Which term describes the amount of air in the respiratory system not including the alveoli?

• A. Dead Space
• B. Tidal Volume
• C. Minute Volume
• D. Residual Volume

Answer: (A)

Air that fills the airways but does not reach the alveoli is dead space. This is the portion of each breath that stays in the trachea, bronchi, and bronchioles and cannot participate in gas exchange. In a typical adult, anatomical dead space is about 150 mL per breath, though physiologic dead space can be a bit larger if some alveoli aren’t perfused well. Tidal volume refers to the total amount of air moved in and out with each breath, which includes both dead space air and alveolar air. Minute volume is that amount per minute (tidal volume multiplied by respiratory rate). Residual volume is the amount of air remaining in the lungs after a forceful exhale, which includes air in both alveoli and airways and isn’t specifically about non-exchange air.