CHAPTER 12 HIGH BLOOD PRESSURE - Yale University

CHAPTER 12

HIGH BLOOD PRESSURE

MARVIN MOSER, M.D.

INTRODUCTION

High blood pressure, or hypertension as the disease is known medically, is our most common chronic illness. Estimates of exactly how many Americans have high blood pressure vary--the American Heart Association and the National Heart, Lung, and Blood Institute put the figure at about 55?60 million, but some of the individuals included in this estimate may only have had transient elevation of pressure; a more accurate estimate is probably 35?40 million. In either calculation, the number of people affected and the amount of the nation's health budget that goes toward treating high blood pressure or its complications are huge.

Because high blood pressure is the leading cause of strokes and a major risk factor for heart attacks, one of the most important aspects of preventive cardiology should be to identify as many people who have the disease as possible and to take steps to lower the blood pressure before it causes damage to the blood vessels, heart, kidneys, eyes, and other organs. Fortunately, the last 30 to 35 years have seen remarkable advances in the treatment of high blood pressure, with major payoffs. The death toll from strokes is down by more than 54 percent and heart attack mortality has dropped by more than 45 percent

since 1973?74. At that time, the National High Blood Pressure Education Program directed at both physicians and the general public raised consciousness about the dangers of untreated high blood pressure and the importance of early effective treatment. We are now reaping the benefits of this and other major programs.

Even so, it's still too early to declare victory over high blood pressure. Despite massive public education programs, misconceptions about the disease abound. Many people still harbor misconceptions about what constitutes an elevated blood pressure (see box, "Common Facts and Myths"), and there probably still are many people whose high blood pressure has not been diagnosed--especially in minority populations. There also are several millions of others whose hypertension has been diagnosed but who are not being adequately treated to normal blood pressure levels.

WHAT IS HIGH BLOOD PRESSURE OR HYPERTENSION

To understand why lowering high blood pressure is so important in preventing heart and blood vessel

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diseases, it is important to know something about the basic physiology involved. As noted in Chapter 1, the blood circulates through some 60,000 miles of blood vessels. (See color atlas, #4.) With each heartbeat, 2 or 3 ounces of freshly oxygenated blood are forced out of the heart's main pumping chamber, the left ventricle, into the aorta, the body's largest artery.

The circulatory system can be likened to a tree. The aorta is comparable to the main tree trunk. It branches into smaller arteries (like the thick branches that come off the main trunk), which in turn divide into even smaller vessels (like smaller branches and twigs) called arterioles, which carry blood to the capillaries (like the leaves). Capillaries are the microscopic vessels that supply blood, with its load of oxygen and other nutrients, to each cell in the body. After the oxygen is used up, the blood returns to the heart via a branching system of veins.

A certain amount of force is needed to keep blood moving through this intricate system of blood vessels. The amount of force that is exerted on the artery walls as blood flows through them is what we refer to as blood pressure. The "head" of pressure comes from the heart, but it is the smallest arteries, the arterioles, that actually determine how much pressure is registered in the blood vessels. To raise blood pressure, the arterioles narrow or constrict to lower it, they open up or dilate.

Exactly how much pressure is needed varies according to the body's activities. For example, the heart does not need to beat as fast or as hard to keep blood circulating when you are resting as it does when you are exercising. During exercise, however, more blood is needed to carry oxygen to the muscles, so blood pressure rises to meet increased demand. The heart pumps faster and pushes out more blood with each beat. In other situations, such as when someone stands up suddenly after lying down, the body must make an almost instantaneous adjustment in blood pressure in order to ensure a steady supply of blood to the brain. Blood vessels in the abdomen and legs constrict and the heart speeds up. Sometimes there may be a slight delay in this adjustment, and as a result, you may feel dizzy for a few seconds. This is more common in older people whose blood vessel reflexes might be impaired. A longer delay can bring on a fainting spell, which is the body's way of increasing the flow of blood to the brain (when someone lies down, blood flow to the brain increases).

Similarly, some people feel light-headed, or even faint, after standing for long periods, during which time blood may collect or "pool" in the legs, thereby reducing the amount that is available to carry oxygen

to the brain. Good examples of this bodily response are the numerous instances of healthy soldiers who fainted after standing at attention for long periods of time in hot weather. Other reflexes maybe triggered and result in a sudden loss of blood to the brain and an episode of light-headedness or fainting. These episodes are not serious but can be frightening. An example of this response is fainting after only a small amount of blood is drawn for a blood test. A nerve reflex slows the heart and causes blood vessels to dilate or open up, Less blood gets to the brain and fainting occurs. As we all know, if the affected individual rests quietly for just a few minutes, all is well.

