Chronic ventilatory effects of diazepam and barbiturates in conscious cats

The chronic ventilatory effects of several hypnotics were investigated in six conscious cats recorded during control periods and during three consecutive days' administration of either diazepam (5 mg), pentobarbital (30 mg) or phenobarbital (60 mg). Ventilation was analyzed in terms of tidal volume (VT), breathing rate (BR) and minute ventilation (V = VT X BR). Minute ventilation was increased with diazepam owing to an increase in breathing rate in spite of a small decrease in tidal volume. With pentobarbital, minute ventilation was not changed because the decrease in breathing rate was compensated for by an increase in tidal volume. With phenobarbital, the results were more variable from one animal to another and on average, only tidal volume was increased. The animals were often excited following the administration of diazepam and sometimes drowsy with pentobarbital; with phenobarbital, behaviour varied among animals. Obviously, the present results cannot be extrapolated if different doses and perhaps different duration of drug administration are used. It is suggested that the ventilatory effects of the drugs cannot be explained only by a direct action on the brain stem respiratory network. Since the level of vigilance was altered by the various drugs, it is proposed that the ventilatory changes observed could be secondary to a supra-pontine action of the drugs which could modify both the level of alertness and respiratory activity.