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A possible role for the Hering-Breuer deflation reflex in apnea of prematurity
S Hannam1, D M Ingram, A D Milner
1Department of Child Health, King's College Hospital, London, UK.
Background:
The vagally mediated Hering-Breuer deflation reflex terminates expiration and initiates inspiration when lung volume is reduced to less than functional residual capacity. The effects of prematurity on this reflex are not known.
Study Design:
Fifteen term and 20 preterm nonventilated infants were studied. Lung deflation was achieved by chest compression using an inflatable jacket. Relative changes in expiratory time and inspiratory time on chest compression were calculated from airflow recordings. Esophageal pressure changes in the term infants and chest wall movements in the preterm infants were also measured.
Results:
The term infants had a mean prolongation of inspiratory time on squeezing of 15% versus a 24% shortening in the preterm infants (p < 0.001). The term infants had a mean shortening of expiratory time on squeezing of 35% versus 18% in the preterm infants (p < 0.001). Fifteen of the 20 preterm infants demonstrated a tendency to have short apneas (2 to 5 seconds) on squeezing, 88% of which were central in origin. In these infants shortening of inspiratory time was greater than that seen in the preterm infants not having apneas (p < 0.05).
Conclusions:
Preterm infants responded to a rapid reduction in lung volume with a shortened inspiratory effort and a tendency to have central apneas. This may be due to an immaturity in part of the reflex arc responsible for transmitting the Hering-Breuer deflation reflex.