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Micturition Syncope: Definition & Causes

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Micturition syncope is a medical condition where a person's blood pressure suddenly drops right after they urinate, causing them to faint. What causes such a thing to happen? Read this lesson to learn more about micturition syncope.

What Is Micturition Syncope?

This is a somewhat mysterious condition, but micturition syncope is a condition where someone faints after urinating due to a sudden drop in blood pressure. In some cases, the person may even faint during urination. This particular condition usually affects more older men than other sectors of the population, and almost 2/3 of people who experience micturition syncope also experience some other type of syncope (fainting).

There are a number of things that can cause fainting, but ultimately there is decreased blood flow to the brain.
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What Causes Micturition Syncope?

Urination seems like a strange trigger to induce a fainting episode, so what actually happens in the body to cause this? It's believed that micturition syncope is related to the vasovagal response. The vasovagal response occurs from some type of 'trigger' activity that causes a sudden drop in blood pressure. The trigger leads the heart to slow and the blood vessels to dilate (get wider), causing blood to pool in the lower half of the body. As a result, blood flow to the brain is temporarily limited, causing a fainting episode to occur. If you have ever seen someone faint at the sight of blood, they are likely experiencing vasovagal syncope (blood is a relatively common trigger).

The underlying mechanism linking urination to the vasovagal response is still not well understood, because urinating is usually not a stressful event leading to a sudden drop in blood pressure. However, there is evidence suggesting the bladder may become hyper-reflexic and this may be enhanced by alcohol consumption, feeling warm, taking certain medications, or experiencing a spinal cord injury. A person may experience other symptoms immediately before fainting, including nausea and sweating.

Some patients even experience an increase in blood pressure when 'having to go', so the fainting could be triggered by the rapid swing from elevated to decreased blood pressure over such a short period. Others only experience micturition syncope after they wake up from a deep sleep. Straining during urination and heart irregularities may also induce fainting.

As you can see, there have been multiple causes hypothesized, and research is still being done to investigate this particular condition.

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