#671 Why do people pass out from pain?

Why do people pass out from pain? Sudden pain can make the heart rate decrease, which lowers blood pressure, which can cause people to pass out.

Fainting is technically known as syncope. Syncope can also mean when a word is contracted by not pronouncing the middle letters, such as favorite (we don’t say the o), or camera (we don’t say the e). We are going to look at the medical version of syncope, where it means fainting.

Syncope can be caused by different things, but the most common cause is low blood pressure. Many of us may have passed out after standing up suddenly, or at least coming close to it. A “head rush”, or almost fainting is called presyncope as it is the stage that comes before syncope. We don’t actually faint because blood pressure is restored before we can collapse. Standing up suddenly is a good example of why low blood pressure can cause fainting. We have evolved to be able to pump about 70 ml of blood with every heartbeat and to move about 5 to 7 liters of blood around our circulation every minute. We have evolved to be able to do that under the force of gravity here on Earth. It is obviously easier for blood to go down towards the legs than it is to get it up to the brain because going up the blood fights gravity. In order to get blood to the brain, the blood vessels widen or constrict to keep the blood pressure at the same level.

When you sit down, you lower the distance from your heart to your legs and blood collects in the legs. This means less blood is circulating in the system. When you stand up, the pooled blood takes a little while to move around the system again and for a short while there is not enough blood in circulation. Your blood pressure drops rapidly. The brain instructs the heart to beat faster and cells in the blood vessels detect the low pressure and start to contract, increasing the blood pressure. That means, for the shortest time, the brain doesn’t have enough oxygenated blood and begins to shut down. If your body can recover the blood pressure fast enough, then you go a little bit dizzy and that’s it, which is presyncope. If your body can’t recover the blood pressure fast enough, you shut down and collapse to the floor.

It might seem counterproductive to collapse because there is the real danger of harming yourself on the floor. However, making the body horizontal removes the low blood pressure problem because the heart doesn’t have to fight against gravity so much anymore. Most people recover fairly quickly once they are lying down. The evolutionary advantage of fainting could be in order to make us horizontal, although, it is far more likely that the body cannot keep itself vertical once the brain shuts down and collapsing is the only option.

So, why do people faint when they are in a lot of pain or scared? It is because of the vasovagal reaction. The vagal nerves are the nerves that control many things in the body, including the digestion, immune system, and heart rate. The vagus nerve can easily overreact when it is under stress. This stress can be caused by extreme heat, anxiety, hunger, stress, or pain. When it gets an overload of sensations, as in when a person is experiencing extreme pain, it overreacts and slows down the heart rate, At the same time, the blood vessels in the legs relax. This means a lot of blood collects in the lower body and the blood pressure in the body drops. Without enough blood pressure to circulate blood, there is not enough oxygenated blood reaching the brain. As with any type of fainting, without oxygen the brain starts to shut down and the person faints.

There are several reasons as to why this might happen. The first reason is to protect the body. If someone is undergoing intense pain, there is a high likelihood that they are also severely injured. Lowering the heart rate and allowing blood to collect in the lower body is a good way of preventing blood loss through an injured site. Another reason is to protect the person from an overload of pain. There is only so much pain that a person can deal with and the vasovagal reaction could be there to shut the brain down. Either way, once the blood pressure is restored, the person will come to. And this is what I learned today.

Photo by Engin Akyurt: https://www.pexels.com/photo/woman-in-blue-and-white-face-mask-4056211/

Sources

https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/dizziness-orthostatic-hypotension

https://www.ninds.nih.gov/health-information/disorders/orthostatic-hypotension

https://www.mayoclinic.org/diseases-conditions/orthostatic-hypotension/symptoms-causes/syc-20352548

https://www.houstonmethodist.org/blog/articles/2021/oct/why-do-i-get-dizzy-lightheaded-when-standing-up/

https://goaskalice.columbia.edu/answered-questions/fainting-and-low-pain-tolerance/

https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/fainting

https://academic.oup.com/europace/article/17/3/345/585876

https://en.wikipedia.org/wiki/Syncope_(medicine)

https://www.etymonline.com/word/syncope

https://byjus.com/question-answer/how-much-amount-of-blood-is-pumped-during-each-heartbeat-100-ml-55-ml-50/