Diuretics add to the dehydration that occurs with exercise from sweating, insensible and respiratory water loss; the diver also has to take into consideration some additional concerns for fluid loss and replacement.
1. Scuba tanks have extremely dry air inside. As this air is taken into the lungs and saturated--nearly twice the normal amount of water is lost from the body.
2. Negative pressure breathing causes divers to lose about 350 cc/hour from their circulating blood volume, a phenomenon called immersion diuresis and seen also in snorkelers and swimmers.
3. Cold inhibits anti diuretic hormone, causes peripheral vasoconstriction, driving fluid back into the core and stimulating diuresis resulting in losses of plasma volume.
4. The hypercarbia (high blood carbon dioxide) associated with diving decreases anti diuretic hormone, promoting fluid loss from the plasma volume.
5. Diuretics such as alcohol, coffee, tea also contribute to fluid losses, contributing to predive dehydration.
6. Khosla in 1979 found that there is a 4% hemodilution in early immersion from ECF (extracellular fluid) shift into the bloodstream, resulting in an increase in central blood volume. This alters stimulation of pressure and volume receptors, leading to further inhibition of ADH (anti-diuretic hormone) and fluid loss.
7. In addition to the above, the state of chronic hypovolemia (low fluid vloume) and hypokalemia (low serum potassium) caused by oral diuretics is dangerous to divers by increasing their susceptibility to decompression illness and cardiac arrhythmias, respectively.
start in reading about this
would be in "Diving Medicine", Bove and Davis, Philadelphia, WB
1990, ed 2.
Also try Edmonds
C., Lowry C, Pennefather J.:Diving and
Oxford, Butterworth-Heinemann, 1992,ed 3., and Bennett and Elliott (Eds): The Physiology and Medicine of Diving. London, WB Saunders, 1993, ed 4.
The importance of entering a dive well-hydrated cannot be over-stated. Prehydration of divers should include regular ingestion of fluids several hours before, 15-20 minutes before and between dives, particularly if multiple dives are to be made each day. The urine should be "clear and copious", the urine test for divers proposed by Dr. Jeff Davis.
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