Can anyone tell me what 'Normal' ranges are for blood pressure?
© 1997 Andrew Lundin, M.D. All rights
reserved. Reproduced with permission.
It depends mostly on age. Children and adolescents should
always be fairly low. I am not sure of the ranges. For adults the
most often recommended upper limit is less than 130/90 mmHg. However,
anyone who has BP levels lower than this and feels perfectly functional
is in a good position. Those who have higher blood pressures and
feel nonfunctional when the BP comes below this number, in most instances are storing
extra but invisible fluid amounting to several lbs. In older patients
one must be careful not to bring the BP down too fast. If arteries
are narrowed then a stroke or heart attack could occur. Nevertheless, when
done with appropriate caution, in my experience, almost everyone
can be made normotensive on dialysis.
For those that have had a problem with low bp how do
you correct the problem?
Blood pressure is controlled by an interaction between
the heart and peripheral arterioles (small arteries) that are in line
just before the capillaries (small tufts of vessels that connect the arteries
and veins, in the kidney they are called glomeruli). Think of the
vascular system as two adjoining trees connected only at the smallest branches.
A fistula or graft would be making a connection between two
of the larger branches.
To get to the point, high blood pressure is due to an increase
in the cardiac output of blood or increased constriction of the
arterioles or variable combinations of both. It is thought that the increased
cardiac output comes first stimulating a constricting response
in the arterioles that eventually dominates the picture. Most antihypertensive
medications today are directed at dilating the arterioles. It is not
clear whether the hypertensive effect of EPO in some patients is due
to increase blood volume (increased cardiac output) or release of substances
that constrict the arterioles.
Causes of hypotension must therefore be due to decreases
in cardiac output or dilatation of the arterioles. A diseased heart
could cause the former but that is unusual. More likely, if the heart is
involved, the low BP is due to volume depletion (being below dry weight).
This is seen in patients who have good appetites and are eating well.
Blood pressure medications often work better when the patient is dry.
It can be a vicious cycle. Some medications like Ca channel blocks
and ACE inhibitors can cause fluid retention, which negates their antihypertensive
benefits. In non-ESRD hypertensive patients diuretics are often required.
For dialysis patients getting to dry weight offers the ability
to stop BP meds.
- Pete Lundin, M.D.
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