TAKING THE PRESSURE

Almost everyone knows what it is like to have his blood pressure taken. But few really know what the doctor is doing, and fewer still comprehend the meaning of the figures that register blood pressure. Actually, taking blood pressure and interpreting the results is a simple process.

The device used to measure blood pressure is called a sphygmomanometer (from the Greek, meaning pulse measurement); it measures the air pressure needed to raise a column of mercury. To use it, the doctor pumps air into a cloth cuff wound tightly round the patient's arm. As the cuff expands, the column of mercury rises in response to the increasing air pressure. That pressure also causes the cuff to press against the brachial artery, stopping the flow of blood. The doctor, his stethoscope pressed against the patient's forearm, knows that the flow has ceased when he can no longer hear the heartbeat. At that point, he slowly releases the air from the cuff. As pressure drops, the mercury column begins to descend; the cuff loosens, and blood begins to flow through the arm again. The doctor notes the level of the mercury column when he can once more hear the heartbeat. This reading is the systolic measurement. It is the higher of the two figures used in the measurement of blood pressure and reflects the force with which the heart is delivering blood to the body.

To get the diastolic, or lower reading, the doctor lets more air out of the cuff and continues to listen; the pulse momentarily gets louder and then fades. The level at which the sound of the pulse disappears is the diastolic, or the pressure in the circulatory system when the heart is relaxing and refilling.

Because blood pressure tends to increase naturally with age, a reading of 110 over 60, considered good for a young man, would be high enough to cause concern if it were recorded in a small child. A 45-year-old man with a reading of 120 over 80 (or less) is in good shape, but a contemporary with a higher reading of 150 over 100 is in trouble. According to insurance-company figures, his life expectancy is 11 1/2 years less.

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