The Various Faces of Orthostatic Intolerance

Orthostatic intolerance (OI) involves a series of physical symptoms that are triggered by standing up and relieved by reclining once again. Multiple disorders are associated with orthostatic intolerance, including dysautonomia, an autonomic nervous system disorder. Some causes are less serious, however, and do not generally require medical attention or intervention.

Some people experience mild forms of OI after a recurrent illness or simply from standing up too quickly. Dehydration and infectious diseases can also lead to the condition, which arises due to a body's inability to regulate blood flow. Other causes include chronic fatigue syndrome, neurally mediated hypotension, postural tachycardia syndrome, and fibromyalgia.

The symptoms of orthostatic intolerance include visual difficulties, change in blood pressure, lightheadedness upon standing, dizziness upon standing, nausea, and cognitive impairments like an inability to focus. A change in blood pressure can be both a symptom and a cause of OI. Visual issues include seeing stars and darkening vision. In more extreme cases, some people experience syncope or fainting.

Dysautonomia can cause orthostatic intolerance, as can flaws in the central nervous system (CNS). Such dysfunction can lead to syncope, lightheadedness, and neurocognitive problems due to altered blood flow to the brain, sometimes relating to the brainstem.

Orthostatic intolerance is a symptom of chronic fatigue syndrome or CFS. The condition is often an aspect of postural tachycardia syndrome (POTS) and neurally mediated hypotension (NMH). One study found that OI in people with chronic fatigue syndrome is more frequent than reports suggest. Symptoms usually take the form of dizziness and lightheadedness. The same study also found that symptoms are worsened after physical exertion.

Neurally mediated hypotension is a form of chronic orthostatic intolerance caused by decreased blood volume in the circulatory system and a defect in the nervous and circulatory systems. This defect starts in the nervous system: blood pressure drops because the body cannot reflexively control the veins and arteries through the release of adrenaline. Although the body is releasing the hormone, the blood vessels do not respond and constrict as they should. In turn, people who experience orthostatic hypotension become lightheaded or dizzy upon standing, sometimes to the point of fainting.

Postural tachycardia syndrome, known as POTS, is a form of chronic OI in which the heart rate does not regulate upon standing, and the heart beats too quickly. People with POTS have unstable blood flow, especially to the brain’s cerebrum, and sometimes experience hyperventilation, which can bring on OI. They also have sympathetic nerve activity that contributes to the onset of orthostatic intolerance similarly to people with NMS.

Postural tachycardia syndrome, neurally mediated hypotension, and chronic fatigue syndrome are all connected, with similar symptoms and causes. Fibromyalgia (FM) is also associated with orthostatic intolerance, but in a way experts do not entirely understand. Researchers believe fibromyalgia is linked to autonomic nervous system dysfunction. The same dysfunction can cause orthostatic intolerance, though the reason for the link is unclear. One study found a similarity between POTS and FM in their nervous system symptoms.

The methods of treating OI are dependent on the disorder that causes it. For example, managing the neural symptoms of fibromyalgia by improving function can be more effective than treating the symptoms. Many treatments that are specifically directed toward orthostatic intolerance work to increase blood pressure or avoid triggers. These include avoiding prolonged standing, wearing pressure garments, increasing fluid intake, and medication. Some doctors prescribe physical therapy, as well.

Rehydration and medical treatment can cure orthostatic intolerance caused by dehydration or infectious disease. Chronic forms of OI, however, cannot be cured. If a person's orthostatic intolerance is a byproduct of a chronic illness, it can be managed. For people with diseases like NMS or fibromyalgia, medication and long-term personalized treatment can help them manage OI.