The influence of vagal afferents on renal sympathetic nerve activity was studied in nine rabbits anesthetized with sodium pentobarbital and artificially ventilated with oxygen. Arterial Pco 2 and pH were kept normal. The aortic depressor and the carotid sinus nerves were cut. The mean impulse frequency was determined from multifiber preparations of the renal nerve. Blood volume was altered either by bleeding or by infusing dextran. With vagi intact, an increase in blood volume of approximately 1OSE caused the nerve activity to decrease 41 ± 4%; it returned toward the control level after withdrawal of the same volume. A similar decrease in volume increased the nerve activity 33 ± 7%; it decreased toward the control level after reinfusion. These changes were unaffected by cutting the vagi at the diaphragm but were abolished or markedly attenuated by cooling or cutting the vagi in the neck. Interruption of vagal afferents resulted in a 21 ± 2% increase in nerve activity, indicating that the afferents exerted a continuous inhibition on the sympathetic outflow to the kidney. These experiments demonstrated a role for the low-pressure intrathoracic receptors in the control of renal sympathetic nerve activity in response to changes in blood volume.KEY WORDS low-pressure receptors blood volume control cardiopulmonary receptors hemorrhage vagal cooling hypervolemia bilateral vagotomy• Evidence is accumulating that, in response to hemorrhage, receptors in the cardiopulmonary area are important in the control of the renal resistance vessels (1, 2). However, the magnitude of the renal response to the same hemorrhage can be strikingly different depending on the technique used to determine the reactions of the renal vessels (2, 3). Local factors in the kidney, such as autoregulation, may cause these differences and make it difficult to assess the role of renal sympathetic nerve activity in determining the magnitude of the response. In the present experiments, From the Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55901.This investigation was supported in part by U. S. Public Health Service Grant HL-5883 from the National Heart and Lung Institute and by a grant from the Medical Research Council of Canada (Dr. Pelletier). Dr. Clement is a U. S. Public Health Service International Fellow on leave from the State University of Ghent, Belgium.Received July 17, 1972. Accepted for publication September 29, 1972. electroneurographic recordings from the renal nerve were made to establish more directly the relationship between the impulse frequency in the renal sympathetic nerves and the activation of the low-pressure mechanoreceptors during increases and decreases in blood volume.Kezdi and Geller (4) have shown an inverse relationship between the carotid sinus pressure and the frequency of renal sympathetic nerve discharge. The influence of the receptors subserved by the vagal afferents on renal sympathetic nerve activity in response to alterations in blood volume has not yet been investigated. MethodsPreparation.-Nin...

Pressure-dependent changes in afferent activity in the aortic and the sinus nerves were studied in 17 anesthetized dogs that were artificially ventilated with oxygen. Systemic arterial blood pressure was varied either continuously or in steps over the range of mean aortic blood pressure from 220 to 50 mm Hg with a pressurized reservoir connected to the abdominal aorta. Multifiber preparations from 20 aortic and 8 sinus nerves were used, and stimulusresponse curves were defined by measuring the mean impulse frequency at the various levels of pressure. Heart rate and pulse pressure were similar during recordings from both nerves. The two curves were S-shaped, with that for the aortic nerve being to the right of that for the sinus nerve. The change in activity was approximately linear from 200 to 120 mm Hg (mean aortic blood pressure) in the aortic nerve and from 180 to 80 mm Hg in the sinus nerve; there was no significant change in impulse frequency below mean blood pressures of 100 and 70 mm Hg, respectively. The threshold systolic blood pressure was 95 ± 3 (SE) mm Hg for the aortic receptors and 62 ± 4 mm Hg for the carotid sinus receptors. Thus, in the dog, the aortic baroreceptors are involved mainly in the control of high blood pressure, whereas at lower pressures the major control occurs through the carotid sinus baroreflex.

