Characterisation of the Hering-Breuer deflation reflex in the human neonate

Human infants have been observed making inspiratory efforts in response to chest compression. These may be a manifestation of the Hering-Breuer deflat ion reflex. We sought to stimulate the reflex in 33 term infants by rapidly reducing lung volume using an inflatable jacket. The effect of altering th e timing, magnitude or rate of application of the lung deflation on the str ength of the inspiratory response was investigated. Inspiratory effort was quantified by measuring (1) the rate of fall in oesophageal pressure on ins piration; and (2) the mean inspiratory flow (MIF) in response to lung defla tion. Variables which significantly affected (1) and resulted in increased inspiratory effort were, in order of importance: larger rises in oesophagea l pressure on chest compression (38%) (percentage of variance explained), g reater reductions in lung volume below functional residual capacity (FRC) ( 26%), faster rates of lung deflation (19%) and slower respiratory rates (11 %). Increased inspiratory efforts, as assessed by response (2), were genera ted by greater reductions in FRC (23%), larger rises in oesophageal pressur e (11%) and faster rates of lung deflation (10%). Increasing deflation pres sures eventually resulted in a plateau in both measures of inspiratory resp onse. These results were consistent with the Hering-Breuer deflation reflex being activated which could have a role in protecting the FRC of the newbo rn infant. (C) 2000 Elsevier Science B.V. All rights reserved.