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|Classification and external resources|
|ICD-9||458or more commonly used 796.3|
In physiology and medicine, hypotension is low blood pressure, especially in the arteries of the systemic circulation. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Hypotension is generally considered to be systolic blood pressure less than 90 millimeters of mercury (mm Hg) or diastolic less than 60 mm Hg. However in practice, blood pressure is considered too low only if noticeable symptoms are present.
Hypotension is the opposite of hypertension, which is high blood pressure. It is best understood as a physiological state, rather than a disease. It is often associated with shock, though not necessarily indicative of it.
For some people who exercise and are in top physical condition, low blood pressure is a sign of good health and fitness. For many people, low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine or neurological disorders. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock.
Signs and symptoms 
Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:
- Chest pain
- Shortness of breath
- Irregular heartbeat
- Fever higher than 38.3°C (101°F)
- Stiff neck
- Severe upper back pain
- Cough with phlegm
- Prolonged diarrhea or vomiting
- Dyspepsia (indigestion)
- Dysuria (painful urination)
- Adverse effect of medications
- Acute, life-threatening allergic reaction
- Loss of consciousness
- Profound fatigue
- Temporary blurring or loss of vision
- Connective tissue disorder Ehlers-Danlos Syndrome
- Black tarry stools
Low blood pressure can be caused by low blood volume, hormonal changes, widening of blood vessels, medicine side effects, anemia, heart problems or endocrine problems.
Reduced blood volume, hypovolemia, is the most common cause of hypotension. This can result from hemorrhage; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia is often induced by excessive use of diuretics.
Other medications can produce hypotension by different mechanisms. Chronic use of alpha blockers or beta blockers can lead to hypotension. Beta blockers can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle.
Decreased cardiac output despite normal blood volume, due to severe congestive heart failure, large myocardial infarction, heart valve problems, or extremely low heart rate (bradycardia), often produces hypotension and can rapidly progress to cardiogenic shock. Arrhythmias often result in hypotension by this mechanism.
Some heart conditions can lead to low blood pressure, including extremely low heart rate (bradycardia), heart valve problems, heart attack and heart failure. These conditions may cause low blood pressure because they prevent the body from being able to circulate enough blood.
Excessive vasodilation, 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 AT1 receptor antagonists (Angiotensin II acts on AT1 receptors). Many anesthetic agents and techniques, including spinal anesthesia and most inhalational agents, produce significant vasodilation.
Lower blood pressure is a side effect of certain botanicals, which can also interact with hypotensive medications. An example is the theobromine in Theobroma cacao, which lowers blood pressure through its actions as both a vasodilator and a diuretic, and has been used to treat high blood pressure.
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.
Orthostatic hypotension, 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 blood pressure-lowering medications, many psychiatric medications, in particular antidepressants, can have this side effect. Simple blood pressure and heart rate measurements while lying, seated, and standing (with a two-minute delay in between each position change) can confirm the presence of orthostatic hypotension. Orthostatic hypotension is indicated if there is a drop in 20 mmHg of systolic pressure (and a 10 mmHg drop in diastolic pressure in some facilities) and a 20 beats per minute increase in heart rate.
Neurocardiogenic syncope 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 postprandial hypotension, a drastic decline in blood pressure which occurs 30 to 75 minutes after eating substantial meals. When a great deal of blood is diverted to the intestines (a kind of "splanchnic blood pooling") to facilitate digestion and absorption, the body must increase cardiac output and peripheral vasoconstriction to maintain enough blood pressure to perfuse vital organs, such as the brain. Postprandial hypotension is believed to be caused by the autonomic nervous system not compensating appropriately, because of aging or a specific disorder.
The treatment for hypotension depends on its cause. Chronic hypotension rarely exists as more than a symptom. Asymptomatic hypotension in healthy people usually does not require treatment. Adding electrolytes to a diet can relieve symptoms of mild hypotension. A morning dose of caffeine can also be effective. In mild cases, where the patient is still responsive, laying the person in dorsal decubitus (lying on the back) position and lifting the legs will increase venous return, thus making more blood available to critical organs at the chest and head. The Trendelenburg position, though used historically, is no longer recommended.
