Study of the Lyapunov exponents in heart rate variability signals

Heart rate variability signals obtained from 24 h recordings are analyzed for normal and pathological subjects. This time series contains information about the autonomic nervous system action regulating the beat-to-beat heart rate. Nonlinear contributions to the long period variability have been assessed by the calculation of the entire spectrum of Lyapunov exponents, after the system trajectory reconstruction, starting from the original variability signal. The positivity of Lyapunov exponent values, obtained from an unknown process, can establish whether the structure generating it shows nonlinear chaotic characteristics. This is what happens for the cardiovascular signals. Moreover, the different values obtained for the Lyapunov exponents operate a classification among the considered pathophysiological cases.     

Continuous proteolysis with a stabilized protease. II. Continuous experiments

Batch proteolysis experiments were performed in order to choose a protein-protease system to prepare a correct hydrolysate suitable for the enrichment of soft-drinks. The system eventually studied was casein-Alcalase. Comparative batch and continuous proteolysis of casein by Alcalase showed that the reaction, which does not exactly follow first order kinetics with respect to the substrate concentration, is inhibited by the reaction products. Furthermore, experiments were done in order to determine the reaction conditions (pH8.8 in the reactor, casein concentration 5%, 40 degrees C). Determining the molecular weight of Alcalase (43,000) suggested the choice of ultrafiltration membrane PM 30. Sutdies of continuous proteolysis with the chemically stabilized enzyme retained by the ultrafiltration reactor showed that protease reuse for seven days at 40 degrees C is possible and that the growth of microorganisms is practically inhibited under these conditions. Gel chromatography showed the molecular weight.range of the peptides to be less than 2,000. Triangular taste tests showed that the threshold identification concentration of the dry hydrolysate in orange juice is about 0.65%.