Learning Objective: By the end of this section, the learner should be able to explain how the volume of a body compartment can be measured using tracer substances, understand the concept of volume of distribution (VOD), and calculate compartment volumes using the V = A/C formula.
Volume Measurement of Compartments
To measure the volume of a body compartment, a tracer substance is used. The tracer should meet the following criteria:
- Easily measurable
- Well distributed within the target compartment
- Not rapidly metabolized or removed from the compartment
The volume of the compartment (V) can be calculated using the formula:
Where:
- A = amount of tracer injected
- C = concentration of tracer at equilibrium
Example
- 300 mg of a dye is injected intravenously.
- At equilibrium, the dye concentration in the blood is 0.05 mg/mL.
The volume of distribution (VOD) is calculated as:
This represents the volume of the compartment that contains the dye.
