title: Bifurcations of the respiratory pattern associated with reduced lung volume in the rat.
abstract: Rats with intact vagal reflexes exhibit patterns of breathing that contain greater degrees of freedom than those seen after vagotomy. To determine how alterations in end-expiratory volume modify the respiratory pattern, continuous positive (CPAP) and negative (CNAP) airway pressure was applied to tracheal openings of nine urethan-anesthetized vagi-intact rats (+3 to -9 cmH2O). Phase portraits (e.g., volume vs. flow curves), power spectra, correlation integral curves, and inspiratory-to-expiratory duration (TI/TE) ratios are used to interpret the vagal-dependent responses to changes in mean tracheal pressure (Ptr). With CPAP, respiratory oscillation was highly periodic and one dimensional, with TI/TE near 1.0. As Ptr was reduced in a stepwise manner, transient bursts of inspiratory airflow developed local to the expiratory-inspiratory transition, with amplitude increasing proportionally with the level of CNAP. These oscillatory "expiratory interrupts" (doubling TI/TE in five of nine cases) produced highly variable and asymmetric respiratory patterns. Progressive increases in correlation dimension (maximum = 1.8-3.0) and tendencies toward broadband power spectra were seen as Ptr was lowered. The irregular phase-switching dynamics seen with CNAP (which disappeared after vagotomy) are consistent with onset of low-dimensional chaos, probably correlated with activation of feedback mechanisms responsive to lung deflation.
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: M
authors.initials: M
authors.lastname: Sammon
authors.forename: J R
authors.initials: JR
authors.lastname: Romaniuk
authors.forename: E N
authors.initials: EN
authors.lastname: Bruce
mesh_terms: D000465:Algorithms; D000818:Animals; D004576:Electromyography; D005246:Feedback / Q000502:physiology; D005652:Functional Residual Capacity / Q000502:physiology; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology*; D008176:Lung Volume Measurements; D008954:Models, Biological; D010991:Plethysmography; D011175:Positive-Pressure Respiration; D051381:Rats; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology