A Weird Thought about Blood Pressure

By: Joseph Maa

Date: June 10, 2017

Hi everyone!

Just a weird thought about blood pressure for today. The common numbers that everyone knows is 120/80 mmHg mercury for normal blood pressure. The mmHg just means the pressure to push a column of mercury 120 mm at sea level.

I was really confused today after thinking about getting stabbed and bleeding out because normal atmospheric pressure is 760 mmHg. It makes sense that if the outer atmospheric pressure were higher than our circulation, that blood would just stay in our body when we got a cut.

Screen Shot 2017-06-10 at 2.14.45 PM.png
Figure 1: A picture of an artery. All our blood vessels would collapse if they were actually at a absolute pressure of 120/80 mmHg all the time [1]
However, after looking online, [2] I found that the 120/80 mmHg actually measures the blood pressure OVER atmospheric pressure, also known as the gauge pressure. In other words, if I stuck a pressure gauge in my blood, I would expect to get 760 + x mmHg pressure that my heart was exerting.

Hopefully you enjoyed this random fact and hope your day is absolutely swell!

Your friend,

Joseph

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