Blood Pressure and Velocity in Relation to Bernoulli’s Principle and Pascal’s Law

By Crystal Bishop

What is Bernoulli’s Principle in relation to blood pressure and velocity?

However, let’s go back to the original question, keeping in mind that work imposed on the veins may originate with the work of the muscles (how blood actually gets circulated around the body), and that can lead to an explanation of why there tends to be a higher velocity/low pressure in the veins as compared to capillaries; but, it doesn’t explain the pressure and velocity within the veins/capillaries itself. But, if we look at the examples above, it is the system of balance that results from an exchange between the object and fluid and is explained and quantified through Bernoulli’s Principle.

Daniel Bernoulli, a medical student, discovered that fluids (which have no shape and yield to external pressure, such as a liquid or gas) with high pressure will have low velocity. Conversely, low-pressure fluids will have high velocity. Amazingly, he was studying blood pressure in relation to circulation. What he found in his experiments using constricted tubes was high pressure=low velocity and low pressure=high velocity. You may also be wondering if the size of a “container” or “tube” is relevant; it’s not, but the shape and compressibility of the container or tube will have a bearing. It’s interesting to note that having more of something (liquid/gas) doesn’t cause higher or lower pressure. 

What about Pascal’s Law in relation to blood pressure and velocity?

That subject leads to a discussion concerning the compressibility of molecules that bounce around and impact the walls of the “container” or “tube.’  This concerns Pascal’s laws of fluids under pressure. Pascal’s law states that the pressure of a gas or liquid at rest exerts force equally in all directions against the walls of its container. The force is measured per unit area (pounds per square inch—psi). Wait a minute, isn’t blood pressure measured by something else? Yes.  It’s measured as millimeters of mercury instead of psi. Why? Because using mm/hg allows for a better or more precise measurement with extremely low pressure in fluids. Here is an article to explain it https://www.mobilehydraulictips.com/comparing-blood-pressure-fluid-power-pressure/