The treatment of hypotensive shock always follows the first four following steps. Outcomes, in terms of mortality, are directly linked to the speed in which hypotension is corrected. In parentheses are the still debated methods for achieving, and benchmarks for evaluating, progress in correcting hypotension. A study on septic shock provided the delineation of these general principles. However, since it focuses on hypotension due to infection, it is not applicable to all forms of severe hypotension.
- Volume resuscitation (usually with crystalloid)
- Blood pressure support with a vasopressor (all seem to be equivalent)
- Ensure adequate tissue perfusion (maintain SvO2 >70 with use of blood or dobutamine)
- Address the underlying problem (i.e. antibiotic for infection, stent or CABG (coronary artery bypass graft surgery) for infarction, steroids for adrenal insufficiency, etc...)
Medium-term (and less well-demonstrated) treatments of hypotension include:
- Blood sugar control (80-150 by one study)
- Early nutrition (by mouth or by tube to prevent ileus)
- Steroid support
See also 
- [http://www.thefreedictionary.com/hypotension TheFreeDictionary > hypotension. Citing: The American Heritage Science Dictionary Copyright 2005
- "Diseases and Conditions Index - Hypotension". National Heart Lung and Blood Institute. September 2008. Retrieved 2008-09-16.
- "Low blood pressure (hypotension) — Definition". MayoClinic.com. Mayo Foundation for Medical Education and Research. 2009-05-23. Retrieved 2010-10-19.
- "Low blood pressure (hypotension) — Causes". MayoClinic.com. Mayo Foundation for Medical Education and Research. 2009-05-23. Retrieved 2010-10-19.
- "BUPA: Low blood pressure".
- Tabassum, Nahida; Feroz Ahmad (6). "Role of natural herbs in the treatment of hypertension". Pharmacognosy Review 5 (9): 30–40. doi:10.4103/0973-7847.79097. PMID 22096316. Retrieved 14 September 2012.
- Mitchell ES, Slettenaar M, vd Meer N, Transler C, Jans L, Quadt F, Berry M. Differential contributions of theobromine and caffeine on mood, psychomotor performance and blood pressure. Physiol Behav. 2011 Oct 24;104(5):816-22. Epub 2011 Aug 4. "Theobromine ... lowered blood pressure relative to placebo." http://www.ncbi.nlm.nih.gov/pubmed/21839757
- William Marias Malisoff (1943). Dictionary of Bio-Chemistry and Related Subjects. Philosophical Library. pp. 311, 530, 573. ISBN B0006AQ0NU Check
- Kelly, Caleb J (August 2005). "Effects of theobromine should be considered in future studies". American Journal of Clinical Nutrition 82 (2): 486–7; author reply 487–8. PMID 16087999.
- Merck Manual Home Edition. "Postprandial Hypotension." Last accessed October 26, 2011.
- Chobanian AV, Bakris GL, Black HR, Cushman WC, Green LA, Izzo JL, Jones DW, Materson BJ, Oparil S, Wright JT, Roccella EJ (December 2003). "Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure". Hypertension 42 (6): 1206–52. doi:10.1161/01.HYP.0000107251.49515.c2. PMID 14656957. Retrieved 2009-11-03..
- "BestBets: Use of the Trendelenburg Position to Improve Hemodynamics During Hypovolemic Shock".
- Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B, Peterson E, Tomlanovich M (2001-11-08). "Early goal-directed therapy in the treatment of severe sepsis and septic shock". N Engl J Med. (NEJM) 345 (19): 1368–77. doi:10.1056/NEJMoa010307. PMID 11794169.
- Havel, C; Arrich, J, Losert, H, Gamper, G, Müllner, M, Herkner, H (2011-05-11). "Vasopressors for hypotensive shock". In Herkner, Harald. Cochrane database of systematic reviews (Online) 5 (5): CD003709. doi:10.1002/14651858.CD003709.pub3. PMID 21563137.