EVIDENCE FOR PRESERVED CARDIOPULMONARY BAROREFLEX CONTROL OF RENAL CORTICAL BLOOD-FLOW IN HUMANS WITH ADVANCED HEART-FAILURE - A POSITRON EMISSION TOMOGRAPHY STUDY

Background The effect of cardiopulmonary baroreflexes on the renal cir culation in healthy humans and patients with heart failure is unknown because of the technical limitations of studying the renal circulation . Positron emission tomography (PET) imaging is a new method to measur e renal cortical blood flow in humans that is precise, rapid, reproduc ible, and noninvasive. The purpose of this study was to compare the ef fect of acute cardiopulmonary baroreceptor unloading by phlebotomy on regional blood flow in healthy humans and humans with advanced heart f ailure. Methods and Results We compared renal cortical blood flow and forearm blood flow in 10 healthy volunteers and 8 patients with heart failure (left ventricular ejection fraction, 0.24+/-0.02) during cardi opulmonary baroreceptor unloading with phlebotomy (450 mL). The major findings of this study are: (1) At rest, renal cortical blood flow is markedly diminished in humans with heart failure compared with healthy humans (heart failure, 2.4+/-0.1 versus healthy, 4.3+/-0.2 mL . min(- 1). g(-1), P<.001). (2) In healthy humans, during phlebotomy, forearm blood flow decreased substantially (basal, 3.3+/-0.4 versus phlebotomy , 2.6+/-0.3 mL . min(-1). 100 mL(-1), P=.02) and renal cortical blood flow decreased slightly but significantly (basal, 4.3+/-0.2 versus phl ebotomy, 4.0+/-0.3 mL . min(-1). g(-1), P=.01). (3) The small magnitud e of reflex renal vasoconstriction is not explained by the inability o f the renal circulation to vasoconstrict, since the cold presser stimu lus induced substantial decreases in renal cortical blood flow in heal thy subjects (basal, 4.4+/-0.1 versus cold presser, 3.7+/-0.1 mL . min (-1). g(-1), P=.003). (4) In humans with heart failure, during phlebot omy, forearm blood flow did not change (basal, 2.6+/-0.3 versus phlebo tomy, 2.7+/-0.2 mL . min(-1). 100 mL(-1), P=NS), but renal cortical bl ood flow decreased slightly but significantly (basal, 2.4+/-0.1 versus phlebotomy, 2.1+/-0.1 mL . min(-1). g(-1), P=.01). (5) The cold press er stimulus induced substantial decreases in renal cortical blood flow in patients with heart failure (basal, 2.9+/-0.1 versus cold presser, 2.3+/-0.1 mL . min(-1). g(-1), P=.008). Thus, in patients with heart failure, there is an abnormality in cardiopulmonary baroreflex control of the forearm circulation but not the renal circulation. Conclusions This study demonstrates the power of PET imaging to study normal phys iological and pathophysiological reflex central of the renal circulati on in humans and describes the novel finding of selective dysfunction of cardiopulmonary baroreflex control of one vascular region but its p reservation in another in patients with heart failure.