Bethann Price, age 9, of Huntsville, Alabama, for her question:
How and why do they measure blood pressure?
A blood pressure test tells the doctor how well your heart is doing its job. As you know, your body breathes, digests your food and performs dozens of other duties. It is busy day and night without your telling it what to do. All its different operations work together in harmony to keep you healthy. But all these different operations depend on your beating heart. This is why the blood pressure tells so much about how everything inside the body is working.
The blood stream circulates through a network of tubes. It carries nourishment to all the living cells and oxygen to give them the energy they need to do their work. The beating heart keeps the blood stream circulating around and around the body. First, it relaxes to fill with blood. Then it contracts like a tight fist to push the blood on its way. The doctor uses a stethoscope to listen in on the sounds it makes. As the heart relaxes and contracts, the lub dub sound it makes is somewhat like a double drum beat.
Each pulsing beat pushes the blood stream on its way and each push presses against the walls of the arterial blood vessels. The doctor measures this pulsing blood pressure with a special instrument. He calls it a sphygmomanometer. Before you use this grand sounding word to amaze your friends, be sure to remember that it means a meter for measuring the pressure of the pulsing blood.
The sphygmomanometer has a long cloth bag with a rubber bulb to fill it with air. It also has a mercury meter to measure the pulsing. pressure of the heart beat. The doctor wraps the cloth bag snugly around your arm. Then he places the listening end of his stethoscope just below it. He listens to the secret sounds of the blood pulsing through an artery. Then he squeezes the rubber bulb to pump the cloth bag full of air. It begins to feel like a tight cuff.
The air filled bag squeezes your arm and stops the blood flowing through its arteries. The pulsing sound stops and all is quiet until the doctor begins to let the air out of the bag. The bag becomes looser and the blood starts pulsing again.
The meter measures its pulsing pressure. This shows the doctor how well your heart contracts to pump each pulseon its way. He calls it the systolic pressure. Next the meter measures the diastolic pressure. This tells how well the heart relaxes between one beat and the next. The systolic and diastolic together tell the blood pressure when the heart is busy and when it rests.
The meter measures how far the mercury rises and falls in a glass tube. There are almost 1,000 little millimeters in one yard and a ladder of millimeters is marked beside the mercury tube. When things are normal, the systolic pressure reads 120 millimeters and the diastolic pressure reads 90 millimeters. Some people have lower than normal blood pressure. Blood pressure may go higher than normal when a person exercises hard or gets excited. And certain sicknesses cause a patient to have higher than normal blood pressure.