Florida Fire State Practice Exam

When oxygen concentrations are below what percentage does the human body increase its respiratory rate?

1. 20%

2. 18%

3. 15%

4. 10%

The correct answer is: 18%

The human body typically increases its respiratory rate when oxygen concentrations drop significantly below normal levels. Under normal atmospheric conditions, the oxygen concentration is about 21%. When this concentration decreases to around 18%, the body begins to sense the drop in available oxygen through chemoreceptors, which monitor oxygen levels in the blood. This signals the respiratory center in the brain to increase respiratory effort in order to intake more oxygen and maintain necessary physiological functions. At concentrations below 18%, the body must compensate for the decrease in oxygen availability, leading to changes in both respiratory rate and depth of breathing. This adaptive mechanism is crucial for functions such as maintaining energy levels and ensuring that vital organs receive adequate oxygen supply. Concentrations lower than this, such as 15% or 10%, would lead to more severe effects on the body, including respiratory distress and potential loss of consciousness, but the significant increase in respiratory rate typically starts at around 18%.