ABSTRACT
In the ensuing discussion of the final common path, with respect to heart rate conditioning in particular, this chapter focuses on the fundamental questions and modes of approach. One implication of marked species differences for electrophysiological analyses of the final common path for heart rate conditioning is that the cells of origin of the vagal cardioinhibitory fibers must first be definitively localized for each species of interest. To gain a first approximation to describing the relative contributions, the traditional approach has been to investigate the effects on heart rate conditioning performance of different combinations of surgical cardiac denervation and/or pharmacological blockade. The issue of whether the occurrence of conditioned respiratory changes affects the heart rate response is far from resolved. There have been two direct approaches to resolving this problem: control of respiration by instruction and training in human experiments, and pharmacological immobilization with artificial ventilation in animal experiments.
