Fluid Dynamics and Physiology
Part of the wonder of medical and dental training is learning how complex the body is. Physiology was one of my favorite courses as a medical student. You’ll find that learning the “how” behind the “what” of the body’s operations is rewarding. It was also in Physiology course that I saw the clearest association between what I learned in my undergraduate basic science classes and what I was learning in medical school. During my clinical years, these connections proved even more valuable.
Dr. Landry previously commented on how physics supported his understanding of electrophysiology and heart function as an emergency medicine physician. There are a few other concepts in physics that help us understand and predict cardiovascular function. One of those is fluid dynamics. Using certain mathematical equations, we’re able to predict how liquids will behave when they’re in a confined space and subjected to various forces. You might recall from your physics textbook diagrams of some liquid (usually water) in a tube with several arrows facing different directions. As confusing as these diagrams can be (they certainly were for me), we use the same concepts to understand fluid movement in the bodies of our patients.
Reproduced from http://en.wikipedia.org/wiki/Capillary
The movement of fluid into and out of the blood vessels, specifically capillaries, depends on a delicate balance between two types of forces: oncotic pressure and hydrostatic pressure. These two forces can be directly affected by certain diseases, hormonal changes, and a host of other factors. Understanding how oncotic and hydrostatic pressure respond to various states of health helps physicians and dentists make diagnoses. For example, a person who is unable to produce sufficient levels of protein due to liver disease may have decreased capillary oncotic pressure. This throws of the balance of fluid flow across the capillary walls. Plasma from the blood may then leak into the tissue outside of the blood vessels. This can lead to edema, or tissue swelling secondary to fluid infiltration. Similarly, increased capillary hydrostatic pressure can also result in edema. The balance between all of the forces that can affect fluid flow is mathematically represented by Starling’s Equation. We rarely use the equation in clinical practice, but understanding the physiological principles it represents is important for patient care.
It can be easy to get lost in the details of physics as an undergraduate student. Things can quickly become complicated. You can rest assured, though, that an appreciation of the give-and-take nature of the forces in the natural world will serve you well as a medical or dental student. These same forces are very much present in our bodies and have significant effects on our health. I’ll admit that one of the most difficult lessons of my undergraduate education proved to be one of the most useful.