Hydrostatic Pressure - Medical Applications (Fluid Mechanics - Lesson 4)

[@AshishGupta-pp4sv]

IMO - Excellent - That applies to each and every one of your videos - Exact vocabulary and near-perfect layering of complex scientific & medical principles - Your instruction has greatly enhanced my understanding, has enabled me to think better and ultimately be a better physician - Thank you so very much Prof./Dr. Strong

[@osteogenesiscongenita7600]

This is excellent. I was perplexed as to why Guyton, without explanation, employs cm water for pleural pressure and continued to use mm Hg for alveolar pressure. This helped.

[@georgeseese]

I really appreciate your videos but I find this a little confusing. The title starts, “Hydrostatic Pressure...” defined in the previous video as “pressure in a fluid when it’s at rest”. That video provided an example of an aquarium that doesn’t leak. To be equal to that, the heart must be stopped and all the capillaries clamped to prevent leaks. The arterial system becomes a complex aquarium. If you could insert a tube into the arterial system at various heights, it would “measure” the range of hydrostatic pressures. For a person standing on their feet, the pressure would be greatest in the foot area, corresponding to the bottom of the right-lower side of the aquarium. The numbers from a standard Blood Pressure procedure are reflections of air pressure on an arm artery that has moving fluid. Even the diastolic pressure is when blood is moving into capillaries that leak into their adjacent space. The blood is not at rest, so why is it called an example of hydrostatic pressure? And if it’s not hydrostatic pressure, what is it?

[@georgeseese]

The hydrostatic pressure of a fluid "at rest" does not disappear if the fluid starts to move (acted upon by another force). Perhaps the term "at rest" is misleading; the equation for hydrostatic pressure includes Acceleration of gravity (a force towards earth, shown in the barometer). If another [stronger] force acts in another direction (e.g. sideways or up) the body of fluid reacts to that stronger force (e.g. heart injecting more blood into the aorta). Isn't blood pressure more related to Dynamic pressure that has other properties and equations?

[@tysken0251]

But why does JVP= height over sternum from where you stop seeing pulsations? Even if the blood was standing still the JVP=rho*g*h where h is height difference from head to internal jugular vein? Is it because you assume the pressure is 0 where you cannot see the jugular vein pulsate anymore and how is this assumption validated? And what is the reference pressure? Is it the atmospheric pressure?

[@StrongMed]

I have more recent video which provides a better explanation for JVP (including a little on why its not as great a measure of intracardiac pressure as often taught in medical school): kzbin.info/www/bejne/oX6qYX-on7etbbM

[@yankzaddict02]

When the heart squeezes blood out of the heart during systole and reaches maximum velocity through the arteries, shouldn't that result in lower blood pressure as per the Bernoulli principle, which you explained in Lesson 8?

[@ericstrong875]

Neil, the Bernoulli Principle is essentially a statement of the Conservation of Energy within a flowing fluid. When comparing the systolic and diastolic phases of the cardiac cycle, energy density within the blood is not being conserved because kinetic energy is added during systole, and disapates as friction during diastole. Therefore Bernoulli doesn't apply.

[@yankzaddict02]

ohhh, that makes sense now. Thank you, Eric. Your videos are awesome! I just wish you kept making more of these lessons--they really help with MCAT studying.

[@oleseljestad]

Great and funny!