Medicine For People!

June 2015

High Blood Pressure: What Is It and Why Should I Worry?

High Idle Speed

"Tom, your blood pressure has been running a little high for a couple of years. Today it is 145/95. Do you want to talk about that?"

Whatever conversation follows usually ends up with the question "How dangerous do you think this is, doctor?"

The analogy I think works best is to compare your heart with an engine. It's difficult to measure the blood pressure of a moving patient, so we measure blood pressure when you are sitting. We can think of this as your idle speed. Just as your automobile engine revs up when your car speeds up a hill, so does your blood pressure rise when you walk around or exercise. Muscles need oxygen, and the heart speeds up and increases pressure to do this. One study[1] of young athletes who had an average resting blood pressure of 120/75 found that, for example, one athlete's blood pressure rose to 195/128 during exercise. A more typical rise would be to about 160/120.

Consequences

I can't predict what will happen to your car if it always runs at a high idle speed. In the case of humans, observation shows that high resting blood pressure can triple the chances of heart disease or stroke. Even if those problems don't occur, a 50-year old person with significant untreated high blood pressure can expect to lose about 5 years of life.

Healthy athletes do not drop dead when their blood pressure temporarily rises to 180/120. Your car's engine will not break just because the idle speed is faster than the factory setting. But in both cases, whether it's constant high blood pressure or a constant fast idle speed, the machinery just isn't going to last as long.

What Do The Numbers Mean?

I explained to Tom that the pressure we were measuring is the pressure in the artery in his arm, which is about the same as the pressure in all his arteries, including the aorta, the big artery arising from his heart. Just as the air in a bagpipe is pressurized so the bagpipe makes a sound even when the piper has to draw breath, so the aorta and the other arteries are elastic and pressurized so that the blood flows even when the heart pauses between pumps. The top number we called the systolic pressure; 145 is the pressure in Tom's arterial system when his heart is pushing the most blood into the system. Before the next heartbeat, blood drains off to the arterial system into all the organs of Tom's body, and the pressure falls to 95. This is called the diastolic pressure. At that point, the heart muscle once again forces a few ounces of blood into the pressurized arterial system and up goes the pressure again.

These pressures measure the height in millimeters to which a column of mercury is raised by the pressure in your arterial tree. When the blood pressure cuff around a normal young adult's arm is connected to the mercury filled glass tube in the blood pressure device, their systolic pressure, their maximum pressure, occurs when the very heavy mercury is pushed up 120 millimeters (about 5 inches) into the tube. Let's express this in a more everyday way: that same pressure would push a column of water to a height of 5 feet and 4 inches. Imagine a clear garden hose with water in it. You are blowing into the end of the hose. The pressure you would have to use to keep the water level at 5 feet and 4 inches above your mouth is the normal maximum pressure of 120 millimeters of mercury. Tom, with his systolic pressure of 145, would have to blow with more pressure and raise that column of water to 6 feet and 5 inches. His heart is working that much harder.

We don't use pressure calibrated in millimeters of mercury because we wish to confuse you. It's just too difficult to have water-filled blood pressure devices standing 12 feet tall (which is what would be required when measuring really high blood pressure). Mercury is heavier than water; it allows us to use a smaller device.

I Never Get The Same Reading Twice!

You should also know that blood pressure varies all the time, even when we are not exercising. The man in the graph below is wearing an automatic blood pressure device that records his systolic pressure every few minutes through the 24 hours. The tracing begins at midnight when his systolic pressure is under 125, records a couple of moments during the night when his systolic pressure is about 75, and picks up a maximum reading of about 175 in the middle of the afternoon. These variations are greater than in a healthy person, but as you can see his average pressure is 130, which is not out of line. We call this labile hypertension, meaning that high readings are not always present. This kind of hypertension often precedes sustained hypertension, which is why I suggested to Tom that he buy a blood pressure cuff and record his readings at home.

Graph

Source: [2]

How Long Do I Have Left, Doc?

Now that we've covered the basics, here's a calculator that estimates the 10-year risk of heart attack based upon your blood pressure, cholesterol, and the answers to a couple of simple questions.

And this one, with a few more questions, presumes to predict your lifespan. Of course, using our automobile analogy, your mileage may vary!

Postscript: Things I Tell Every Patient With High Blood Pressure

  1. Just because two medications reduce your blood pressure to normal doesn't mean both of them will increase longevity by the same amount. We need to choose those medications carefully!
  2. There's a fair amount of bias in much research on high blood pressure (and many other medical topics, for that matter). Interpret what you see in the media with skepticism. There are some breakthroughs, but not nearly as many as the headlines indicate.
  3. Blood pressure medication need not be taken for life. Sometimes people change their lifestyle, or they take medications for something else that lower blood pressure as a side effect, or we develop new methods of treatment. All you can do is take care of "now" and let the future take care of itself.
  4. Many times we can find blood pressure medication that can also remedy other problems, such as irregular heartbeat, kidney failure, anxiety, cigarette smoking, or substance abuse.

Stay active! Be well!

Endnotes

[1] Steven T. Linsenbardt,* Tom R. Thomas,** and Richard W. Madsen.*** Effect of breathing techniques on blood pressure response to resistance exercise. Br J Sp Med 1992; 26(2)

*Hammons Heart Institute, Springfield MO; **Department of Health and Physical Education, University of Missouri, Columbia MO; ***Department of Statistics, University of Missouri, Columbia MO.

[2] Graph distributed at a medical conference over thirty years ago, source not identified, credited or attributed.

Edited by Jody Bowers

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Medicine for People! is published by Douwe Rienstra, MD at Port Townsend, Washington.