The effect of the presence of the respiratory distress syndrome (RDS) or related factors (static compliance of the respiratory system and transcutaneous blood gases) and gestational age on the strength of the Breuer-Hering inflation reflex (BHIR) was studied in three groups of infants. Twenty-six ventilated preterm infants with and without RDS were studied 6 h after birth (group 1). In 24 preterm infants, we followed the development of reflex strength during the first year of life (group 2). Twenty-one healthy nonintubated term infants were studied within the first week of life (group 3). The BHIR was initiated by end-inspiratory occlusions, and the strength was characterized by the ratio of expiratory time after and without preceding airway occlusion. The static compliance of the respiratory system in ventilated infants was assessed by the multiple-occlusion technique. In group 1, reflex strength declined with increasing gestational age; in the presence of RDS or low respiratory compliance, the decline was less. Transcutaneous blood gases did not affect reflex strength. At term age, reflex strength was similar in spontaneously breathing preterm (group 2) and term infants (group 3). The BHIR decreased in strength during the first year after preterm birth. We conclude that 1) the strength of the BHIR decreases with increasing gestational and postnatal ages and 2) RDS, due to changes in respiratory system mechanics, causes an increase in reflex strength.
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