Dynamic Power Spectral and Coherence in Hypoglossal and Phrenic Outputs

Abstract

In order to assess the functional organization of fast rhythm generation in the respiratory control system, we characterized the dynamic changes in power and coherence as a function of frequency during eupnea in phrenic (Ph) and hypoglossal (XII) outputs in nine unanesthetized, decerebrate adult rat. This analysis was accomplished by developing and applying a novel algorithm to estimate time-frequency power spectral and coherence functions from periods during the inspiratory bursts only. Our results revealed a bimodal distribution of Ph power, classified as medium- (MFO) and high-frequency oscillations (HFO). HFO were prevalent in the first 2/3 of the eupneic Ph burst, while MFO spanned the final 2/3 of the burst. The power distribution in XII was multimodal during eupnea, exhibiting a pyramidal shape with an apex at 190 Hz with most of the power contained in frequencies >120 Hz. The power at the dominant frequency started well before the onset of Ph activity, and peaked during Ph activity. Coherence between the left and right Ph activity during epnea was higher for HFO than MFO, the former following a similar time course as the power in that band, and the latter restricted to late inspiration. Contralateral Ph-XII coherence showed three main peaks, the largest in the 170–200 Hz band. This prominent band spanned the (Ph-related portion) of the XII/Ph burst, while smaller MFO peaks were primarily late-burst occurring. Our results suggest that the mechanisms responsible for producing fast oscillations are coupled bilaterally and between outputs, and more strongly for HFO than MFO.