Information for Patients: What is Hypertension?
What is Hypertension?
Everybody knows that high blood pressure is bad, but most people have only a hazy idea as to why, and what the term really means. In fact, all of us have high blood pressure some of the time, and we wouldn't be able to function if we didn't. High blood pressure is only of concern when it persists for long periods of time, and its adverse effects actually take many years to develop. It's very common: according to official government figures it affects 50 million people in the United States. The other name for it is hypertension, a word that often causes confusion. People who have high blood pressure are not particularly "hyper" or tense, in the usual sense of the word. The term simply refers to the increased tension or pressure in the arteries.
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 The arteries are the elastic tubes that carry blood from the heart to the tissues. They are configured like a tree: the central trunk, or aorta, leaves the heart and then branches repeatedly. The smallest branches, which are visible only under a microscope, are called arterioles. They have muscle cells in their walls so that they can constrict and dilate, and hence direct the flow of blood to where it is most needed. The arterioles branch into even finer vessels, called capillaries, which form a delicate mesh that supplies the tissues with oxygen and other nutrients. For the blood to be able to circulate properly, a certain level of pressure is needed to force it through the arterioles and capillaries.
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It's important to realize that blood pressure is continually varying in order to meet the ever-changing needs of our bodies. Blood pressure is normally regulated very tightly by the brain. When we're asleep, and our bodies are at rest, we consume less oxygen than when we're awake and active, and so the brain lets the pressure fall to a lower level. At the other extreme, when we're exercising, our muscles need a greater supply of blood to keep them going, and the pressure goes up.
How is Hypertension Diagnosed?
You probably recognize the numbers 120/80 as a normal blood pressure. But why two numbers? The explanation is quite simple. Your heart beats about 70 times a minute, and with each beat blood is pumped into the arteries. As this happens, the pressure inside the arteries goes up, until the end of that heartbeat. The peak level of pressure is called the systolic pressure. Then the heart relaxes, and begins filling with blood for the next beat, and the pressure in the arteries starts to fall and reaches a minimum level just before the next heartbeat, which is the diastolic pressure. So the number 120 refers to the systolic pressure, and 80 to the diastolic pressure. Each heartbeat produces a slightly different pressure, but usually the two numbers go up and down together.
The blood pressure is expressed as millimeters of mercury, usually abbreviated as mm Hg (Hg is the shortened version of the Latin name for mercury). The reasons for using mm Hg are both historical and practical. The pressure gauge used by doctors to measure blood pressure is called a sphygmomanometer, which has a column of mercury, the height of which is recorded in millimeters, and is a measure of the pressure inside the cuff.
Which Doctors Treat Hypertension?
Although it is so common, hypertension has not traditionally been treated by specialists, but by a variety of physicians, including family practitioners, internists, cardiologists (heart specialists), and nephrologists (kidney specialists). This works fine for many patients, but others benefit from more specialized care. Some patients have rare (but curable) causes of hypertension that often go undiagnosed for many years, and others just can't seem to find the right mix of medicines to keep their blood pressure under control. A recent development has been the recognition of Hypertension specialists whose primary focus is on diagnosing and treating all forms of hypertension and its complications.
Twenty-Four-Hour Blood Pressure Monitoring
The blood pressure that your doctor records in the office is generally assumed to be representative of your "true" blood pressure, or the average level over prolonged periods of time. But this isn't necessarily always the case: many people get nervous when they're seeing their doctor, so their blood pressure goes up. This phenomenon is called "white coat hypertension." Twenty-four-hour (or ambulatory) monitoring is a technique that enables blood pressure to be measured outside the rather artificial setting of the doctor's office while you go about your normal daily activities. The monitor is about the size of a Walkman radio, and it is worn on a belt around the waist. Connected by a thin tube to a blood pressure cuff on the upper arm, it is relatively unobtrusive. It can be pre-programmed to take readings at regular intervals, typically every 15 to 30 minutes throughout the day and night, and it is fully automatic, which means that it pumps up the cuff, deflates it, and stores the reading in its memory. All you have to do is to hold your arm still while the reading is being taken and record what you were doing at the time. At the end of the 24 hours you have the
monitor disconnected, and the readings are transferred into a personal computer. Up to 100 readings may be taken, so it's possible to get a much better idea of what your true blood pressure really is.
We have been using this procedure for many years, particularly in patients in whom it's unclear whether or not their blood pressure is really high. However, there are a lot of doctors who still regard it as experimental, and many insurance companies do not reimburse for it. Medicare should start to reimburse for it in 2002. The cost is $200.
Home (Self) Monitoring
You may be advised to start monitoring your blood pressure at home. This is a very convenient way of measuring blood pressure changes over time, particularly when treatment is being started or changed. There are now a
number of easy-to-use devices that are available in drug stores and electronics suppliers that cost about $70. A typical monitor is battery-operated and has a cuff that you wrap around the upper arm. You
press a button on the device, which pumps up the cuff and takes a reading. This reading is displayed on a screen, so all you have to do is to write down the numbers, typically systolic pressure, diastolic
pressure, and the pulse rate. There are also monitors that record blood pressure from the wrist or the finger, but these readings are not as reliable. Most of our patients now monitor their own pressure, and when they start we advise them to bring the monitor in so that it can be checked for accuracy. The readings recorded at home are nearly always
lower than the ones we obtain in the clinic and may be useful for diagnosing white coat hypertension.
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