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Biomedical subjects

C W Thomas

Publications and source records attributed to C W Thomas.

18 recordsLinked to original sources
PubMed1992

Eye movements during motion after-effect.

Using the magnetic search coil technique, we measured torsional eye movements in four male subjects during and after rotation of a visual display around the line of sight. During rotation of the display, subjects developed a torsional nystagmus with slow-phases in the direction of target rotation that had a typical gain of less than 0.01. Upon cessation of display motion, subjects experienced a motion after-effect (MAE) in the direction opposite prior target rotation, which persisted for greater than 15 sec. During this MAE, slow-phase eye movements of low velocity were in the same direction as the MAE, but did not persist as long as perceptual effects. In separate experiments, horizontal eye movements were recorded during horizontal stimulus motion; during MAE, no eye movements occurred due to stronger fixation mechanisms. We conclude that MAE is not caused by retinal slip of images, but MAE and the accompanying eye movements might be produced by shared or similar mechanisms.

Adult↗
PubMed1992

Experimental tests of a superposition hypothesis to explain the relationship between the vestibuloocular reflex and smooth pursuit during horizontal combined eye-head tracking in humans.

1. We used a modeling approach to test the hypothesis that, in humans, the smooth pursuit (SP) system provides the primary signal for cancelling the vestibuloocular reflex (VOR) during combined eye-head tracking (CEHT) of a target moving smoothly in the horizontal plane. Separate models for SP and the VOR were developed. The optimal values of parameters of the two models were calculated using measured responses of four subjects to trials of SP and the visually enhanced VOR. After optimal parameter values were specified, each model generated waveforms that accurately reflected the subjects' responses to SP and vestibular stimuli. The models were then combined into a CEHT model wherein the final eye movement command signal was generated as the linear summation of the signals from the SP and VOR pathways. 2. The SP-VOR superposition hypothesis was tested using two types of CEHT stimuli, both of which involved passive rotation of subjects in a vestibular chair. The first stimulus consisted of a "chair brake" or sudden stop of the subject's head during CEHT; the visual target continued to move. The second stimulus consisted of a sudden change from the visually enhanced VOR to CEHT ("delayed target onset" paradigm); as the vestibular chair rotated past the angular position of the stationary visual stimulus, the latter started to move in synchrony with the chair. Data collected during experiments that employed these stimuli were compared quantitatively with predictions made by the CEHT model. 3. During CEHT, when the chair was suddenly and unexpectedly stopped, the eye promptly began to move in the orbit to track the moving target. Initially, gaze velocity did not completely match target velocity, however; this finally occurred approximately 100 ms after the brake onset. The model did predict the prompt onset of eye-in-orbit motion after the brake, but it did not predict that gaze velocity would initially be only approximately 70% of target velocity. One possible explanation for this discrepancy is that VOR gain can be dynamically modulated and, during sustained CEHT, it may assume a lower value. Consequently, during CEHT, a smaller-amplitude SP signal would be needed to cancel the lower-gain VOR. This reduction of the SP signal could account for the attenuated tracking response observed immediately after the brake. We found evidence for the dynamic modulation of VOR gain by noting differences in responses to the onset and offset of head rotation in trials of the visually enhanced VOR.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

An adjustment to eye movement measurements that compensates for the eccentric position of the eye relative to the center of the head.

We describe a procedure for modifying horizontal eye movement measurements in a way that effectively removes signal contributions due to the eccentric location of the eyes relative to the center of rotation of the head. This procedure helps standardize measured signals so that data collected under different experimental conditions and from different subjects may be compared directly. We also present techniques for accurately determining specific parameters of head geometry that are required by the procedure. This method may be used for modifying eye movement responses to visual target motion, head motion, or both, and does not assume continual fixation of the visual target. Also, this method may be employed when either curved (iso-distance) or flat display screens are used for presenting the visual stimuli.

Eye↗
PubMed1992

The value of dental radiographic equipment in a Navy field hospital.

The portable dental X-ray machine has been used to augment standard field x-ray equipment. This allows for more rapid assessment of combat casualties. The data presented describe the use of the portable dental X-ray machine during the 100-hour ground war against Iraq.

Dental Service, Hospital↗
PubMed1991

Electrocardiographic body surface potential mapping in the Wolff-Parkinson-White syndrome. Noninvasive determination of the ventricular insertion sites of accessory atrioventricular connections.

