Checking Blood Pressure

People under 65 without hypertension (high blood pressure) should have their blood pressure checked at least once every five years. Those over 65 should have a check approximately every 2 years.

However, blood pressure may be checked much more frequently, for instance in women taking the contraceptive pill or who are pregnant, or in people with other medical conditions or who are taking certain medications. In most circumstances your General Practitioner will be able to advise.

Blood Pressure Values

• Normal blood pressure is less than 140/90mmHg.
  
• Mildly High blood pressure is 140/90mmHg. or above.
  
• Definitely High blood pressure is 160/100mmHg or above.

People with slightly raised blood pressure should have annual tests, scientists have suggested. Such regular checks are needed, they say, because 'high-normal' blood pressure can develop into dangerously high blood pressure - known as hypertension - in just four years. Hypertension is linked to advancing age and weight increase.

A study published in the Lancet also suggests people with normal blood pressure rates should be checked every two years.

The Body's Control of Blood Pressure

The body has many mechanisms that control blood pressure: The body can change the amount of blood the heart pumps, the diameter of arteries, and the volume of blood in the bloodstream. To increase blood pressure, the heart can pump more blood by pumping more forcefully or more rapidly. Small arteries (arterioles) can narrow (constrict), forcing the blood from each heartbeat through a narrower space than normal. Because the space in the arteries is narrower, the same amount of blood passing through them increases the blood pressure. Veins can constrict to reduce their capacity to hold blood, forcing more blood into the arteries. As a result, blood pressure increases. Fluid can be added to the bloodstream to increase blood volume and thus increase blood pressure. Conversely, to decrease blood pressure, the heart can pump less forcefully or rapidly, arterioles and veins can widen (dilate), and fluid can be removed from the bloodstream.

These mechanisms are controlled by the sympathetic division of the autonomic nervous system (the part of the nervous system that regulates internal body processes requiring no conscious effort) and by the kidneys. The sympathetic division uses several means to temporarily increase blood pressure during the fight-or-flight response (the body's physical reaction to a threat). The sympathetic division stimulates the adrenal glands to release the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones stimulate the heart to beat faster and more forcefully, most arterioles to constrict, and some arterioles to dilate. The arterioles that dilate are those in areas where an increased blood supply is needed (such as in skeletal muscle—the muscles controlled by conscious effort). The sympathetic division also stimulates the kidneys to decrease their excretion of salt and water, thereby increasing blood volume.

The kidneys also respond directly to changes in blood pressure. If blood pressure increases, the kidneys increase their excretion of salt and water, so that blood volume decreases and blood pressure returns to normal. Conversely, if blood pressure decreases, the kidneys decrease their excretion of salt and water, so that blood volume increases and blood pressure returns to normal. The kidneys can increase blood pressure by secreting the enzyme renin, which eventually results in the production of the hormone angiotensin II. Angiotensin II helps increase blood pressure by causing the arterioles to constrict and by triggering the release of another hormone, aldosterone, which causes the kidneys to increase the retention of salt and water.