A 58-year-old man from Delhi presents with progressive dyspnea and a pulsatile hepatomegaly. On cardiac auscultation, a prominent S3 is heard at the apex, followed by a pansystolic (holosystolic) murmur that increases with inspiration. The murmur is best heard at the left lower sternal border and radiates to the xiphoid process. Echocardiography shows severe tricuspid regurgitation (TR) with a dilated right ventricle. Which physiological mechanism explains why this murmur increases with inspiration?