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Systemic Blood Pressure Response to Changes in Right Ventricular Function By Alan L. Pinkerson, M.D., and Peter A. Kot, M.D. Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 • Previous investigations have described areas in the circulation which, when appropriately stimulated, induce changes in total peripheral vascular resistance.1"3 Such receptor areas have been demonstrated in vessels of the lesser and greater circulation and three of the heart chambers. Whether similar vascular reflexes can originate in the right ventricle has been questioned.4 Although increasing pressure in the vascularly isolated left ventricle results in a decrease in total peripheral vascular resistance,4'" a similar response is not elicited from the isolated right ventricle.4 A reflex increase in pulmonary blood flow without changes in systemic vascular resistance has been demonstrated following elevation of the systolic pressure in the intact right ventricle.0 The present report describes a pressor reflex which originates in the intact functioning right ventricle. An increase in systemic blood pressure and vascular resistance is shown after a rise in right ventricular systolic pressure. Experiments were performed in open-chest anesthetized dogs. The systemic vascular response was measured 1) with the circulation intact, 2) during total perfusion of the systemic circulation with a mechanical pump, 3) after the administration of atropine, and 4) following bilateral cervical vagotomy. positive pressure ventilation maintained with a Starling Ideal pump. A cotton tie was passed around the main pulmonary artery. Intravascular pressures were measured in the inferior vena cava, right atrium, right ventricle, pulmonary artery, and abdominal aorta via polyethylene catheters and recorded on a direct-writing, multichannel oscillograph. Right ventricular systolic pressure was increased by gradual constriction of the main pulmonary artery at its bifurcation or at the level of the pulmonic valve by gradual tightening of the cotton ligature. After initial studies in dogs with an intact circulation, a mechanical pump, which could be preset to deliver a constant stroke volume at a fixed rate, was connected between the left atrium and descending thoracic aorta7 (fig. 1). When blood draining from the left atrium into the reservoir was pumped through the T tube into the aorta, aortic diastolic pressure remained higher than left ventricular systolic pressure. The aortic valves therefore remained closed and the systemic cir- Methods Fifteen mongrel dogs weighing 10 to 20 kg were anesthetized with sodium pentobarbital (25 mg/kg). A left thoracotomy was performed under FIGURE 1 From the Departments of Physiology and Medicine, Georgetown University School of Medicine, Washington, D. C. Supported in part by Grant H-1904 from the National Heart Institute, U. S. Public Health Service. Received for publication November 4, 1963. Circulation Research, Volume XIV, May 1964 Schematic diagram of the technique used to bypass the left ventricle. Tygon tube is tied into the left atrium and the pulmonary venous return drained out of the atrium into the open reservoir. Blood is pumped into the aorta through the T tube. Arrows show the direction of blood flow. 461 PINKERSON, KOT 462 culation, including the coronary arteries, was perfused only by blood from the pump. Complete diversion of blood from the left atrium to the pump reservoir was determined by inspection of the aortic pulse contour as previously described.7 The effect of gradual and total occlusion of the main pulmonary artery was then recorded with the vagi intact, following the administration of atropine (0.4 mg/kg) and after bilateral cervical vagotomy. Results In each instance as the main pulmonary artery was gradually constricted, right ventricular systolic pressure progessively increased above base line values. Right ventricular end diastolic, right atrial, and venous pressures remained constant until the main pulmonary artery was markedly constricted (figs. 2 and 3). Mean pulmonary artery pressure showed no consistent changes during the early stages of stenosis. When right ventricular end diastolic pressure began to rise, pulmonary artery pressure and the pump reservoir level 40 Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 20 PA 0 40 20 RA 0 40 20 Vtn 0 80 RV wmM 40 —.200 100 Ao 3 mm Hg FIGURE 2 Effects of