Selective resection of the phrenic nerve roots in rabbits. Part I: Cartography of the residual innervation.

Partial unilateral diaphragmatic paralysis remains poorly understood. This study evaluates the residual innervation of the diaphragm after selective resection of one or several roots of the right phrenic nerve in rabbits. Forty-seven animals were operated on according to five root resection modalities. Seven animals served as control. Eight weeks after surgery, the different regions of each hemidiaphragm were analyzed. Electromyographic activity was measured during quiet inspiration and the following histomorphometric parameters were studied: mean fiber area, fiber area dispersion, and ratio large diameter over small diameter. The results obtained from the two measurements were similar. When the accessory phrenic nerve was spared, the crural diaphragmatic region was preserved; denervation was encountered in anterior and lateral parts of the hemidiaphragm. When the highest root of the right phrenic nerve was resected, denervation denervation was limited to the sternal region. When resection of the two highest roots was performed, partial denervation was observed in each region, with residual innervation in the posterior hemidiaphragm. When resection of both the lowest roots was performed, denervation was maximal in the costal region; sternal region remained intact. No contralateral innervation was observed. We conclude that in rabbits: 1) resection of a single root of the phrenic nerve preserves consistent residual innervation. 2) somatotopy of the diaphragm innvervation follows an anteroposterior distribution.