Orthostatic hypotension

Orthostatic hypotension, also known as postural hypotension or commonly known as headrush, is a medical condition wherein a person's blood pressure drops (hypotension) when they are standing up (orthostasis) or sitting down. Primary orthostatic hypotension is also often referred to as neurogenic orthostatic hypotension. The drop in blood pressure may be sudden (vasovagal orthostatic hypotension), within 3 minutes (classic orthostatic hypotension) or gradual (delayed orthostatic hypotension). It is defined as a fall in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg after 3 minutes of standing. It occurs predominantly by delayed (or absent) constriction of the lower body blood vessels, which is normally required to maintain adequate blood pressure when changing the 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 and inadequate blood flow to the brain.

Very mild occasional 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. Moderate drops in blood pressure can cause confusion/inattention, delirium, and episodes of ataxia. Chronic orthostatic hypotension is associated with cerebral hypoperfusion that may accelerate the pathophysiology of dementia. Whether it is a causative factor in dementia is unclear.

The numerous possible causes for orthostatic hypotension include certain medications (e.g. alpha blockers), autonomic neuropathy, decreased blood volume, multiple system atrophy, 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). Salt loading (dramatic increases in salt intake) must be supervised by a doctor, as this can cause severe neurological problems if done too aggressively.

Anatomy and physiology

To maintain sufficient blood pressure, the body has several compensatory mechanisms. Baroreceptors, a kind of mechanoreceptors, play a crucial role in conveying data about blood pressure in the autonomic nervous system. The data is conveyed to regulate the peripheral resistance and heart output, keeping blood pressure within an established normal limit. There are two kinds of baroreceptors: high-pressure arterial baroreceptors and low-pressure volume receptors, both activated by the stretching of vessel walls. This results in decreased blood pressure, which leads to an increase in heart rate. Some people may experience severe orthostatic hypotension with the only symptoms being confusion or extreme fatigue. Chronic severe orthostatic hypotension may present as fluctuating cognition/delirium. Women who are pregnant are also susceptible to orthostatic hypotension.

Associated diseases

The disorder may be associated with Addison's disease, atherosclerosis (build-up of fatty deposits in the arteries), diabetes, pheochromocytoma, porphyria, long COVID, and certain neurological disorders, including autoimmune autonomic ganglionopathy, 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 or Lewy body dementias 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 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 normal blood pressure and blood flow to the upper part of the body.

Causes

Some causes of orthostatic hypotension include neurodegenerative disorders, low blood volume (e.g. caused by dehydration, bleeding, or the use of diuretics), drugs that cause vasodilation, other types of drugs (notably, narcotics and marijuana), discontinuation of vasoconstrictors, prolonged bed rest (immobility), significant recent weight loss, anemia, vitamin B12 deficiency, or recent bariatric surgery.

Medication

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Orthostatic hypotension can be a side effect of certain antidepressants, such as tricyclics or monoamine oxidase inhibitors (MAOIs) Alcohol can potentiate orthostatic hypotension to the point of syncope. 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. Other antihypertensive medications may also cause orthostatic hypotension, in addition to anticholinergics, dopaminergic drugs, opiates and psychoactive medications. The overall effect is insufficient blood perfusion in the upper part of the body.

Normally, a series of cardiac, vascular, neurologic, muscular, and neurohumoral responses occurs quickly so the blood pressure does not fall very much. One response is 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 the horizontal position.) Therefore, some factor that inhibits one of these responses and causes a greater than normal fall in blood pressure is required. Such factors include low blood volume, diseases, and medications.

Diagnosis

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 or the diastolic blood pressure of at least 10 mmHg between the supine reading and the upright reading. Also, the heart rate should 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. A related syndrome, postural orthostatic tachycardia syndrome (POTS), is diagnosed when at least a 30 bpm increase in heart rate occurs with little or no change in blood pressure. A tilt table test may also be performed.

Definition

Orthostatic hypotension (or postural hypotension) is a drop in blood pressure upon standing. One definition (AAFP) calls for a systolic blood pressure decrease of at least 20 mm Hg or a diastolic blood pressure decrease of at least 10 mm Hg within 3 minutes of standing. A common first symptom is lightheadedness upon standing, possibly followed by more severe symptoms: narrowing or loss of vision, dizziness, weakness, and even syncope (fainting).

Subcategories

Orthostatic hypotension can be subcategorized into three groups – initial, classic, and delayed.

Initial orthostatic hypotension is frequently characterized by a systolic blood pressure decrease of ≥40 mmHg or diastolic blood pressure decrease of ≥20 mmHg within 15 seconds of standing. with the main side effect being piloerection ("goose bumps"). with few, mostly mild side effects reported.

Atomoxetine, a norepinephrine reuptake inhibitor (NRI), has been studied and used in the treatment of orthostatic hypotension. While acutely effective, tachyphylaxis has been found to occur with continuous administration. Bupropion, a norepinephrine–dopamine reuptake inhibitor (NDRI), may be helpful as well.

Amezinium metilsulfate is approved and widely used for the treatment of orthostatic hypotension in Japan. It has a unique mechanism of action of acting as a dual monoamine oxidase inhibitor (MAOI) and NRI.

Findings are mixed for the α2-adrenergic receptor antagonist yohimbine.

Prognosis

Orthostatic hypotension may cause accidental falls. It is also linked to an increased risk of cardiovascular disease, heart failure, and stroke. Also, observational data suggest that orthostatic hypotension in middle age increases the risk of eventual dementia and reduced cognitive function.

References

External links

Postural hypotension : what it is and how to manage it – Centers for Disease Control and Prevention