Based on the anatomical and physiological differences between an infant and an adult, which finding would suggest respiratory distress in an infant, but would be less likely to be observed in an adult

Answer: Excessive movements of the walls of the abdomen

Basically babies belly breathe, that is they undergo abdominal pattern of respiration (instead of the abdomino - thoracic pattern in adult), through their abdomen.

This is because, their thoracic walls are not fully functional to undergo the normal adult mechanisms of breathing.

The ribs are short in length due to incomplete ossification. They curve out wards, at low angle, their sternum, is shaped horizontally.

These features reduce the activities of the inter coastal muscles and the thoracic cage in the mechanism of infants breathing, compare to the long ribs, obliquely shaped rib cage, with lower sternum of adult which permit the abdominal-thoracic breathing pattern.

Therefore, when the diaphragm distends during breathing, its movement pushes the organs of the abdomen down; because infants have rapid respiratory rates, the distends created rapid expansion and contraction of the walls of the abdomen to gain enough abdominal pressure.

This together with the movement of organs of the abdomen from the pathways of diaphragm created the excessive movements of the abdominal walls. This rapid abdominal wall movements creates discomfort and distress for the infant during this mechanisms.