BACKGROUND: A reliable, noninvasive procedure to determine the location of accessory atrioventricular connections in patients with Wolff-Parkinson-White syndrome would add an important diagnostic tool to the clinical armamentarium. METHODS AND RESULTS: Body surface potential mapping (BSPM) using 180 electrodes in various-sized vests and displayed as a calibrated color map was used to determine the ventricular insertion site of the accessory atrioventricular (AV) connections in 34 patients with Wolff-Parkinson-White syndrome. Attempts were made to determine the 17 ventricular insertion sites described by Guiraudon et al. All 34 patients had an electrophysiologic study (EPS) at cardiac catheterization, and 18 had surgery so the ventricular insertion sites could be accurately located using EPS at surgery. A number of physiologic observations were also made with BSPM. CONCLUSIONS: The following conclusions were drawn: 1) BSPM using QRS analysis accurately predicts the ventricular insertion site of accessory AV connections in the presence of a delta wave in the electrocardiogram; 2) the ventricular insertion sites of accessory AV connections determined by BSPM and by EPS at surgery were identical or within one mapping site (1.5 cm or less) in all but four of 18 cases; three of the four exceptions had more than one accessory AV connection, and the other had a very broad ventricular insertion; 3) BSPM and EPS locations of the accessory AV connections correlated very well in the 34 cases despite the fact that BSPM determines the ventricular insertion site and EPS determines the atrial insertion site of the accessory AV connection; 4) as suggested by the three cases of multiple accessory AV connections, EPS and BSPM may be complementary since BSPM identified one pathway and EPS identified the other (in the case with a broad ventricular insertion, BSPM and EPS demonstrated different proportions of that insertion); 5) BSPM using ST-T analysis is very much less accurate in predicting the ventricular insertion site of accessory AV connections unless there is marked preexcitation; 6) standard electrocardiography using the Gallagher grid methodology (but with no attempt at stimulating maximal preexcitation) was not as accurate as QRS analysis of BSPM in predicting the ventricular insertion site of the accessory AV connection; however, exact comparison is hampered by the different number and size of the Gallagher and Guiraudon insertion sites; 7) BSPM using QRS analysis appears to be very accurate in predicting right ventricular versus left ventricular posteroseptal accessory AV connections; 8) typical epicardial right ventricular breakthrough, indicative of conduction via the specialized AV conduction system, occurs in all patients with left ventricular free wall accessory AV connections; 9) epicardial right ventricular breakthrough was not observed in cases with right ventricular free wall or anteroseptal accessory AV connections; 10) epicardial right ventricular breakthrough can occur in the presence of posteroseptal accessory AV connections, whether right or left ventricular; and 11) the delay in epicardial right ventricular breakthrough in cases with left ventricular insertion may provide a marker to estimate the degree of ventricular preexcitation.

Adult↗
PubMed1990

Stylized chromosome images.

Stylized chromosome images 1) serve as a format to test effects of preprocessing algorithms used in automated karyotyping; 2) enhance the ability of humans to perform quantitative analysis of chromosomal aberrations; 3) provide an alternative format for karyotype hard copies produced by automated systems. Stylized chromosomes are two-dimensional computer-generated images based on information extracted from one-dimensional width and density profiles. These profiles correspond to what cytogeneticists observe through the microscope as the shape and banding patterns of stained chromosomes. Stylized presentation sharpens chromosome band boundaries and perimeters, reduces "noise," and enhances gray level variations, which are difficult to distinguish by humans on photographic or computer generated karyotypes. Karyotyping accuracy using stylized images was used to detect difficult areas for automated chromosome identification. Landmark bands sufficient to classify chromosomes were identified; shapes of chromosomes reflected in width profiles were said to aid classification. A two-step automated karyotyping strategy proposed is: 1) classify chromosomes by landmarks, minimum information needed for identification; 2) subsequently employ the full banding pattern with maximum resolution to detect aberrations. Stylized images of abnormal chromosomes have potential for testing hypothesis regarding breakpoints and quantitative analysis, but improvements are needed in homologue normalization and definition of termini of chromosomes.

Algorithms↗
PubMed1990

QRS onset and offset detection accuracy improvement by additional spatial information in body surface potential maps.

A new automatic spatiotemporal algorithm has been developed for detecting QRS onset and offset in body surface potential mapping. The new algorithm, based on a spatial and temporal approach, along with three other algorithms (total energy, 3-lead, and median), was tested in 73 normal and abnormal patients. The reference or gold standard onset and offset times were determined visually by two experienced investigators. The results demonstrate that the new method is less sensitive to noise, to the temporal overlap of the QRS and other components, and to the spatial location changes of QRS initial and final activation. The spatiotemporal method resulted in very consistent findings, with a standard deviation of less than one third of the standard deviation in the next best method.

