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 systolic blood pressure less than 90 millimeters
of mercury 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, excessively 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 symptoms of hypotension include lightheadedness or dizziness.
If the blood pressure is sufficiently low, fainting and often seizures 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 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.
Low blood pressure may also be attributed to heat stroke. The body may have enough fluid
but does not retain electrolytes. Absence of perspiration, light headedness and dark
coloured urine are also indicators. 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, 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,
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, 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. Many anesthetic agents and techniques, including
spinal anesthesia and most inhalational agents, produce significant vasodilation.
Meditation, yoga, or other mental-physiological disciplines may produce hypotensive effects.
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. Pathophysiology
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. Syndromes
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 can confirm the presence of orthostatic hypotension. Orthostatic hypotension is indicated
if there is a drop in 20 mmHg of systolic pressure 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 that occurs
30 to 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 to maintain enough blood pressure to perfuse
vital organs, such as the brain. Postprandial hypotension is believed caused by the autonomic
nervous system not compensating appropriately, because of aging or a specific disorder.
Diagnosis For most adults, the healthiest blood pressure
is at or below 120/80 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. 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. A morning
dose of caffeine can also be effective. In mild cases, where the patient is still responsive,
laying the person in dorsal decubitus position and lifting the legs increases venous return,
thus making more blood available to critical organs in the chest and head. The Trendelenburg
position, though used historically, is no longer recommended.
Hypotensive shock treatment always follows the first four following steps. Outcomes,
in terms of mortality, are directly linked to the speed that hypotension is corrected.
Still-debated methods are in parentheses, as are 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
Blood pressure support with a vasopressor Ensure adequate tissue perfusion
Address the underlying problem for infarction, steroids for adrenal insufficiency, etc…)
Medium-term treatments of hypotension include: Blood sugar control
Early nutrition Steroid support
See also Dysautonomia
Hypotensive transfusion reaction Orthostatic intolerance
References External links
Understanding Low Blood Pressure – the Basics WebMD
Hypotension PubMed Health