Which of the following is a sign of respiratory distress in newborns?

Apnea is a recognized sign of respiratory distress in newborns. It refers to periods of cessation of breathing lasting longer than 20 seconds, which can result from various underlying conditions including inadequate respiratory function. In newborns, apnea is particularly concerning as it can lead to hypoxia (low oxygen levels) and bradycardia (a significant drop in heart rate), leading to further complications.

Assessing a newborn's respiratory function is critical; signs of distress may include not just apnea but also irregular breathing patterns, grunting, nasal flaring, or retractions. Recognizing apnea as a sign of respiratory distress is vital for timely intervention and resuscitation if necessary.

The other options do not indicate respiratory distress. High blood pressure is not a typical indicator of respiratory issues in neonates and may suggest different physiological problems. A normal heart rate generally signifies that the newborn does not have immediate respiratory compromise, while unchanged muscle tone often indicates that there is no immediate distress affecting the neuromuscular function. Thus, apnea stands out as a direct sign of potential respiratory distress in newborns.