November 14, 2002 (Ira Pilgrim)

Blood Pressure

Everywhere he feels his Heart because its vessels run to all his limbs.

The Ebbers Papyrus (Egypt, ca.1550 BC)

Your physician may tell you that your blood pressure is normal, low or high. What does he mean? What is blood pressure?

If you put a tube in an artery and connected it to a manometer, an instrument that measures the pressure of a fluid(a gas or liquid), you would find that the pressure fluctuates with every beat of the heart. When the left ventricle of the heart(which is the main pump) contracts(called the systole) the pressure will go up. That highest measurement is called the systolic pressure. When the ventricle relaxes(diastole), the pressure goes down. Its lowest point is called the diastolic pressure; the pressure in the artery when the left ventricle is relaxed.

The doctor doesn't stick a tube into your artery. He measures blood pressure in an indirect way. He puts a cuff around your arm which is attached to a manometer that measures the air pressure in the cuff. Then he puts a stethoscope over the artery in your forearm. He then pumps up the cuff so that it acts as a tourniquet and stops the blood from flowing in both the arteries and veins. Then he lets the air out slowly until he can hear a heartbeat (a pulse beat). That point is where the air pressure in the cuff equals the maximum pressure in the artery. The blood can now enter the artery in the forearm, but because the vein is still blocked it "hammers" like water may in a blocked pipe. That pressure point is about the same as the systolic pressure obtained with a tube in the artery.

He continues to let the pressure drop until he can't hear the pulse any more. At that point, where the pressure in the cuff equals the pressure in the veins, the veins opens up and lets the blood through freely; which stops the sound of the pulse. This approximates the diastolic pressure as measured by a tube in the artery.

These values will be charted as 120/60 (called 120 over 60). The measurements are in millimeters of mercury and represent the pressure that it takes to raise a column of mercury, so many millimeters. The 120 is the systolic pressure and the 60 is the diastolic pressure. If you want to know what's normal, ask your doctor. Different medical people have different ideas of what's normal, just as they differ on who is crazy.

You can think of the circulation of the blood as consisting of a pump(the heart) that circulates liquid(blood) through a complex bed of tubes and pipes, some of which are very small, and then back to the pump inlet. It is a closed system where little is added or taken away. The blood is pumped round and round for as long as you live.

What will cause the pressure to stay high (high blood pressure)? Anything that interferes with the free flow of blood in the arteries. This can be arteriosclerosis (hardening of the arteries), where the arteries both lose their elasticity and are sometimes narrowed by deposits in their walls. This is the most common cause, but there are many other causes.

A sphygmomanometer (blood pressure measurer) is cheap, can be purchased mail order, and can be fun to play with. You and your kids can have some fun with it. It's one of the more socially acceptable ways to "play doctor".

Besides, measuring your own blood pressure can be useful. There are some people whose blood pressure goes up every time they go into a doctor's office. The doctor will find high blood pressure, but when they take their own pressure at home it's perfectly normal. If your doctor says that you have high blood pressure it might be a good idea to take your pressure at home several times before you start taking medicines. If your doctor considers a systolic pressure of over 140 to be something that should be treated and you measure 145 in his office, and 135 at home, you may be able to save yourself some unnecessary medication; which is always a good idea. If your measurement at home is lower than in the doctors office, that home measurement is probably the correct one, even though you're an amateur and you did it for free.

Anyone can take a blood pressure; it's easy. Any medic or nurse can check you out if you have any doubt.

Don't expect it to be the same all the time. It may be different when you're standing or lying down. It may be different at the end of the day from what it is when you just wake up. It will be higher after exertion or anger. A pretty nurse can make a man's blood pressure rise. No two instruments will measure exactly alike. Small differences are of no importance. It makes no difference if your pressure is 120/60 or 130/80 --they're both normal.

Now remember, if you find that you have no blood pressure at all, either you're dead or you've put the ear pieces of the stethoscope in your nose instead of in your ears.

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