What heart sound may indicate a patent ductus arteriosus in a newborn?

A soft murmur may indicate a patent ductus arteriosus (PDA) in a newborn. This is because, in the case of a PDA, there is turbulent blood flow across the ductus arteriosus due to the connection between the aorta and the pulmonary artery remaining open after birth. As a result, the turbulent flow creates a characteristic sound, typically described as a continuous or "machine-like" murmur. This murmur can often be soft and may be best heard in the left infraclavicular area, which highlights the underlying hemodynamics affected by the patent vessel.

Characteristics of the other options do not align with the typical presentations of PDA. A strong heart sound does not suggest the turbulent flow associated with a PDA, while a high-pitched whistling sound is more consistent with conditions involving stenosis or high-velocity jets rather than a PDA. An absent heart sound is not associated with PDA either, as there would still be audible sounds related to blood flow, even if diminished. Understanding these nuances helps in effectively identifying the presence of a patent ductus arteriosus during physical examination of a newborn.