Vital signs. Now there’s a phrase that brings a particular image to mind: An emergency room in a hospital with doctors and nurses flurrying about in life and death struggles; monitors and machines beeping, humming and whirring all clamoring to provide their piece of information as part of the care and treatment being provided. One such piece of vital information is blood pressure.

Do you know what your blood pressure is? No, I don’t mean the actual numbers like 120/80. I mean, do you know what your blood pressure is? Do you know what those numbers represent?

It is fair to say that most people are aware that blood pressure is a measurement related to the heart. But beyond that, what are medical people talking about when they talk about blood pressure?

A discussion of blood pressure began a few centuries ago with a physician in London, William Harvey (1578-1657). Prior to Harvey, the prevailing view of circulation was that veins originated in the liver and arteries originated in the heart.

Harvey was the first to conceptualize the heart as a pump whose sole purpose was to force blood through the body’s myriad system of arteries and veins.

He understood that the pulse represented the contraction of the heart and that this contraction initiated the flow of the body’s blood and that the enormous network of arteries, veins and capillaries, from the largest to the tiniest microscopic caliber, comprised the resistance, or pressure, against which it had to pump.

Finally, to fully understand the nature of blood pressure you must also understand some very basic concepts in physics. First, viscosity, the property of a fluid that resists the force tending to cause the fluid to flow.

As the liquid becomes thicker, the pressure required to force the flow increases. Second, laminar vs. tubular flow. Laminar flow is when a liquid flows unobstructed against smooth, straight walls. It is fast and almost soundless.

Tubular flow is when a liquid flows against walls that twist and turn, through tubes that change caliber and/or against walls that are no longer smooth but roughened to various degrees.

The smooth flow is disrupted by numerous smaller currents, whorls and eddies and in turn causes vibrations that can be heard.

Putting all these pieces together you can understand what your blood pressure truly is. It is the measure of the force blood exerts when pumped by the heart against the blood vessel walls.

The healthier your heart and entire cardiovascular system, the less force is needed to keep things flowing as measured by a lower blood pressure.

A cardiovascular system that is troubled by arteriosclerosis and plaque formations (otherwise known as “hardening of the arteries”) or other medical problems related to viscosity and flow can reveal itself by the measurement of blood pressure.

So when was the last time you had your blood pressure checked?


• Agnes Oblas is an adult nurse practitioner with a private practice and residence in Ahwatukee Foothills. For questions, or if there is a topic you would like her to address, call (602) 405-6320 or email Her website is

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