Brewer Sarah - Eat to beat high blood pressure : natural self-help for hypertension, including 60 recipes

Everyone needs a certain blood pressure (BP) to keep blood moving around their body and maintain their circulation. Blood pressure exists because your heart pumps blood around a closed system, rather like a boiler pumping water through a series of central heating pipes. The pressure in your arteries therefore depends on a number of factors, including the volume of fluid inside your circulation, how hard your heart is pumping at any given time, and the elasticity or resistance of the vessels the blood is passing through.

Normal BP varies naturally throughout the day and night, going up and down in response to your emotions and level of activity. If you have high blood pressure, however, your BP will remain consistently high, even when you are asleep.

The heart alternately contracts and relaxes as it pumps to produce the heartbeat. Each contraction produces a surge in pressure. The highest pressure reached in the arteries during this surge is known as the systolic pressure as it is due to contraction (systole) of the heart. As the heart rests between beats, blood pressure falls again and the lowest blood pressure recorded while the heart rests (diastole) is known as the diastolic pressure. In general, as the heart pumps more strongly, systolic pressure rises, while a reduction in elasticity of the peripheral arteries causes diastolic pressure to go up.

Blood pressure (BP) is measured using an instrument called a sphygmomanometer. This has an inflatable cuff which goes around your upper arm, a small pump to push air into the cuff and a column of mercury (or a dial) to record the pressure within the cuff.

As the cuff is inflated with air, the person measuring your BP usually feels for a pulse (brachial artery) in the crook of your elbow. While the pressure within your artery stays higher than that in the cuff, blood can be felt pulsing through. Once the pressure in the cuff becomes greater than that in your artery, the vessel is squashed flat and blood stops flowing through it at that point. By inflating the cuff to an initial pressure that is higher than the expected systolic pressure, then listening with a stethoscope over your brachial artery as the pressure is slowly released, the point at which blood manages to squirt through again with each pulse can be heard distinctly as a tapping sound. The pressure registering in the cuff at this point is taken as your systolic BP. The cuff is then slowly deflated further while listening over your artery. The tapping sounds become louder, then change to a dull whooshing noise before disappearing. The point at which blood can no longer be heard whooshing through the vessel is taken as your diastolic BP. The pulsing noise heard in the artery between these two pressures is a result of turbulence as the cuff impinges on the vessel and deforms its walls. We therefore know that the blood pressure in the artery is the same as that in the cuff at the point where the sounds disappear, as turbulence is no longer occurring. BP can also be measured with modern digital cuffs that fit around the wrist.

BP is measured according to the length of a column of mercury it can support. It is therefore expressed in millimetres of mercury (mmHg). BP is written down as the higher pressure (systole) over the lower figure (diastole).

A typical 20-year-old may have a BP of around 120/70 mmHg.

BP naturally tends to rise with age and a fit 50-year-old may have a BP of around 135/85 mmHg.

The pulse pressure the difference between the systolic and diastolic pressures is normally around 50 mmHg.

If your BP is consistently higher than 140/90, then you are suffering from high blood pressure, or hypertension.

Blood pressure is normally controlled and kept within safe limits by the body in a number of ways, including:

changing the rate at which the heart pumps

widening or constricting small arteries

altering the amount of blood pooled in the veins

varying the amount of salt and fluids filtered from the circulation via the kidneys.

These factors are controlled by nerve signals from the brain, and by several different hormones. As a result, normal BP varies naturally throughout the day, going up and down in response to your emotions and level of activity. It is lowest during sleep (usually at around 3am) and highest in the morning from just before you wake until around 11 am. If you have high blood pressure, however, your BP will remain high all the time, even at rest.

As many as one in five adults have high blood pressure, known medically as hypertension. This means that blood is forced through their system under a constantly high pressure. Hypertension is diagnosed when systolic pressure is consistently greater than 140 mmHg and diastolic pressure consistently greater than 90 mmHg. A systolic blood pressure between 140160 mmHg and diastolic values between 9095 mmHg are sometimes referred to as mild hypertension.