Medical & biological engineering & computing
-
Med Biol Eng Comput · Sep 2004
Reduction of false arterial blood pressure alarms using signal quality assessment and relationships between the electrocardiogram and arterial blood pressure.
The paper presents an algorithm for reducing false alarms related to changes in arterial blood pressure (ABP) in intensive care unit (ICU) monitoring. The algorithm assesses the ABP signal quality, analyses the relationship between the electrocardiogram and ABP using a fuzzy logic approach and post-processes (accepts or rejects) ABP alarms produced by a commercial monitor. ⋯ By rejecting 98.2% (159 of 162) of the false ABP alarms produced by the monitor using the test set of data, the algorithm was able to reduce the false ABP alarm rate from 26.8% to 0.5% of ABP alarms, while accepting 99.8% (441 of 442) of true ABP alarms. The results show that the algorithm is effective and practical, and its use in future patient monitoring systems is feasible.
-
Med Biol Eng Comput · Jul 2004
Advances in surface electromyographic signal simulation with analytical and numerical descriptions of the volume conductor.
Surface electromyographic (EMG) signal modelling is important for signal interpretation, testing of processing algorithms, detection system design and didactic purposes. Various surface EMG signal models have been proposed in the literature. This study focuses on the proposal of a method for modelling surface EMG signals, using either analytical or numerical descriptions of the volume conductor for space-invariant systems, and on the development of advanced models of the volume conductor by numerical approaches, accurately describing the volume conductor geometry and the conductivity, as mainly done in the past, but also the conductivity tensor of the muscle tissue. ⋯ In some cases (e.g. multi-pinnate muscles), accurate description of the conductivity tensor can be very complex. A method for relating the conductivity tensor of the muscle tissue, to be used in a numerical approach, to the curve describing the muscle fibres is presented and applied to investigate representatively a bi-pinnate muscle with rectilinear and curvilinear fibres. The study thus proposes an approach for surface EMG signal simulation in space invariant systems, as well as new models of the volume conductor using numerical methods.
-
Med Biol Eng Comput · Jul 2004
Influence of electrode impedance on threshold voltage for transcranial electrical stimulation in motor evoked potential monitoring.
Motor potentials evoked by transcranial electrical stimulation (TES) are used for monitoring the motor pathways, with emphasis on the spinal cord and brainstem. The stimulus voltage threshold is the voltage below which no motor response can be elicited. It has frequently been used as a monitoring parameter. ⋯ Below 460 omega, which included 91% of the category with the largest electrode surfaces, 25% of the multiple EEG electrodes and 75% of type II corkscrew electrodes, no significant correlation (R2=0.0064; p=0.15) was found. It was concluded that the correlation between the TES voltage threshold and electrode impedance can be markedly reduced by using TES electrodes with large contact surfaces, resulting in limit values for these parameters. This also may improve the reliability of TES motor evoked potential monitoring.
-
A new bellows-less lung simulator utilising a fixed-volume pressure controller to simulate spontaneous breathing is presented as an alternative to the traditional bellows-driven mechanical lung system in the human patient simulator (HPS). The HPS is a fully interactive, life-like simulator used to train medical students and anaesthesia residents. The lung simulator simulates carinal pressure, which allows for simulation of actively breathing or ventilated patients. ⋯ A bellows-less lung simulator has been designed and built which successfully simulates airflow in and out of the mouth by controlling the carina pressure. The new system is able to simulate tidal volumes between 400 and 500 ml, with flow rates of 4.3-5.71 min(-1) at a respiratory rate of 12 breaths per minute. The new design not only matches the ventilation performance of the HPS, but also simulates at 60 breaths per minute, which the HPS cannot maintain.
-
Med Biol Eng Comput · Jan 2004
Improved neuromonitoring during spinal surgery using double-train transcranial electrical stimulation.
Motor evoked potentials (MEPs) evoked by transcranial electrical stimulation (TES) have become an important technique for monitoring spinal cord function intra-operatively, but can fail in some patients. A new technique of double-train stimulation is described. A multipulse transcranial electrical stimulus is preceded by a preconditioning pulse train that leads to larger MEP responses. ⋯ It was concluded that double-train TES stimulation can markedly facilitate responses to a single stimulus train (STS). The facilitation appears to be most effective when the responses to STS would otherwise be small or absent. This preconditioning stimulation technique is therefore useful when an STS leads to responses that are too small for effective monitoring.