Modulation of rabbit carotid baroreflex during positive end-expiratory pressure.

Modification of carotid baroreflex heart and vascular responses during increased lung positive end-expiratory pressure (PEEP) were measured anesthetized aortic-denervated rabbits. Static carotid intrasinus pressure (ISP) was varied in increments of 12.5 mmHg over 25-140 mmHg during lung inflation conditions ranging from spontaneous breathing (SB) to positive-pressure respiration at 0.0-7.5 cmH2O PEEP. To distinguish cardiopulmonary vagally and nonvagally mediated influences, heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and total peripheral resistance (TPR) were measured and compared before and after sequential vagotomy and beta- and alpha-receptor blockade. When compared with responses of SB animals the HR-ISP relationship was not significantly altered during controlled respiration (CR) with PEEP before or after vagotomy. With CR and then PEEP, MAP-ISP relationship curves and linear slope values (ISP range 62-113 mmHg) were significantly depressed when compared with those of SB rabbits. Before vagotomy slope values were -1.61 (SB), -1.22 (CR + 0.0 cmH2O PEEP), and -0.82 (CR + 7.5 cmH2O PEEP); respective values after vagotomy were -2.26, -0.96, and -0.64. Results of CO and TPR responses during low ISP and PEEP demonstrated components of both vagally and nonvagally mediated influences from inflation sensitive cardiopulmonary receptors.U