All adults should have blood pressure measured routinely at least every 5 years until the age of 80 years. Seated blood pressure when measured after 5 minutes’ resting with appropriate cuff size and arm supported is usually sufficient, but standing blood...
Elevated arterial blood pressure is a major cause of premature vascular disease leading to cerebrovascular events, ischaemic heart disease and peripheral vascular disease. Blood pressure is a characteristic of each individual, like height and weight, with marked inter individual variation, and has a continuous (bell-shaped) distribution. The levels of blood pressure observed depend on the characteristics of the population studied – in particular, the age and ethnic background. Blood pressure in industrialized countries rises with age, certainly up to the seventh decade. This rise is more marked for systolic pressure and is more pronounced in men. Hypertension is very common in the developed world. Depending on the diagnostic criteria, hypertension is present in 20–30% of the adult population. Hypertension rates are much higher in black Africans (40–45% of adults). Blood pressure is expressed by two measurements, the systolic and diastolic pressures, which are the maximum and minimum pressures, respectively, in the arterial system. The systolic pressure occurs when the left ventricle is most contracted; the diastolic pressure occurs when the left ventricle is most relaxed prior to the next contraction. Normal blood pressure at rest is within the range of 100–140 mmHg systolic and 60–90 mmHg diastolic. Hypertension is present if the blood pressure is persistently at or above 140/90 millimetres mercury (mmHg) for most adults
The risk of mortality or morbidity rises progressively with increasing systolic and diastolic pressures, with each measure having an independent prognostic value; for example, isolated systolic hypertension is associated with a two- to three-fold increase in cardiac mortality.
A prehypertension category has been added to reflect the continium between normal and abnormal blood pressure
These account for over 80% of the cases of secondary hypertension. The common causes are:
■ Diabetic nephropathy
■ chronic glomerulonephritis
■ Adult polycystic disease
■ chronic tubulointerstitial nephritis
■ Reno vascular disease.
Hypertension can itself cause or worsen renal disease. The mechanism of this blood pressure elevation is primarily due to sodium and water retention, although there can be inappropriate elevation of plasma renin levels
All adults should have blood pressure measured routinely at least every 5 years until the age of 80 years. Seated blood pressure when measured after 5 minutes’ resting with appropriate cuff size and arm supported is usually sufficient, but standing blood pressure should be measured in diabetic and elderly subjects to exclude orthostatic hypotension. The cuff should be deflated at 2 mm/s and the blood pressure measured to the nearest 2 mmHg. Two consistent blood pressure measurements are needed to estimate blood pressure, and more are recommended if there is variation in the pressure.
When assessing the cardiovascular risk, the average blood pressure at separate visits is more accurate than measurements taken at a single visit.
Fat people have higher blood pressures than thin people. There is a risk, however, of overestimation if the blood pressure is measured with a small cuff. Adjust the bladder size to the arm circumference. Sleep disordered breathing often seen with obesity may be an additional risk factor. Most studies have shown a close relationship between the consumption of alcohol and blood pressure level. However, subjects who consume small amounts of alcohol seem to have lower blood pressure level than those who consume no alcohol. A high sodium intake has been suggested to be a major determinant of blood pressure differences between and within populations around the world. Populations with higher sodium intakes have higher average blood pressures than those with lower sodium intake. Migration from a rural to an urban environment is associated with an increase in blood pressure that is in part related to the amount of salt in the diet. Studies of the restriction of salt intake have shown a beneficial effect on blood pressure in hypertensives. There is some evidence that a high potassium diet can protect against the effects of a high sodium intake. Whilst acute pain or stress can raise blood pressure, the relationship between chronic stress and blood pressure is uncertain.
In chronic hypertension, the cardiac output is normal and it is an increased peripheral resistance that maintains the elevated blood pressure. The resistance vessels (the small arteries and arterioles) show structural changes in hypertension with an increase in wall thickness and a reduction in the vessel lumen diameter. There is also some evidence for rarefaction (decreased density) of these vessels. These mechanisms would result in an increased overall peripheral vascular resistance.
Hypertension also causes changes in the large arteries. There is thickening of the media, an increase in collagen and the secondary deposition of calcium. These changes result in a loss of arterial compliance, which in turn leads to a more pronounced arterial pressure wave.
Pulse wave velocity is a measure of arterial stiffness and is inversely related to distensibility. With each systolic contraction a pulse wave travels down the arterial wall before the flow of blood. Thus, the more rigid the arterial wall, the faster the wave travels. It can be measured but is not in routine use. Atheroma develops in the large arteries owing to the interaction of these mechanical stresses and low growth factors Endothelial dysfunction with alternations in agents such as nitric oxide and endothelins appear to be involved. Left ventricular hypertrophy, which results from increased peripheral vascular resistance and increased left ventricular load, is a significant prognostic indicator of future cardiovascular events.
Cerebrovascular disease and coronary artery disease are the most common causes of death, although hypertensive patients are also prone to renal failure and peripheral vascular disease. Hypertensives have a sixfold increase in stroke (both haemorrhagic and atherothrombotic). There is a threefold increase in cardiac death (due either to coronary events or to cardiac failure). Furthermore, peripheral arterial disease is twice as common.