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The four-quadrant plots and polar plots to examine the trending abilities of PPV against SVV under normal vasomotor tone (PHE-) and under increase vasomotor tone (PHE+). Half-circle polar plots are shown with data transformed to positive directional data only. We applied an exclusion zone when the percentage of change of data was below 15% (0.5). SVV: stroke volume variation, PPV: pulse pressure variation.
