Transient and Steady State Effects of C0₂ on Mechanisms Determining Rate and Depth of Breathing

Abstract

Abstract Breath‐by‐breath analysis of tidal volume, VT, inspiratory duration, Tr, and expiratory duration, TE, was performed on cats under light pentobarbitone anesthesia or after decerebra‐tion before and after vagotomy. In response to step changes in inspired CO 2 V T changes earlier and more rapidly than the corresponding changes in the timing. The VT–Tj points may thus form a ‘hysteresis loop’ embracing the volume threshold curve of Clark and Euler (1972). The transient responses were present also after peripheral chemodenervation and after bilateral vagotomy. In contrast to earlier papers vagotomized cats under pentobarbitone anesthesia often showed some decrease of T(with increased steady state CO2 levels. In decerebrate vagotomized cats T[was more independent of variations in steady state PCO2 levels, but after administration of pentobarbitone Ti showed some steady state shortening of Tj with increased CO 2 . It is concluded that the controller of depth and rate of breathing contains at least 2 functional components which depend on PCO 2 in such a way that they exert opposite effects on Ti which cancel out to a great extent and that this relative match can be disturbed by pentobarbitone. It is postulated that the transient increase in mismatch is due to the fact that the 2 (or more) CO 2 effects have slightly different dynamic features.