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Ever Wonder About Blood Pressure?

The other day, I tried the free blood pressure monitor at the drug store. I decided to look into what it was telling me.

The sphygmomanometer, the splendid name for this gadget, had a cuff that I stuck my arm into, just above the elbow. I pushed the start button and the cuff inflated, squeezing my bicep until it cut off the blood flow to my forearm. The cuff slowly deflated and took measurements.

Blood pressure is commonly measured in mm Hg (millimetres of mercury). This refers to how high the pressure would have to be to push a column of mercury. It’s a bit old school considering that the metric unit for pressure is supposed to be pascal (Pa) and nowadays, the devices are often digital. Habit, I guess. Blood pressure readings are recorded as a high number over a low number.

 My doctor takes blood pressure readings in her office with a rubber bulb connected to a portable cuff. She listens with her stethoscope for Korotkoff sounds, the sound of the blood passing through the arteries. The first sounds indicate when the blood begins to squeeze through. This is systolic pressure, the high number, which measures the pressure in the arteries when the heart pumps. When the sounds disappear, you get the diastolic pressure, which measures the pressure in the arteries between pumps. This is the lower number.

Like a Goldilocks situation, you don’t want your blood pressure too high or too low, you want it just right. The ideal numbers are 120 over 80 mm Hg. The machine told me that I was at the fringes of normal, although other sources defined that as “prehypertension." Many factors can affect your blood pressure and you’re supposed to take the time to relax before getting it measured. Some people have "white coat hypertension” where just visiting the doctor makes them so nervous that their blood pressure goes up. If you're fine at the doctor's, but higher elsewhere, you have "masked hypertension."

High blood pressure or hypertension can lead to all kinds of problems. It tends to be more common as we age because our arteries harden up, which restricts blood flow, resulting in higher pressure. Regular exercise keeps the arteries more flexible. Salt is a major culprit in higher blood pressure with its ubiquity in processed foods and modern eating habits. More salt in the blood results in kidneys retaining more water, which results in higher blood pressure. Obesity also increases blood pressure by adding fatty tissue, which means you need more blood circulating to supply nutrients to tissues, which increases blood pressure.

Low blood pressure might indicate that the heart is not working well. It might also be the result of blood loss or dehydration. And if you are pregnant, the expansion of your circulatory system can lead to a drop in blood pressure.

So, there’s a lot is going on behind those two little numbers and you should probably keep an eye on them—but no pressure, of course.