Immersion Diuresis

[scubakat]

I don't recall who posted the link to the Rodale's article on dehydration but thanks!

So, from reading the article I deduced that since "dehydration lowers blood volume, causing your body to shunt blood away from skin and muscles and reroute it to vital organs" and that in turn stimulates the kidneys to produce urine, that dehydration might actually contribute to immursion diuresis?

Kind doc's, Is there any sense or truth to that deduction?

thanks!
kate

 

[large_diver]

Hi Kate -- that was me who posted the article

I've seen a couple of different blurbs on ID -- some say it is due to the pressure; some say it is due to the heat loss/cold the body experiences while diving. Not sure what effect dehydration has on it.

 

[rcohn]

Diving Physiology in Plain English
DAN Item: 401-1400

by Jolie Bookspan, Ph.D.
DESCRIPTION
246 pages
7 chapters plus glossary, appendix, figures and index
Softcover
1995

CHAPTERS:

Decompression Tables and Computers
Immersion Effects
Diving in Cold and Heat
Gender Facts and Folklore
Diving Injuries
Exercise
Nutrition

In non-scientific terms, Dr. Bookspan discusses decompression tables and computers, the effects of immersion, diving in cold and heat, women and men in diving, and then discusses nutrition and fitness for all divers. This book covers diving injuries and marine animal injuries as well. Bookspan also addresses the scientific meaning behind many questions the inquisitive diver has wondered about, such as: Are women more susceptible to DCS than men? Do women chill more quickly than men?

This is a useful book, although I'm aware of at least one error, that explains this type of question. Your library might have it. It is available from DAN and other sources of books such as Amazon, etc.

Ralph

 

[Dr Deco]

Dear Kate:

I doubt that dehydration contributes to immersion diuresis. This increase of urination is an effect that results when blood volume is shifted from the legs to the trunk and cardiac output (= blood flow from the heart) is increased. This results because more blood can enter the heart chambers (= increased preload). The increase in flow will occur also through the kidneys. One of their functions is to regulate the volume of blood. Sensing the shift as an increase in volume, the kidneys will increase their output of urine while the diver is immersed.

Curiously, any effect that shifts this volume will produce a similar effect. In space with null gravity, this thoracic shift of blood also occurs and increased urination results in a loss of blood volume. Upon return to Earth and unit gravity, the blood shifts to the legs, the blood volume falls, and astronauts become light headed and prone to fainting.

Dr Deco

 

[scubadoc]

Here is the physiology of head out immersion and 'immersion diuresis':

Respiration

Pressure outside chest wall is now positive, averaging about 10 cmH2O ("negative pressure breathing"). Intrathoracic pressure less negative at end-expiration. Negative pressure breathing causes divers to lose about 350 cc/hour from their circulating blood volume from immersion diuresis, seen also in snorkelers and swimmers.

Result: about a 60% increase in the work of breathing.

Cardiovascular

Increased venous return due to elevated abdominal pressure and decreased pooling in peripheral veins. Cold inhibits anti-diuretic hormone, causes peripheral vasoconstriction, driving fluid back into the core and stimulating diuresis resulting in losses of plasma volume. The hypercarbia associated with diving decreases anti-diuretic hormone, promoting fluid loss from the plasma volume.

Increased venous return leads to increased central blood volume (approximately 500 ml). Right atrial pressure increases from about -2 to +16 mmHg.

Cardiac output and stroke volume increase about 30%.

Renal

Increased intrathoracic blood volume is thought to be the basic cause of this phenomenon that also includes a loss of sodium and potassium, atrial natriuretic factor playing a large part in the process. The causes are still being debated, however.

Urine flow increases 4-5 times but osmolal clearance increases very slightly.