Robert Rogers
2/10/06
Title: Core Oscillator: Dynamics of Fast Rhythms in Respiratory Motor Outputs
Abstract:
The network of neurons responsible for generating the respiratory rhythm and pattern of
motor outputs is located in the pons and brainstem. The output of this network is
ultimately responsible for activating the phrenic and intercostal motor neurons in the
spinal cord, which drive the respiratory pump muscles (i.e., the diaphragm and intercostal
muscles). In addition to the basic rhythmic activity at the respiratory frequency, the
respiratory motor nerves are known to contain fast oscillations at much higher
frequencies than the basic breathing rhythm, including what are known as medium- and
high-frequency oscillations (MFO and HFO, respectively). In this work, we characterize
dynamic nature of the fast oscillations in the activity of two respiratory motor nerves, the
phrenic nerve and the (genioglossal branch of the) hypoglossal nerve, under three distinct
behavioral conditions. Using time-frequency analysis, we first describe the changes in
dynamic power spectral components that accompany these states. We note that HFO
dominate the first 2/3 of inspiration, while MFO dominate the final 2/3 of inspiration
under normal eupneic breathing. In addition, we find that the phrenic HFO are increased
in amplitude, then absent, when the system changes from eupnea to hyperpnoea to
gasping behavioral pattern. Next, we describe the dynamic coherence associated with
these states. We find that the phrenic-phrenic coherence follows much the same dyamic
pattern and state-dependent alterations as its power spectrum. The (contralateral)
hypoglossal-phrenic coherence is HFO-dominated during eupnea, and shifts significantly
towards lower frequencies during gasping. Finally, in order to estimate the "functional
coupling strength" between phrenic and hypoglossal outputs, we combine power and
coherence estimations to yield a physiologically-relevant metric which also provides
insight into the structure of the central pattern generator. Our results indicate a statedependent reconfiguration of the central pattern generator, which has clear implications
for physiological activation of the respiratory musculature.
Paper:
Review of HFO