Fig. 4.

Impact of HF-ES on the phrenic activity recorded ipsilateral to C2Hx. Representative traces of integrated ipsilateral phrenic waveform averages are shown from rats that were either 2 or 12 wk post-C2Hx injury and received HF-ES to either the cervical or thoracic spinal cord. Waveform averages were calculated from the 10 respiratory cycles immediately preceding the initiation of stimulation (baseline) and from the 10 cycles immediately following each bout of stimulation. For each plot, time 0 represents the start of the inspiratory phase of the respiratory cycle, which is shaded in gray. Note the increase in tonic phrenic output in both the inspiratory and expiratory phases of the respiratory cycle following 500- and 1,000-µA stimulation (as evidenced by the upward shift in the waveform baseline).