Everybody knows that blood pressure affects health. We’ve become educated about the risks of high blood pressure or hypertension; untreated, it can lead to heart attacks, congestive heart failure, strokes, and kidney failure. And, it’s a common problem; 50 million Americans have blood pressure readings over 140/90–placing them in the hypertensive category. But do you understand the numbers in your blood pressure reading? This week, I’ll talk about the reason for pumping up and what the numbers mean.
The heart is an efficient pump composed of smooth muscle that does its job from the time we are born until the day we die. The blood it pumps contains oxygen and nutrients which are delivered through a series of arteries to the rest of the body. Our “blood pressure” is a measurement of the pressure of circulating blood against the walls of the arteries. Consequently, it actually measures the resistance to blood flow in the walls of the blood vessels rather than the strength of the heart muscle. In healthy animals of any species, blood pressures are maintained within a certain average range with a fair degree of consistency.
Blood pressure is measured in two components, systolic and diastolic, which are recorded as a ratio. The systolic blood pressure (numerator) is the pressure exerted on arteries when the heart is beating. The diastolic pressure (denominator) is the pressure present in arteries when the heart is ‘relaxing’ as it fills with blood returned to it by the venous circulation. These numbers are measured in millimeters of mercury by an instrument called a sphygmomanometer. The most efficient and reliable sphygmomanometer consists of a cuff which is wrapped around the upper arm, inflated, and connected to a pressure-detecting device. Though there are finger/wrist blood pressure monitoring devices, these do not tend to be as accurate as the arm cuff model. These smaller devices are too sensitive to position and body temperature–generating many faulty readings as a result.
When checking blood pressure readings, if a stethoscope is used,systolic pressure is the point at which the inflated cuff stops the circulation and no blood flow is heard. As the cuff is slowly deflated, a swishing or flowing sound is heard until a point when smooth flow is reestablished and the sound disappears. The reading at this point is the diastolic blood pressure. An average ‘good’ blood pressure reading is 120/80–though exercise and anxiety will predictably raise blood pressure transiently, and rest and sleep tend to lower it. Readings consistently over 140/90 define hypertension and should be treated appropriately. There’s a common misconception that a “hyper” person will undoubtedly have hypertension. Though anxiety can elevate blood pressure, there are many usually calm and relaxed individuals who have hypertension. So avoiding stress, is not a sure-fire protection from developing hypertension. Additionally, blood vessel walls tend to thicken and become less elastic as we age. Consequently, the systolic blood pressure rises over time in most people. This phenomenon can cause a form of high blood pressure termed isolated systolic hypertension; the systolic pressure stays consistently over 140 even when the diastolic pressure remains normal. This form of blood pressure elevation should also be treated since heart attacks and strokes can be reduced in people aged 60 and over who have isolated systolic hypertension.
If you have hypertension or just want to monitor your own blood pressure readings over time, there are a variety of home monitoring devices on the market. Aneroid monitors have a dial gauge which is read by looking at a pointer. The cuff is inflated manually. Digital monitors can have either manual or automatic cuffs and the readings are flashed on a screen. Aneroid monitors tend to cost between $20–$30, while digital models can range from $40–$100. In general, digital monitors are easier to use and good for hearing-impaired folks, but their accuracy is changed by body movement and irregular heart beats; and remember, they require batteries. Whichever model you choose, remember that correct cuff size is essential. If the arm cuff is either too large or too small for your arm, your blood pressure readings will be inaccurate. We keep the large adult cuff on hand in our office for ready use with all full-figured individuals. Don’t use the finger or wrist monitors unless someone gives them to you as a gift; they are predictably less accurate. And if you do purchase a home monitoring device, take it to your doctor’s office to be checked for accuracy.
Remember, hypertension is common in American adults and can lead to serious health consequences if untreated. Most people with elevated pressures do not “feel” their hypertension, so monitoring blood pressure periodically is the only reliable way to know how your blood pressure’s doing. I am hopeful that after this week’s Insight, you’ll be pumped up by my off-the-cuff remarks. Preventive medicine is good medicine, and you can prevent the complications of hypertension by treating it early.
Stephen L. Hines, M.D.
July 2000
