Gibson's murmur

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Gibson's murmur is a continuous murmur that heard in patent ductus arteriosus.

PDA is an abnormal connection between the aorta and the pulmonary artery, which normally should be closed in infancy. Since aortic pressure is higher than pulmonary pressure, a continuous murmur occurs, which is often described as a machinery murmur or Gibson's murmur.

The maximum intensity of the murmur usually occurs at S2. The duration of the murmur depends upon the pressure difference between aorta and pulmonary artery.

Pathophysiology
In patients with pulmonary hypertension, pulmonary artery diastolic pressure increases; when it approaches systemic level, the diastolic portion of the continuous murmur becomes shorter and ultimately absent

In patients with more severe pulmonary hypertension, pulmonary artery systolic pressure can equalize with aortic systolic pressure and the systolic component of the murmur may also be absent (silent ductus).

Differential Diagnosis
Cyanosis due to the reversal of the shunt and signs of pulmonary hypertension with or without evidence of right sided heart failure are the only physical findings that are recognizable at the bedside in these circumstances.

Additional Reading

 * Moss and Adams' Heart Disease in Infants, Children, and Adolescents Hugh D. Allen, Arthur J. Moss, David J. Driscoll, Forrest H. Adams, Timothy F. Feltes, Robert E. Shaddy, 2007 ISBN 0781786843
 * Hurst's the Heart, Fuster V, 12th ed. 2008, ISBN 978-0-07-149928-6
 * Willerson JT, Cardiovascular Medicine, 3rd ed., 2007, ISBN 978-1-84628-188-4