Select the correct formula for functional residual capacity.

A. Pleural cavity: The pleural cavity is the potential space between the parietal pleura (lining the thoracic wall) and the visceral pleura (covering the lungs). It contains a small amount of lubricating fluid that reduces friction during lung expansion and contraction, allowing smooth respiratory movements while maintaining negative pressure to facilitate lung inflation.

B. Bronchial space: The bronchial space refers to the lumen of the bronchi through which air passes. It is not a cavity between pleural layers and does not play a role in pleural fluid dynamics or lung expansion.

C. Alveolar cavity: Alveolar cavities are microscopic air spaces within the lungs where gas exchange occurs. They are internal to the lung tissue and do not exist between the pleural layers.

D. Thoracic cavity: The thoracic cavity is the large compartment of the chest housing the lungs, heart, and major vessels. While it contains the pleural cavities, it is not specifically the space between the parietal and visceral pleurae.

A. Forced Expiratory Volume (FEV1): FEV1 is the maximal volume of air a person can forcibly exhale in the first second of a forced expiration following full inhalation. It is a critical measure in pulmonary function testing, used to assess airway obstruction, as seen in conditions like asthma or chronic obstructive pulmonary disease (COPD).

B. Forced Vital Capacity (FVC): FVC represents the total volume of air exhaled forcefully after a maximal inhalation, regardless of time. While FEV1 is measured within the first second of this maneuver, FVC measures the complete exhaled volume and not the rate or initial flow.

C. Residual Volume (RV): RV is the volume of air remaining in the lungs after maximal exhalation. It cannot be voluntarily expelled and serves to prevent alveolar collapse. RV is unrelated to forced exhalation measurements like FEV1.

D. Expiratory Reserve Volume (ERV): ERV is the additional volume of air that can be exhaled after a normal tidal exhalation. It does not reflect the maximal forced expiratory flow over one second and is only a portion of the total exhaled capacity.

E. Tidal Volume (TV): TV is the volume of air inhaled or exhaled during normal, quiet breathing. It is a small, routine respiratory volume and does not represent maximal or forced expiratory capacity.