Static Lung Volumes: Functional Residual Capacity (FRC) and Components

Static lung volumes are measured during a breath hold (no airflow). When respiratory muscles are relaxed, the lungs recoil and chest wall expands until their elastic recoil pressures equalize at the functional residual capacity (FRC).

Three Static Lung Volumes

• Tidal Volume (VT): Air moved in/out per breath.
• Inspiratory Reserve Volume (IRV): Additional air that can be inhaled after a normal breath.
• Expiratory Reserve Volume (ERV): Additional air that can be exhaled after a normal breath.