Analysis of heart rate variability (HRV) is used to assess autonomic control of the heart. Many technical aspects may influence the outcome of the HRV analysis. One of these aspects is the accuracy of onset QRS detection. Inconsistent determination of QRS onset may result in artificial variations, especially in patients with wide QRS complexes. The purpose of the present study was to investigate the effect of QRS width on the outcome of HRV analysis. After manual correction of the onset of QRS: HRV variables averaged over 24 hours showed changes up to 10% in patients with wide QRS complexes. However, comparing single 5 minute segments before and after manual correction of onset QRS, much larger differences were observed. Especially variables reflecting beat to beat changes (time as well as frequency domain) showed substantial differences. The average effect of manual QRS onset correction in single 5 minute segments proved to be 5.3% for rMSSD, 5.2% for high frequency power (0.15-0.40 Hz) and 1.3% for low frequency power (0.04-0.15 Hz). We conclude that accurate detection of QRS onset plays an important role in the outcome of HRV analysis, especially in the analysis of short segments and patients with wide QRS complexes.
Cerebral aneurysms are localised pathological dilatations of cerebral arteries, most commonly found in the circle of Willis. Although not all aneurysms are unstable, the major clinical concern involved is the risk of rupture. High morbidity and mortality rates are associated with the haemorrhage resulting from rupture. New indicators of aneurysm stability are sought, since current indicators based on morphological factors have been shown to be unreliable. Haemodynamical factors are known to be relevant in vascular wall remodelling, and therefore believed to play an important role in aneurysmdevelopment and stability. Studies suggest that intra-aneurysmal wall shear stress and flow patterns, for example, are candidate parameters in aneurysm stability assessment. These factors can be estimated if the 3D patient-specific intra-aneurysmal velocity is known, which can be obtained via a combination of in vivo measurements and computational fluid dynamics models. The main determinants of the velocity field are the vascular geometry and flow through this geometry. Over the last decade the extraction of the vascular geometry has become well established. More recently, there has been a shift of attention towards extracting boundary conditions for the 3D vascular segment of interest. The aim of this research is to improve the reliability of the model-based representation of the velocity field in the aneurysmal sac. To this end, a protocol is proposed such that patient-specific boundary conditions for the 3D segment of interest can be estimated without the need for added invasive procedures. This is facilitated by a 1D wave propagation model based on patient-specific geometry and boundary conditions measured non-invasively in more accessible regions. Such a protocol offers improved statistical reliability owing to the increased number of patients that can participate in studies aiming to identify parameters of interest in aneurysm stability assessment. In chapter 2 the intra-aneurysmal velocity field in an idealised aneurysm model is validated with particle image velocimetry experiments, after which the flow patterns are evaluated using a vortex identification method. Chapter 3 describes a 1D model wave propagation model of the cerebral circulation with a patient-specific vascular geometry. The resulting flow pulses at the boundaries of the 3D segment of interest are compared to those obtained with a patient-generic geometry. The influence of these different boundary conditions on the 3D intra-aneurysmal velocity field is evaluated in chapter 4 by prescribing the end-diastolic flows extracted from the 1D models. In order to measure blood flow with videodensitometric methods, an injection of contrast agent is required. The effect of this injection on the flow of interest is assessed in chapter 5. In chapter 6, pressure measurements in the internal carotid are used to evaluate the variability of pressure waveform and its effect on the boundary conditions for the 1D model. Finally, a protocol for full patient-specific modelling is discussed in chapter 7.
DOI: 10.1049/cp.2009.0719 ISBN: 978 1 84919 126 5 Location: Prague, Czech Republic Conference date: 8-11 June 2009 Format: PDF Based on the focus of Smart Grid, we directed our electrical energy storage towards distributed energy sources such as solar panels, micro-cogeneration and hybrid vehicles. The research has two coupled branches: development of storage packages and hardware for improving lifetime and efficiency of battery packages. The aim of this paper is storage development for solar panels used in households. (3 pages) Inspec keywords: solar absorber-convertors; domestic appliances; thermal energy storage Subjects: Storage in thermal energy; Photothermal conversion
