Chapter 10 - Connections to Thermodynamics

Abstract

This chapter addresses the issues relevant to thermodynamics. The issues are provided with chemical basics and chemical details. One of the issues discussed is why computerized axial tomography (CAT) scans often cause a “warm flush” sensation. The ionic nature of the contrast medium and the body's attempt to regulate the concentrations of all substances in the blood is responsible for this. Introduction of a water-soluble ionic substance into the vascular system results in an increase in the number of particles in the bloodstream as the contrast substance dissolves. The body possesses several internal regulation systems and, when perturbed by an injection, it attempts to restore the concentrations of substances in the blood to their normal or pre-injection levels. To re-equilibrate the system, water from the cells of surrounding body tissue moves into the blood plasma through capillary membranes. To accommodate the increase in water volume, the blood vessels must dilate or expand in size. An increase in the volume of circulating blood causes an extra expenditure of energy by the body, producing the flushed or warm feeling.