THE HERING-BREUER DEFLATIONARY REFLEX IN THE NEWBORN-INFANT

Initial observations on healthy term infants using the forced partial expiratory flow-volume technique with an inflatable jacket suggested t hat this technique was stimulating the Hering-Breuer deflationary refl ex,(1) a reflex which has not been systematically studied in man. To i nvestigate this fully, esophageal pressure, jacket pressure, flow and volume at the mouth were recorded during the forced partial expiratory flow-volume maneuver on 10 infants (mean age, 3.1 days; birth weight, 3533 g; gestation, 39.8 weeks). A total of 186 measurements were perf ormed at different points in the respiratory cycle. In 159 (85%) recor dings inspiratory effort was evident with a fall in esophageal pressur e within 166 msec; in some cases this occurred before the jacket was f ully inflated. This was associated with a reduction of 23.4 cm H2O in mean intrathoracic pressure, which was 2.5 times that occurring during normal tidal breathing. In the remaining 27 measurements a plateau pr essure was associated with closure of the upper airway. When the squee ze was applied at low lung volumes (end-expiration) the inspiratory ef fort occurred significantly earlier (133 msec) and stronger (reducing peak intrathoracic pressure to 15.8 cm H2O) than when applied at end-i nspiration (181 msec with a reduction in intrathoracic pressure to 25. 2 cm H2O). The observed inspiratory response was highly consistent, re presenting the deflationary reflex as described by Hering and Breuer i n 1868.(2,3) The stronger and more rapid onset of inspiration at low l ung volume supports the claim made by Breuer that it has a protective role on functional residual capacity (FRC) in young infants. (C) 1994 Wiley-Liss, Inc.