Biomedical subjects

M J Cox

Publications and source records attributed to M J Cox.

At least 37 records · Page 2Linked to original sources

PubMed1998

Venomous snakebite in Thailand. II: Clinical experience.

We reviewed a total of 2,525 snakebite patients in Bangkok. Of these, 1,415 were bitten by venomous snakes, 91 by neurotoxic snakes of genus Naja or Bungarus and 1,324 by snakes of family Viperidae or Crotalidae. Seventy-one percent of bites were on the lower extremity. There were two fatal cobra bites; both patients were dead on arrival at the hospital. Bites from vipers caused morbidity but no deaths. Species-specific antivenins are effective in reversing respiratory failure from cobra bites and coagulopathies from bites by Viperidae and Crotalidae snakes. However, early respiratory and wound care will save lives even in the absence of specific cobra and krait antivenin. Care of a snakebite victim should consist of immobilization and bandaging of the bitten limb with elastic bandages during transport to the hospital, early surgical debridement of necrotic tissue, appropriate infusion of antivenin, aggressive respiratory support, management of shock and infection, and peritoneal dialysis or hemodialysis. Incision of bite wounds, suctioning, application of ice, and tourniquets are of no proven value and may be dangerous. All snakebite victims in southeast Asia should survive if they receive early competent care.

Adult↗

PubMed1998

Cross immunity and vaccination against multiple microparasite strains.

We explore the equilibrium properties of a series of compartmental, ODE models describing the interaction between different strains of pathogen. The interaction is conceptualized as acting through shared antigens: infection and recovery from one strain leaves the host with a primed immune response against subsequent strains. The models consider the effect of this priming on susceptibility (the ability to be infected) and transmission (the ability to infect) in an SIR model. In these models, the specific past history of infection is encapsulated in different susceptible compartments within the model. In a third, SIS, model, specific past history is not included, but strains have differential abilities to infect previously infected hosts. Equilibrium results include criteria for the coexistence of strains. For the SIR models, the region of coexistence defined by parameters shrinks as the effect of strains on each other (increased antigenic similarity) increases. For the SIS model, coexistence depends critically on the rate at which complete susceptibility is recovered following infection, and coexisting strains must have differential abilities to infect completely and partially susceptible hosts. Interestingly, this model provides analogies to commensalism (the first species gains from the presence of the second; the second neither gains nor loses from the interaction) and symbiosis (the presence of both species benefits the other). Additionally, we show that the maximum number of coexisting strains is two in this model. The effect of vaccination depends on the initial strain structure, the ability of vaccination to mount protection to both strains and the coverage. Vaccination may allow a previously excluded strain to coexist or exist alone, and may allow a previously rarer strain to become more common with the possibility of increasing incidence of disease. We discuss the dynamics of these models, compare model results to observed patterns and consider additional model structures. The importance of these results to specific multi-strain pathogens, in particular rotavirus, is considered.

Animals↗

PubMed1997

Grating detection and orientation discrimination in amblyopia.

PURPOSE: We examined whether the misperceptions associated with amblyopic visual perception can be revealed under natural viewing conditions by comparing the ability to detect the presence of a grating with the ability to identify the grating orientation. METHODS: Grating detection and orientation discrimination performance (horizontal versus vertical) were determined, using stimuli that consisted of sinusoidal gratings of fixed contrast (75%) but with variable spatial frequency. A total of four amblyopic subjects (two strabismic and two non-strabismic) and four age-matched normals participated in the experiment. RESULTS: Psychometric functions for grating detection and orientation identification were found to be closely matched in the normal subjects and in all four amblyopic subjects, indicating that orientation could be correctly identified at detection threshold. CONCLUSIONS: The absence of orientation uncertainty in the psychophysical data for the amblyopic observers is not consistent with the several previous reports of spatial aliasing in the central field of amblyopes. Our results suggest that non veridical visual perception in central amblyopic vision can not be revealed under natural viewing conditions by comparing the ability to detect the presence of a grating with the ability to identify its orientation. Possible reasons for the failure of this technique to reveal spatial aliasing in amblyopes are discussed.

