Abstract 16261: Baroreflex Induced Changes in Stressed Blood Volume, Not Cardiac Output Curve, is the Central Mechanism Preventing Volume Load Induced Pulmonary Edema
Background: We previously demonstrated that baroreflex (BR) failure predisposes volume induced pulmonary edema (AHA 2011). Since the BR changes both cardiac and vascular properties, how exactly the BR failure causes volume intolerance remains unknown. The aim of this investigation was to examine the mechanism of BR failure induced volume tolerance.
Method: In 8 anesthetized dogs, we isolated bilateral carotid sinuses and controlled intra-carotid sinus pressure (CSP) by a servo-controlled piston pump, while measuring the left (PLA) and right (PRA) atrial pressure, arterial pressure (AP) and aortic flow (CO). We closed the BR feedback loop by matching CSP to instantaneous AP, whereas opened by maintaining CSP constant independent of AP. We infused total of 22.5ml/kg of dextran in an increment of 2.5ml/kg. In each step, we measured PLA, PRA and CO in both open and closed loop conditions. We fitted the CO curve to a logarithmic function and determined its functional slope S, as a measure of cardiac performance, for the left ventricle (SL) and right ventricle (SR). We determined stressed blood volume and mean circulatory filling pressure (Pmcf).
Results: Increases in PLA was lower in the closed loop than in the open loop condition (9±3 vs. 12±5 mmHg, p<0.05). Both SL and SR were lower in the closed loop than in the open loop condition (SL: 23±5 vs. 27±6 ml/kg/min/mmHg, p<0.01, SR: 23±5 vs. 27±6 ml/kg/min/mmHg, p<0.01) indicating that the BR lowers cardiac performance against volume overload. Pmcf after infusion of 22.5ml/kg of dextran was lower in the closed loop than in the open loop condition (10±1 vs. 13±1 mmHg, p<0.005).
Conclusion: In response to volume challenge, the BR lowered cardiac performance and prevented the increases in Pmcf. Although those two responses have antagonizing impact on PLA, the fact that the BR lowered PLA indicates that the BR induced changes in stressed volume is the central mechanism preventing pulmonary edema.
- © 2012 by American Heart Association, Inc.