The Role of Vagal Cardiac Nerves and Arterial Baroreceptors in the Circulatory Adjustments to Hemorrhage in the Cat

Abstract

Abstract The relative importance of arterial baroreceptors and receptors with afferent fibres in the cardiac nerves, respectively, in producing compensatory circulatory adjustments in moderate hemorrhage was analyzed in chloralose‐anesthetized cats. — The effects of standardized hemorrhage on blood pressure, heart rate and renal and skeletal muscle blood flows were observed before and after section of respective receptor afferents. Both groups of receptors, when operating in the absence of the other, were capable of producing tachycardia and vasoconstriction during a blood loss, but the pattern of response, elicited via the two sets of afferents, differed. Compensation via cardiac nerve afferents thus implied a particularly strong engagement of vasomotor neurons, controlling the heart and the renal vessels, while the arterial baroreceptor adjustments seemed to involve a more uniform exitation of all vasomotor centre neurons. Very rapid hemorrhages often produced a pronounced bradycardia, resembling that seen in the “vaso‐vagal” syncope in man. This response was found to be mediated through a vago‐vagal reflex arch, and probably constitutes a protective mechanism, causing a break on the heart in situations of extremely poor diastolic filling.