RESPIRATORY MUSCLE ACTIVITIES AFTER BIRTH IN ASPHYXIATED PRETERM LAMBS

Laryngeal and pump muscle activities are important in the establishmen t and maintenance of functional residual capacity (FRC) after birth. T he aim of this study was to determine the expiratory mechanisms by whi ch laryngeal and diaphragmatic activities achieve the increments in FR C postnatally. Wire electrodes were placed in: the laryngeal abductor, a major laryngeal adductor, the inferior pharyngeal constrictor and t he diaphragm of six fetal sheep. The lambs were delivered prematurely by cesarean section and a face mask with a pneumotachograph applied. A grunting respiratory pattern was characterized by severe expiratory a irflow retardation, associated with laryngeal adductor activity. In gr unting breaths, minimal volume loss at end-expiration and incremental increases in FRC occurred when the onset of diaphragmatic activity pre ceded the onset of laryngeal muscle activities associated with larynge al opening. Thus the timing order of laryngeal and diaphragmatic muscl e activities near end-expiration is a determinant of increments in FRC .