Effects of Anesthesia on Breathing Pattern

Abstract

In recent years, it has been shown that in anesthetized cats an inverse relationship is observed between the tidal volume (V_T) and the inspiratory duration (T_I) when V_T increases as a result of hypercapnia or transient artificial inflations. This relationship, sometimes found as hyperbolic, has been related to the BreuerHering reflex since, after vagotomy, T_I seems only slightly dependent on V_T ¹. In the awake cat, on the other hand, changes in T_I are variable and small when V_T increases² and the V_T–T_I relationship is therefore quite similar to that described for man by many authors. From these observations, it may be concluded that the Breuer-Hering reflex is stronger in the anesthetized cat than in the awake one. Since several reports have discussed the small role played by the Breuer-Hering reflex in the control of breathing of awake man³, it was of interest to know if the effect of anesthesia on the respiratory pattern was nhe same in man as in cat. Surprisingly, the components of breathing (V_T, T_I, T_E, ($\dot{V}$ _I) have been studied very little in the anesthetized man. Studies have dealt mainly with the total ventilatory responses ($\dot{V}$ _E) to hypercapnia or hypoxia under different kinds of drugs.