Influence of volume dependency and timing of airway occlusions on the Hering-Breuer reflex in infants

Bothend-inspiratory (EIO) and end-expiratory (EEO) airway occlusions areused to calculate the strength of the Hering-Breuer inflation reflex(HBIR) in infants. However, the influence of the timing of suchocclusions is unknown, as is the extent to which changes in volumewithin and above the tidal range affect this reflex. The purpose ofthis study was to compare both techniques and to evaluate the volumedependency of the HBIR in healthy, sleeping infants up to 1 yr of age.The strength of the HBIR was expressed as the ratio of expiratory orinspiratory time during EIO or EEO, respectively, to that recordedduring spontaneous breathing, i.e., as the "inhibitory ratio"(IR). Paired measurements of the EIO and EEO in 26 naturally sleepingnewborn and 15 lightly sedated infants at ~1 yr showed nostatistically significant differences in the IR according to technique:mean (95% CI) of the difference (EIO  EEO) being0.02 (0.17, 0.13) during the first week of life and 0.04 (0.14, 0.22) at 1 yr. During tidalbreathing, a volume threshold of ~4 ml/kg was required to evoke theHBIR. Marked volume and age dependency were observed. In newborninfants, occlusions at ~10 ml/kg during sighs always resulted in anIR > 4, whereas a similar response was only evoked at 25 ml/kg inolder infants. Age-related changes in the volume threshold may reflectmaturational changes in the control of breathing and respiratorymechanics throughout the first year of life.