Figure 4.

Muscle sympathetic nerve activity (MSNA) responses during the postdrug/placebo administration cold pressor test (CPT). MSNA burst frequency and burst incidence values increased from rest to the CPT in both trials (A and C). The increases in MSNA burst frequency (Cohen’s d = 1.50) and burst incidence during the CPT were attenuated for fentanyl compared with placebo trials (B and D). We present data as means ± SD with individual responses (n = 11). For A and C, we compared data using repeated-measures two-way ANOVAs (main effects of rest/CPT and trial). We employed Tukey’s multiple comparison testing for post hoc analyses when appropriate. For B and D, we compared data using paired, two-tailed t tests.