Regulation of Coronary Blood Flow by the Carotid Body Chemoreceptors in Ovine Heart Failure

Abstract

BackgroundThe carotid body (CB) is an arterial chemoreceptor organ located in the carotid bifurcation, which carries out essential functions in cardiorespiratory control. In response to hypoxia, carotid chemosensory discharge produces respiratory, autonomic, and cardiovascular adjustments critical for body homeostasis. Previous studies have shown that chemoreflex sensitivity is augmented animal models of heart failure (HF). However, the role of the chemoreflex in modulating coronary blood flow during HF is not clear. We hypothesized that carotid chemoreceptor stimulation would increase coronary blood flow in both normal sheep and sheep with HF.MethodsHeart failure was induced by the microembolization technique and instrumentation was performed when ejection fraction was below 40%. Both groups of sheep were implanted with a coronary artery flow probe and an arterial pressure catheter. The responses of mean arterial pressure (MAP) and coronary blood flow (CoBF) were determined in conscious sheep following CB stimulation with intracarotid potassium cyanide (KCN; 30μg/kg). To determine the cardiac vagal contribution to the CoBF response, CB activation was repeated following atropine infusion (8 mg bolus followed by 24 mg/h infusion for 30 minutes).ResultsIn control animals, activation of the CB increased MAP (114±1%) and CoBF (116±4%) but coronary vascular conductance (CVC) was unaltered. In the HF group, CB stimulation increased MAP (108±1%), CoBF (126±3%), and CVC (114±2%). The MAP increase was significantly attenuated after atropine infusion in both animal groups, however, the CoBF and CVC responses to KCN were unchanged. These responses persisted when the heart was paced at a constant rate to eliminate the role of altered metabolic demand.DiscussionOur data indicate that in an ovine model of HF, carotid body mediated increases in MAP are attenuated compared to control animals. There was a significant increase in coronary vascular conductance in the HF animals following CB activation which was absent in the normal animals. Overall, our data suggest that the hyperactive carotid body chemoreflex may serve to increase coronary blood flow in the HF condition.Support or Funding InformationHealth Research Council of New Zealand, National Heart Foundation of New Zealand