Afferent C-fibers and cardiorespiratory chemoreflexes.

Abstract

Introduction The title of this paper is a further acknowledg· ment of the wide range of Julius Comroe's contributions to cardiovascular and respiratory physiology, for the field of the cardiorespiratory chemoreflexes is one that he has made his own during the past 40 years. In 1867, von Bezold and Hirt (1) showed that intravenous injection of veratrine in animals caused decreases in arterial blood pressure and heart rate and an arrest of breathing; they attributed the depressor effects to a vagal reflex produced by excitation of afferent endings in the heart. Their observation was overshadowed for many years by the discovery of the depressor mechanisms of the aortic arch and carotid sinus, and by the finding that depressor effects could also be evoked reflexly from the lungs. Indeed, not until the work of Jarisch and associates (2) in the 1930s was it generally accepted that chemical agents could evoke reflex bradycardia and systemic hypotension by stimulating afferent vagal endings in the heart. Thereafter, the study of cardiovascular and respiratory chemoreflexes became increasingly attractive to physiologists and pharmacologists, until, by the 1950s, there seemed to be no end to the number and variety of substances capable of evoking profound, but imperfectly understood, reflex changes in heart rate, blood pressure, and breathing. In 1954, Dawes and Comroe (3) reviewed the vagal cardiopulmonary chemoreflexes in a paper that has become a landmark in the history