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

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Abstract
The effects of anesthesia, body position and blood volume expansion on baroreflex control of heart rate were studied. Five male rhesus monkeys [Macaca mulatta] (7.0-10.5 kg) were given bolus injection of 4.0 .mu.g/kg phenylephrine during each of the following situations: awake sitting, anesthetized (AN) (10 mg/kg ketamine-HCl) sitting, AN recumbent, AN 90.degree. head down tilt and AN 50% blood volume expansion with normal saline. .beta.-Receptor blockade was performed on each treatment after anesthesia. Four additional animals were similarly treated after 20% blood volume expansion. R-R interval was plotted against systolic aortic pressure and the slope was determined by linear regression. Baroreflex slope was significantly (P < 0.05) reduced by 90.degree. head down tilt and 50% volume expansion both before and after .beta.-receptor blockade. A similar trend was seen after 20% volume expansion. These data are consistent with the thesis that baroreflex control of heart rate is reduced by central blood volume shifts.

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