A 40-year-old man with tuberculous pericardial effusion has muffled heart sounds, raised JVP, and systolic blood pressure that falls by 18 mmHg during quiet inspiration. The inspiratory fall in systolic pressure is best explained by:
- A Increased pulmonary venous return to the left atrium during inspiration
- B Direct compression of the thoracic aorta by the distended pericardium
- C Competing right and left ventricular filling within a fixed pericardial volume, so inspiration augments right-sided filling at the cost of left-sided output ✓
- D Reflex withdrawal of sympathetic tone triggered by pericardial stretch receptors
Correct answer: C. Competing right and left ventricular filling within a fixed pericardial volume, so inspiration augments right-sided filling at the cost of left-sided output
Explanation
Pulsus paradoxus exceeding 10 mmHg is classic for cardiac tamponade. Inspiration lowers intrathoracic pressure, increasing systemic venous return to the right ventricle. Because the fluid-filled pericardium fixes total cardiac volume, septum shifts leftward, reducing left ventricular filling and stroke volume, hence the exaggerated inspiratory dip in systolic pressure. Increased pulmonary venous return would raise rather than lower left-sided filling, and no specific aortic compression or reflex mechanism produces this sign.
Reference: Harrison Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.