Fractal cardiovascular dynamics and baroreflex sensitivity after stellate ganglion block.

Background: It has been shown that stellate ganglion block can attenuate baroreflex sensitivity. Our primary purpose in this study was to determine whether fractal dynamics (dynamic change of self-similar fluctuation patterns) of not only heart rate but also systolic blood pressure variability are involved in attenuation of baroreflex sensitivity after stellate ganglion block.

Methods: Sixteen young, healthy volunteers entered the study. Spectral analysis of heart rate and systolic blood pressure variability was performed before and 30, 60, 90, and 120 min after either right or left stellate ganglion block, separated by a 1 to 1(1/2)-mo interval, with 6 mL of 1% mepivacaine. Shortly after each spectral analysis, baroreflex sensitivity was assessed with the head-up tilt test.

Results: Baroreflex sensitivity, assessed by the head-up tilt test, was significantly attenuated at 30 min after either right or left stellate ganglion block (1.26 +/- 0.18 to 0.46 +/- 0.08 bpm/mm Hg, P < 0.05 and 1.17 +/- 0.35 to 0.51 +/- 0.13 bpm/min, P < 0.01, respectively). Fractal slopes reflecting the degree of self-similarity of fluctuations were significantly increased at 30 min after either right or left stellate ganglion block (right stellate ganglion block--heart rate; -1.08 +/- 0.30 to -1.62 +/- 0.22, P < 0.01; right stellate ganglion block--systolic blood pressure; -1.30 +/- 0.80 to -2.40 +/- 0.80, P < 0.05; left stellate ganglion block--systolic blood pressure; -1.20 +/- 0.40 to -2.13 +/- 0.50, P < 0.05). Fractal slope did not change after left stellate ganglion block with heart rate variability analysis.

Conclusions: Loss of complexity (status of being complex behavior) of both heart rate and systolic blood pressure variability, indicated by increased fractal slopes, is one mechanism in attenuating baroreflex sensitivity after stellate ganglion block.