New York State Basic Emergency Medical Technician (EMT-B) Practice Exam

In a healthy individual, respiration is primarily controlled by the levels of which gas?

1. Carbon monoxide

2. Blood sugar

3. Oxygen

4. Carbon dioxide

The correct answer is: Carbon dioxide

Respiration in a healthy individual is primarily controlled by the levels of carbon dioxide in the blood. The body closely monitors carbon dioxide levels because they provide a crucial indication of metabolic activity and the need for gas exchange. When carbon dioxide levels rise, it leads to an increase in the acidity of the blood, signaling the respiratory center in the brain to increase the rate and depth of breathing. Oxygen levels do play a role in respiration; however, they are not the primary driver for normal breathing rhythms. The body can tolerate quite low levels of oxygen for a time, whereas elevated carbon dioxide levels require immediate action to avoid respiratory acidosis and other complications. Thus, carbon dioxide is the key gas that the body uses to regulate breathing, making it the correct answer to this question.