Journal of Applied Physiology, Vol 51, Issue 1 19-25, Copyright © 1981 by American Physiological Society
Respiratory timing and depth of breathing in dogs anesthetized with halothane or enflurane
H. M. Marsh, K. Rehder and R. E. Hyatt
Tidal volume (VT) and inspiratory (TI) and expiratory (TE) times were
measured during enflurane and halothane anesthesia in 12 prone dogs before
and after bilateral vagotomy. "Elastic" loading or airway occlusion was
used to obtain a VT-to-TI relationship in each state and to examine the
rate of change in airway pressure. VT, TI, and TE were significantly (P
less than 0.05) larger during enflurane than during halothane anesthesia,
both before and after bilateral vagotomy. Before vagotomy, the rate of
change in airway pressure during airway occlusion was similar for the two
agents, as was an index of impedance of the respiratory system (Z'rs). Thus
the difference in maximal pressure generated and in VT was most likely due
to the difference in TI. Before vagotomy, TI increased as VT decreased with
loading during enflurane but not halothane anesthesia, demonstrating a
different effect of the two agents on the phasic vagal inspiratory
inhibitory mechanism. After bilateral vagotomy, TI was unaltered during
elastic loading with both agents but was still significantly longer during
enflurane than halothane anesthesia. Thus it was concluded that TI was
longer in the enfluraneanesthetized dogs than in the halothane-anesthetized
dogs because of a different effect of these two agents on the bulbopontine
"pacemaker" mechanism and not because of different effects on the phasic
vagal inspiratory inhibitory mechanism.
