Analysis of respiratory patterns in the awake and in the halothane anaesthetised rat.

Respiratory patterns have been studied in awake and halothane anaesthetised rats. Tidal volume (VT) was shown to be age-sensitive over 44-200 days; failure to account for this gave the appearance of an increased ventilatory sensitivity to CO2 with age. Inspiration of CO2 (0-10.5%) produced linear responses of VT whereas frequency responses stabilised at 6% CO2. Initially expiratory duration (TE) decreased more than inspiratory duration (TI) and both decreased linearly relative to increased VT; above 6% CO2, increases in VT occurred with only minor changes in TI and TE. Halothane anaesthesia dominantly depressed the frequency response to CO2. We conclude that the rat shows a great influence of vagal control on breathing in the awake state and in halothane anaesthesia; that TE is controlled independently of TI; and that respiratory frequency is more rigorously controlled than VT.