The short-term effect of upper abdominal incision versus sham incision on efferent phrenic nerve activity (Protocol A). (A-F) One hour after the upper abdominal incision (Postop), spike frequency area-under-the-curve (AUC)/respiratory cycle (A), spike frequency AUC/minute (B), integrated phrenic neurogram (∫Phr) AUC/respiratory cycle (C), ∫Phr AUC/minute (D), central respiratory rate (E), and inspiratory-to-expiratory duration ratio (T_I:T_E; F) significantly decreased compared with baseline. The Ipsilateral (n = 7) and the Contralateral group (n = 7) respectively represent nerve activity recorded from the phrenic nerves on the same side and the opposite side of the abdominal incision. The control group underwent the sham incision (Sham group, n = 8). Data are presented as mean ± SD. **P < 0.01; ***P < 0.001; ****P < 0.0001 versus Baseline, and ††P < 0.01; †††P < 0.001; ††††P < 0.0001 versus Sham by two-way ANOVA with repeated measured in one factor, followed by Sidak’s multiple comparison tests.