Inspiratory muscle activity during rebreathing in intact and vagotomized rabbits

Abstract

The relation between relative peak ‘integrated’ diaphramagmatic (Adi) and cranial (u) or caudal (1) inspiratory intercostal activity (Aic) was assessed in intact and vagotomized rabbits during rebreathing. During unloaded rebreathing Aic increased markedly more than Adi, and Aic u more than Aic l, independently of intact vagi. Vagal signals facilitated inspiratory intercostals, since vagotomy or vagal blocks increased Adi more than Aic without changing diaphargm acitivity time course, and ΔAic/ΔAdi in the same range of Adi values was greater before than after vagotomy. Reflexes from the chest wall were not involved since phrenic block after vagotomy modified rib cage motion without changin Aic, independently of chemical drive. Possibly chemical and vagal dependent changes in fusimotor activity are responsible for greater Aic increase, which in turn explains the decreasing relative diaphragm contribution of V t, as the latter increases. Obstruction at FRC shifted postvagotomy Aic vs. Adi relationship upwards, suggesting reflex facilitation of intercostals by chest wall receptors. The strength of this reflax was largely independent of intact vagi, since pre- and postvagotomy Aic vs. Adi relations coincided, and of chemical drive, since postvagotomy ΔAic/ΔAdi for obstructed and unimpeded rebreathing were similar.