In a healthy young adult, auscultation at the pulmonic area reveals wide splitting of the second heart sound during inspiration that disappears during expiration. What is the mechanism of the inspiratory widening?

• A Inspiration brings the pulmonic component closer to the stethoscope, unmasking pre-existing delay
• B Inspiration advances aortic valve closure by reducing left ventricular preload
• C Inspiration delays aortic valve closure by increasing systemic venous return
• D Inspiration delays pulmonary valve closure by increasing right ventricular stroke volume ✓

Explanation

During inspiration, negative intrathoracic pressure increases systemic venous return, prolonging right ventricular ejection and delaying pulmonic valve closure. Simultaneously, expanded pulmonary vessels hold more blood, briefly reducing left-sided filling so aortic closure comes slightly earlier. Both effects widen the D2-P2 gap, normally under 30 milliseconds at expiration. Option A describes accentuation of a fixed split, which is the mechanism behind the wide fixed splitting of atrial septal defect, not physiological splitting.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.