So this is why I need to pee so often?

[Dave Zimmerly]

Searching the web on DCI articles, I came upon this site:

http://www.ucpress.edu/books/pages/8864/8864.excerpts.html

"Decompression sickness is not the only difficulty that faces the diver. Even just immersing the body in water up to the neck causes physiological changes. When you are standing upright on the seashore, there is a pressure gradient down your body due to the force of gravity, which causes the blood to pool in your legs. If you now immerse yourself in the sea up to your neck, this effect is counteracted by the external pressure of the water so that about half a litre of blood shifts upwards from the legs to the chest, distending the great veins and the right atrium of the heart and increasing your cardiac output. One consequence of stretching the atrial wall is that it alters the level of two hormones that influence water uptake by the kidney, and thereby stimulates urine production. This explains why you so often, and so annoyingly, need to pee just after entering the water."

Can any doctor types out there confirm this?

Regards,
Dave (aka "Squirt")

 

[Footslogger]

Pretty certain it's referrred to as "Immersion Enuresis" in medicine ...however I am not aware of the specific physiologic mechanism that triggers it.

'Slogger

 

[divingjd]

I've seen it referred to as "immersion diuresis." See the US Navy Diving Manual, Chapter 3, at 3-12.1.1, where it is discussed as a cause of dehydration. As the body cools, blood is withdrawn from the periphery to the core, resulting in increased kidney output. I remember covering it in the diving physiology portion of my DiveCon class. The version Dave posted is different, but I suppose both things could be happening, or maybe this just applies for partial immersion.

 

[shakeybrainsurgeon]

It's due to the reduction in the hormone ADH, or antidiuretic hormone. The kidneys actually produce enough urine per hour (several liters) to dehydrate us to death in a less than a day. After producing the urine in a microscopic set of filters known as glomeruli, however, much of the water is reabsorbed in another part of the kidney's plumbing known as the distal tubule. Thus, urine output is constant in the kidney... what determines how much fluid leaves the kidneys and goes to the bladder is how much urine is sucked back up again, and this, in turn, is controlled by ADH hormone. ADH is turned on and off by venous pressure --- too much pressure and the body is fluid overloaded, ADH is turned off and more urine is allowed to esacpe the kidneys and enter the wetsuit.

When we are fully immersed in water, the thoracic cavity's veins sense a fluid overload and signal a decrease in ADH. This, in turn, reduces the reabsorption of urine in the distal tubules and leads to increased urine output.

 

[GrandpaScuba]

It is also influenced by loss of body heat. As you lose body heat, your body "thickens" the blood by reducing the water content. This also contributes to immersion diuresis.

On the other hand, have you had your prostate checked?

 

[stillhope]

what does caffeine do to this mechanism? Does it affect ADH or have it's own special mechanism?

 

[shakeybrainsurgeon]

what does caffeine do to this mechanism? Does it affect ADH or have it's own special mechanism?

Caffeine inhibits ADH, as does cold temperature.

 

[sambolino44]

Are there any antiduretics that I can take? Is it actually wise to take them?

 

[super7]

ADH=vasopressin should do the job, but you don't want to mess with hormonal balance.
Get yourself a dry suit with a pee valve. This should have minimal or no side effects other than a lighter wallet

 

[HBO MD]

Ahhh guys, actually the increasing positive pressure is transmitted to the heart which releases a hormone known as Natriuretic Peptide. This is a diuretic...hence your need to pee.
Advice : hydrate before the dive.:blinking: