|orthostasis, postural hypotension|
|Classification and external resources|
Orthostatic hypotension, also known as postural hypotension or shortened to orthostasis and colloquially called head rush, occurs when a person's blood pressure falls when suddenly standing up from a lying or sitting position. It is defined as a fall in systolic blood pressure of at least 20 mm Hg or diastolic blood pressure of at least 10 mm Hg when a person assumes a standing position. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain an adequate blood pressure when changing position to standing. As a result, blood pools in the blood vessels of the legs for a longer period, and less is returned to the heart, thereby leading to a reduced cardiac output. Mild orthostatic hypotension is common and can occur briefly in anyone, although it is prevalent in particular among the elderly, and those with known low blood pressure. Severe drops in blood pressure can lead to fainting with a possibility of injury.
There are numerous possible causes for orthostatic hypotension, such as certain medications (e.g. alpha blockers), autonomic neuropathy, decreased blood volume, and age-related blood vessel stiffness.
Apart from addressing the underlying cause, orthostatic hypotension may be treated with a recommendation to increase salt and water intake (to increase the blood volume), wearing compression stockings, and sometimes medication (fludrocortisone, midodrine or others).
Signs and symptoms
Orthostatic hypotension is characterised by symptoms that occur after standing (from lying or sitting), particularly when this is done rapidly. Many report lightheadedness (a feeling that one might be about to faint), sometimes severe. Generalized weakness or tiredness may also occur. Some also report difficulty concentrating, blurred vision, tremulousness, vertigo, anxiety, palpitations (awareness of the heartbeat), feeling sweaty or clammy, and sometimes nausea. A person may look pale.
Orthostatic hypotension is caused primarily by gravity-induced blood-pooling in the lower extremities, which in turn compromises venous return, resulting in decreased cardiac output and subsequent lowering of arterial pressure. For example, changing from a lying position to standing loses about 700 ml of blood from the thorax, with a decrease in systolic and diastolic blood pressures. The overall effect is an insufficient blood perfusion in the upper part of the body.
Still, the blood pressure does not normally fall very much, because it immediately triggers a vasoconstriction (baroreceptor reflex), pressing the blood up into the body again. (Often, this mechanism is exaggerated and is why diastolic blood pressure is a bit higher when a person is standing up, compared to a person in horizontal position.) Therefore, a secondary factor that causes a greater than normal fall in blood pressure is often required. Such factors include low blood volume, diseases, and medications.
Orthostatic hypotension may be caused by low blood volume, resulting from bleeding, the excessive use of diuretics, vasodilators, or other types of drugs, dehydration, or prolonged bed rest. It also occurs in people with anemia.
The disorder may be associated with Addison's disease, atherosclerosis (build-up of fatty deposits in the arteries), diabetes, pheochromocytoma, and certain neurological disorders, including multiple system atrophy and other forms of dysautonomia. It is also associated with Ehlers-Danlos syndrome and anorexia nervosa. It is also present in many patients with Parkinson's disease resulting from sympathetic denervation of the heart or as a side-effect of dopaminomimetic therapy. This rarely leads to fainting unless the person has developed true autonomic failure or has an unrelated heart problem.
Another disease, dopamine beta hydroxylase deficiency, also thought to be underdiagnosed, causes loss of sympathetic noradrenergic function and is characterized by a low or extremely low levels of norepinephrine, but an excess of dopamine.
Quadriplegics and paraplegics also might experience these symptoms due to multiple systems' inability to maintain a normal blood pressure and blood flow to the upper part of the body.
Orthostatic hypotension can be a side-effect of certain antidepressants, such as tricyclics or monoamine oxidase inhibitors (MAOIs). Marijuana and tetrahydrocannabinol can on occasion produce marked orthostatic hypotension. Orthostatic hypotension can also be a side effect of Alpha-1 blockers (alpha1 adrenergic blocking agents). Alpha1 blockers inhibit vasoconstriction normally initiated by the baroreceptor reflex upon postural change and the subsequent drop in pressure.
Patients prone to orthostatic hypotension are the elderly, post partum mothers, and those having been on bedrest. People suffering from anorexia nervosa and bulimia nervosa often suffer from orthostatic hypotension as a common side-effect. Consuming alcohol may also lead to orthostatic hypotension due to its dehydrating effects.
Orthostatic hypotension can be confirmed by measuring a person's blood pressure after lying flat for 5 minutes, then 1 minute after standing, and 3 minutes after standing. Orthostatic hypotension is defined as a fall in systolic blood pressure of at least 20 mmHg and/or in the diastolic blood pressure of at least 10 mmHg between the supine reading and the upright reading. In addition, the heart rate should also be measured for both positions. A significant increase in heart rate from supine to standing may indicate a compensatory effort by the heart to maintain cardiac output or postural orthostatic tachycardia syndrome (POTS). A tilt table test may also be performed.
Apart from treating underlying reversible causes (e.g. stopping or reducing certain medications) there are a number of measures that can improve the symptoms of orthostatic hypotension and prevent episodes of syncope. Even small increases in the blood pressure may be sufficient to maintain blood flow to the brain on standing. In people who do not have a diagnosis of high blood pressure, drinking 2-3 liters of fluid a day and taking 10 grams of salt can improve symptoms; keeping the head of the bed slightly elevated reduces the return of this fluid to the kidneys at night and causing nighttime urine production and blood pressure increases. Various measures can be used to improve the return of blood to the heart: the wearing of compression stockings and exercises ("physical counterpressure manoeuvres" or PCMs) that can be undertaken just before standing up (such as leg crossing and squatting). The medication midodrine can benefit people with orthostatic hypotension, The main side-effect is piloerection ("goose bumps"). Fludrocortisone is also used, although based on more limited evidence.
A number of other measures have slight evidence to support their use indomethacin, fluoxetine, dopamine antagonists, metoclopramide, domperidone, monoamine oxidase inhibitors with tyramine (can produce severe hypertension), oxilofrine, potassium chloride, and yohimbine.
- Orthostatic intolerance
- Orthostatic hypertension
- Postural orthostatic tachycardia syndrome
- Vasovagal response
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