Intraalveolar pressure at end inspiration and end expiration during passive breathing is what value?

• A. -5 cm H2O
• B. 10 cm H2O
• C. 0 cm H2O
• D. 5 cm H2O

Answer: (C)

During quiet, passive breathing, air moves because alveolar pressure dips below atmospheric during inspiration and rises above atmospheric during expiration. When each phase ends, airflow stops and the alveolar pressure returns to atmospheric pressure. Since atmospheric pressure is the reference (0 cm H2O), the intraalveolar pressure at the end of both inspiration and expiration is 0 cm H2O.