Praxis SLP Licensure Exam

A person has a vital capacity of 5 liters and performs restful breathing, exchanging half a liter. What is their expiratory reserve volume?

1. 1.5 liters

2. 2 liters

3. 2.5 liters

4. 3.5 liters

The correct answer is: 1.5 liters

To determine the expiratory reserve volume (ERV) in this scenario, it's essential to understand the definitions and relationships among vital capacity, tidal volume, and expiratory reserve volume. Vital capacity refers to the maximum amount of air that can be exhaled after a maximum inhalation and includes several components: tidal volume (the amount of air exchanged during restful breathing), inspiratory reserve volume, and expiratory reserve volume. In this case, the person has a vital capacity of 5 liters and is performing restful breathing, where they are exchanging half a liter with each breath. Tidal volume, therefore, is 0.5 liters. Given the formula for calculating vital capacity: Vital Capacity = Tidal Volume + Inspiratory Reserve Volume + Expiratory Reserve Volume If we denote the inspiratory reserve volume as IRV and recognize that during restful breathing, a person does not actively utilize this volume, we can abstract it for this question. The vital capacity has to account for all three components. Given that the total vital capacity is 5 liters, we can break it down: 5 liters = 0.5 liters (Tidal Volume) + IRV + ERV. When we want to isolate ERV, it becomes: ERV =