IV -
Why does high blood pressure exist?
4.1
- Most of the time, there is no explanation for this high blood pressure
But sometimes a disease is responsible for
hypertension:
the secondary arterial hypertensions
4.2
- The medical procedure
4.3 - Causes
4.3.1
- Drugs
4.3.2
- An hormonal disorder
4.3.3
- High blood pressure induced by the kidney
4.3.4
- A rare cause: presence of an obstacle in the aorta
4.3.3
- High
blood pressure induced by the kidney
Two kinds
of kidney diseases can be the cause of high blood pressure: renal artery
disease, which supplies blood to the kidney, and the disease of the
kidney itself.
1 - Disease of the
renal artery which supplies the blood to the kidney
Sometimes, the artery supplying the blood to the kidney is blocked and causes
a stenosis, often due to an arteriosclerosis. As the kidney is less supplied
in blood, it synthesizes substances supporting the supply of blood in the kidney.
These substances are called renin, angiotensin, and aldosterone, and involve
a rise in the blood pressure.
In this case, physicians speak
of a secondary hyperaldosteronism, i.e. that the aldosterone is not
secreted directly by the suprarenal gland but indirectly by a cascade
of chemical reactions due to the obstruction of the renal artery.
The causes of this renal
artery obstruction is often a thickening of the renal artery in women,
in particular young women; and in men, arteriosclerosis is more likely
to be responsible for the occlusion of the renal artery, especially
if the man is a smoker, older, or presenting other factors of cardiovascular
risk (too much cholesterol, diabetes mellitus).
What is the physician
doing?
He first confirms the diagnosis
of stenosis of the renal arteries which supply blood to the kidney.
A renal echography with doppler of the renal arteries is then practiced
and a renal arteriography is done afterwards if necessary.
With the results of these
investigations, the doctor either chooses to treat his patient by anti-hypertensive
drugs alone if the renal artery stenosis is not very significant, or
he may decide to open this artery.
For that, he has the possibility
of dilating the artery by using a small balloon directly placed in
contact with the stenosis and then inflated. Sometimes a small spiral
spring is introduced to maintain the renal artery in an open position.
Treatment is rarely surgical
using the use of a bridging i.e. a surgical by-pass of an artery taken
in another part of the body and installed after the renal artery stenosis.
The long-term complications
of a renal artery obstruction are primarily the destruction of the
kidney, which will secrete many toxic substances responsible for high
blood pressure. At this stage, the treatment consists in surgically
extracting the kidney which is not effective anymore.
2 - Kidney disease
All the serious and chronic
diseases of the kidney can induce a high blood pressure. The mechanisms
for a high blood pressure are mixed: on the one hand the kidney filters
less water and thus increases the pressure in the arteries, and on
the other hand, the kidney secretes substances which induce a contraction
of the arteries responsible for an increase in the blood pressure.
What is the physician
doing?
He detects the kidney disease
using biological tests in blood and in the urine, and adapts his treatment
to suit. Very often the treatment of the cause is not so effective
and the doctor has to use antihypertensive drugs in tablet form.
At a very advanced stage,
the treatment of a renal insufficiency by dialysis is necessary, which
reduces the high blood pressure.
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last reviewed on : 18 dec 2011 |
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