Effects of central venous blood volume shifts on arterial baroreflex control of heart rate

9 male rhesus monkeys (7.0-10.5 kg)

Central venous blood volume shifts induced by body position changes (90 degrees head down tilt) and blood volume expansion (20% or 50% with normal saline) under anesthesia (10 mg/kg ketamine-HCl), with and without beta-receptor blockade

Awake sitting, anesthetized sitting, and anesthetized recumbent positions

Baroreflex slope (determined by linear regression of R-R interval plotted against systolic aortic pressure after 4.0 micrograms/kg phenylephrine bolus injection)surrogate