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Bifurcation analyses of respiratory vagal reflexes

Sammon, Michel P.
http://rave.ohiolink.edu/etdc/view?acc_num=case1060098227

Abstract Details

1992, Doctor of Philosophy, Case Western Reserve University, Biomedical Engineering.
Rats with intact vagal reflexes exhibit respiratory patterns containing greater degrees-of-freedom than those seen after vagotomy. To determine vagal-dependent mechanisms which might be responsible for this change in the dimension of breathing, two experimental protocols were employed to modify vagal feedback in tracheostomized, urethane-anesthetized rats while measuring airflow: (Protocol #1) So as to produce graded changes in lung volume, continuous positive (CPAP) and negative (CNAP) airway pressure was applied to tracheal openings of vagi-intact rats. As CNAP was applied in a stepwise manner, transient bursts of premature inspiratory activity developed locally to the expiratory-inspiratory transition (E-I). In contrast to larger mammals, rats appear to rely strongly upon deflation reflexes for control of E-I phase-switching, presumably to aid in maintenance of volume. (Protocol #2) To evaluate processing of vagal afferent feedback by the respiratory central pattern generator (RCPG), brief electrical stimuli were applied to one afferent vagus of bilaterally vagotomized rats during every breath at varying phases of the respiratory cycle. Stimuli applied during early or late inspiration of every breath evoke highly predictable, 1-dimensional responses: reversible (GI = graded inhibition) or irreversible (OS = off-switching) inhibition of inspiration, respectively. Stimulation during midinspiration produces higher-dimensional oscillations which wander with a chaotic motion over a continuum of GI and OS. Stimuli applied during late expiration produce chaotic E-I phase-switching similar to that seen in with CNAP (Protocol #1). Based upon experimental observations, a new mathematical model for respiratory phase-switching is proposed which confines the respiratory trajectory to the interior of a heteroclinic orbit between saddle equilibria located at E-I and I-E. When feedback is included in the model, these equilibria possess complex eigenvalues; conditions are shown where feedback perturbs the symmetry of the oscillator, producing Silnikov bifurcations and inducing chaotic phase-switching similar to that seen experimentally. Within this dynamical framework, it is our view that the medullary RCPG normally functions in a highly symmetric state when isolated from external events; its oscillation occurs over a single degree-of-freedom attractor near a stable heteroclinic orbit. Information from a noisy, perturbing environment is presented to the RCPG by a variety of feedback loops and modulates the distance from the respiratory pattern to its central heteroclinic orbit. In doing so, these signals do more than simply modulate timing and amplitude of the pattern; they provide additional degrees-of-freedom, altering the dynamic stability, topology and symmetry of RCPG states in the process. (Abstract shortened with permission of author.)
Eugene Bruce (Advisor)
279 p.
Engineering, Biomedical
Rats; Respiratory vagal reflexes

Recommended Citations

Citations

  • Sammon, M. P. (1992). Bifurcation analyses of respiratory vagal reflexes [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1060098227

    APA Style (7th edition)

  • Sammon, Michel. Bifurcation analyses of respiratory vagal reflexes. 1992. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1060098227.

    MLA Style (8th edition)

  • Sammon, Michel. "Bifurcation analyses of respiratory vagal reflexes." Doctoral dissertation, Case Western Reserve University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1060098227

    Chicago Manual of Style (17th edition)

case1060098227
683
© 1992, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.