Causes Of Orthostatic Intolerance

Orthostatic intolerance is a form of dysautonomia, which is an autonomic nervous system disorder. Patients may have acute orthostatic intolerance or chronic orthostatic intolerance. Acute sufferers experience temporary loss of consciousness, vision problems, anxiety, fatigue, headache, heart palpitations associated with blood pressure drop, difficulty breathing, and sweating. Individuals with chronic orthostatic intolerance experience problems nearly every day for at least three months. In addition to the symptoms of acute orthostatic intolerance, chronic patients also experience nausea, difficulty sleeping, sensitivity to heat, and attention issues or other neurocognitive problems.

Staying Upright For Prolonged Periods

The simple act of standing up results in a gravitational pull of about ten to fifteen percent of the body's blood volume settling in the lower extremities, abdomen, and arms. This shift in blood means less is circulating to the brain, and in some patients, causes lightheadedness, blurred vision, or fainting. Healthy individuals typically do not experience these symptoms after staying upright for prolonged periods or standing up quickly as their leg muscles can adequately pump blood and redistribute it back up the body to the heart, lungs, and brain.

Additionally, the body releases adrenaline, the combination of norepinephrine and epinephrine, which causes the heart to beat slightly faster and increase the efficiency of the body's ability to pump blood. Most individuals never feel this increased heart rate, but those who may have a heart condition or other underlying health issue may not only feel the heart beating faster, but also feel the effects of the body's inability to redistribute the blood to the upper portion of the body.