Blood pressure is the force with which blood pushes against the artery walls as it travels through the body. Like air in a balloon, blood fills arteries to a certain capacity—and just as too much air pressure can cause damage to a balloon, too much blood pressure can harm healthy arteries. Blood pressure is measured by two numbers—systolic pressure and diastolic pressure. Systolic pressure measures cardiac output and refers to the pressure in the arterial system at its highest. Diastolic pressure measures peripheral resistance and refers to arterial pressure at its lowest. Blood pressure is normally measured at the brachial artery with a sphygmomanometer (pressure cuff) in millimeters of mercury (mm Hg) and given as systolic over diastolic pressure.
A blood pressure reading thus appears as two numbers. The upper number is the systolic pressure, which is the peak force of blood as the heart pumps it. The lower number is the diastolic pressure, which is the pressure when the heart is filling or relaxing before the next beat. Normal blood pressure for an adult is 120/70 (on average), but normal for an individual varies with the height, weight, fitness level, age, and health of a person.
What Is Hypertension?
Hypertension, or high blood pressure, is defined as a reading of 140/90 on three consecutive measurements at least six hours apart. The definition varies for pregnant women, where hypertension is defined as 140/90 on two consecutive measurements six hours apart. Consistently high blood pressure causes the heart to work harder than it should and can damage the coronary arteries, the brain, the kidneys, and the eyes. Hypertension is a major cause of stroke .
Types of Hypertension
Hypertension is classified as either primary (or essential ) hypertension or secondary hypertension. Primary hypertension has no specific origin but is strongly associated with lifestyle. It is responsible for 90 to 95 percent of diagnosed hypertension and is treated with stress management, changes in diet , increased physical activity, and medication (if needed). Secondary hypertension is responsible for 5 to 10 percent of diagnosed hypertension. It is caused by a preexisting medical condition such as congestive heart failure, kidney failure, liver failure, or damage to the endocrine ( hormone ) system.
Pregnancy-induced hypertension (PIH) may appear in otherwise healthy women after the twentieth week of pregnancy. It is more likely to occur in women who are overweight or obese . PIH may be mild or severe, and it is accompanied by water retention and protein in the urine. About 5 percent of PIH cases progress to preeclampsia. Preeclampsia is characterized by dizziness, headache, visual disturbance, abdominal pain, facial edema , poor appetite, nausea , and vomiting. Severe preeclampsia affects the mother's blood system, kidneys, brain, and other organs. In rare cases, the woman can die. Preeclampsia is more likely to occur during first pregnancies, multiple fetuses, in women with existing hypertension, and in women younger than twenty-five years old or over thirty-five years old. If convulsions occur with PIH, it is called eclampsia. PIH disappears within a few weeks after birth.
Causes of Hypertension
Many prescription and over-the-counter drugs can cause or exacerbate hypertension . For example, corticosteroids and immunosuppressive drugs increase blood pressure in most solid-organ transplant recipients. Medication taken for pain and inflammation such as nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase-2 (COX-2) inhibitors may raise blood pressure since their antiprostaglandin properties affect the kidneys.
Tobacco products (cigarettes, cigars, smokeless tobacco) contain nicotine, which temporarily increases blood pressure (for about thirty minutes or less). The blood pressure of smokers should be rechecked after thirty minutes if initial readings are high. Nicotine patches that are used for smoking cessation do not appear to increase blood pressure.
There does not appear to be a direct relationship between caffeine and chronic hypertension, even though caffeine intake can cause an acute (rapid but brief) increase in blood pressure. This may be due to the fact that tolerance to caffeine develops rapidly.
Chronic overuse of alcohol is a potentially reversible cause of hypertension. Five percent of hypertension is due to alcohol consumption and 30 to 60 percent of alcoholics have hypertension. Alcohol-induced hypertension is more likely to occur in women than men.
Diet and Hypertension
Sodium intake has been a primary target for hypertension control, though it is ranked fourth as the lifestyle factor associated with hypertension. About 50 percent of individuals appear to be "sodium sensitive." This means that excessive sodium intake tends to increase blood pressure in these groups of people, and they do not appear to excrete excessive amount of salt via the kidneys. Sodium-sensitive individuals include the elderly, obese individuals, and African Americans. The Dietary Guidelines for Americans recommend that adults consume no more than 2,400 milligrams of sodium daily. There are a number of ways to limit sodium in the diet, including:
- Do not use salt at the table
- Check food labels for sodium content
- Choose unprocessed foods
- Limit processed meats and cheeses
- Limit pickled meats and vegetables
- Limit salty snacks
- Limit intake of soy sauce, BBQ sauce, and other condiments and foods that may be high in sodium
Potassium supplements (2–4 grams daily) have been shown to moderately decrease blood pressure. Fruits and vegetables are excellent sources of potassium. The Dietary Guidelines for Americans recommend that adults consume at least 3,500 milligrams of potassium daily. A diet high in fruits and vegetables has been linked to a decreased risk of both hypertension and stroke. Foods high in omega-3 fatty acids have positive effects on hypertension and cardiovascular disease by relaxing arteries and thinning the blood. In addition, several studies have demonstrated that individuals with hypertension may benefit from daily doses of calcium (800 mg) or magnesium (300 mg).
The DASH Eating Plan
Research has shown that a diet that is low in sodium but rich in calcium, potassium, and magnesium can decrease blood pressure, especially among African Americans. This eating plan is called the DASH (Dietary Approach to Stop Hypertension) eating plan and it is as effective in decreasing blood pressure as some medications commonly used to treat hypertension. The DASH eating plan is based on 2,000 calories a day with 18 percent of the calories coming from protein, 55 percent from carbohydrates , and 27 percent from fats. The eating plan contains less fat than the Food Guide Pyramid, more fruits and vegetables, and includes a serving of nuts.
Pharmacological Treatment of Hypertension
Hypertension is commonly treated with medication, and a combination of two or more drugs is common. Patients are usually given a diuretic to help them excrete excess fluids. However, most diuretics also cause excretion of potassium in the urine, and individuals on diuretics should monitor their potassium intakes. Drugs used to control hyertension include beta-blockers (e.g., atenolol [Tenorim]) which act to slow heart rate and cause some vasodilation (widening of the lumen, or interior, of blood vessels). Drugs that contain calcium channel blockers (e.g., amlopidine [Norvasc]) or angiotensinconverting enzyme (ACE) inhibitors also cause vasodilation.
Lifestyle Treatment of Hypertension
Most of the risk factors for primary hypertension are preventable, and lifestyle modification may prevent as well as treat the condition. Secondary hypertension can be managed by treating the underlying cause. Individuals in the high normal and stage 1 hypertension categories should attempt to lower blood pressure through diet and lifestyle changes before going on a regimen of medications. Recommendations include:
- Eliminate tobacco
- Control stress
- Maintain weight at 15 percent or less of desirable weight
- Restrict alcohol intake to no more than two drinks a day for men and one for women (one drink equals 12 ounces of beer, 5 ounces of wine, or 1.5 ounces 80-proof whiskey)
- Restrict sodium intake to 1.5 to 2.5 grams per day (4 to 6 tsp salt)
- Exercise five to seven days a week for sixty minutes per session
- Increase intake of fruits and vegetables
- Increase intake of low-fat dairy products
Delores C. S. James
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Onusko, E. (2003). "Diagnosing Secondary Hypertension." American Family Physician 67:67–74. Also available from <http://www.aafp.org/afp>
National Heart, Lung, and Blood Institute. "Facts about the DASH Eating Plan." Available from <http://www.nhlbi.gov/health>