Hypotension
Encyclopedia
In physiology
and medicine
, hypotension is abnormally low blood pressure
, especially in the arteries of the systemic circulation
. It 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 the opposite of hypertension
, which is high blood pressure. Blood pressure
is the force of blood pushing against the walls of the arteries as the heart pumps out blood. If it is lower than normal then it is called low blood pressure or hypotension. Hypotension is generally considered as 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.
It is true that, 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.
or dizziness
.
If the blood pressure is sufficiently low, fainting and often seizure
s will occur.
Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:
, heart & endocrine problems.
Reduced blood volume, 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.
Decreased cardiac output
despite normal blood volume, due to severe congestive heart failure
, large myocardial infarction
, heart valve problems, heart attack, heart failure, or extremely low heart rate bradycardia
, often produces hypotension and can rapidly progress to cardiogenic shock
. Arrhythmias 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. Varieties of meditation and/or other mental-physiological disciplines can create temporary hypotension effects, as well, and should not be considered unusual.
Some heart conditions that can lead to low blood pressure include 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, angiotensin II receptor blockers ACE inhibitors. 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 theobromine
, which lowers blood pressure through its actions as both a vasodilator and a diuretic
, and has been used to treat high blood pressure.
, using an elaborate network of receptors, nerve
s, and hormone
s 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.
, 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 antidepressant
s, 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 bpm 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 30–75 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
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 aging or a specific disorder.
is at or below 115/75 mmHg. A small drop in blood pressure, even as little as 20 mmHg, can result in transient hypotension.
Evaluation of neurocardiogenic syncope is done with a tilt table test
.
, 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.
Medium-term (and less well-demonstrated) treatments of hypotension include:
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
and medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, hypotension is abnormally low blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
, especially in the arteries of the systemic circulation
Systemic circulation
Systemic circulation is the part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. This physiologic theory of circulation was first described by William Harvey...
. It 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 the opposite of hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
, which is high blood pressure. Blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
is the force of blood pushing against the walls of the arteries as the heart pumps out blood. If it is lower than normal then it is called low blood pressure or hypotension. Hypotension is generally considered as systolic
Systole (medicine)
Systole is the contraction of the heart. Used alone, it usually means the contraction of the left ventricle.In all mammals, the heart has 4 chambers. The left and right ventricles pump together. The atria and ventricles pump in sequence...
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.
It is true that, 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
The cardinal symptom of hypotension is lightheadednessLightheadedness
Light-headedness is a common and often unpleasant sensation of dizziness and/or feeling that one may be about to faint, which may be transient, recurrent, or occasionally chronic. In some cases, the individual may feel as though his or her head is weightless. The individual may also feel as...
or dizziness
Dizziness
Dizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness....
.
If the blood pressure is sufficiently low, fainting and often seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s will occur.
Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:
Causes
Low blood pressure causes can be due to low blood volume, hormonal changes, widening of blood vessels, medicine side effects, anemiaAnemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, heart & endocrine problems.
Reduced blood volume, called hypovolemia
Hypovolemia
In physiology and medicine, hypovolemia is a state of decreased blood volume; more specifically, decrease in volume of blood plasma...
, 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
Diuretic
A diuretic provides a means of forced diuresis which elevates the rate of urination. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.- Medical uses :...
s. Other medications can produce hypotension by different mechanisms.
Decreased cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
despite normal blood volume, due to severe congestive heart failure
Congestive heart failure
Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...
, large myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
, heart valve problems, heart attack, heart failure, or extremely low heart rate bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
, often produces hypotension and can rapidly progress to cardiogenic shock
Cardiogenic shock
Cardiogenic shock is based upon an inadequate circulation of blood due to primary failure of the ventricles of the heart to function effectively....
. Arrhythmias often result in hypotension by this mechanism. Beta blocker
Beta blocker
Beta blockers or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists or beta antagonists, are a class of drugs used for various indications. They are particularly for the management of cardiac arrhythmias, cardioprotection after myocardial infarction ,...
s can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle. Varieties of meditation and/or other mental-physiological disciplines can create temporary hypotension effects, as well, and should not be considered unusual.
Some heart conditions that can lead to low blood pressure include extremely low heart rate (bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
), 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
Vasodilation
Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...
, 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
Dysautonomia
Dysautonomia is a broad term that describes any disease or malfunction of the autonomic nervous system. This includes postural orthostatic tachycardia syndrome , inappropriate sinus tachycardia , vasovagal syncope, mitral valve prolapse dysautonomia, pure autonomic failure, neurocardiogenic...
