Circulatory system

What is high blood pressure?

Blood pressure is the force of blood against the walls of arteries. It's normal for blood pressure to fluctuate over the course of the day. However, when blood pressure continues to stay elevated over time, a person is said to have high blood pressure, or hypertension. High blood pressure places increased load on the heart, making it work harder than it should. As a result, a person may develop hardening of the arteries (artherosclerosis), coronary heart disease, and stroke. High blood pressure can also result in other conditions such as congestive heart failure, kidney disease, and blindness.¹

What causes high blood pressure?

Causes of high blood pressure vary from one person to another. Most of the time, the cause isn't known, although in some cases it may be the result of:

• narrowing of the arteries or artherosclerosis
• a greater than normal volume of blood
• the heart's beating more rapidly than it should (arrhythmia)
• the heart's beating more forcefully than it should
• a pre-existing medical condition such as diabetes

How is high blood pressure diagnosed?

You should have your blood pressure checked at least once a year. Using a blood pressure cuff, or sphygmomanometer, a doctor can measure your blood pressure to determine if you are at risk for stroke or for coronary heart disease, a condition that may lead to heart attack.

Blood pressure is measured in millimetres of mercury (mm Hg) and is represented by two numbers. The first number, systolic pressure, represents the force of blood flow through the arteries when the heart beats. The second number, diastolic pressure, represents the force of blood flow between heart beats when the heart is a rest. High blood pressure, or hypertension, is defined in an adult as a blood pressure equal to or greater than 140 mm Hg systolic pressure or diastolic pressure greater than or equal to 90 mm Hg.²

While both numbers—systolic and diastolic pressure—are important, in people over the age of 50, it is systolic pressure that gives the more accurate diagnosis of high blood pressure.³

Who's at risk?

Although high blood pressure can occur in people of all ages, including children, it's more common in adults over the age of 35—that is, middle-aged and elderly people. In fact, approximately two-thirds of people over age 65 have high blood pressure. People in their 50s who do not currently have high blood pressure face a 90 percent chance of developing it later in life. High blood pressure, therefore, affects most people at some point in their lives.⁴

High blood pressure is particularly common in black people, heavy drinkers, obese people, people using narcotics or street drugs, and women taking birth control pills. Although high blood pressure is known to run in families, many people with a strong family history of high blood pressure may never have hypertension themselves. Those suffering from diabetes, gout, or kidney disease are also more likely to be affected by high blood pressure.⁵

Table 1. American Heart Association recommended blood pressure levels⁶

Blood Pressure Category	Systolic (mm Hg)		Diastolic (mm Hg)
Normal	less than 120	and	less than 80
Prehypertension	120–139	or	80–89
High blood pressure
Stage 1	140–159	or	90–99
Stage 2	higher than 160	or	100 or higher

Those classified as having prehypertension do not currently have high blood pressure but are likely to develop it in the future.

Types of high blood pressure

Systolic blood pressure

As mentioned earlier, systolic blood pressure refers to the force of blood flow in the arteries while the heart beats. A systolic pressure of 140 mm Hg or more indicates high blood pressure. Diastolic blood pressure does not need to be high in order for a person to be diagnosed with high blood pressure. In this instance, the individual is said to have isolated systolic hypertension.⁷

Isolated systolic hypertension is the most common form of high blood pressure in older people. Systolic blood pressure increases with age as does diastolic pressure. At about age 55, however, diastolic pressure declines. In some people, this may result in isolated systolic hypertension. Approximately 65 percent of hypertensives over age 60 have isolated systolic hypertension. Many report no symptoms and may feel perfectly fine. Nevertheless, isolated systolic hypertension, like other forms of high blood pressure, can be dangerous if left untreated, leading to stroke, heart attack, congestive heart failure, kidney damage, blindness, and other conditions.⁸

While at present there is no cure for isolated systolic hypertension, it can be controlled. Treatment typically requires changes in lifestyle and diet as well as medication. Treating isolated systolic hypertension greatly reduces illness and improves quality of life.⁹

Diastolic blood pressure

As we've seen already, diastolic blood pressure is the force of blood flow in the arteries as the heart relaxes between heartbeats. In younger people especially, diastolic pressure is a key indicator of high blood pressure. The higher a person's diastolic pressure, the greater that person's risk for heart attack, stroke, and kidney failure. As people age, diastolic pressure declines and systolic pressure increases. In later life, it is systolic pressure that becomes the key indicator of high blood pressure. Increase in systolic blood pressure may also increase the risk of heart attacks, stroke, and kidney failure.¹⁰

What are the effects of high blood pressure?

In addition to increasing a person's risk of heart attack, stroke, and kidney failure, high blood pressure can also have other adverse effects on the body.

High blood pressure can cause weakened blood vessels in the brain to break and bleed. This can cause a stroke. If a blood clot obstructs one of the narrowed arteries, this may also lead to stroke. Similarly, high blood pressure can also cause vessels in the eye to rupture and bleed, resulting in blurred or impaired vision or even permanent blindness.

As people age, arteries in the body may develop buildup of fatty deposits, or plaque. Accumulation of plaque can lead to a condition known as artherosclerosis in which arteries—particularly those of the heart, brain, and kidneys—become narrow and hard. When this happens, the kidneys need to work harder. Over time, this increased load can lead to renal failure.

Arteries bring oxygen to the heart and help nourish the heart muscle. When this muscle, the myocardium, is deprived of oxygen, it becomes damaged and may even die. This is what causes myocardial infarction, or heart attack. High blood pressure is a major risk factor for heart attack and angina, acute chest pain that occurs when the heart cannot get enough oxygen.

High blood pressure can also cause headaches, nosebleeds, and shortness of breath.

Treating high blood pressure

While at present there is no cure for high blood pressure, it can be controlled. Treatment typically requires changes in lifestyle and diet, as well as medication. If your doctor has prescribed medication to help you control high blood pressure, take it as advised and consult your doctor about any side effects such as dizziness, headaches, tiredness, or impaired sexual function.

Try to maintain a sensible diet that is low in salt and fats and cholesterol. Exercise regularly and under the supervision of your doctor. Your doctor can help you design an exercise program than involves 30 minutes of aerobic activity (i.e. brisk walking or jogging) at least three times a week. Exercise will keep your heart muscle in good condition and will also improve overall health. In combination with diet, exercise can also help you lose weight. Weight loss is strongly encouraged if you are overweight. Finally, you can further control high blood pressure by cutting back on alcohol.

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1. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.
2. What is High Blood Pressure? American Heart Association, Inc. (2004)
3. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.
4. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.
5. What is High Blood Pressure? American Heart Association, Inc. (2004)
6. What is High Blood Pressure? American Heart Association, Inc. (2004)
7. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.
8. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.
9. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.
10. What are High Blood Pressure and Hypertension? Your Guide to Lowering High Blood Pressure. National Heart, Lung, and Blood Institute. US Department of Health and Human Services.