1861 PROLONGATION OF INSPIRATORY TIME BY LOWER AIRWAY OCCLUSION IN CHILDREN

Abstract

Inspiration is strongly inhibited by volume-related vagal afferents in human neonates and animals but this reflex is not as active in human adults during normal breathing. To determine if volume-related inspiratory inhibition occurs beyond the neonatal period we performed 10±1 end expiratory occlusions in 5 patients (3-17mos.) with cuffed tracheostomy or endotracheal tubes. Occlusion pressure and surface diaphragm electromyogram (DIA EMG) were simultaneously recorded. DIA EMG duration (TIDIA) was measured from the raw signal, and peak amplitude, time to peak and rate of rise of DIA EMG were quantified from moving average signals. Inspiratory time (Ti) was measured from flow signal during the breath immediately preceding occlusion and from occlusion pressure (JAP 38:335, 1975) during the first occluded effort. During control breaths TIDIA was longer than Ti from flow (790±110vs 550±130ms, p<0.01). Occlusion consistently increased Ti (550±1130 to 710±230ms, p<0.05) and TIDIA (790±110 to 990±130ms, p<0.001). Peak amplitude and time to peak DIA EMG increased by 22±6%, p<0.005 and 30±4%, p<0.001, respectively, during occlusion but rate of rise did not change. In summary, in patients with isolated lower airways, end expiratory occlusions prolonged inspiratory efforts and DIA EMG. These findings indicate that during normal breathing volume-related afferents shorten inspiration in children. Isolation of lower airways suggests that these reflexes are not mediated by upper airway mechanoreceptors. Thus, the Hering-Breuer reflex may he present beyond the neonatal period. (Supp. NIH HL31173 and HL25830)