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.

Extended Bedrest

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Long periods of lying down cause the body to adjust to this new normal. Changes in the muscular, neurological, and cardiovascular systems adjust to the minimal activity and body's reclined position. The hormonal and chemical makeup in the body, which helps control blood pressure and heart rate, begins to adjust as well. After just one day in bed, the fluid in the body's tissue begins to shift into the blood vessels, and hormones begin to release salt and water through increased urine. 

As a result, blood volume reduces to a new normal, and there is less blood flowing throughout the body to distribute oxygen and nourish the organs, tissue, and muscles. Upon standing, the body needs to readjust to the new upright position, but may have difficulty with less blood flow.

Inadequate Fluid And Salt Intake


The body must be properly hydrated for effective blood circulation and blood oxygen levels in the body. When the body is dehydrated, blood vessels constrict and limit blood flow throughout the body, which also causes blood pressure and heart rate to lower. This means the heart is pumping less blood to the organs, tissue, and muscles, and the body is receiving less oxygen. A decrease in oxygen or a decrease in blood pressure can cause many issues, including nausea, lightheadedness, and diminished cognitive ability.

Salt has been associated with cardiovascular issues, but in proper amounts, it is essential for good health. Those who drastically restrict their salt intake may experience an increase in hormones and lipids in the blood, disrupting the volume of blood plasma needed for proper body function and tissue health. When salt levels reach low points, blood pressure also drops, which can cause lightheadedness and fainting. If changes are made to one's diet, it is important to not have inadequate fluid and salt intake.

Astronauts Returning From Space

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Just as standing up quickly can cause dizziness and lightheadedness, gravity can have the same effect. When astronauts are returning from space, the blood rushes down their bodies as they reenter the atmosphere. This dramatic change in blood volume disrupts the amount of blood and oxygen reaching the brain and affects blood pressure, heart rate, and oxygen levels, resulting in lightheadedness. 

The physiological adjustments that occur due to changes in body posture and atmosphere cause issues with spatial awareness and within the cardiovascular and respiratory systems. The body undergoes pressure with these changes and must adapt to significant adjustments necessary for organ function.

Stressful Events


Stress can be the result of many things from life changes to traumatic events, and the results of stress can perpetuate the issues. Individuals experiencing high levels of stress often experience a lack of sleep, which can negatively affect cognitive ability, blood pressure, and body function. Stress can weaken the body's immune system, putting an individual at risk of illnesses that can disrupt hormone levels and all functional systems of the body. Severe illnesses can land an individual on extended bed rest, which is also a cause of orthostatic intolerance. Stressful events can also cause the heart rate and blood pressure to increase significantly, and while low blood pressure is commonly a cause for orthostatic intolerance, high blood pressure and rapid heart rate can pump too much blood too quickly and disrupt proper body function.

While some individuals may experience orthostatic intolerance as a secondary condition related to another health issue, there are some common causes for the condition. Understanding these causes can be helpful in preventing or minimizing the effects of orthostatic intolerance, and in some cases, making small adjustments in diet and fluid intake may be the key to feeling healthier. Ongoing issues may require the care of a healthcare professional, so it is best to consult with a physician if symptoms continue or if there is an unknown cause for the symptoms.


    HealthPrep Staff