Blood pressure & its causes

What is blood pressure?

The direct answer to the question, is a short one:

Blood pressure is the force that moves blood through our circulatory system.

It is a life force because, without blood pressure, the following two basic provisions would not be pushed around our circulatory system to feed tissues and organs:

Oxygen

Nutrients.

Blood pressure is vital also because it delivers white blood cells and antibodies for immunity, and hormones such as insulin.

Just as important as providing oxygen and nutrients, the fresh blood that gets delivered is able to pick up the toxic waste products of metabolism, including the carbon dioxide we exhale with every breath, and the toxins we clear through our liver and kidneys.

Blood itself carries a number of other properties, including its temperature. It also carries one of our defences against tissue damage, the clotting platelets that stem blood loss. See What is blood? for more information.

But what exactly is it that causes blood to exert a pressure in our arteries? Part of the answer is simple - the heart creates blood pressure by forcing out blood when it contracts with every heartbeat. Blood pressure, however, cannot be created solely by the pumping heart.

Measuring blood pressure

The way that blood pressure is measured today can be traced back to 18553 - the devices show how much pressure is needed before the pulse in our arm stops briefly: the arterial blood pressure is represented at that point.

Lady having her blood pressure checked by a doctor

When the pressure from the arm cuff stops the pulse briefly, it gives the top figure of arterial blood pressure that we are familiar with from medical dramas - for example, "140 over 90"

Once the cuff is inflated enough to stop the pulse, a reading is taken, either electronically or on an analogue dial.4

The reading is expressed in terms of the pressure it takes to move mercury round a tube against gravity in traditional scientific manometers - hence the unit, millimetres of mercury, that is abbreviated to mmHg.

Modern blood pressure devices can also be used at home for people who need a more representative record of their blood pressure than the one given by a one-off clinic reading.

What Is "Normal" Blood Pressure?

A blood pressure reading has a top number (systolic) and bottom number (diastolic). The ranges are:

Normal: Less than 120 over 80 (120/80)

Prehypertension: 120-139 over 80-89

Stage 1 high blood pressure: 140-159 over 90-99

Stage 2 high blood pressure: 160 and above over 100 and above

High blood pressure in people over age 60: 150 and above over 90 and above

People whose blood pressure is above the normal range should consult their doctor about steps to take to lower it.

What Causes High Blood Pressure?

The exact causes of high blood pressure are not known, but several factors and conditions may play a role in its development, including:

Smoking

Being overweight or obese

Lack of physical activity

Too much salt in the diet

Too much alcohol consumption (more than 1 to 2 drinks per day)

Stress

Older age

Genetics

Family history of high blood pressure

Chronic kidney disease

Adrenal and thyroid disorders

Essential Hypertension

The underlying cause cannot be determined. This type of high blood pressure is called essential hypertension.

Though essential hypertension remains somewhat mysterious, it has been linked to certain risk factors. High blood pressure tends to run in families and is more likely to affect men than women. Age and race also play a role. In the United States, blacks are twice as likely as whites to have high blood pressure, although the gap begins to narrow around age 44. After age 65, black women have the highest incidence of high blood pressure.

Essential hypertension is also greatly influenced by diet and lifestyle. The link between salt and high blood pressure is especially compelling. People living on the northern islands of Japan eat more salt per capita than anyone else in the world and have the highest incidence of essential hypertension. By contrast, people who add no salt to their food show virtually no traces of essential hypertension.

The majority of all people with high blood pressure are "salt sensitive," meaning that anything more than the minimal bodily need for salt is too much for them and increases their blood pressure. Other factors that can raise the risk of having essential hypertension include obesity; diabetes; stress; insufficient intake of potassium, calcium, and magnesium; lack of physical activity; and chronic alcohol consumption.

Secondary Hypertension

When a direct cause for high blood pressure can be identified, the condition is described as secondary hypertension. Among the known causes of secondary hypertension, kidney disease ranks highest. Hypertension can also be triggered by tumors or other abnormalities that cause the adrenal glands (small glands that sit atop the kidneys) to secrete excess amounts of the hormones that elevate blood pressure. Birth control pills  specifically those containing estrogen  and pregnancy can boost blood pressure, as can medications that constrict blood vessels.

Maintaining a healthy level

The guidelines for doctors list the following measures patients can take to help keep a healthy blood pressure

Keep a healthy body weight
Eat a diet rich in fruits, vegetables, and low-fat dairy products
Cut down on sodium intake (salt in the diet)
Take regular aerobic exercise (eg, brisk walking) at least 30 minutes a day, most days of the week
Moderate your alcohol drinking - keep under a maximum of 2 drinks a day for men and 1 drink a day for women/men of lighter weight.