Adult↗

PubMed1997

Reliability and validity studies of a new computer-assisted crossed-cylinder aberroscope.

PURPOSE: We assessed the reliability and validity of a new computer-assisted crossed-cylinder aberroscope technique which measures the monochromatic optical aberrations of the human eye. METHODS: Intra-image variability, the variability occurring when the same image is repeatedly measured, and inter-image variability, the variability occurring when different images collected from the same eye are measured, were assessed using 10 repeated measures on each of 10 different subjects. We compared the measurements made using the computer-assisted technique with manual measurements made when a human operator performed all the aberroscope grid intersection location tasks. RESULTS: One-way repeated measures analyses of variance (ANOVA) on the inter-image and intra-image variability showed that the mean of the measurements made was statistically independent of the occasion on which a group of subjects was measured, and inter-image variability was larger than intra-image variability. A two-way repeated measures ANOVA comparing computer-assisted results with manual results showed that the means of the measurements made with the two methods are not statistically different from one another. The manual results showed greater variability than computer-assisted measurements. CONCLUSIONS: The technique is reliable and valid compared to earlier objective crossed-cylinder aberroscopic techniques.

Humans↗

PubMed1997

Families as systems.

In this chapter, we discuss theoretical and conceptual models that use an organismic or systems metaphor for understanding families. We suggest that such theories are important for stimulating new research and organizing existing data, and that advances in these theories over the past few decades have expanded the potential for understanding child development, as well as adult adaptation and the development of close relationships. These paradigms follow from models that view development as resulting from the transactional regulatory processes of dynamic systems. Such models are helpful for considering multiple influences on development and adaptation and have implications for the design of effective interventions. We focus on the specifics of systems theories as applied to families, and the research generated by or consistent with these views. Our review is not exhaustive; rather, we intend to give a sense of the direction of this work and its importance for the understanding of development and adaptation.

Adult↗

PubMed1997

Making things move--the options for computer-based displays.

Two methods for producing moving stimuli on computer-controlled displays are discussed. The first method, memory manipulation, can take several forms: moving a memory window over a fixed memory image (memory windowing); moving the memory associated with objects and background for such objects (memory movement); and changing all the memory within the image on every frame of the display (memory animation). Memory windowing and movement are suitable for low memory or low processing-capacity computer systems, but are limited in their range of temporal stimulus properties. Memory animation is the most flexible of all display techniques available but requires higher memory or processing capacity or both. The second method, palette-manipulation, is akin to being able to change the contents of a book simply by changing the page numbers in its index. Look-up-table splitting, look-up-table bit-splitting and look-up-table rotation are all suitable for low memory or low processing-capacity computing systems. Look-up-table splitting allows independent control of the motion of one or several objects but severely limits the spatio-temporal properties of those objects. Look-up-table bit-splitting gives much more flexible control of the spatio-temporal properties of the stimulus but is useful only for very brief stimulus presentations. Look-up-table rotation provides good control of stimulus temporal properties but limits the spatial properties of the stimuli. Look-up-table animation provides excellent spatial and temporal control of periodic stimuli but, unless stimuli are presented in spatio-temporal quadrature, requires high memory or processing capacity or both.

Computer Graphics↗

PubMed1997

Peritoneal healing with adhesion formation: current comment.

Intra-abdominal adhesions are fibrotic structures, which lie in the form of a string or attachment between the abdominal organs and connect these together. They are responsible for serious clinical complications that include intestinal obstruction, infertility, and pelvic pain. During the last century, surgeons' comprehensive understanding of the biology of peritoneal healing and wound repair has allowed them to identify a variety of new therapeutic techniques that limit the development of adhesion formation. New drugs, dextran 70 and poloxamer 407, have been developed to prevent adhesion formation. In addition, three new biomaterials (oxidized regenerated cellulose, hyaluronate membrane, and polytetrafluoroethylene) are synthetic barriers being used to prevent adhesions.

Biocompatible Materials↗

PubMed1997

Archaic African and Asian lineages in the genetic ancestry of modern humans.

