Scubadoc (aka Ern Campbell, MD) recently responded to this question as follows:
"Posted: Tue Oct 12, 2004 11:23 am Post subject: Diuretic treatment for Hypertension
I take a blood pressure pill called Istin plus a Dieuretic pill and have controlled Blood pressure 140 - 85. As the dieuretic is a new idea by my doctor I need to know if the problem of DCS due to dehydration is increased. I suspect it is but am not sure.
Good Morning Gordon:
Your suspicion is right on, as there is evidence that diuretics can cause dehydration and dehydration is one of the factors that can increase the risk for decompression sickness. In addition, hypertensives are also at increased risk for an adverse coronary event.
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 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 high 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 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 and fluid loss. [pee factor]
7. In addition to the above, the state of chronic low blood volume and low potassium blood levels caused by oral diuretics is dangerous to divers by increasing their susceptibility to decompression illness and cardiac arrhythmias, respectively.
A good start in reading about this problem would be in "Diving Medicine", Bove and Davis, Philadelphia, WB Saunders, 1990, ed 2.
Also try Edmonds C., Lowry C, Pennefather J. Diving and Subaquatic Medicine. 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.
More study links for diuretics and dehydration:
Hypertension and Diving
http://www.scuba-doc.com/hyptdiv.htm
Medications, Drugs and Diving
http://www.scuba-doc.com/drugsdiv.htm
Let me know if there are any other questions.
scubadoc"
Best regards.
DocVikingo
