BLOOD PRESSURE

 

What is high Blood Pressure?

 

High Blood Pressure (or “hypertension” as it is called by doctors) is a common condition, which affects between one in five and one in ten of the population, particularly in middle age. The rest of the population has a normal blood pressure.

 

The term ‘blood pressure’ is applied to the pressure of blood in the arteries, which conduct blood from the heart to the rest of the body. The circulation requires pressure to maintain the flow of blood.

 

Systolic and diastolic pressure

 

The heart is not a continuous pump. It beats and than relaxes. Each heartbeat produces a pressure wave. The peak or maximum of this wave is called the systolic pressure and the trough or lowest point between beats is the diastolic pressure. The height of the systolic pressure is partly due to the amount of blood expelled when the heart contracts and partly to the resistance to flow of blood produced by the blood vessels. In younger people the larger blood vessels are fairly elastic: the ‘give’, which this produces, tends to damp down the pressure wave.

Measuring blood pressure

 

Pressures are usually measured with an instrument called a sphygmomanometer. A cuff containing a rubber balloon is placed around the upper arm and inflated to a pressure above the systolic so that no blood can get through. Pressure in the cuff is then slowly released while an observer listens over the artery at the elbow below the cuff. As the blood starts to flow again at the height of the pressure wave it creates a thumping noise and the pressure in the cuff at this time is equal to the systolic pressure. As the pressure in the cuff falls further the sound suddenly becomes muffled and then disappears, as the flow is no longer obstructed. Some doctors take the point of muffling as the diastolic pressure, but the majority now use the point at which the sounds disappear.

 

What is normal blood pressure?

 

For a young person a typical reading might be 120 systolic and diastolic. These values are expressed in millimetres of mercury and it is conventional to record the values as systolic/diastolic e.g. 120/80. Blood pressure is an individual is not fixed property but varies from minute to minute depending on activity and time of day. It fails to low levels when you are asleep at night and may become very high when you are startled or under stress: intense mental arithmetic for instance has quite a profound effect. In some subjects blood pressure may rise transiently in response to anxiety generated by the act of measuring the pressure or attendance at a surgery or hospital clinic. In most cases the blood pressured on the first occasion is higher than that recorded on subsequent visits, when patients are more at ease. Doctors make allowance for this. There is also tendency for blood pressure to rise with age. This particularly affects the systolic pressure and is partly due to the fact that the larger arteries become harder and lose some of their ‘give’. Thus a systolic blood pressure of 145 would be abnormal in women of 18, but would be perfectly acceptable in someone of 70.

 

What causes high blood pressure?

 

In over nine patients out of ten with high blood pressure no underlying disease can be found. The term “essential hypertension” is sometimes used in this case. This absence of a cause is not as surprising as might appear at first sight. Blood pressure, like height or weight, is the result of many influences. Just as in the case of stature, heredity is important. If your parent’s blood pressure were on the high side, the chances of you also developing hypertension are increased. The similarity with stature goes further than that however.  There is no clear division between normal and raised blood pressure, in the same way that there is no separation between people who are tall and those who are of normal height. It is not strictly correct therefore to talk of individuals as ‘having’ or ‘not having’ essential hypertension although doctors usually do this because it is convenient. There are borderline blood pressure levels, which would be regarded as hypertensive by some doctors but normal by others, just as we differ in our definition of tallness or obesity. On rare occasions a definable cause may be identified, such as narrowing of the artery to a kidney or abnormal production of hormone from the adrenal gland. Occasionally high blood pressure may be due to other forms of severe kidney disease. These situations are very unusual however and can be easily identified by blood tests and x-rays. Occasionally blood pressure may be worsened by medication. Some tablets used in treating ulcers, arthritis or depression may raise blood pressure. If you are taking medicine, which your doctor may not know about (either bought at a chemist’s or prescribed by another doctor), it is vital that you tell your doctor. It is preferable to take it with you when you attend for blood pressure measurement.

 

 

How do I know that I have high blood pressure?

 

Contrary to popular belief, most patients with high blood pressure have no symptoms. Occasionally patients have symptoms such as headache, but only if the pressure is very high. Symptoms like headache are far more likely to be due to other causes such as anxiety. When patients attending a hypertension clinic some years ago were asked whether they suffered from headache, far more of those who had been told they had high blood pressure complained of headache than those who did not know they were hypertensive. In this case ignorance was bliss! Because most people with high blood pressure have no symptoms the condition commonly goes undetected. To identify hypertension there is no substitute therefore to having your blood pressure measured. Improved detection of high blood pressure depends on an increase in public awareness of the need to have blood pressure measured. This is particularly true for people approaching middle age when high blood pressure becomes more common and for people who have relatives with high blood pressure. Measurements are made as a routine at insurance and employment medicals but your doctor or practice nurse will usually measure your blood pressure on request. It is often convenient to have a measurement during routine consultation, which has been sought for other reasons. Machines are available for you to measure your own pressure. Some of these can be purchased and some work on the ‘coin in the slot’ principle. Whilst they have undoubtedly allowed hypertension to be diagnosed in some people it is preferable for your blood pressure to be measured by a trained person such as doctor or nurse. There is often no check upon the accuracy of ‘do it yourself’ machines. Such factors as position of the cuff on your arm, muscle tension and poster may have a profound influence upon blood pressure reading and lead to either unnecessary alarm or a false sense of security.