Browsing by Author "Klein, Norbert"

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    Cardiac Autonomic Dysfunction and Incidence of de novo Atrial Fibrillation: Heart Rate Variability vs. Heart Rate Complexity
    (Lausanne : Frontiers Media, 2020) Wessel, Niels; Berg, Karsten; Kraemer, Jan F.; Gapelyuk, Andrej; Rietsch, Katrin; Hauser, Tino; Kurths, Jürgen; Wenzel, Dave; Klein, Norbert; Kolb, Christof; Belke, Roberto; Schirdewan, Alexander; Kääb, Stefan
    Background: The REACT DX registry evaluates standard therapies to episodes of long-lasting atrial tachyarrhythmias and assesses the quality of sensing and stability of the lead and the implantable cardioverter-defibrillator (ICD) (BIOTRONIK Lumax VR-T DX and successors) over at least a 1-year follow-up period. Objective: To study the association between the risk of de novo device-detected atrial fibrillation (AF), the autonomic perturbations before the onset of paroxysmal AF and a 7-days heart rate variability (7dHRV) 1 month after ICD implantation. Methods: The registry consists of 234 patients implanted with an ICD, including 10 with de novo long-lasting atrial tachyarrhythmias with no prior history of AF. The patients were matched via the propensity-score methodology as well as for properties directly influencing the ECGs recorded using GE CardioMem CM 3000. Heart rate variability (HRV) analysis was performed using standard parameters from time- and frequency-domains, and from non-linear dynamics. Results: No linear HRV was associated with an increased risk of AF (p = n.s.). The only significant approach was derived from symbolic dynamics with the parameter “forbidden words” which distinguished both groups on all 7 days of measurements (p < 0.05), thereby quantifying the heart rate complexity (HRC) as drastically lower in the de novo AF group. Conclusion: Cardiac autonomic dysfunction denoted by low HRC may be associated with higher AF incidence. For patients with mild to moderate heart failure, standard HRV parameters are not appropriate to quantify cardiac autonomic perturbations before the onset of AF. Further studies are needed to determine the individual risk for AF that would enable interventions to restore autonomic balance in the general population. © Copyright © 2020 Wessel, Berg, Kraemer, Gapelyuk, Rietsch, Hauser, Kurths, Wenzel, Klein, Kolb, Belke, Schirdewan and Kääb.
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    Manufacture of glass composites reinforced with long and short fibres by extrusion
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Roeder, Erwin; Klein, Norbert; Langhans, Klaus
    In the case of fibre-reinforced glass composites the glass matrix is the property-determining component, i.e., in the first place the composite possesses the characteristic properties of the glass. The embedded fibres serve for increasing the strength, the work of fracture and thus, the toughness of the glass. In contrast to the manufacture of composites by hot pressing, the extrusion method produces samples with high length-to-diameter ratios. The continuous flowing of the glass melt within the deformation zone and within the die channel leads to a preferential orientation of the fibres parallel to the direction of extrusion. Since the processing temperature is rather low compared with hot pressing, a thermal damage of the fibres can nearly be avoided. The manufacture of the glass composites is shown exemplarily for the embedding of continuous and discontinuous SiC fibres. The desizing, the impregnation of the long fibres and the homogeneous mixing of the short fibres with the glass powder are introduced and explained. This is followed by a schematic description of the extrusion method for both kinds of reinforcement. By means of some composite rods produced in this way the principal suitability of this processing for the unidirectional aligning of the reinforcing component is shown. The improvement of properties achieved by embedding the fibres into the samples is demonstrated by measured impact strength values.