Interference with monitoring physiological signals

Much has been written about compatibility between pieces of electronic equipment such that one does not interfere with another. There are now regulations and recommendations seeking to limit this interference to acceptable levels. It is here that a problem lies in the medical world. Whilst these limits might well satisfy other equipment, they often do not satisfy physiological signal monitoring situations which can be many orders of magnitude more sensitive. In all modern hospitals physiological signals are recorded to help in the diagnosis of diseases or to monitor the progress of patients undergoing therapeutic procedures. If these signals are disrupted, interpretation or diagnosis becomes difficult if not impossible and could give rise to misdiagnosis or inappropriate treatment. This can be especially so in the case of interference mimicking certain pathological conditions. It could threaten the health of patients or lead to legal action for malpractice. Currently there are moves towards more computerised or automated diagnosis and in these circumstances clean signals become even more imperative. The interference signals might be generated in the measuring devices or recording equipment or be transmitted into the system from external sources. Various types of signals and how they can be recorded successfully are discussed. Sources of interfering signals and how to track them down are also considered. Examples are given which illustrate the difficulties that often arise in these cases and how these can be successfully solved