In low-birth-weight infants, the innocent pulmonary flow murmur is transmitted to which regions?

• A. Right chest only
• B. Neck and back
• C. Right and left chest, both axillae, and back
• D. Abdomen

Answer: (C)

Innocent pulmonary flow murmurs come from turbulent flow across the pulmonary valve due to relatively high pulmonary blood flow, which is common in newborns, especially those with low birth weight or prematurity. This type of murmur is typically a soft systolic ejection sound heard best at the left upper sternal border, but it often radiates widely because sound travels through the chest wall and into adjacent areas as the blood flow pattern extends outward from the pulmonary outflow tract.

In low-birth-weight infants, thinner chest structures and actively circulating blood make it easy for the murmur to be transmitted to multiple regions. That’s why you can hear it not only over the chest on both sides but also in the axillae and the back. Its absence in the abdomen helps distinguish it from murmurs that localize there. So the pattern of transmission—right chest, left chest, both axillae, and back—fits an innocent pulmonary flow murmur in this population.