Background: Bioprostheses preserved with glutaraldehyde, both porcine and pericardial, have been available as second-generation prostheses for valve replacement surgery. The performance with regard to structural valve deterioration with the Carpentier-Edwards supra-annular (CE-SAV) porcine bioprosthesis and the Carpentier-Edwards Perimount (CE-P) pericardial bioprosthesis (Baxter Healthcare Corp, Edwards Division, Santa Ana, Calif) was evaluated to determine whether there was a difference in mitral valve replacement. Methods: The CE-SAV bioprosthesis was implanted in 1266 overall mitral valve replacements (isolated mitral, 1066; mitral in multiple, 200) and the CE-P bioprosthesis in 429 overall mitral valve replacements (isolated mitral, 328; mitral in multiple, 101). The mean age of the CE-SAV population was 64.2 ± 12.2 years and that of the CE-P population, 60.7 ± 11.7 years (P = .0001). For the study, structural valve deterioration was diagnosed at reoperation for explantation. Results: The freedom from structural valve deterioration was evaluated to 10 years, and the freedom rates reported are at 10 years. For the overall mitral valve replacement groups, the actuarial freedom from deterioration was significant (P = .0001): CE-P > CE-SAV for 40 years or younger, 80% versus 60%; 41 to 50 years, 91% versus 61%; 51 to 60 years, 84% versus 69%; 61 to 70 years, 95% versus 75%. The older than 70-year group was 100% versus 92% (no significant difference). The actual freedom from structural valve deterioration also demonstrated the same pattern at 10 years: 40 years or younger, CE-P 82% versus CE-SAV 68%; 41 to 50 years, 92% versus 70%; 51 to 60 years, 90% versus 80%; 61 to 70 years, 97% versus 88%; and older than 70 years, 100% versus 97%. The independent risk factors of structural valve deterioration for the overall mitral valve replacement group were age and age groups and prosthesis type (CE-SAV > CE-P). The prosthesis type either in isolated replacement or in multiple replacement was not predictive of structural valve deterioration. The pathology of structural valve deterioration was different: 70% of CE-P failures were due to calcification and 57% of CE-SAV failures were due to combined calcification and leaflet tear.

Experiments were conducted in 35 anesthetized dogs to study the circulatory adjustments, after hemorrhage, mediated by vagal afferents from the cardiopulmonary area. With the aortic baroreceptors and chemoreceptors denervated and carotid baroreceptor and chemoreceptor activity held constant, hemorrhage of 10% of blood volume caused an increase in heart rate and constriction of the resistance vessels of the hindlimb, renal, and mesenteric beds and of the splanchnic venous bed. Vagotomy abolished these responses to hemorrhage, resulting in a greater decrease in blood pressure. With the carotid baroreflex operative, the constriction of the renal and mesenteric resistance vessels and of the splanchnic venous bed were similar to that obtained with only the vagi operative, but the constriction of the hindlimb resistance vessels was much greater and aortic pressure was better maintained. It is concluded that receptors in the cardiopulmonary area, subserved by vagal afferents, exert their main influence on the splanchnic resistance and capacitance vessels and on the renal circulation, whereas the carotid baroreceptors predominantly affect the muscle vessels.

More is known about the baroreflex of the carotid sinus than about the baroreflexes originating from the heart and the great vessels because of the easy surgical preparation of the carotid sinus area. The "isolated innervated sinus preparation" introduced by Moissejeff in 1926 and its various modifications have provided a convenient method for studying the carotid sinus reflex (1). The present paper briefly reviews some recent developments in the study of the baroreflexes originating from the aortic arch, the chambers of the heart, and the coronary vessels and discusses whether these reflexes are tonically active in normal situations. AORTIC BARORECEPTORSAlthough the aortic arch has long been implicated in the reflex control of the circulation (1), it is often assumed that the baroreflexes from both carotid and aortic areas are equivalent in the reflex regulation of arterial blood pressure. However, recent studies in dogs have shown that the aortic baroreflex, unlike the carotid baroreflex, is relatively ineffective in buffering a decrease in systemic arterial blood pressure below normal; therefore, the aortic baroreflex acts predominantly as an antihypertensive mechanism.In one study (2), a comparison of the reflex vascular responses with the changes in nonpulsatile pressure in vascularly isolated, blood-perfused aortic arch and carotid sinus preparations in the same dogs was made; the average threshold pressure for the aortic arch baroreceptor reflex was about 110 mm Hg compared with about 50 mm Hg for the carotid sinus. Similar or higher values for the threshold for reflex vascular responses from the aortic baroreceptors have been reported by others From the Department of Physiology and Biophysics, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55901. using similar techniques (3-5). In another study (6), the afferent electrical activity from multifiber preparations of the aortic nerves and the sinus nerves was compared during changes in pulsatile arterial blood pressure in the closed-chest dog. The threshold systolic pressure that caused a significant change in mean impulse frequency averaged 95 mm Hg for the aortic receptors and 62 mm Hg for the carotid sinus receptors. Both studies showed that the maximal sensitivity of the aortic arch system was set over a range of higher blood pressure than that of the carotid sinus system. This difference in threshold pressure does not apply for all species however. In the rabbit aortic nerve activity increases almost linearly between pressures of about 40 to 110 mm Hg, with an average threshold pressure of approximately 50 mm Hg (7, 8).Further analysis has been performed by using acute decreases in blood pressure in the vagotomized dog. With only the carotid reflex operative, hemorrhage (8% of the blood volume) caused a decrease of 14% in systemic arterial blood pressure; however, when only the aortic reflex was operative, the pressure decreased by 38% (9). No explanation can be given for the different reflex characteristics of the baroreceptors in these two areas...