title: Significance of using a nonlinear analysis technique, the Lyapunov exponent, on the understanding of the dynamics of the cardiorespiratory system in rats.
abstract: OBJECTIVE
  Pneumocardiography (PNCG) is the recording method of cardiac-induced tracheal air flow and pressure pulsations in the respiratory airways. PNCG signals reflect both the lung and heart actions and could be accurately recorded in spontaneously breathing anesthetized rats. Nonlinear analysis methods, including the Lyapunov exponent, can be used to explain the biological dynamics of systems such as the cardiorespiratory system.
  
  
  METHODS
  In this study, we recorded tracheal air flow signals, including PNCG signals, from 3 representative anesthetized rats and analyzed the nonlinear behavior of these complex signals using Lyapunov exponents.
  
  
  RESULTS
  Lyapunov exponents may also be used to determine the normal and pathological structure of biological systems. If the signals have at least one positive Lyapunov exponent, the signals reflect chaotic activity, as seen in PNCG signals in rats; the largest Lyapunov exponents of the signals of the healthy rats were greater than zero in this study.
  
  
  CONCLUSIONS
  A method was proposed to determine the diagnostic and prognostic values of the cardiorespiratory system of rats using the arrangement of the PNCG and Lyapunov exponents, which may be monitored as vitality indicators.
authors: Department of Biophysics, Faculty of Medicine, Celal Bayar University, Manisa, Turkey.
authors: Tamer
authors: T
authors: Zeren
authors: Department of Physiology, Faculty of Medicine, Celal Bayar University, Manisa, Turkey.
authors: Mustafa
authors: M
authors: Özbek
authors: Department of Physiology, Faculty of Medicine, Celal Bayar University, Manisa, Turkey.
authors: Necip
authors: N
authors: Kutlu
authors: Department of Physics, Faculty of Science, İstanbul University, İstanbul, Turkey.
authors: Mahmut
authors: M
authors: Akilli
mesh_terms: D000818:Animals; D006321:Heart; D017711:Nonlinear Dynamics; D051381:Rats; D012119:Respiration
keywords: Cardiorespiratory system; Lyapunov exponent; cardioventilatory coupling; nonlinear analysis; pneumocardiography; vitality indicator