Fig. 2.
Experimental protocols for the in vivo efferent phrenic nerve recording and whole-body plethysmography. For Protocols A, B, and D, efferent phrenic nerve activity was recorded in the urethane-anesthetized, vagotomized, paralyzed, and mechanically ventilated rats, using a bipolar hook electrode. The inset in the top left corner shows a schematic diagram of the preparation. In Protocol A, efferent phrenic nerve activity was recorded before and 1 h after the upper abdominal incision or sham incision. In the Ipsilateral group, the phrenic nerves on the same side of the incision were recorded, and in the Contralateral group, the phrenic nerves on the opposite side were recorded. In Protocol B, phrenic nerve activity was recorded 1 day or 10 days after the upper abdominal incision, and was compared to the sham incision group. In Protocol D, the effect of epidural bupivacaine or phosphate-buffered saline administered before incision on the phrenic nerve activity was evaluated. The nerve activity was recorded before and after the upper abdominal incision. For Protocols C and E, ventilatory parameters in the unanesthetized and unrestrained rats were measured using a whole-body plethysmography system. In Protocol C, the measurements were performed before, and at multiple time points after, the upper abdominal incision or sham incision. In Protocol E, the effect of epidural bupivacaine or phosphate-buffered saline (PBS) administered 1 day after the incision on ventilatory parameters was evaluated. More detailed description of the experimental protocols can be found in the Materials and Methods section. PO 1 h, 1 h postoperatively; PO 4 h, 4 h postoperatively; POD, postoperative day; Post-Epidural, Post-epidural injection; Postop, postoperative period.