Please note that my initial question compares psi to mmHg as if they’re similar things; that was my incorrect understanding. I had been viewing “mmHg” as “pressure”. Millions of people today are being told their blood pressure is a number with “mmHg”. But mmHg is a statement of distance; there is no force or area. It is not utilized in pressure calculations. I came to realize this the day after I posted the question.

I could now revise my initial question to, “When the nurse says our BP is 120/80, what is the actual pressure (force over area) on the aorta walls when the left ventricle contracts to push a small volume of blood (systole)”?

The relationship of mmHg to psi in atmospheric pressure helps to answer that. One Earth atmosphere at sea level is 14.7 pounds per square inch. (Not sure how they determine that, but it’s accepted.) That pressure on a barometer pushes mercury to a height of 76 cm or 7600 mm. There are two interesting numbers from that relationship: 517 mmHg for each psi and 0.00193 psi for each mmHg. (7600 / 14.7 = 517. 14.7 / 7600 = 0.00193) I suggest these are valuable factors for Dimensional Analysis.

On Mars, if its atmosphere is 0.095 psi, a barometer would show 49.2 mmHg (0.095 / 0.00193). On another planet, if a barometer shows 120 mmHg, the atmospheric pressure is 0.23 psi (120 x 0.00193) same as BP 120.

To answer my initial question, the pressure statement is independent of the mmHg factor. When talking about planetary pressure, “pounds/square inch” is OK. When talking about blood pressure, “grams/square mm” may be preferred.

Note that a blood pressure monitor starts with the actual physical pressure and changes it to a number (a distance value) we can easily remember. Could the monitor be reverse-engineered to find the actual pressure? Finding the pressure at the aorta (or left arm) is important when considering the pressure in other parts of the circulation system, at capillary beds etc..

Please note that my initial question compares psi to mmHg as if they’re similar things; that was my incorrect understanding. I had been viewing “mmHg” as “pressure”. Millions of people today are being told their blood pressure is a number with “mmHg”. But mmHg is a statement of distance; there is no force or area. It is not utilized in pressure calculations. I came to realize this the day after I posted the question.

I could now revise my initial question to, “When the nurse says our BP is 120/80, what is the actual pressure (force over area) on the aorta walls when the left ventricle contracts to push a small volume of blood (systole)”?

The relationship of mmHg to psi in atmospheric pressure helps to answer that. One Earth atmosphere at sea level is 14.7 pounds per square inch. (Not sure how they determine that, but it’s accepted.) That pressure on a barometer pushes mercury to a height of 76 cm or 7600 mm. There are two interesting numbers from that relationship: 517 mmHg for each psi and 0.00193 psi for each mmHg. (7600 / 14.7 = 517. 14.7 / 7600 = 0.00193) I suggest these are valuable factors for Dimensional Analysis.

Sorry: numbers are wrong but concept remains. Edit: 7600 mm should be 760 mm. (10 mm in each cm) Edit: 7600/14.7 should be 760/14.7=51.7. Edit: 14.7/760=0.019. Edit: Two numbers: 51.7mmHg for each mmHg, 0.019psi for each mmHg.
Edit: Correction on planet: On another planet, if a barometer shows 120 mmHg, the atmospheric pressure is 2.28 psi (120 x 0.019) same as BP 120.

To answer my initial question, the pressure statement is independent of the mmHg factor. When talking about planetary pressure, “pounds/square inch” is OK. When talking about blood pressure, “grams/square mm” may be preferred.

Note that a blood pressure monitor starts with the actual physical pressure and changes it to a number (a distance value) we can easily remember. Could the monitor be reverse-engineered to find the actual pressure? Finding the pressure at the aorta (or left arm) is important when considering the pressure in other parts of the circulation system, at capillary beds etc..