Continuous (Machinery) Murmurs

How to Cite This Chapter: Ibrahim O, Sibbald M, Szczeklik W, Leśniak W. Continuous (Machinery) Murmurs. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed July 01, 2022.
Last Updated: December 14, 2020
Last Reviewed: April 10, 2021
Chapter Information

1. Mechanism: High- or low-pressure shunts usually caused by abnormal communications between arteries.

2. Causes: Aortopulmonary shunts such as from patent ductus arteriosus, atrial septal defect (under specific conditions), as well as various arteriovenous malformations, fistulae, or aneurysms. One type of continuous murmur is a physiologic venous hum originating from the internal jugular vein. It is frequently audible in children and young adults (most often pregnant women) or in patients with hyperdynamic circulation.

3. Auscultation: Continuous murmurs are audible throughout the entire cardiac cycle without an interval between systole and diastole. They begin in systole, usually achieve their maximum intensity close to the S2, and persist throughout the entire or part of diastole. Venous hum is best audible between the clavicle and the sternocleidomastoid muscle, more often on the right side. It is loudest in diastole and increases in the upright position and upon turning the head to the opposite side; it decreases or disappears in the supine position and upon gentle compression of the internal jugular vein above the point where the stethoscope is placed. Obliterating the jugular vein with pressure abolishes the murmur.

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