Algorithms↗
PubMed1990

Multicategory classification of body surface potential maps.

A statistical classification method is suggested for body surface potential maps (BSPM). The initial data reduction utilizes the Fourier expansion and time integration, resulting in physiological-oriented features. Based on Fischer's criterion, optimal discriminant vectors are used to map the features to an optimal subdomain. Experimental criteria determine the dimensionality of the subdomain and the number of features to be mapped into it. Classification is performed in two steps. In the first, a k-nearest neighbor (k-NN) rule is used for every two-category problem, the results of which are fed into a voting rule for final classification. The method is tested with 123 patients divided into four categories: normal (NR), ischemia (IS), myocardial infarction (MI), and left bundle branch block (LB) patients. The success is between 88% (for IS) and 100% (for LB) for QRS segment integration. Departure maps were used to explain the misclassified patterns.

Algorithms↗
PubMed1989

A cardiac potential mapping system.

The technical aspects of a multiple-purpose cardiac mapping system are presented. The authors begin with a brief history of hardware and software development and then concentrate on the major problems in acquiring high-quality recordings from the torso surface or from the epicardial surface and on the processing of the signals for display of color maps or other analysis. To achieve the desired adaptability to a variety of cardiac applications and experiments, they incorporated three parallel microprocessors that can record the signals from 240 electrodes and simultaneously provide display and analysis of the incoming cardiac data. While the parallel processors and modular software offer computational and flexibility advantages, the user interacts with an ordinary AT-compatible computer. This discussion is not a survey of the systems used in the many research laboratories or specific cardiac applications but is focused on experience in developing the specific hardware for such a multi-purpose instrument, and less specifically on the software that makes the system easy to use and adaptable to a variety of experimental and clinical situations.

Action Potentials↗
PubMed1977

Penetrating torso injuries: the role of paracentesis and lavage.

Controversy still exists regarding the proper approach to patients with penetrating torso injuries. Mandatory immediate celiotomy and selective observation both have associated risks. Paracentesis with lavage is a rapid, easily performed and readily available technique which can, with a high degree of accuracy, differentiate on initial evaluation those patients with penetrating visceral injuries from those without such injuries. Complications are minimal. The use of these two procedures in evaluating penetrating torso injuries has led to improved patient care and produced major lowering of medical and socioeconomic costs.

Abdominal Injuries↗
PubMed1976

Blood lead concentrations of children and dogs from 83 Illinois families.

In comparison of blood lead concentrations (BLC) of 119 children and 94 dogs from 83 low-income suburban Illinois families, the mean BLC in the children was 8.9 mug/100 ml greater than that in the dogs. Demonstration of a BLC of diagnostic significance in a family dog increased the probability sixfold of finding a child in the same family with a BLC similarly increased. A history of pica in a family dog also increased the likelihood of finding pica in the family's children. It was concluded that family dogs may be useful sentinels of lead poisoning in children, and that veterinarians seeing dogs in clinical situations may have public health responsibilities with regard to lead poisoning.

Animals↗
PubMed1975

Blood lead concentrations in three groups of dogs from a suburban Illinois community.

Of 89 clinically normal dogs that were regular patients of a suburban Illinois veterinary hospital, all had blood-lead concentrations (BLC) within the range cited as normal in the literature. In contrast, 22% of 50 dogs from city pound and 15.3% of 98 dogs owned by low-income families of the community had BLC in excess of the normal limits. Additionally, 8% of dogs from the city pound and 4.1% of dogs from low-income families had BLC that are reported to the reliably associated with clinical lead poisoning. Socioeconomic characcteristics of the dog-owning family were more reliably associated with abnormally high BLC than were either history or clinical signs.

Animals↗
PubMed1975

Acute drug reactions among the elderly.

Research in the field of social gerontology has not examined rug use and abuse amont the aged despite the potential significance of this issue to many students of gerontology. This report, based on an analysis of the records of patients who were treated for acute drug reactions at Jackson Memorial Hospital in Miami, Florida, during 1972, examines characteristics of acute drug reactions among a sample of 60 elderly patients and compares these characteristics with those of other age cohorts. The findings show that acute drug reactions were more likely to occur among whites and females, that a substantial number of the reactions followed the ingestion of two or more substances, that roughly one-third of the admissions were directly related to suicide attempts, and that the vast majority of acute drug reactions among the elderly admissions involved the ingestion of legally manufactured and distributed drugs.

Acute Disease↗