What Is Blood Pressure?

If you want to understand What Is Blood Pressure from a simple and easy to read explanation then come to the genuine Doctor's Practical Guide.

So without fanfare we'll begin the explanation:

What Is Blood Pressure?

First is the definition from Hammond and Barnhart's Dictionary of Science:

Blood Pressure: The pressure of the blood against the inner walls of the blood vessels, varying with the strength of the heartbeat, the volume of the blood, the elasticity of the arteries and the person's health, age and physical condition.

Another definition of What Is Blood Pressure; this one from the top medical dictionary—Dorland's Medical Dictionary:

First, defining the more general word, pressure:

Pressure: Force per unit area.

Then defining the more narrow and specific kind of pressure, blood pressure:

Blood Pressure: The pressure of the blood on the walls of the arteries, dependent on the energy of the heart action, the elasticity of the walls of the arteries, and the volume and viscosity of the blood.

Still not satisfied? Me neither, not completely. I think this expresses it a little better:

The heart pumps the blood around the body and thus imparts force to the blood. The blood exerts this force on the inner walls of the blood vessels which contain the force and channel the blood in the desired direction. When we measure this force in terms of unit area it becomes pressure.

Better. This satisfies me. It tells us What Is Blood Pressure.

What Effects Blood Pressure?

Blood pressure is mainly dependent on four factors:

  1. Changing the heart rate or the force of the beat or both will change the blood pressure.
  2. Expanding or contracting the size of the small veins causes a decrease or increase respectively in the pressure.
  3. Expanding or contracting the size of the small arteries causes a decrease or increase respectively in the pressure.
  4. Decreasing or increasing the amount of fluid (blood) in the blood vessels by the kidneys will decrease or increase pressure respectively.

There are a host of other factors that affect the four listed factors. See this page Normal Blood Pressure One example would be anxiety which causes the heart to beat faster and stronger which then causes a rise in blood pressure.

Doctor's Practical Guide:

Not much to add to this explanation. Just remember that to know your true blood pressure level you must take it yourself. See How To Take Blood Pressure which tells Why as well as How.

Here is a table of desirable Blood Pressure levels:

Blood Pressure Classification
Systolic Diastolic Class
115 75 Desirable
120-139 80-89 Prehypertension
140-159 90-99 Hypertension Stage 1
160 or over 100 or over Hypertension Stage 2

My background as a semi-retired physician includes an undergraduate major in Physics with minors in both Math and Chemistry, four years in Electronics (Navy) and the obvious lifelong study of Medicine.


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