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Residual Volume (RV)
Air that remains in the lungs at the end of maximum exhalation. Approximately 1,200 mL.

Expiratory Reserve Volume (ERV)
Maximum volume of air that can be exhaled after a normal exhalation to residual volume. Usually one third of VC, or approximately 1,200 mL.

Inspiratory Reserve Volume (IRV)
Maximum volume of air that can be inhaled after a tidal breath has been taken. Allows for a sigh to reinflate partially collapsed alveoli. Approximately 3,600 mL.

Tidal Volume (VT)
The volume of gas moved in or out of the lungs in a normal resting breath. Inspiration delivers new atmospheric gas to the lungs, and expiration removes carbon dioxide. A general estimate of normal VT is 10 mL/kg of body weight, or approximately 500 mL.

Functional Residual Capacity (FRC) Sum of RV + ERV
Volume of air in lungs after normal expiration. Serves as a gas reservoir and maintains alveoli in their partially expanded state. Approximately 2,400 mL.

Inspiratory Capacity (IC) Sum of IRV + VT
Maximum volume of gas inspired from resting expiratory level. Usually two thirds of VC, or approximately 3,600 mL.

Total Lung Capacity (TLC) Sum of all lung volumes
Volume of air in lungs after a maximal inspiration. Approximately 6,000 mL.

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Functional Residual Capacity (FRC) Sum of RV + ERV
Volume of air in lungs after normal expiration. Serves as a gas reservoir and maintains alveoli in their partially expanded state. Approximately 2,400 mL.

Vital Capacity (VC) Sum of ERV + IC
Maximum volume of air exhaled after maximum inspiration. Can be approximated at 65 mL/kg of body weight, or approximately 4,800 mL. (A decrease of VC in the neuromuscularly diseased patient indicates that the patient is unable to cough or move secretions. Not true, however, if decrease is due to restrictive lung disease.)