorrhage , or blood loss; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia is often induced by excessive use of
Diuretic s. (Other medications can produce hypotension by different mechanisms.)
despite normal blood volume, due to severe
Congestive Heart Failure , large
Myocardial Infarction , or
Bradycardia , often produces hypotension and can rapidly progress to
Cardiogenic Shock .
Arrhythmia s often result in hypotension by this mechanism.
Beta Blocker s can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle.
or insufficient constriction of the resistance blood vessels (mostly
Arterioles ), causes hypotension. This can be due to decreased sympathetic nervous system output or to increased parasympathetic activity occurring as a consequence of injury to the brain or spinal cord or of
Dysautonomia , an intrinsic abnormality in autonomic system functioning. Excessive vasodilation can also result from
Sepsis ,
Acidosis , or medications, such as
Nitrate Preparations ,
Calcium Channel Blockers , or
ACE Inhibitors . Many anesthetic agents and techniques, including
Spinal Anesthesia and most
Inhalational Agents , produce significant vasodilation.
, also called "postural hypotension", is a common form of low blood pressure. It occurs after a change in body position, typically when a person stands up from either a seated or lying position. It is usually transient and represents a delay in the normal compensatory ability of the autonomic nervous system. It is commonly seen in hypovolemia and as a result of various medications. In addition to the classes of blood pressure-lowering medications listed above, many psychiatric medications, in particular
Antidepressants , can have this side effect. Simple blood pressure and heart rate measurements while lying, seated, and standing can confirm the presence of orthostatic hypotension.
is a form of dysautonomia characterized by an inappropriate drop in blood pressure while in the upright position. Neurocardiogenic syncope is related to
Vasovagal Syncope in that both occur as a result of increased activity of the
Vagus Nerve , the mainstay of the parasympathetic nervous system.
Another, but rarer form, is , which occurs 30–75 minutes after eating substantial meals. When a great deal of blood is diverted to the
Intestines to facilitate
Digestion and
Absorption , the body must increase
Cardiac Output and peripheral
Vasoconstriction in order to maintain enough blood pressure to perfuse vital organs, such as the brain. It is believed that postprandial hypotension is caused by the
Autonomic Nervous System not compensating appropriately, because of ageing or a specific disorder.
For most individuals, a healthy
Blood Pressure lies from 90/50
MmHg to 135/90 mmHg. A small drop in blood pressure, even as little as 20 mmHg, can result in transient hypotension.
Evaluating
Neurocardiogenic Syncope is done with a
Tilt Table Test .
The cardinal symptom of hypotension is
Lightheadedness or
Dizziness .
If the blood pressure is sufficiently low,
Fainting and often
Seizure s will occur.
Hypotension, depending on one's own body chemistry and genetics, may often cause mild
Depression , mostly in regard to taking other medications which do not fit one's personal unique needs.
Low blood pressure is often accompanied by:
(Most of these are related to causes rather than effects of hypotension.)
The treatment for hypotension depends on its cause. Asymptomatic hypotension in healthy people usually does not require treatment. Severe hypotension needs to be aggressively treated because reduced
Blood flow to critical organs including the
Brain ,
Heart and
Kidneys may cause organ failure and can ultimately lead to
Death . Treatment options include
Systemic Vasoconstrictors and other drugs.