, an intrinsic abnormality in autonomic system functioning. Excessive vasodilation can also result from sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
, acidosis
Acidosis
Acidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....
, or medications, such as nitrate preparations, calcium channel blockers, angiotensin II receptor blockers ACE inhibitors. Many anesthetic agents and techniques, including spinal anesthesia and most inhalational agents
Inhalational anaesthetic
An inhalational anaesthetic is a chemical compound possessing general anaesthetic properties that can be delivered via inhalation. They are administered by anaesthetists through an anaesthesia mask, laryngeal mask airway or tracheal tube connected to some type of anaesthetic vaporiser and an...
, produce significant vasodilation
Vasodilation
Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...
.
Lower blood pressure is a side effect of certain botanicals, which can also interact with hypotensive medications. An example is theobromine
Theobromine
Theobromine , also known as xantheose, is a bitter alkaloid of the cacao plant, with the chemical formula C7H8N4O2. It is found in chocolate, as well as in a number of other foods, including the leaves of the tea plant, and the kola nut...
, which lowers blood pressure through its actions as both a vasodilator and a diuretic
Diuretic
A diuretic provides a means of forced diuresis which elevates the rate of urination. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.- Medical uses :...
, and has been used to treat high blood pressure.
Pathophysiology
Blood pressure is continuously regulated by the autonomic nervous systemAutonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
, using an elaborate network of receptors, nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s, and hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s to balance the effects of the sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
, which tends to raise blood pressure, and the parasympathetic nervous system
Parasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
, 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.
Syndromes
Orthostatic hypotensionOrthostatic hypotension
Orthostatic hypotension, also known as postural hypotension, orthostasis, and colloquially as head rush or dizzy spell, is a form of hypotension in which a person's blood pressure suddenly falls when the person stands up or stretches. The decrease is typically greater than 20/10 mm Hg, and may be...
, 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
Hypovolemia
In physiology and medicine, hypovolemia is a state of decreased blood volume; more specifically, decrease in volume of blood plasma...
and as a result of various medications. In addition to blood pressure-lowering medications, many psychiatric medications, in particular antidepressant
Antidepressant
An antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...
s, 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 bpm 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
Vasovagal syncope
A vasovagal episode or vasovagal response or vasovagal attack is a malaise mediated by the vagus nerve. When it leads to syncope or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.There are a number of different syncope syndromes which all fall under the...
in that both occur as a result of increased activity of the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
, the mainstay of the parasympathetic nervous system.
Another, but rarer form, is postprandial
Postprandial
Postprandial means after eating a meal while preprandial is before a meal.-Usages of the term:This term is used in many contexts but also in relation to blood sugar levels, which are normally measured 2 hours after and before eating in a postprandial glucose test...
hypotension, a drastic decline in blood pressure which occurs 30–75 minutes after eating substantial meals. When a great deal of blood is diverted to the intestines (a kind of "splanchnic
Splanchnic
Splanchnic, from a Greek word spēn, meaning organ, usually used to describe visceral organs.More specifically, it can also refer to:* An adjective describing the intestines* Splanchnic nerves* Splanchnic mesoderm...
blood pooling") to facilitate digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
and absorption, the body must increase cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
and peripheral vasoconstriction
Vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
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
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
not compensating appropriately, because of aging or a specific disorder.
Diagnosis
For most adults, the healthiest blood pressureBlood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
is at or below 115/75 mmHg. A small drop in blood pressure, even as little as 20 mmHg, can result in transient hypotension.
Evaluation of neurocardiogenic syncope is done with a tilt table test
Tilt table test
A tilt table test, occasionally called upright tilt testing, is a medical procedure often used to diagnose dysautonomia or syncope. Patients with symptoms of dizziness or lightheadedness, with or without a loss of consciousness , suspected to be associated with a drop in blood pressure or...
.
Treatment
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. 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 positionTrendelenburg position
In the Trendelenburg position the body is laid flat on the back with the feet higher than the head by 15-30 degrees, in contrast to the reverse Trendelenburg position, where the body is tilted in the opposite direction. This is a standard position used in abdominal and gynecological surgery...
, 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 ileusIleusIleus is a disruption of the normal propulsive ability of the gastrointestinal tract.Ileus is commonly defined simply as bowel obstruction. However, authoritative sources define it as decreased motor activity of the GI tract due to non-mechanical causes...
) - Steroid support
External links
- Understanding Low Blood Pressure - the Basics WebMDWebMDWebMD is an American corporation which provides health information services. It was founded in 1996 by Jim Clark and Pavan Nigam as Healthscape, later Healtheon, and then acquired WebMD in 1999 to form Healtheon/WebMD...
- Low blood pressure