Individual cardiovascular response to different levels of sympathetic blockade varies widely, depending on the degree of sympathetic tone before the block.
It was suggested that the sympathetic control of heart rate modified the dominating parasympathetic tone, rather than functioning as an active cardiac accelerator. In this study there was no compensation for changes in preload; therefore cardiopulmonary baroreceptors affected by changes in central volume secondary to peripheral vasodilatation or vasoconstriction might have altered arterial baroreceptor heart rate reflex as well. To minimize that influence, Goertz et al gave plasma volume expanders to equalize left ventricular preload conditions as assessed by transesophageal echocardiography". High TEA added to general anaesthesia significantly decreased the cardiac acceleration in response to decreasing blood pressure, suggesting that baroreflex-mediated heart rate response to a decrease in arterial blood pressure depends on the integrity of the sympathetic nervous system. However general anaesthesia, in addition to high levels of epidural anaesthesia, may have modified the balance between sympathetic and parasympathetic tone as well.
B T Veering, M J Cousins. Anaesthesia and Intensive Care. Edgecliff:Dec 2000. Vol. 28, Iss. 6, p. 620-35 (16 pp.)
Copyright Australian Society of Anaesthetists Dec 2000