An analysis of mechanical feedback to the central respiratory pattern generator

Analyzing the role of sensory feedback to the central respiratory pattern generator (CRPG) in modulating the pattern of respiration is difficult because of the complexity and uncertainty of the underlying systems. To overcome this difficulty we apply an analytic approach which focuses on the essential features of the CRPG without the need to specify the precise mechanism of rhythm generation. The limit cycle behavior of the isolated CRPG allows a general model of the closed system to be simplified to one that depends on the amplitude of respiration and the phase difference between the CRPG and the lungs. This simplification does not require the use of any unmeasurable parameters or unproven hypotheses. Using this analytic approach we can explicitly obtain the entire experimentally determined relationship between respiratory volume and period, and demonstrate that this relies upon the existence of a nonlinear threshold to mechanical feedback. Computational experiments with several different models confirm this result and its independence from the source of the limit cycle.