Fig. 4. Protocol 1: Effects of three different pentobarbital doses on respiratory muscle function (means ± SEM). (  A ) Phasic activity of genioglossus (  circles ) and diaphragm (  squares ). *  P < 0.05  versus deep sedation, same muscle. +  P < 0.05  versus diaphragm. (  B ) Negative pressure reflex. Increase in phasic genioglossus electromyogram in response to negative pharyngeal pressure application. *  P < 0.05  versus preceding breath. (  C ) Tonic genioglossus activity. *  P < 0.05  versus deep sedation, +  P < 0.05  versus light anesthesia. AU = arbitrary units; EMG = electromyogram; GG = genioglossus.