Fig. 5.

Average changes in phrenic and hypoglossal nerve activity following C4 HF-ES. Depicted are changes in phasic (A–C), tonic (D–F), and total (G–I) phrenic and hypoglossal nerve activity following HF-ES of the C4 spinal cord, delivered at 2 and 12 wk postinjury. Data were calculated over the 3 min following each bout of stimulation and are represented as %change from baseline activity. HF-ES delivered to the C4 spinal cord at 12 wk post-C2Hx resulted in an increase in phasic phrenic activity. No other group differences were observed, although dose-dependent increases in amplitude (%change above baseline) were observed following HF-ES across both groups, with the greatest amplitude changes occurring following the highest stimulation intensities (e.g., 500 and 1,000 µA). Note that profound increases in tonic activity comprised much of the increase in total activity and that the ipsilateral phrenic nerve demonstrated the most dramatic changes in nerve amplitude relative to baseline. *P < 0.05, different from 100 µA. #P < 0.05, different from 500 µA. %P < 0.05, different from 2 wk at same stimulus current. Data were evaluated using 2-way repeated-measures ANOVA with Holm-Sidak post hoc tests for individual comparisons (groups: 2-wk C4, n = 8; 12-wk C4, n = 8).