The pathogenesis of essential hypertension

Prof. Dr. Khairy Abdel Dayem Prof. Of Cardiology Ain Shams University
The pathogenesis of essential hypertension
ESSENTIAL Hypertension is diagnosed when the systolic blood pressure reaches or exceeds 140
mm Hg or if the diastolic blood pressure reaches or exceeds 90 mm Hg.
These values should be the last or the average of 3 measurement in 3 separate occasions in the resting posetabsirtive state with no smoking during the previous hour.
Blood pressure levels between 130 and 140 mm Hg systolic and 85 to 90 mm Hg diastolic should be viewed with suspicion as they commonly progress to hypertensive levels and are associated with increased complication rate.
These values are called high normal blood pressure and require continuous follow up and reducing excess weight and salt intake.
There are three basic pathophysiologic mechanism that may lead to elevated blood pressure:
A- Increased peripheral resistance:
ls commonest mechanism underlying elevation of diastolic blood pressure.
It is caused mainly by vaso
constriction of the systemic arterioles.
When the blood pressure is elevated for a long time the muscle layer of the arterioles hypertrophies and causes narrowing of the vessel even when relaxed.
This «Remodeling» is partly responsible for progressive elevation of the blood pressure even if its original cause is stable and may be responsible for the persistence of blood pressure elevation even it the cause is removed.
The peripheral ressistance is increased in response to a multitude of causes that include:
1- Increased activity of the sympathetic nervous system.
2- Increased activity of the renin angiotensin aldosterone system as angiotensin is a very potent vasoconstrictor.
3- Genetic predisposition inherited through a number of genes i.e. multifactorial inheritance.
4- Neurogenic factor, such as polyneuritis, increased intracranial tension etc.
5- Endocrine causes such as pheochormocytoma and hyperparathyroidism.
6- Renal artery stenosis which in duces the kidney to excrete angiotensin.
B- Increased blood flow and volume:
The cardiac stroke volume is increased in several conditions including:
1- Aortic regurgitation
2- Thyrotoxicosis
3- Patent ductus arteriousus and arteriovenous fistulae.
4- Hypertinetic heart syndrome.
These conditions usually lead to elevated systolic blood pressure but with time vascular remodeling may cause some elevation of diastolic blood pressure also increase in the blood volume also causes systolic and diastolic hypertension Several conditions may be involved e.g.
1- Genetic causes may also operate through increased blood volume by causing abnormalities of the renin angiotensin aldosterone system.
Angiotensin. in addition to being a vasoconstrictor also promotesthe secretion of aldosterone which causes sodium and water retention by the kidney.
Genetic defects in the ability of the kidney to excrete a sodium load cause «Salt sensitivity» and sodium and water retention.
2- Some patients have low renin level and expanded plasma volumes. The cause of this condition which exists in 20% of patient with essential hypertension is unknown but may be due to excessive production of yet unidentified mineralocorticoid hormone.
3- Renal prenchymal disease decreases the ability of the kidney to excrete water and electrolytes resulting in sodium and water retention, increased intravascular volume and hypertension.
4- Endocrine causes such as cushing syndrome, acromegally and primary aldosleronism all increase blood pressure by increasing intravascular volume.
5- Drug induced hypertension that may follow the chronicuse of steroids. and oral contraceptives.
C - decrease arerial compliance:
ls the third major rnechanism of elevation of blood pressure.
It affects mainly the systolic component and may lead to «isolated systolic hypenertsion“.
This is defined a systolic blood pressure over 140 mm Hg in the presence of a diastolic blood pressure less than 90.