A 40-year-old man with tuberculous pericardial effusion has jugular venous distension, muffled heart sounds, and a systolic blood pressure that falls by 22 mmHg during inspiration. The primary mechanism of this inspiratory fall in systolic pressure is:
- A Right ventricular expansion shifting the interventricular septum leftward, reducing left ventricular filling ✓
- B Increased pulmonary venous return to the left atrium during inspiration
- C Inspiratory increase in systemic vascular resistance reducing stroke volume
- D Negative intrathoracic pressure increasing left ventricular afterload
Correct answer: A. Right ventricular expansion shifting the interventricular septum leftward, reducing left ventricular filling
Explanation
The rigid pericardial sac makes total cardiac volume fixed. On inspiration, venous return to the right ventricle increases, and the right ventricle expands at the expense of the left ventricle through septal displacement, reducing left ventricular preload and stroke volume. B drop greater than 10 mmHg defines pulsus paradoxus. Option B is wrong because pulmonary venous return to the left heart actually falls during inspiration.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.