Electromyographic activity of expiratory muscles in the rat.

We examined the participation of expiratory muscles on breathing in the rat. The experiments were performed on 16 male rats in halothane [1.5%] or urethane [1.3 g/kg i.p.] anaesthesia. We recorded the electromyographic [EMG] activity of intercostal and abdominal muscles with a concentric needle electrode during quiet breathing, breathing against increased pressure in the airways and during the expiration reflex. In halothane anaesthesia the EMG expiratory phasic activity was observed only in internal intercostal muscles in 40% of spots examined during quiet breathing and in 58.5% when breathing against increased pressure. The EMG activity during the expiratory reflex was difficult to evaluate. In the abdominal muscles permanent EMG activity was found in 66% of trials. In urethane anaesthesia no phasic expiratory EMG activity was observed in intercostal or abdominal muscles. In abdominal muscles in 9% of trials a permanent activity was found.