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Hypertension is, unfortunately, a very common disease. In industrialized countries (= western style), about 20% of the population suffer from this disease.
By definition, hypertension is present when the systolic pressure is higher than 160 mmHg and/or the diastolic pressure higher than 100 mmHg.
Remember that the blood pressure is determined by
a) the heartand
b) the peripheral resistance.
If the heart pumps too much, either by increasing the frequency or increasing the stroke volume (or both), then the blood pressure will increase. This is called hyperdynamic hypertension.
Or, the peripheral resistance (which is caused by the resistance of all the blood vessels together) can be too high, for example by vasoconstriction of the blood vessels. This is called resistance hypertension.
It is important to note that a brief increase in blood pressure is NOT hypertension. For example, during exercise, it is necessary to increase the blood pressure to get more blood to the exercising muscles.
But if the blood pressure is too high all the time (chronically), then this is hypertension.
Therefore, when making a diagnosis of hypertension, it is important to measure the blood pressure several times, on different days, to be sure that a patient suffers from hypertension.
This can be caused by an increase in:
An increase in extracellular volume will increase venous blood, which increases the venous return to the heart, which increases the diastolic filling, stretching of the ventricles (Frank-Starling mechanism), and increase the cardiac output.
Increase sensitivity to catecholamine’s can be caused by an increase in cortisol (from the adrenal cortex) and/or an increase in the thyroid hormones (T3, T4) in the case of hyperthyroidism.
Resistance hypertension is mainly caused by:
Vasoconstriction can be due to:
For example, because the heart is pumping more and against a higher pressure (after-load!), hypertrophy of the left ventricle will occur.
If this condition last too long, then the left ventricle will suffer (coronary arteries), possibly leading to cardiac failure.
Furthermore, several organs, such as the kidneys, will “protect” themselves from this continuous high pressure by vaso-constricting the blood vessels to those organs.
In contrast to all this knowledge, the reason why somebody develops hypertension are less well known.
Stress? Managers, pilots, personality (“frustrated fighter type”), salt-sensitive patient, sensitivity to catecholamine’s are all possibilities but not yet proven or clarified.
In 10% of the patients, those that suffer from Secondary Hypertension, the cause of hypertension is due a definite disease (which makes it potentially treatable):
Renal diseases:
Many diseases of the kidney may induce renal ischaemia, which in turn induces the release of renin into the blood stream. This in turn will activate angiotensinogen into angiotensin I which leads to an increase in angiotensin II (in the lungs by ACE). This will constrict the blood vessels and increase the blood pressure.
Hormonal diseases:
A tumour in the adrenal cortex releases unregulated amounts of aldosterone, leading to Na+ retention and increase in extracellular volume.
Inadequate ACTH release (neurogenic or tumour in the hypophyses) or a tumour in the adrenal cortex increase glucocorticoid in the plasma. This increases the catecholamine effect (increased cardiac output) and mineral corticoid effect (increased Na+ retention).
A tumour in the adrenal medulla produces uncontrolled catecholamine’s, which increases epinephrine and norepinephrine, thereby inducing both hyperdynamic and resistance hypertension.
Environmental factors:
Foetal factors.
A low birth weight is often correlated with hypertension later in life.Diabetes.
Insulin resistance > metabolic syndrome > HypertensionPregnancy.
Normally, cardiac output (CO) increases while peripheral resistance (PR) decreases, so blood pressure stays normal
But sometimes, hypertension develops with possibility of developing pre-eclampsia.
Pre-eclampsia is hypertension during pregnancy with proteinuria (loss of proteins in the urine). This can lead to eclampsia: convulsions, cerebral oedema, clotting abnormalities, foetal death, maternal death.
Many! And serious complications:
