Time-frequency coherence analysis of phrenic and hypoglossal activity in the decerebrate rat during eupnea, hyperpnea, and gasping

Abstract

Fast respiratory rhythms include medium- (MFO) and high-frequency oscillations (HFO), which are much faster than the fundamental breathing rhythm. According to previous studies, HFO is characterized by high coherence (Coh) in phrenic (Ph) nerve activity, thereby providing a means of distinguishing between these two types of oscillations. Changes in Coh between the Ph and hypoglossal (XII) nerves during the transition from normal eupnic breathing to gasping have not been characterized. Experiments were performed on nine unanesthetized, chemo- and barodenervated, decerebrate adult rats, in which sustained asphyxia elicited hyperpnea and gasping. A gated time-frequency Coh analysis was developed and applied to whole Ph and medial XII nerve recordings. The results showed dynamic Ph-Ph Coh during eupnea, including MFO and HFO. XII-XII Coh during eupnea was broadband and included four distinct peaks, with low-frequency Coh dominating the epochs preceding the onset of Ph activity. During gasping, only MFO-peaks were present in Ph-Ph Coh. Bilateral XII activity showed a significant reduction in Coh and a shift toward lower frequencies during gasping. In contrast, contralateral Ph-XII Coh progressively increased during state changes from eupnea to gasping, a tendency mirrored in the startup part of the Ph activity. These data suggest significant hypoxia/hypercapnia-induced alterations in synchronization between respiratory outputs during the transition from eupnea to gasping, reflecting a reconfiguration of the respiratory network and/or alterations in the circuitry associated with the motor pools, including dynamic coupling between outputs.

Temperature and state dependence of dynamic phrenic oscillations in the decerebrate juvenile rat

“…6) differed significantly in frequency from those reported for adult rats in vivo (14). When considering our present results with those previously characterized in adult rats in vivo (14,15), one reasonably concludes that the major fast oscillation bands increase in frequency during development. Although it is not clear whether entirely new circuit and cellular mechanisms develop to produce HFO in the adult or if the same mechanisms operate in a different regimen, the generation of significant oscillations in this band associated with maturation has been described in pigs (3,24), cats (9,23), and rats (9).…”

“…Functional coupling between the left and right Ph output has been noted in neonates (30), and our results suggest that it is quite robust in juveniles. Furthermore, HFO tend to have more consistently high coherence than the MFO in adult rats (15). In the present study, we note that MFO analog in the juvenile rat displays coherence values equal to those of HFO (Figs.…”

“…1 and 2). Eupnea, hyperpnea, and gasping were classified as described in the classic literature (8,12,16,17,20) and in our previous publications (14,15). According to these studies, respiratory responses to hypoxia in mammals typically progress through four phases: hyperpnea, primary apnea, gasping, and terminal apnea.…”

“…A commonly used measure of phase constancy in coupled oscillations is coherence, which may be caused by common inputs, direct coupling, or both. In an earlier study, we examined the intraburst dynamics of Ph and XII coherence in the adult unanesthetized decerebrate rat and found significant dynamic coupling between the left and right Phs, the left and right XIIs, and between Ph and XII activity during eupnea, hyperpnea, and gasping, with the highest coherence observed during the hyperpneic state (15). Applying this metric to pairwise relations between Ph, XII, and vagal efferent activity in the juvenile rat in situ, Leiter and St-John (10) concluded that significant coherence existed between different nerves only during gasping.…”

Wavelet Analysis of Electrical Activities from Respiratory Muscles during Coughing and Sneezing in Anaesthetized Rabbits

“…HFOs detected from the inspiratory motor output during eupnoea are presumably generated within the respiratory central pattern generator -CPG (Cohen et al 1979(Cohen et al , 1987. Variances of synchronization in respiratory outputs during transition between different motor patterns were explained by the respiratory network reconfiguration and alterations in the circuitry associated with the motor pools (Marchenko and Rogers 2006).…”