In order to facilitate equivalent circuit modelling, the ideal capacitance is often substituted by an empirical constant phase element (CPE). The CPE is not physically realisable with ordinary lumped electric components but it is usually described as a capacitance that is frequency dependent. The use of a CPE reflects the nonhomogeneity of the system under investigation.
Published in Chapter:
Electrical Impedance Spectroscopy as a Powerful Analytical Tool for Monitoring Microbiological Growth on Medical Implants
Louise M. Oliver (University of Ulster, UK), E. T. McAdams (University of Ulster, UK), P. S.M. Dunlop (University of Ulster, UK), J. A. Byrne (University of Ulster, UK), I. S. Blair (University of Ulster, UK), M. Boyle (Royal College of Surgeons, Ireland), and K. G. McGuigan (Royal College of Surgeons, Ireland)
Copyright: © 2008
|Pages: 10
DOI: 10.4018/978-1-59904-889-5.ch062
Abstract
Hospital-acquired infections (HAI) are defined as infections that are neither present nor incubating when a patient enters the hospital (Bourn, 2000). Their effects vary from discomfort to prolonged or permanent disability and they may contribute directly or substantially to a patient’s death. HAI’s are estimated to cost the National Health Service (NHS) in England £1 billion annually (Bourn, 2000) with as many as 5,000 patients dying as a result of acquiring such an infection (Anon, 2001). Not all hospital-acquired infections are preventable but Infection Control Teams believe that they could be reduced by at least 15%, with yearly savings of £150 million (Anon, 2001). Central intravascular catheters have been found to be a common source of infection. Catheters can become infected via a number of different routes with the infection proliferating in multiple areas along the catheter surface. It has been reported that over 40% of the identified micro-organisms causing hospital-acquired infection were Staphylococci, an organism that is typically found on the natural skin flora (Bourn, 2000).