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Biomedical subjects

E Shwedyk

Publications and source records attributed to E Shwedyk.

15 recordsLinked to original sources
PubMed1992

Dielectric measurement of cerebral water content using a Network Analyzer.

At present, no practical method exists for monitoring the progression and severity of cerebral oedema in a clinical setting on a continuous basis. In search for such a method, we investigated the electrical characteristics of cerebral tissue at microwave frequencies to quantify cerebral oedema. The dielectric constants of normal and oedematous canine cerebral white matter were measured using a Network Analyzer and then compared to the tissue's water content. In addition, salt infiltration and time elapsed after excision of the tissue were examined to determine their effects on the measurements. The water content and dielectric constant of the white matter were linearly related (correlation coefficient, r = 0.903), comparable to results obtained with a Time Domain Reflectometer in previous research. The Network Analyzer, however, is a more robust measurement device and, because of this, can potentially be used for long term measurements. Further, it was found that neither an increased tissue salt content nor the amount of time after excision of the tissue significantly affected the results. This indicates that the dielectric constant of cerebral white matter is mainly a function of the tissue's water content.

Body Water↗
PubMed1991

Haemodynamic modelling for the arterial pulsatile component of the intracranial pulse wave.

Vasospasm of cerebral arteries narrows the amplitude of the intracranial pressure wave, indicating that the arterial segment of the cerebral circulation is partially responsible for its formation. We investigated the fundamental mechanism of pressure pulse transmission from an artery to the surrounding environment. A mathematical model was derived expressing the amplitude of container pulsation (delta Po) as a function of mean intraluminal pressure (MPi), mean container pressure (MPo) and arterial pulse amplitude (delta Pi): delta Po = (-2(MPi - MPo) + b) (MPo + 1) delta Pi. This mathematical model was experimentally validated using an in vivo system of a single artery sealed inside a fluid-filled elastic container.

Animals↗
PubMed1991

Measurement of canine cerebral oedema using vector impedance methods.

The introduction of distilled water in vitro into brain tissue increases the water content of the cerebral white matter. The increase in water content for canine white matter may be predicted from impedance measurements on the tissue and the empirical equations determined in this study. However, the equations may only be valid for osmotic oedema induced in vitro as the behaviour of impedance related parameters is dependent on the type of oedema induced. The tissue volume measured with this technique may be reduced by the use of a smaller diameter probe. New equations relating impedance parameters to the water content for this probe and more accurate instrumentation may be required.

Animals↗
PubMed1990

Measurement of canine cerebral oedema using time domain reflectometry.

The complex dielectric constant of canine cerebral white matter correlates with its water content. Time domain reflectometry was used to measure the real dielectric constant and loss factor of 27 oedematous brain samples at frequencies of 100, 250, 500, 750, and 1,000 MHz. The real dielectric constant increased with water content at each frequency. Correlation was least for 100 MHz (R = 0.76) and between 0.87 and 0.89 for the other frequencies. The loss factor decreased with frequency with a correlation coefficient from 0.81-0.84. The in vitro results indicate that use of time domain reflectometry can predict oedema at a sensitivity of approximately 1-2% change of tissue water content.

Animals↗
PubMed1990

Three-dimensional measurement system for functional arm motion study.

An easy-to-use and inexpensive system for studying human movement is described and applied to the study of arm movement during feeding. A typical time to produce kinematic data for an experiment is one hour, including the experiment. System error was found to be less than three per cent. Besides the kinematic data the system inherently provides for a permanent video copy of the studied movement.

Arm↗
PubMed1990

Normal functional range of motion of upper limb joints during performance of three feeding activities.

