National League for Nursing (NLN PAX) Practice Exam

The increase in a person's respiratory rate during exercise is primarily caused by an increase in carbon dioxide (CO2) concentration in the blood. As the body engages in physical activity, muscles consume more oxygen and produce more CO2 as a waste product of metabolism. This elevated level of CO2 is detected by chemoreceptors in the body, which respond by signaling the respiratory centers in the brain to increase the rate and depth of breathing. This process helps to enhance gas exchange in the lungs, allowing for more CO2 to be expelled and facilitating improved oxygen intake to meet the body's heightened demands during exercise.

The other options do not accurately reflect the primary stimulus for increased respiratory rate during exercise. A decrease in oxygen concentration in the lungs may occur, but it is not the most immediate or significant trigger compared to rising CO2 levels. An increase in hemoglobin in the blood would typically imply an enhanced capacity for oxygen transport, but it does not directly lead to increased respiratory rate. Lastly, a decrease in CO2 concentration would not trigger an increase in respiratory rate, as the body regulates breathing primarily in response to rising levels of CO2.