Define tidal volume (VT).

• A. The air remaining in the lungs after a maximal exhalation
• B. The total amount exhaled after a maximal inspiration
• C. The air reaches the alveoli per breath
• D. The volume inhaled or exhaled during a normal resting breath

Answer: (D)

Tidal volume is the amount of air moved in or out of the lungs during a normal resting breath. It reflects the typical, everyday ventilation that keeps gas exchange going. For an average adult, this is about 500 mL, though it varies with body size and breathing depth. It’s not the air left after a full exhale (that’s residual volume), nor the total air you could exhale after a maximal inhale (that’s vital capacity). Also, while tidal volume includes air that fills the lungs, only part of it reaches the gas-exchange surfaces; the portion that actually reaches the alveoli is tidal volume minus the dead space air in the conducting airways.