2. Why is knowing blood pressure important?
Raised blood pressure is the most important worldwide cause of death and disability. Epidemiological studies in many countries have established that increased blood pressure leads to higher risk of heart attacks, strokes and kidney disease. Blood pressure levels are normally given as two figures, systolic (the peak pressure at each heartbeat) and diastolic (during the momentary rest between each beat), both expressed in millimetres of mercury (mmHg). Thus, a typical reading might be 120/80 mmHg.
Even quite small increases in blood pressure, if they persist, can have significant effects. For example, an average increase in the population of 2 mmHg in systolic blood pressure increases the death rate from stroke by ten per cent and from coronary heart disease by seven per cent.
Against this background, repeated blood pressure measurements are a standard part of medical examination. Monitoring individuals’ blood pressure is vital for prevention and treatment of disease, and especially for those who have other risk factors for cardiovascular disease, or have already shown evidence of such disease, and for the elderly. It is also important for pregnant women, for early warning of the possible onset of pre-eclampsia , a hazardous condition associated most strongly with high blood pressure.
Blood pressure measuring devices need to be reliable in heavy use, and suitable for a wide variety of patients. It is increasingly common for patients to measure their own blood pressure at home, either as single measurements or at regular intervals over a 24-hour period. This ambulatory monitoring, recorded while the patient goes about their daily routine, can give more reliable results than blood pressure measurements in the clinic.
Epidemiological studies enroll large numbers of subjects who may be followed up for years or decades. This calls for standardised blood pressure measurement to ensure valid data are gathered at many different sites, and the measurements are comparable over time.