Both these effects can develop in any person having high blood pressure. After a few years of treatment the chances of developing any of them will be reduced. The risk will become roughly proportional to the lower blood pressure level one would have reached with treatment, not to the higher level one had before one’s treatment started.
- Heart – Partial blocking of the coronary arteries (the blood vessels supplying the heart) causes pain in the joint of the chest when walking up the hills or stairs (angina).
Complete blockage of a coronary artery destroys part of the heart muscle (a heart attack, coronary thrombosis or myocardial infarction-these terms are usually used interchangeably).
- Aorta – The aorta is the largest of all the arteries in the body and normally the most elastic. After years of high blood pressure and high blood cholesterol it becomes less elastic, with its lining roughened by plaque, and stretches to produce a swelling (aneurysm) rather like a sausage-shaped balloon usually in the upper abdomen. Blood clots may form on this roughened aortic lining, gradually building up to an inch or more in depth. Such a clot may break loose as an embolus, which may lodge further down in an artery supplying a kidney or in a thigh artery, interrupting the blood supply to one kidney or leg.
- Legs and Feet – Partial blocking by plaque of the arteries in the lower trunk or higher causes pain in the calf on walking uphill (claudication). Complete blockage of the leg arteries (either from an embolus originating in the aorta or from clots forming in the thigh arteries) cause gangrene in the toes or foot.
- Brain – Roughening of the carotid arteries (on both sides of the front of the neck) may cause a build up of blood clots, which may break up intermittently into very small fragments (called micro-emboli). These travel up to the brain, causing a temporary loss of vision as they pass through the retina (the back of the eye) and giddiness, faintness or confusion lasting a few seconds (transient ischemic attacks or TIAs). They then break up into such small particles that they cause no further trouble.
If a blood clot in a carotid artery fails to break up into microemboli, but instead travels intact as a large embolus up into the brain it may completely block the supply of blood to part of the brain, causing an ambolic stroke.
Kinking of partially blocked arteries in the back of the neck provoked by looking upwards and tilting the head backwards on the neck (as when hanging out washing or looking up at an aeroplane) may cause temporary blocks or giddiness lasting a few seconds (vertebrobasilar insufficiency).
- Eyes – For reasons not fully understood, but presumably connected with changes in blood circulation, people with high blood pressure are more likely than others to develop obstructed arterial circulation in the eye (central retinal artery occlusion), obstructed nerves in the eye (central retinal venous thrombosis) or retinal detachment. All these are less likely to occur when high blood pressure is well controlled by treatment.
- Other Organs – Virtually any other organ in the body can have its blood supply impaired or stopped by all those blocking effects which are rare except in exceptional circumstances.
- Heart – High blood pressure means extremely hard work for the heart, which has to pump against the increased resistance of a generally narrowed and tightened-up artery system. Eventually the heart doesn’t actually burst, but fails to pump blood out of the left ventricle (the left side of the heart) as fast as it comes into the lungs from the right ventricle. If this happens suddenly, it causes acute heart failure, with extreme breathlessness and a sensation of drowning in dammed up blood). If it happens slowly, You gradually feel more and more short of breath, first on exercise eventually even at rest, often with a dry cough and swollen ankles.
Strictly speaking, heart failure of this kind is not really a bursting effect, but it behaves like one (it is almost entirely preventable by good control of high blood pressure).
- Aorta – As mentioned in the section on blocking effects, aneurysms (swellings) can occur in aorta. Such an aortic aneurysm can burst at very high levels of blood pressure, or at lower pressures if it has become very large and its wall has become weaker. This usually happen in two stages: first, a split in the aortic lining so that blood spurts into and between the layers of the aortic wall (this usually takes place over several hours causing chest pain easily mistaken for a coronary heart attack) and, second, a split into the outer aortic wall, fatal within seconds or minutes.
- Brain – Aneurysms in brain arteries are small bubble-like distensions of the artery wall. They may occur because you have had a local weakness in the artery wall since you were born or because a normal artery wall has been stretched by high blood pressure. They may occur on the surface of the brain (when they are usually of the type caused by high blood pressure).
If a surface aneurysm bursts it releases blood into the cerebrospinal fluid which bathes the brain (subarachnoid haemorrhage), causing very severe headache, so suddenly that people often think someone has struck them from behind, but with no immediate loss of consciousness or paralysis. If an interior aneurysm bursts (intracerebral haemorrhage) this usually destroys part of the brain, sometimes with loss of consciousness and usually with paralyses usually of one side chemi (plegia), developing either immediately or within an hour or two.
- Eyes – The retina of the eye is the only part of the body where the smallest arteries (arterioles) are directly visible-they can be examined easily using an instrument called ophthalmoscope. At very high pressure (diastolic always more than 120 mm Hg, sometimes as much as 180 mm Hg or even more) fluid begins to leak from these arterioles into the retina, causing blurred vision, and visible evidence of imminent serious risk of brain haemorrhage, kidney failure or permanent blindness from destruction of the retina. It is therefore important for anyone with a diastolic pressure above 120 mm Hg to have the retina of both eyes examined with an ophthalmoscope either in a dark room or after the pupils of their eyes have been dialated with suitable eye drops. If blood pressure is not reduced from this extremely high level within a few hours, there may be substantial bleeding from these arterioles, with permanent damage to vision.
Similar changes may occur in people with diabetes at lower pressures-one reason why it is important for them to keep good control of both their diabetes and their blood pressure and to have their eyes checked at least once a year.
- Kidneys – At very high pressures (and as with eye damage, sometimes sooner and at lower blood pressure in people with diabetes), the smallest arteries (arterioles) in the kidneys begin to burst in the same way as those in the retina, resulting in rapid but still reversible loss of kidney function and eventually (but usually only after weeks or months without treatment) irreversible kidney failure. They first easily detected sign of this is the appearance of protein in the urine (easily and quickly) detected by a simple test on a urine sample.
However, one needs to remember that high blood pressure is not the only cause of these complications, so in no way can one’s treatment completely eliminate the possibility that one of them may occur in the future, although it will greatly reduce it.
As one might expect, because the blocking effects result from many years of sustained high blood pressure, usually combined with high cholesterol and often with smoking, they are only partly and slowly reversible by reducing blood pressure once they have occurred. Treatment for high blood pressure and reduction of blood cholesterol and stopping smoking then makes all of them roughly 20 percent less likely than in people with similar blood pressure who have had no treatment, but the reduction in risk is gradual and incomplete. Hence the emphasis is on controlling blood pressure before any of these complications occur. Prevention really is the best medicine.
All the bursting effects are either largely or completely preventable by well controlled treatment for high blood pressure. Kidney and eye damage can be virtually eliminated, and so can heart failure as a direct result of uncontrolled high blood pressure. Since coronary heart attacks can be reduced only by 20-30 percent and some of these destroys enough heart muscle to cause heart failure, this cannot be entirely eliminated as an eventual consequence, but it can be made extremely unlikely for many years. Strokes from all causes are reduced by about 45 percent by wellmaintained treatment but some strokes still occur because there are many other contributory causes apart from high blood pressure. High blood cholesterol and smoking both make stroke more likely, but are much less powerful causes of stroke than of coronary heart disease.