Morphology of sighs and their role in the control of breathing in preterm infants, term infants and adults

Background: Although there is evidence that sighs are important to restore lung volume, the factors responsible for inducing a sigh and the effects of sighs on the stability of the respiratory system remain unclear.

Objective: To compare newborn with adult sigh morphology in order to better understand the physiological mechanisms that induce sighs and the role sighs play on the control of breathing in infants.

Design/methods: We measured respiratory variables during control, the pre-sigh, the sigh, and the post-sigh period during quiet and REM sleep in 10 preterm infants, 10 term infants and 10 adults using a flow-through system.

Results: No significant differences were observed in any of the respiratory variables between the pre-sigh and the control breaths in any of the subjects in any of the two sleep states, suggesting that indices of respiratory drive are not predictive of an impending sigh. Sighs were relatively larger in infants than in adults and had a characteristic biphasic inspiratory flow observed almost exclusively in infants. While post-sigh ventilation was usually increased in adults, it was usually decreased in infants due to the presence of apneas.

Conclusions: The established indexes of respiratory drive are not predictive of an impeding sigh. When compared with control breaths, sighs are much larger in preterm and term infants than in adults. These big augmented breaths in infants are often followed by apnea and hypoventilation likely secondary to the increased activity of the peripheral chemoreceptors present in neonates.