THE HERING-BREUER REFLEX IN ANESTHETIZED INFANTS - END-INSPIRATORY VS. END-EXPIRATORY OCCLUSION TECHNIQUE

Both end-inspiratory (EIO) and end-expiratory (EEO) occlusions have be en used to measure the strength of the Hering-Breuer inflation reflex (HBIR) in infants. The purpose of this study was to compare both techn iques in anesthetized infants. In each infant, HBIR activity was calcu lated as the relative prolongation of expiratory and inspiratory time during EIO and EEO, respectively. Respiratory drive was assessed from the change in airway pressure during inspiratory effort against the oc clusion, both at a fixed time interval of 100 ms (P-0.1) and a fixed p roportion (10%) of the occluded inspiratory time (P-10%). Twenty-two i nfants [age 14.3 +/- 6.4 (SD) mo] were studied. No HBIR activity was p resent during EIO [-11.8 +/- 15.9 (SD) %]. By contrast, there was sign ificant, albeit weak, reflex activity during EEO [HBIR: 27.2 +/- 17.4% ]. A strong HBIR (up to 310%) was elicited in six of seven infants in whom EIO was repeated after lung inflation. P-0.1 was similar during b oth types of occlusions, whereas mean +/- SD P-10% was lower during EE O than during EIO: 0.198 +/- 0.09 vs. 0.367 +/- 0.15 kPa, respectively (P < 0.01). These data suggest a difference in the central integratio n of stretch receptor activity in infants during anesthesia compared w ith during sleep.