A 3-kb region encompassing the beta-globin gene has been analyzed for allelic sequence polymorphism in nine populations from Africa, Asia, and Europe. A unique gene tree was constructed from 326 sequences of 349 in the total sample. New maximum-likelihood methods for analyzing gene trees on the basis of coalescence theory have been used. The most recent common ancestor of the beta-globin gene tree is a sequence found only in Africa and estimated to have arisen approximately 800,000 years ago. There is no evidence for an exponential expansion out of a bottlenecked founding population, and an effective population size of approximately 10,000 has been maintained. Modest differences in levels of beta-globin diversity between Africa and Asia are better explained by greater African effective population size than by greater time depth. There may have been a reduction of Asian effective population size in recent evolutionary history. Characteristically Asian ancestry is estimated to be older than 200,000 years, suggesting that the ancestral hominid population at this time was widely dispersed across Africa and Asia. Patterns of beta-globin diversity suggest extensive worldwide late Pleistocene gene flow and are not easily reconciled with a unidirectional migration out of Africa 100,000 years ago and total replacement of archaic populations in Asia.

Africa↗

PubMed1997

Factor V Leiden and thermolabile methylenetetrahydrofolate reductase in extreme old age.

Both factor V Leiden and the C677T methylenetetrahydrofolate reductase (MTHFR) gene mutation are associated with premature vascular disease, and yet are found at surprisingly high allele frequencies in European populations, 2.7% and 35% respectively. We have investigated the prevalence of these mutations in 87 UK residents over the age of ninety, to look for any evidence of their association with premature death. Five factor V Leiden heterozygotes were found, giving an allele frequency of 2.9%, similar to that in the general UK population. The frequency of the thermolabile C677T MTHFR mutation was 36% with 11% homozygotes, again similar to that in the UK population; these genotypes are in Hardy-Weinberg equilibrium, suggesting that there is not strong selection against the homozygous state. One person was both heterozygous for factor V Leiden and homozygous for the C677T mutation. This study suggests that neither factor V Leiden nor thermolabile MTHFR are risk factors for premature death.

Aged↗

PubMed1997

A new computerized control unit for small bone surgical instruments.

The SmartDrive console represents an important advance in small bone surgery because it monitors and coordinates the operation of its handpieces. The SmartDrive console has the following unique features: 1) a handpiece recognition system; 2) an instrument speed display; 3) a handpiece display and monitoring system; 4) a torque instrument control system; 5) a temperature monitoring system; 6) and an irrigation system. Mechanical performance studies have been undertaken that have validated the accuracy of the monitoring systems of the consoles. The consoles provided reliable recordings of the rotational speeds of their hi-speed drills. The MicroAire console automatically shuts off its power as the temperature increased to 110 degrees F (43 degrees C). In contrast, the Stryker Command 2 console has a limited monitoring system that can not alter the operation of the handpieces.

Bone and Bones↗

PubMed1996

Severe burn injury from recreational gasoline use.

This report describes the case of a 13-year-old boy who suffered severe burns with inhalation injury during the recreational use of gasoline. Gasoline sniffing is a popular form of solvent abuse for young children and adolescents in isolated, rural communities. In addition to the neurological and physiological complications of gasoline inhalation, gasoline sniffers face the significant threat of severe burn injury or death resulting from ignition of the gasoline vapor as well as from extensive physical contact with the constituents of liquid gasoline.

Adolescent↗

PubMed1996

Evidence for a single origin of factor V Leiden.

Factor V Leiden is the most common hereditary blood clotting disorder so far identified, with an allele frequency of 4%. The low prevalence of the mutation outside of Europe suggests it occurred as a single event in the European founding population. In this study four polymorphisms have been identified defining different haplotypes in the exon 13 region of the factor V gene. One of these polymorphisms predicts a novel amino acid change, threonine to serine, in the B-domain of factor V. Statistical evidence for a single origin of factor V Leiden is provided through the association of the mutation with a single exon 13 haplotype.

Base Sequence↗

PubMed1996

Evolution of hydrogel polymers as contact lenses, surface coatings, dressings, and drug delivery systems.

