At what position does functional residual capacity (FRC) occur?

At what position does functional residual capacity (FRC) occur?

• A. Full inspiration
• B. During exercise
• C. Resting position
• D. Maximal expiration

Answer: (C)

Functional residual capacity (FRC) is the volume of air remaining in the lungs after a normal expiration. This capacity represents the balance point where the forces of the lungs, which tend to collapse, and the thoracic cavity, which tends to expand, are equal. At resting position, the individual is typically in a state of equilibrium where the respiratory muscles are relaxed and there is no active inhalation or exhalation taking place. This state allows FRC to be measured accurately because it reflects the amount of air that remains in the lungs under these relaxed conditions. In contrast, during full inspiration, maximal expiration, or during exercise, the lung volumes are altered, and FRC is not at the resting state of the respiratory system. Therefore, the definition of FRC aligns precisely with the conditions found at resting position, making this the correct answer.

Functional residual capacity (FRC) is the volume of air remaining in the lungs after a normal expiration. This capacity represents the balance point where the forces of the lungs, which tend to collapse, and the thoracic cavity, which tends to expand, are equal.

At resting position, the individual is typically in a state of equilibrium where the respiratory muscles are relaxed and there is no active inhalation or exhalation taking place. This state allows FRC to be measured accurately because it reflects the amount of air that remains in the lungs under these relaxed conditions.

In contrast, during full inspiration, maximal expiration, or during exercise, the lung volumes are altered, and FRC is not at the resting state of the respiratory system. Therefore, the definition of FRC aligns precisely with the conditions found at resting position, making this the correct answer.