Which statement correctly describes the relationship between pressure and volume in breathing, as per Boyle's Law?

• A. Directly proportional; P=V
• B. Pressure is independent of volume
• C. P=V^2
• D. Inversely proportional; P=1/V; Boyle's Law

Answer: (D)

Boyle's law shows that for a fixed amount of gas at constant temperature, pressure and volume are inversely related: as volume increases, pressure decreases, and as volume decreases, pressure increases (P1V1 = P2V2). In breathing, when the chest wall and diaphragm expand, the lung volume increases, causing the intrapulmonary pressure to fall below atmospheric pressure. That pressure difference draws air into the lungs. When the chest relaxes and lung volume decreases, intrapulmonary pressure rises above atmospheric, pushing air out. This inverse relationship—pressure changing opposite to volume—is what drives airflow during inspiration and expiration. Other ideas, like pressure increasing with volume, pressure being independent of volume, or pressure following a V squared relationship, don’t describe how gases behave in the lungs under these conditions.