Blood pressure is regulated by an intricate system of hormonal controls and nerve sensors, and it may vary considerably during the course of a day. Typically, blood pressure is low when you are resting or asleep, and higher when you are moving about or under stress. For example, when you are frightened or angry, the adrenal glands pump out epinephrine and norepinephrine, stress hormones that are commonly referred to as adrenaline. These hormones, which are responsible for the body's fight-or-flight response, signal the heart to beat faster and harder, resulting in increased blood pressure and flow to the muscles. It is apparent that pressures are typically lowest between 1:00 and 4:00 or 5:00 A.M., rise rapidly during "arousal" from sleep between 6:00 and 8:00 A. M., remain at approximately the same levels during the afternoon and evening, and decrease from about 11:00 to 12:00 at night.

HIGH BLOOD PRESSURE

pressure, is the amount of force exerted when the heart is resting momentarily between beats.

Blood pressure is usually measured with a device called a sphygmomanometer (pronounced sfig-moeman-om-e-ter), which consists of an inflatable rubber cuff, an air pump, and a column of mercury or a dial or digital readout reflecting pressure in an air column. Readings are expressed in millimeters of mercury or mm Hg. (See Figure 12.1.) The cuff is wrapped around the upper arm, and the inflatable cuff is tightened until blood flow through the large artery in the arm is halted. As air is pumped into the cuff, it pushes up a column of mercury or air, in the case of the simpler machines.

The person measuring the blood pressure places a stethoscope over the artery just below the cuff and listens for a cessation of the sound of blood coursing through the artery. He or she then begins to release air from the cuff, allowing blood to flow through the artery again. As air is released, the column of mercury or air begins to fall, and the person listens for the first thumping sound that signals a return of blood flow into the vessel over which the stethoscope has been placed. The height of the column of mercury or the air pressure on the dial at this sound indicates the systolic (or higher) pressure. More air is released

Figure 12.1 Blood pressure is measured using a device called a sphygmomanometer, which consists of an inflatable cuff that goes around the arm. The blood pressure reading is obtained from the height of a column of mercury which is connected to the cuff.

WHAT CONSTITUTES HIGH BLOOD PRESSURE?

Blood does not flow in a steady stream; instead, it moves through the circulatory system in spurts that correlate with the heart's beats. The heart beats about 60 to 70 times a minute at rest and may speed up to 120 to 140 or higher during vigorous exercise, It is not contracting or squeezing all the time, however; after each contraction, the heart muscle rests and gets ready for the next beat. Blood pressure rises and falls with each beat. Thus, blood pressure is expressed in two numbers, such as 120 over 80, or 120/80. The higher number, which is called systolic pressure, represents the maximum force that is exerted on the walls of the blood vessels during a heartbeat. The lower number, which is referred to as the diastolic

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Monitoring Your Own Blood Pressure.

Most people with hypertension do not need to measure their blood pressures at home. Some, however, find home monitoring reassuring. It is important to remember that an occasional high reading does not necessariIy mean that your blood pressure is "out of control. "

in some instances, home monitoring may provide useful information for your doctor, especiaIly if you are starting a new drug regimen or experiencing symptoms, such as dizziness. If you do monitor your blood pressure at home,

you should take your machine with you

periodically when you visit your doctor so that he or she can check whether it is correctly caI i brated. Before starting home monitoring, ask your doctor or nurse to show you the proper way to use your machine. Most people find the electronic machines that do not have a separate stethoscope easier to use than the nonautomated ones. But they may not be quite as accurate. Whichever model you use, follow the instructions from the manufacturer and your doctor. Special points to remember include:

q Avoid caffeine (coffee, tea, colas, etc.) for at `least 30 minutes before measuring your blood

pressure. The same goes for cigarettes or nicotine gum. Both caffeine and nicotine raise blood pressure and can give a falsely high reading.

q If you are experiencing dizziness or feelings of faintness, try taking your blood pressure immediately after standing up to see if it differs from pressure taken while sitting.

from the cuff, and pressure continues to fall. The height of the mercury or the level of air pressure when the thumping sound of blood ceases, indicating the pause between heartbeats, is the diastolic pressure.

People with high blood pressure can learn to monitor their own pressure (See box, "Monitoring Your Own Blood Pressure"), although for most it is not necessary.

