Immersion Diuresis 1o1 - The Well-known Urge to Pee

immersion diuresis - WHY do we pee so much when Freediving?

Have you ever experienced headaches after a long day in the ocean? Have you ever wondered, why you need to pee so much and so often everytime you are SCUBA diving, freediving, spearfishing, surfing, snorkelling or even just swimming in the ocean?

Well, you should know there is two types of people when diving, the ones that pee on their wetsuit and that ones that lie about it. Here we will make our best to explain it.

Please remember, as any other article published by us, this is entirely user responsible guide, meaning that nor OceanSense Freediving, its instructors or representatives could take responsibility for any injuries or any other consequences caused due to practicing any of this information. Never dive alone, and always dive within your and your buddy’s limits.

How does our body work?

On a regular basis, our body process liquids in it and expel the excess through urine. The kidneys filters waste and toxins from our blood and create pee.

The urinary tract is a pathway that includes the:

  • Kidneys: Filter waste from the blood and produce urine.
  • Ureters: Take pee from the kidney to the bladder.
  • Bladder: Holds pee until it’s time to go to the bathroom.
  • Urethra: The tube that carries urine from the bladder out of the body when you pee.

What’s Pee Made Of?

When blood goes through the kidneys, water and some of the other stuff that is in blood (like protein, glucose, and other nutrients) stays in the bloodstream, but all the other stuff, waste and toxins is filtered and added to the urine. Urine is composed by water, urea (waste from broken protein), urochrome (pigmented blood product), creatinine (waste from breakdown of muscle), salts, byproducts of bile coming from the liver, and ammonia.

What causes diuresis?

Diuresis is defined by science as the increased urination and the physiologic process that produces such an increase. It involves extra urine production in the kidneys as part of the body’s homeostatic maintenance of fluid balance. Many factors can trigger this effect, internal and external to our body like from drinking some extra water to even heart deceases. We are going to focus on the main reason that would increase our urination when freediving, the well known urge-to-pee or the p-phenomenon.

Cold induced diuresis

When our body feels cold, the peripheral vasoconstriction happens. Our blood starts to go to our core from our limbs. This increases the pressure on the kidneys, indicating extra liquids and making them start the process of excretion of superfluous fluids as an attempt of compensate that extra pressure.

If we know that our body’s natural temperature is 36 oC and the heat transfer coefficient from water is 25 times faster than the air. So unless you are in in 36 oC or more, your body will activate the thermostat and make you pee.

The Mammalian Reflect

As a freediver you may already know very well this response of your body, or maybe at least may heart about it.

When we start to hold our breathe, we trigger a response in our body that help us hold our breath and mainly protects us. One of this responses is the peripheral vaso constriction, where the vessels from your peripheries (legs and arms) get constricted, forcing the blood to me moved to our core and head, this to keep our tissues and brain fully loaded with higher level of O2. 

This extra blood volume includes our whole urinary track, therefore our body think we are overhydrated and need to expel that extra amount out of water, so our kidneys extract more water than they normally would, load the bladder and pee-riod

This is a diuresis caused due to immersion. 

So, why the headache after diving then?

If our body has expelled more water than it should, thinking it had more than needed, once you are our of the water and your MDR has been deactivated, our body realizes that now we are dehydrated, and not only mildly. Guess what! A headache is one of the first signs of dehydration (after being thirsty of course).

Should we avoid peeing in our wetsuits then?

Short answer, yes avoid it and if done, make sure you rinse and keep yourself hydrated.

What other consequences besides a post diving headache?

Being dehydrated can actually reduce breathhold time by reducing blood volume available to transport red blood cells and carbon dioxide. Your muscles performance is based in many things, including amount of water, so they won’t be in peak conditions if you are dehydrated, be ready for some underwater cramps, it also could increase the possibility of absorbing Nitrogen, therefore the possibility of getting DCS (decompression sickness). 

Want to increase your breathhold? Try this tips!

So, now you know, drink plenty of water before, during and after your in-water sessions. You may not be thirsty at the beginning, because your body thinks you are overhydrated, so force yourself, be disciplined. 

immersion diuresis

Freediving Instructor Gonzalo


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