Fig. 5. Protocol 1: Effects of three different pentobarbital doses on breathing (means ± SEM). ( A ) End-tidal carbon dioxide concentration ( squares ) increased and respiratory rate ( circles ) decreased with increasing pentobarbital doses. * P < 0.05 versus deep sedation. ( B ) Air-flow ( squares ) and tidal-volume ( circles ) decreased with increasing pentobarbital doses. * P < 0.05 versus deep sedation. ( C ) Flow rate (Vt [tidal volume]/TI [inspiration time]) decreased with increasing pentobarbital doses, whereas duty cycle (Ti [inspiratory time] and Ttot [total cycle-time]) did not significantly change. * P < 0.05 versus deep sedation. Vt = tidal volume, Ti = inspiration time, Ttot = total respiratory cycle duration.