How do the lungs and heart mechanically interact during inspiration?

How do the lungs and heart mechanically interact during inspiration?

• A. Diaphragm relaxation increases thoracic volume; heart movement is unaffected.
• B. Diaphragm contraction increases thoracic volume, lowering intrathoracic pressure and aiding venous return; heart movement is influenced by chest wall motion and pressure changes during respiration.
• C. The heart expands chest wall to draw air in; lungs do not contribute.
• D. Inspiration only affects lungs; heart movement has no relation to respiration.

Answer: (B)