HERING-BREUER REFLEX AND RESPIRATORY SYSTEM COMPLIANCE IN THE FIRST YEAR OF LIFE - A LONGITUDINAL-STUDY

The airway occlusion technique for measuring passive respiratory mecha nics in infants relies on an ability to evoke the Hering-Breuer lung i nflation reflex (HBR). However, there is conflicting evidence regardin g the persistence of the HBR beyond the early newborn period This stud y was designed to assess maturational changes in HBR activity and pass ive total respiratory system compliance (Crs) in healthy infants durin g the 1st yr of life. The strength of the HBR was assessed from the re lative change in expiratory time (TE) after brief end-inspiratory airw ay occlusions compared with resting TE during spontaneous breathing. C rs was measured using the multiple-occlusion technique. Paired measure ments of HBR activity and Crs were obtained during sedated sleep in 30 infants at 4-8 wk and at 1 yr of age. Significant HBR activity during tidal breathing persisted throughout the 1st yr of life, with TE incr easing during occlusion by at least 26% in every infant. However, the relative strength of the reflex response decreased from a mean of 88.3 % (range, 34-160%) at similar to 6 wk to 50.3% (range, 26-125%) by 1 y r of age (P < 0.001). All infants showed an increase in Crs with age, with mean Crs increasing from 60.1 +/- 8.9 (SD) to 149.0 +/- 20.6 ml/k Pa between 6 wk and 1 yr. However, there was no apparent relationship between the magnitude of decline in HBR response and the age-related c hanges in Crs. We conclude that the HBR can be demonstrated during tid al breathing in healthy infants until the end of the 1st yr of Life bu t that postnatal age is an important determinant of this response and is independent of concurrent changes in passive respiratory mechanics.