Maturational changes of reflexes influencing inspiratory timing in newborns

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Abstract
Premature infants have frequent apneic spells, which in some cases are triggered by airway obstruction or increases in respiratory load. The response of the preterm infant to increased respiratory loads has not been adequately studied. Utilizing the airway occlusion technique, the percent prolongation of the occluded, compared to the preceding unoccluded breath, was determined in 58 human newborns (gestational age 28-41 wk) during the 1st days of life. A significant correlation was found between gestational age and percent prolongation of inspirations (r = 0.76). At 29 wk gestation, prolongation was zero and increased up to 55% at term. The low mean prolongation obtained in the very premature infants can be explained by the large number of these infants who responded with a shortening of their inspiratory time during airway occlusion. This response may be secondary to the intercostal phrenic inhibitory reflex, which inhibits inspiration when distortions of the chest wall occur. The shortening of inspiration during airway occlusion in many premature newborns reflects their inability to tolerate respiratory loads and may contribute to the high incidence of apnea in these infants. The progressive increase in prolongation with gestational age reflects the maturation of the respiratory system toward the more stable respiratory function of the full-term neonate.