Effects of naloxone on the control of breathing in children with chronic obstructive pulmonary disease.

The effect of naloxone on occlusion pressure (P0.1), the pattern of breathing and the expiratory flows during spontaneous ventilation was studied in 16 children with chronic obstructive pulmonary disease under control conditions, after isotonic saline injection and 5 (N5) and 25 (N25) min after i.v. injection of naloxone (2 micrograms X kg-1). At N5, no change was observed in tidal volume normalized for body weight (VTBW), inspiratory time (TI), respiratory frequency (f), mean inspiratory flow (VTBW/TI) and the ratio of TI and total duration of the respiratory cycle (TI/TT). P0.1 decreased significantly (p less than 0.001) at N5 and returned to control values at N25. The decrease in P0.1 without any change in the breathing pattern suggests that naloxone has an effect on respiratory mechanics. Indeed, at N5, the expiratory flows generated at 25% of VT, measured on the flow-volume curves during spontaneous ventilation, increased significantly when compared to control values. Moreover, the decrease of P0.1 after naloxone was found to be correlated to the reduction of dynamic lung compliance (CLdyn) (p less than 0.02). It is speculated that peripheral airway obstruction, as reflected by the decrease in CLdyn, might be a triggering factor for the release of endorphins. The bronchodilation observed after naloxone could then be due to naloxone's antagonistic effect on endorphin-induced bronchoconstriction.