CPFT Practice Exam 2025 – Complete Test Prep Guide

The body box, also known as the plethysmograph, is significantly associated with Boyle's law, which states that the pressure of a gas is inversely proportional to its volume when temperature is held constant. In pulmonary function testing, the body box measures the total lung volume through a process that utilizes the principles of Boyle's law.

When a person enters the body box, there is a change in pressure within the closed system that corresponds to changes in lung volume as the subject breathes in and out. The device accurately calculates lung volumes based on these pressure changes, thereby allowing for the assessment of lung mechanics and function. This principle is crucial when analyzing conditions such as restrictive lung disease, where lung volume is reduced.

In contrast, other equipment listed—such as the peak flow meter, manometer, and spirometer—does not fundamentally rely on the principles of Boyle's law to function in the same manner as the body box. For example, while a spirometer can assess lung volumes by measuring the amount of air inhaled and exhaled, it does not directly apply Boyle's law in the same context, as it typically doesn’t operate in a closed environment or measure pressure changes in the same specific way that the body box does. Similarly