Dynamic Behavior of Endocardial Structures in the Baboon Heart 1

Abstract

While precise patterns of efferent innervation of the heart have been extensively investigated, a large fraction of the studies have been made in the dog, cat, rabbit and a few other domestic animals with little or no information upon the primate. We have recently described the anatomical distribution of the autonomic cardiac nerves, together with functional responses to their electrical excitation in the baboon (1, 2). The emphasis of these reports, however was almost exclusively upon epicardial innervation. In subsequent experiments, after developing techniques for studies of endocardial structures in the dog (3, 4), strain gauge arches and/or intramyocardial pressure transducers were applied to the interventricular septum and papillary muscles in the intact baboon heart. The present report illustrates and compares changes in contractile force and in intramyocardial pressure development within the septum and epicardial portions of the left ventricle. To our knowledge, these data represent the first such direct expeirimental approaches to determination of endocardial functions in the primate heart.

Methods. Walton-Brodie strain gauge arches were carefully sutured to the endocardial surfaces of the interventricular septum and/or to the longitudinal surfaces of the papillary muscles of the left ventricle through left atriotomy, while the animal was on compete cardiac bypass and the heart was in fibrillation, in seven baboons (Papio anubis). After installation of the transducers, the animals were removed from the bypass pump with defibrillation and restoration of in vivo circulation. The small branchings of both sympathetic and parasympathetic cardiac nerves distal to the stellate and middle cervical ganglia and the cervical vagosympathetic trunk were carefully isolated and electrically stimulated using either a Nuclear Chicago constant current stimulator (model 7151) or a Grass S5 square wave voltage generator (2). Recordings were made upon either a Model R Beckman rectilinear or Offner Model R curvilinear recorder.