As noted earlier, blood pressure varies considerably during the course of an average day. It also varies according to age--a baby's blood pressure may normally be 70/50, whereas the average blood pressure in an adult is about 120/80. Until recent years, there was no clear agreement among physicians as to what constituted high blood pressure, but now it is generally agreed that blood pressure readings that

are consistently above 140/90 warrant a diagnosis of hypertension, and the higher the readings, the more serious the disease. (See Table 12.1.) A reading of about 140/90 does not necessarily indicate that the condition requires immediate therapy, but it does suggest follow up and some treatment.

STEPS IN ESTABLISHING A DIAGNOSIS OF HIGH BLOOD PRESSURE

A diagnosis of high blood pressure should not be based on a single reading, except when it is extremely high--for example, above 170?180/105?110. Other-

Table 12.1 Recommendations for Management of Various Blood Pressure Levels

Range (mm Hg)

Diagnosis

Recommended activity

Diastolic

below 85 Normal blood pressure

Recheck within 2 years.

85-89

High normal blood pressure

Recheck within 1 year.

90-104

Mild hypertension

Confirm within 2 months.

105-114

Moderate hypertension

Therapy should be undertaken.

above 115 Severe hypertension Begin therapy with medication

Isolated systolic hypertension, when diastolic blood pressure is below 90 (mostly seen in older individuals)

below 140 Normal blood pressure

Recheck within 2 years.

140-159

Borderline isolated Confirm within systolic hypertension 2 months.

160-199

Isolated systolic hypertension

Confirm within 2 months. Therapy should be instituted if pressure remain elevated.

above 200 Isolated systolic hypertension

Begin therapy with medication

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wise several measurements taken over a period of time are generally needed to confirm a diagnosis. This is why single readings obtained at health fairs or other blood pressure screening events are often misleading. In addition, the electronic machines used for self-measurement at airports or in pharmacies are often poorly calibrated or improperly used and may give false readings (usually on the high side), Although hypertension screening has its place, people should understand that readings obtained are only an indication to follow up more carefully, and do not justify a definite diagnosis of high blood pressure or hypertension. Unfortunately, many people are unduly frightened, on the basis of just one blood pressure recording, into thinking they have hypertension.

The circumstances under which blood pressure is measured must also be taken into consideration. For example, a blood pressure reading taken when a person is under severe stress maybe misleadingly high. Similarly, a high reading may be obtained if blood pressure is measured soon after a person has had a couple of cups of coffee or smoked a few cigarettes. Thus, if possible, a person should avoid smoking and/or drinking coffee, cola, or other sources of caffeine for about one to two hours before having blood pressure measured.

In a physician's office or clinic, blood pressure is usually measured after the doctor has asked questions about the patient's health history. This also gives the patient a few minutes to relax, although some people remain anxious. (See box, "White-Coat Hypertension.") Two readings may be taken--the first with the person seated, and the second while standing. The reading while standing may be especially useful in older persons whose pressures may fall when they stand up. And it can help to guide treatment decisions, since some blood-pressure-lowering drugs may cause a greater decrease in standing than in sitting blood pressures. Blood pressure may be measured several times during the visit, especially if the first reading was on the high side, The results of all the readings are then usually averaged.

In an adult, blood pressure recordings need only be repeated every one to two years if pressures are below 140/90. If the average falls in the mild to moderate range of high blood pressure, about 140/90 to 160/100, an appointment for additional measurements will be made to confirm the diagnosis. However, very high diastolic blood pressure readings (more than 110 to 115 mm Hg) during the course of an office visit justify starting treatment. If an elevated blood pressure is present in individuals below 60 years of age, both the systolic and diastolic levels are

usually high--for example, above 140 systolic and 90 diastolic. In older people, however, there is a form of hypertension called isolated systolic hypertension. The systolic, or upper, reading may be high, for example, 150?180, but the diastolic, or lower, reading is below 90. (See Table 12.1.) This type of hypertension also results in an increased risk of stroke, heart attack, or heart failure.

In addition to measuring blood pressure, the doctor will also look for signs of organ damage, if the readings are high. Specifically, the examination will include:

? Inspection of the eyes. The eyes are the only place in the body where blood vessels can be looked at directly. By shining a bright light into the eye and inspecting its interior with an ophthalmoscope (a special magnifing device), the doctor can inspect the blood vessels for thickening or narrowing, changes that are characteristic of high blood pressure. He or she will also look for tiny hemorrhages inside the eye, another possible sign of damage from high blood pressure.

? Examination of the heart. This includes a careful examination using a stethoscope to listen for any unusual sounds or beats and palpation of

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