increasing degrees of main pulmonary artery constriction in dogs with an intact circulation. PPA = pulmonary artery pressure. PRi = right atrial pressure. P r E V = venous pressure. PRV = right ventricular pressure. P40 = aortic pressure. Straight lines before the instantaneous pressure recordings indicate mean pressures. Panel C represents the immediate preconstriction control. Panels 1, 2, and 3 show responses to graded increases in main pulmonary artery constriction. Fine lines represent 1-sec intervals. Circulation Research, Volume XIV, May 1964 463 PRESSOR REFLEX FROM RIGHT VENTRICLE POST VAGOTOMY PRE VAGOTOMY so P RV 40 -i 200 «•• r 100 P AO H 0 L mm Hg I c I FIGURE 3 Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 Effects of increasing degrees of main pulmonary artery stenosis in dogs with left ventricle bypassed by an extracorporeal pump. On the left are the recordings before division of the cervical vagi; on the right, after vagotomy. Symbols and time lines are the same as in figure 1. declined rapidly. Similar pressure responses following main pulmonary artery stenosis have been reported previously.0' 8 Prior to vagotomy, both before and after left ventricular bypass, aortic pressure consistently increased with the elevation of right ventricular systolic pressure (figs. 2 and 3). The graphs in figure 4 show this relationship in ten dogs before there was any rise in right ventricular end diastolic pressure. In table 1, under "Vagi intact," are listed the maximum aortic pressure responses to partial pulmonary artery occlusion in eight dogs with controlled perfusion of the systemic circulation. As also shown in table 1, the increases in TABLE 1 Maximum Increase in Mean Aortic Blood Pressure Following Gradual Partial Constriction of the Main Pulmonary Artery in Dogs with Bypass of the Left Ventricle Dog no. 1 2 3 4 5 6 7 8 Vagi intact mm Hg 20 30 22 24 15 15 20 20 Atropine (0.4 mg/kg) Bilateral vagotomy mm Hg mm Hg 0 6 •Q 0 7 0 .15 20 20 Q 0 0 Circulation Research, Volume XIV, May 1964 aortic pressure in four dogs were similar after the administration of atropine. Following bilateral cervical vagotomy, aortic blood pressure showed no increase although right ventricular systolic pressure still increased and the ventricular end diastolic pressure remained unchanged (fig. 3 and table 1). With the left ventricle bypassed, sudden complete occlusion of the main pulmonary artery with total interruption of pulmonary blood flow was associated with an increase in mean aortic pressure of 14 ± 9 mm Hg in seven of nine animals (fig. 5). Following release of the occlusion there was a sudden further rise in aortic pressure. The aortic and right ventricular systolic pressures then returned gradually to base line levels. After division of both cervical vagi, the systemic responses associated with total main pulmonary artery block were markedly diminished or absent (fig. 5). Discussion The experimental results show that appropriate stimulation of receptors in the right ventricle influences peripheral vasomotor activity through autonomic nervous pathways. This interaction between the heart and systemic circulation was demonstrated by gradually increasing right ventricular systolic pres- 464 PINKERSON, KOT Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 sure. The systemic vascular responses were dependent on the presence of intact vagal fibers. Similar increases in aortic pressure following partial occlusion of the main pulmonary artery have been previously noted in animals with intact circulation.9 The possible explanations for the systemic pressure rise include increased blood flow, increased activity of the left ventricle, or increased total systemic resistance. In the present experiments, with use of a mechanical left ventricle, flow to the systemic circulation was controlled. The increased aortic pressure while venous and right atrial pressure remained constant represented an increase in total systemic vascular resistance. An increased vascular resistance in the isolated dog hind limb has been described after occlusion of the main pulmonary artery.10 However in these experiments, total systemic perfusion was not controlled and the increased resistance was attributed to decreased carotid sinus pressure. Although the increases in right ventricular systolic pressure were similar, the rise in INTACT 0 5 aortic pressure was blocked only by vagotomy and not by the administration of