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Low Blood Pressure (cont.)

Allergic Reactions Can Cause Low Blood Pressure

Patient Comments

Major allergic reactions (anaphylactic shock) can cause marked dilation of blood vessels and low blood pressure, associated with:

Orthostatic Hypotension

When standing quickly, it may take a second or two for the body to make adjustments to constrict blood vessels and push blood up to the brain. If there is a delay, then this time of relative low blood pressure may cause symptoms. It can be exacerbated or seen more often in patients who are pregnant, have diabetes, are dehydrated, or taking high blood pressure medications.

Diabetes and Low Blood Pressure

One of the complications of diabetes is damage to the nerves in the body, including those in the autonomic nervous system. In those people with diabetes who have autonomic dysfunction, orthostatic hypotension can occur. The blood vessels are unable to adjust to quick positional changes.

Micturition Syncope (Fainting During Urination or Bowel Movements)

One of the most common causes of syncope, (passing out or fainting), occurs when a person strains to urinate or have a bowel movement. This stimulates the vagus nerve, increasing acetylcholine in the body and dilating blood vessels, causing blood pressure to fall and decreasing blood supply to the brain. Though it is frightening and may result in a fall, micturition syncope is self-limiting, resolves quickly, and may need little treatment.

Medically Reviewed by a Doctor on 9/28/2016

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The eMedicineHealth doctors ask about Low Blood Pressure:

Low Blood Pressure - Allergic Reaction

Has an allergic reaction ever caused your blood pressure to drop?

Low Blood Pressure - Treatment

What was the treatment for your low blood pressure?

Low Blood Pressure - Causes

What caused your blood pressure to be abnormally low?

Low Blood Pressure - Symptoms

Which low blood pressure symptoms (dizziness, lightheadedness, fainting) do you find most troubling?

Read What Your Physician is Reading on Medscape

Shock, Distributive »

Shock is defined as a clinical syndrome due to inadequate tissue perfusion that results in end-organ dysfunction.

Read More on Medscape Reference »

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