Principles of Physics in Surgery: The Laws of Mechanics and Vectors Physics for Surgeons—Part 2

Abstract

In this sequel, to an earlier article, we discuss the laws of Mechanics, Thermodynamics and Vectors as they apply to soft and bony tissues. These include the Laplace's Law as applied to colonic perforation, compression therapy, parturition, variceal rupture, disc herniations etc. The Pascal's Law finds use in hernia repair and the Heimlich maneuver. Trigonometrically derived components of forces, acting after suturing, show ways to reduce cut-through; the thickness and the bite of suture determines the extent of tissue reaction. The heating effect of current explains the optimum gap between the prongs of a bipolar cautery and the use of law of transfer of heat in determining relation between healthy wound healing and ambient temperature.

Basic Physics Revisited for a Surgeon

“…As the flow changes with the radius to its fourth power, a small increase in radius in a large vessel results in a greater improvement in the blood flow in the smaller distal vessel. This result is a greater flow than that achieved by increasing the fractional diameter of the small distal vessel [2]. 4.…”

“…An increase in the diameter of a vessel from 1 to 2 mm will increase the flow rate by 16 times (for r=2, r4=16) if other factors shown above remain constant [2].…”

“…This has a narrow nipple with a small (r), which decreases the flow, clotting of blood and failure of the drain. Use of a wide connector will prevent this [2]. 3.…”

“…4. As the flow rate radius is raised to the fourth power, this principle should be borne in mind while repairing any hollow tubular organ like the intestine, bile duct, vas deference, fallopian tube, and ureters in addition to the blood vessels [2].…”

“…Additionally, it is best to use crystalloid to keep the viscosity (η) low. Higher flow can be achieved by maximizing the pressure difference BΔP^by applying a pressure cuff around the infusion bottle [2].…”