atropine. This difference in systemic response clearly shows that the changes in vascular resistance were dependent on impulses transmitted through vagal afferent fibers from the heart. In addition, the increase in aortic pressure prior to vagotomy could not have been due to release of vasoactive elements directly from the right ventricle into the general circulation or incomplete bypass of the left ventricle. The possibility that occlusion of the main pulmonary artery could stimulate other receptors on the right side of the circulation in addition to those in the right ventricle has been discussed previously." Since central venous, right atrial, and right ventricular end diastolic pressures showed no change, and pulmonary artery pressure responses were variable, the important stimulus must have been in the right ventricle. A slight decrease in pulmonary artery pressure distal to the site of occlusion has been suggested as a stimulus for the increased aortic pressure.9 In many instances in the present study, however, CIRCULATION 10 15 LEFT VENTRICULAR 20 29 0 Rt. Vent Systolic Pressure Change (mm Hg) 5 10 B BYPASS 20 25 30 Rt.Vent. Systolic Pressure Change (mm Hg) FIGURE 4 Relationship between the increase in right ventricular systolic and mean aortic pressure during various degrees of occlusion of the main pulmonary artery. Graplxs on the left are from animals with an intact circulation and on the right, the same animals but with fixed perfusion of the systemic circulation. Each line represents one animal, and the points, the recorded pressure changes. Points on both graphs were calculated before any change occurred in right ventricular end diastolic, right atrial or venous pressure. Circulation Research, Volume XIV, May 1964 PRESSOR REFLEX FROM RIGHT VENTRICLE 465 PRE VAGOTOMY POST VAGOTOMY P ^^ ^^ • v f~* ^^ ^^ v ^^ rvi 40 PPA 20 0 PR V 200 PAO Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 100 _J 0 I— mm Hg ^rl TOTAL OCCLUSION M.P.A. TOTAL OCCLUSION M.P.A. FIGURE 5 Effects of sudden complete occlusion of the main pulmonary artery in dogs with controlled perfusion of the systemic circulation. Tracings on the left are before, and on the right, after bilateral cervical vagotomy. Brackets at the bottom of each panel show the total time from onset to release of the occlusion. Symbols and time lines are the same as in figure 1. pulmonary artery pressure increased with the rise in systemic pressure. An increase in systemic vascular resistance has also been described following acute overdistention of the main pulmonary artery.3 The pressures used to distend the pulmonary artery were from 80 to 200 mm Hg. In the present experiments the changes in systemic pressure were obtained while main pulmonary artery pressures were lower. Stenosis near the pulmonic valve or distally near the bifurcation also did not alter the systemic response. During acute total occlusion of the main pulmonary artery, there was still a direct relationship noted between the elevation in right ventricular systolic and aortic pressures in the pump dog. Under these extreme circumstances there was an associated elevation of right ventricular end diastolic, right atrial, and venous pressures which also probably influenced the systemic response. 4 ' n The further increase in pressure which was seen immediately following release of the main pulmonary artery constriction in the pump dog was interpreted as release of vasoinhibiCirculation Research, Volume XIV, May 1964 tory impulses probably originating in the right atrium 4 while vasoconstrictor impulses from the right ventricle and possibly the veins n were still active. Incomplete drainage of the sudden increased blood volume in the left atrium could also have contributed to the post release rise in aortic pressure. This latter possibility, however, would not explain the marked decrease in response noted after vagotomy. It would appear that in the normal animal as well as during certain pathological states the vasomotor centers in the central nervous system are influenced by nerve impulses transmitted through vagal afferent fibers from the right ventricle. Nervous end organs have been described in histologic preparations of the right ventricle in the endocardium, myocardium, and epicardium.12 The various nerve endings which were seen are similar to sensory receptors in other areas of the body. Electroneurograms of the vagus nerves also have shown bursts of impulse