This study was designed to quantify the range of upper limb joint motion required during the performance of a specific type of functional activity. Ten able-bodied men were studied as they performed three feeding tasks--eating with a spoon, eating with a fork, and drinking from a handled cup. Three shoulder joint rotations, one elbow joint rotation, one forearm joint rotation, and three wrist joint rotations were quantified simultaneously using a three-dimensional measurement system. It was found that the required ranges of motion for the feeding tasks were 5 degrees to 45 degrees shoulder flexion, 5 degrees to 35 degrees shoulder abduction, 5 degrees to 25 degrees shoulder internal rotation, 70 degrees to 130 degrees elbow flexion, from 40 degrees forearm pronation to 60 degrees forearm supination, from 10 degrees wrist flexion to 25 degrees wrist extension, and from 20 degrees wrist ulnar deviation to 5 degrees wrist radial deviation. Wrist rotation was also measured, but it was found to be negligible.

Adult↗
PubMed1989

Dual-pathway model of the human vestibulo-ocular reflex.

The purpose of the study was to investigate, evaluate and refine an existing dual-pathway VOR model by comparing the model responses with the responses of human subjects. Based on data of subjects' VOR responses, the physiological parameters and some gain constants in a dual-pathway model were adjusted to suit the human VOR data. As a result, the improved model can produce and exhibit the fundamental nystagmus patterns of human VOR responses to the head motions around a vertical axis for a wide range of frequencies and magnitudes. It was found that there is good agreement on quantitative analysis between the outcome of human VOR responses and the model output. Also, it was found that the quantitative analysis of slow-phase eye-movement data confirmed the previously published results.

Biomedical Engineering↗
PubMed1989

Automated rule based graded analysis of ambulatory cassette EEGs.

We describe algorithms, developed on a PDP-11/73 microcomputer, which identify spikes/sharp waves (STs), spike-and-wave complexes (SSWs), artifacts and background activity in 4-channel ambulatory EEGs. The algorithms were trained using 40 database segments. Time domain/mimetic methods were used and semantic rules, based on morphology and multi-channel contextual information, were developed to mimic the principles used in visual interpretation. The likelihood of STs/SSWs being genuine was graded from 10 to 1. This approach avoids forced classification of each event as genuine ST/SSW or not. The algorithms were then evaluated using 60 independent segments. STs/SSWs graded greater than 7 had significantly higher probability (P less than 0.005) of being genuine than those graded less than or equal to 7. Less than 4% of STs/SSWs identified by both electroencephalographers were missed. None was distinct. All 113 artifacts resembling STs/WWs were graded less than or equal to 7. Classification of 969/1117 (86%) waves in the background matched that of one electroencephalographer. The algorithms can be extended to 8- or more-channel EEGs.

Algorithms↗
PubMed1988

Filtering characteristics of ambulatory EEG recording systems.

An analysis of the filtering in ambulatory EEG systems is performed. The typical ambulatory EEG system has 3 cascaded time constants each of which distorts the signal. Using a settling time criterion the analysis suggests settings or specifications for the 3 time constants in order to be equivalent to a single overall time constant. The signal distortions due to various settings are illustrated for typical EEG wave forms. It is shown that the distortion can be particularly severe when overload occurs in the ambulatory recording system, a condition that is prevalent due to high amplitude signals such as movement artifact and eyeblink.

Ambulatory Care↗
PubMed1987

Computer database of ambulatory EEG signals.

The paper describes an ambulatory EEG database. The database contains segments of AEEGs done on 45 subjects. Each epoch (1/8th second or more) of AEEG data has been annotated into 1 of 40 classes. The classes represent background activity, paroxysmal patterns and artifacts. The majority of classes have over 200 discrete epochs. The structure is flexible enough to allow additional epochs to be readily added. The database is stored on transportable media such as digital magnetic tape or hard disk and is thus available to other researchers in the field. The database can be used to design, evaluate and compare EEG signal processing algorithms and pattern recognition systems. It can also serve as an educational medium in EEG laboratories.

Adolescent↗
PubMed1985

Artifacts in ambulatory cassette electroencephalograms.

Most artifacts in ambulatory electroencephalograms (AEEGs) are similar to those seen on conventional electroencephalograms (CEEGs) and can be identified as such. Some artifacts may simulate epileptiform or slow wave EEG activity and may occur asymmetrically or focally. We have described the use of a dual write-out method for identifying and detecting the source of artifacts in AEEGs. This technique has improved the quality of AEEGs and facilitated interpretation.

Adolescent↗