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[IP] re: ace inhibitors and dehydration

I work in a cardiovascular and pulmonary rehabilitation program, where we do
a lot of education regarding the importance of hydration, particularly in
the warm weather and *with exercise*... and *especially* for people on
ace-inhibitors as well as other BP meds.  The reason for the extra concern
in the ace-inhibitor situation is that the "renin-angiotensin-aldosterone
system" (on which these meds act) is normally responsible for promoting salt
retention and resultant water retention & elevation of arterial blood
pressure.  In addition, angiotensin II (whose formation is blocked by the
ace inhibitor) is normally a stimulator of thirst - increasing fluid intake,
and thereby increasing plasma volume.  It is also a potent
"vasoconstrictor".... meaning that it constricts (decreases) the diameter of
arterioles throughout your body, thereby increasing blood pressure.  In
certain physiologic situations, vasoconstriction & blood pressure increases
such as this are necessary.... going from lying down to standing quickly,
and in dehydration, for example.  For people on ace-inhibitor therapy,
maintaining hydration then, (and thereby plasma-volume) becomes especially
important.  "Thirst" will not always be a good guide in this situation, as a
result of the fact that we've blocked the thirst mechanism.

	Apologies for all the physiology here.... but it always saddens me to hear
that the medical community is not teaching people about the "why's".  I
always find that when I understand the physiology, the "why's" behind
something, then I "get it"... and I'm more apt to "follow the medical
advice" that way.  If it makes sense to me, then can I embrace it.  I notice
the same in the patients with whom I work.  Understanding makes all the
difference in the world, doesn't it?  :)

Delaine M. Wright, MS, CDE

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