Chaotic behavior of blood pressure and heart rate in the conscious dog

Initial studies in five conscious dogs with their baroreceptors either intact or surgically isolated, demonstrate that deterministic chaos is likely to exist in both heart interval and mean arterial blood pressure. The nature of this chaotic activity is not qualitatively different between the intact and open loop preparations. To assess nonlinear dynamical behavior, we constructed phase space trajectories from the time series data. The fractal dimension of the reconstructed trajectories was measured using the Grassberger-Procaccia algorithm. In four out of five dogs the fractal dimension of the reconstructed trajectory did not clearly converge for embedding dimensions up to 5. In one dog the fractal dimension of the attractor converged to a value between 2 and 3 for both heart interval and blood pressure in open and closed loop cases. Further evidence for deterministic chaos was provided by the reliability of data forecasts based on the fractal attractor.