DYNAMIC SYMPATHETIC REGULATION OF LEFT-VENTRICULAR CONTRACTILITY STUDIED IN THE ISOLATED CANINE HEART

We investigated the dynamic sympathetic regulation of left ventricular end-systolic elastance (E-es) using an isolated canine ventricular pr eparation with functioning sympathetic nerves intact. We estimated the transfer function from both stellate ganglion stimulation to E-es and ganglion stimulation to heart rate (HR) for both left and right gangl ia by means of the white noise approach and transformed those transfer functions into corresponding step responses. The HR response was much larger with right sympathetic stimulation than with left sympathetic stimulation (4.3 +/- 1.4 vs. 0.7 +/- 0.6 beats min(-1).Hz(-1), P < 0.0 1). In contrast, the E-es responses without pacing were not significan tly different between left and right sympathetic stimulation (0.72 +/- 0.34 vs. 0.76 +/- 0.42 mmHg.ml(-1).Hz(-1)). Fixed-rate pacing signifi cantly decreased the E-es response to right sympathetic stimulation (0 .53 +/- 0.43 mmHg.ml(-1).Hz(-1), P < 0.01), but not to left sympatheti c stimulation (0.67 +/- 0.32 mmHg.ml(-1).Hz(-1), not significant). Alt hough the mechanism by which the sympathetic nervous system regulates cardiac contractility is different depending on whether the left or ri ght sympathetic nerves are activated, this difference does not affect the apparent response of E-es to dynamic sympathetic stimulation.