CO₂ concentration map representing different stages of the first respiratory cycle (normal breathing pattern). A sagittal plane taken parallel to the plane of the center of the infant’s nostril is shown at different discrete times within the first modeled respiratory cycle. Blue represents a CO₂ concentration of zero percent (the modeled concentration of ambient air), and red represents a CO₂ concentration of 5% (the usual CO₂ concentration found in exhaled air from a human infant). (a)  sec; (b)  sec; (c)  sec; (d)  sec; (e)  sec.