Effect of lung inflation on ventilation and various phases of the respiratory cycle in preterm infants.

The effect of sudden and sustained lung inflation on inspiratory time (Ti), expiratory time (Te) and duration of apnea, as a translation of the Hering-Breuer reflex, has not been systematically analyzed in preterm infants. To examine such effects, 10 infants (body weight 1,550 +/- 110 g; gestational age 31 +/- 1 weeks) were studied. Lung inflation was obtained by applying negative pressure around the chest using a negative pressure incubator. After a control period, lung volume functional residual capacity was increased by an average of 14, 23, 34 and 53%. During lung inflation, Ti, Te, total respiratory cycle duration, incidence and duration of apnea increased. Minute ventilation decreased due to a decrease in frequency. Tidal volume decreased but not significantly. Inspiratory and expiratory flows decreased. These results (1) confirm the presence of the Hering-Breuer reflex in preterm infants, as reflected by increased Te and appearance of apnea during lung inflation; and (2) show that contrary to expectations, Ti increased significantly with lung inflation.