activity with each ventricular systole.2'13 466 PINKERSON, KOT Summary Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 The relationship between right ventricular and aortic pressure was studied in open-chest anesthetized dogs. A simultaneous increase in both pressures was observed in animals with an intact circulation and animals with the systemic circulation perfused at a constant rate and stroke volume by an extracorporeal pump. With gradual partial constriction of the main pulmonary artery, the increase in right ventricular systolic and aortic pressures occurred without consistent change in other measured parameters. Bilateral cervical vagotomy abolished the systemic vascular response. These observations are consistent with a pressor reflex which is mediated over vagal afferent fibers from the right ventricle. It is suggested that in animals under varying physiologic stimuli an increase in right ventricular pressure is associated with a reflex increase in systemic vascular resistance. In abnormal circumstances with increased resistance to right ventricular emptying, the increased total peripheral vascular resistance would be important in maintaining systemic blood pressure and blood flow. References 1. AVIADO, D. M., JR., AND SCHMIDT, C. F.: Re- flexes from stretch receptors in blood vessels, heart and lungs. Physiol. Rev. 35: 247, 1955. 2. HEYMANS, C , AND NEIL, E.: Reflexogenic Areas of the Cardiovascular System. London, J. and A. Churchill Ltd., 1958. 3. LEWIN, R. J., CROSS, C. E., RIEBIN. P. A., AND SALISBURY, P. F.: Stretch reflexes from the main pulmonary artery to the systemic circulation. Circulation Res. 9: 585, 1961. 4. AVIADO, D. M., JR., L I , T. H., KALOW, W., PES- KIN, E. W., TURNBUL, G. L., AND HESS, M. E.: Respiratory and circulatory reflexes from the perfused heart and pulmonary circulation of the dog. Am. J. Physiol. 165: 261, 1951. 5. SALISBURY, P. F., CROSS, C. E., AND RIEBEN, P. A.: Reflex effects of left ventricular distention. Circulation Res. 8: 530, 1960. 6. TAQUINI, A. C , AND AVIADO, D. M., JR.: Reflex stimulation of heart induced by partial occlusion of pulmonary artery. Am. J. Physiol. 200: 647, 1961. 7. ROSE, J. C , BROIDA, H. P., HUFNAGEL, C. A., GlLLESPIE, J. F., RABILE, P. J., AND FREIS, E. D.: Method for the study of the circulation in the dog using a mechanical left ventricle. J. Appl. Physiol. 7: 580, 1955. 8. FINEBERG, M. H., AND WIGGERS, C. S.: Compen- sation and failure of the right ventricle. Am. Heart J. 11: 255, 1936. 9. GUYTON, A. C , LlNDSEY, A. W., AND GlLLULY, J. J.: Limits of right ventricular compensation following acute increase in pulmonary circulatory resistance. Circulation Res. 2: 326, 1954. 10. AVIADO, D. M., JR., AND SCHMIDT, C. F.: Car- diovascular and respiratory reflexes from the left side of the heart. Am. J. Physiol. 196: 726, 1959. 11. HADDY, F. J., AND GILBERT, R. P.: Relation of a venous arteriolar reflex to transmural pressure and resistance in small and large systemic vessels. Circulation Res. 4: 25, 1956. 12. KING, A. B.: Nerve endings in the cardiac muscle of the rat. Bull. Johns Hopkins Hosp. 65: 489, 1939. 13. PAINTAL, A. S.: A study of ventricular pressure receptors and their role in the Bezold reflex. Quart. J. Exptl. Physiol. 40: 348, 1955. Circulation Research, Volume XIV, May 1964 Systemic Blood Pressure Response to Changes in Right Ventricular Function ALAN L. PINKERSON and PETER A. KOT Downloaded from http://circres.ahajournals.org/ by guest on April 30, 2017 Circ Res. 1964;14:461-466 doi: 10.1161/01.RES.14.5.461 Circulation Research is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1964 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7330. Online ISSN: 1524-4571 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://circres.ahajournals.org/content/14/5/461 Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Circulation Research can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. Once the online version of the published article for which permission is being requested is located, click Request Permissions in the middle column of the Web page under Services. Further information about this process is available in the Permissions and Rights Question and Answer document. Reprints: Information about reprints can be found online at: http://www.lww.com/reprints Subscriptions: Information about subscribing to Circulation Research is online at: http://circres.ahajournals.org//subscriptions/