The term ‘hypertension’ is used to describe a level of blood pressure that, taking all other cardiovascular risk factors into account, would benefit the patient if reduced. Blood pressure readings where systolic and diastolic values
are below 130 / 85 mmHg, respectively, are
considered normal.
Essential hypertension
Essential hypertension (hypertension of unknown cause) is very common in the developed world and accounts for 95% of all cases. Treatment aims to prevent complications, which can be serious, primarily cardiovascular and renal disease. Sometimes complications, such as heart failure, cerebrovascular accident or myocardial infarction, are the first indication of hypertension, but often the condition is symptomless and is only discovered during a routine examination.
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Risk factors
Risk factors for hypertension include obesity, diabetes mellitus, family history, cigarette smoking, a sedentary lifestyle and high intakes of salt or alcohol. Stress may increase blood pressure, and there is a well-documented link between low birth weight and incidence of hypertension in later life
Malignant (accelerated) hypertension
This is a rapid and aggressive acceleration of hypertensive disease. Diastolic pressure in excess of 120 mmHg is common. The effects are serious and quickly become apparent, into the retina, papilloedema (Oedema around the optic disc), encephalopathy (cerebral edema) and progressive renal disease, leading to cardiac failure.
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Secondary hypertension
Hypertension resulting from other diseases accounts for 5% of all cases
Effects and complications of hypertension
The effects of long-standing and progressively rising blood pressure are serious. Hypertension predisposes to atherosclerosis and has specific effects on particular organs.
Heart
The rate and force of cardiac contraction are increased to maintain the cardiac output against a sustained rise in arterial pressure. The left ventricle hypertrophies to increase its contractile strength, but begins to fail when compensation has reached its limit. This is followed by back-pressure and accumulation of blood in the lungs (pulmonary congestion) and hypertrophy of the right ventricle, and eventually by right ventricular failure. Hypertension also predisposes to
ischaemic heart disease and aneurysm formation
Brain
Stroke, caused by cerebral haemorrhage (p. 195), is common, the effects depending on the position and size of the ruptured. vessel. When a series of small blood vessels rupture, e.g. microaneurysms, at different times, there is progressive disability. Rupture of a large vessel causes extensive loss of function or death.
Kidneys
Autoregulation mechanisms (p. 97) protect the kidneys, to an extent, from fluctuations in systemic blood pressure but sustained hypertension causes kidney damage. If damage is sustained for only a short time, recovery may be complete. Otherwise the kidney damage causes further hypertension owing to activation of the RAAS, progressive loss of kidney function and kidney failure.
Blood vessels
High blood pressure damages blood vessels. The walls of small arteries become hardened, and in larger arteries the development of atheroma is accelerated. If other risk factors for vascular disease are present, such as diabetes or smoking, damage is more extensive. The vessel wall may become so badly weakened by these changes that an aneurysm develops, and as the blood vessels become progressively damaged and less elastic, hypertension worsens. The capillaries of the retina and the kidneys are particularly susceptible to the effects of chronic hypertension, leading to retinal bleeding and reduced renal function. Damaged retinal blood vessels are clearly visible through an
ophthalmoscope on examination, and the first indication of hypertension may be picked up during a routine eye test.
Pulmonary hypertension
Normally, the pulmonary circulation is a low-pressure system, to prevent fluid being forced out of the pulmonary capillaries into the alveoli. When blood pressure rises, alveoli begin to fill with fluid (pulmonary oedema), which blocks gas exchange. Rising pulmonary blood pressure may result from left-sided heart failure or other problems with left ventricular function, when blood accumulates in the pulmonary circulation because the left ventricle is not pumping efficiently. Lung disease can also increase in pulmonary blood pressure because of destruction of lung capillaries, e.g. in emphysema. Primary pulmonary hypertension, where there is no identifiable cause, is rare.
Hypotension
This usually occurs as a complication of other conditions, such as shock or Addison’s disease . Low blood pressure leads to inadequate blood supply to the brain. Depending on the cause, unconsciousness may be brief (fainting) or more prolonged, possibly causing death. Postural hypotension is an abrupt fall in blood pressure on standing up suddenly from a sitting or lying position. It causes dizziness and occasionally syncope (fainting). It is
most common in older people, whose baroreceptor reflex
does not respond quickly enough to maintain blood pressure during sudden changes of body position.
