By guest blogger Dr. Suzanne Gaskell
Let’s face it: Most of us have committed the cardinal sin of peeing in our wetsuits — even if we say we haven’t. We either spend half our dive with the unrelenting urge to ascend, frantically peel off our neoprene skin and run to the bathroom, or we just…go. This unpleasant experience can convince people they have a bladder problem, or at the very least, deter them from drinking enough water before a dive. In turn, dehydration can increase the risk of decompression sickness, so it’s important that divers fully understand the science behind why this urge to pee happens when they submerge.
Immersion diuresis literally means “water loss due to immersion.” It is thought that there are two main mechanisms behind the process: low temperature and increasing water pressure.
Water is an excellent conductor of heat, hence the need for wetsuits to keep the body warm even in tropical seas. Low temperature stimulates the peripheral blood vessels to constrict, just as they do in your hands and feet on a cold day. This survival mechanism reduces the surface area available for heat loss and shifts blood to the core, keeping the more important organs, i.e., the heart kidneys and brain, perfused with blood.
From our first dives we are all taught how pressure increases with depth. Perhaps you have noticed how your weight belt suddenly gets loose the deeper you dive? This is the effect of the water pressure compressing us from all directions. In the same way this pressure also compresses the veins in our arms and legs. Veins have a relatively thin muscular wall when compared to arteries, making them more easily collapsible. When they collapse, the blood they carry gets pushed to the body’s core.
Both mechanisms result in the redistribution of blood from the peripheries to the larger veins in the chest. Thus, more blood is being delivered to the heart, specifically the right atrium, which is the receiving chamber for blood to the heart. With more blood being delivered, the muscular wall stretches. Baroreceptors (pressure receptors) detect this increase in blood pressure, which in turn, triggers the release of Atrial Natriuretic Peptide (ANP). One of the net effects of this powerful vasodilator (blood vessel relaxant) is water loss. It has been shown that effects of its release can still be felt up to 12 hours after diving.
If there is more blood supplying the heart, it follows that a larger volume is also going to the other organs, notably the kidneys, which are the filters that produce urine. If there is more blood flow through the kidneys, there is more urine produced.
The intricacies of these mechanisms are quite complicated and there is still a lot more work to be done in the area of dive-medicine research, but here we’ve explained the basics and highlighted the most important point: diving dehydrates us.
So the takeaway from all of this is to remember to keep well hydrated when diving and don’t let the urge to pee put you off drinking plenty of water. If the urge hits on your dive (and it will), you’ve got our permission to go with it. However, if the urge to pee persists long after you’ve surfaced, or symptoms such as burning and stinging when you go appear, this could signify a water infection and you should seek medical advice.