Hydrogel polymers are hydrophilic resins that display excellent biocompatibility, which has allowed their application in diverse fields of surgery and medicine. The original hydrogel polymer, a copolymer of 2-hydroxyethyl methacrylate and ethylene dimethacrylate, was developed by Wichterle and Lim in 1954. The development of the first soft hydrogel contact lenses by Wichterle in 1961 represented the first successful clinical application of hydrogel polymers and remains one of the most important uses of hydrogels today. The biocompatibility of hydrogel polymers may be adapted to diverse tissue types by small variations in the makeup of the polymer, including varying the type and amount of monomers and differing the amounts and characteristics of the cross-linking agents used to create the polymer chains. Hydrogels have been successfully developed for use as coatings, soft contact lenses, wound dressings, and drug delivery systems.

Bandages↗

PubMed1996

Toxic effects of surgical glove powders on the eye.

Surgical gloves are commonly coated with dusting powders that have severe toxic effects on the eye. Talcum powder causes a chronic granulomatous reaction with fibrosis and adhesion formation. Cornstarch has also been shown to cause a granulomatous reaction as well as sterile endophthalmitis. These complications are preventable by the use of powder-free gloves.

Animals↗

PubMed1995

A new computerised video-aberroscope for the determination of the aberration of the human eye.

We have developed a video-based system for the acquisition and analysis of images produced by an aberroscope. The aberroscope uses a helium-neon laser to project a shadow image of a grid onto the retina. The retinal image is, in its turn, imaged onto a CCD video camera. As the grid forms a shadow image, the position of each grid intersection at the retina is affected by the aberrations of the eye. The emergent beam is imaged by the whole pupil, hence the grid shape is little affected by the eye's optics. We compute the aberrations of the eye by measuring the distortions of the grid. A video-digitiser converts the video camera image into data that can be processed by an Apple Power Macintosh computer using an image processing program (NIH Image V1.57). The program locates the grid intersection positions and computes the coefficients of a Taylor polynomial that describes the wavefront aberration. This technique has significant advantages over photographic methods that use manual image assessment. It gives immediate image storage and analysis, the ability to screen out poor quality images, requires significantly less or no operator interaction and is less labour intensive.

Humans↗

PubMed1994

New advances in electronic devices for hole detection.

Holes in surgical gloves are considered to be an important source of transmission of pathogens between surgeon and patient. Two new glove hole detectors have been devised to alert the surgeon to the presence of holes. These devices have been evaluated using six powder-free and seven powdered varieties of surgical gloves that were either dry or exposed to hydration. Eight of the 13 surgical gloves hydrated rapidly with water, altering their resistance to the conduction of electricity. Because the Barrier Integrity Monitor¿ only has a hydration monitor, 68 false positives occurred during the evaluation, indicating to the surgeon that he/she should change gloves unnecessarily because the glove had no hole. In contrast, the Surgic Alert Monitor¿ (SAM¿) had a hydration alarm as well as a glove hole detection alarm. During the 104 tests, the SAM¿ device showed no false positives. In the testing of five of the rapidly hydrating types of surgical gloves, the SAM¿ device could not reliably detect holes. On the basis of this study, the SAM¿ device, in conjunction with gloves that resist hydration, appeared to be a reliable hole detection monitor.

Equipment Design↗

PubMed1994

The analysis of motion of two-dimensional patterns: do Fourier components provide the first stage?

Human observers were required to report the direction of motion of simple two-dimensional (2-D) "plaid" patterns made by adding together two sinusoidal gratings of identical contrast (0.5 or 1.5 log units above threshold), spatial frequency (1 or 5 c/deg) and orthogonal orientations (horizontal and vertical, or +/- 45 deg). The patterns were made to move either by moving both gratings at the same speed (pattern motion) or by moving one component with the other stationary (component motion). In one task (direction discrimination) the observer knew the axis of motion, and was required to discriminate the direction of motion along that axis in a temporal two-alternative forced-choice paradigm; in the other task (direction identification) the observer did not know the axis of motion and was required to identify the direction of motion and the axis of motion. In both tasks the discrimination of pattern motion was consistently better than the discrimination of component motion, contrary to the predictions of the "two-stage" model of motion analysis, in which it is assumed that the motion of a 2-D pattern is calculated from the 1-D motions of its Fourier components. The variation in direction discrimination of pattern motion with speed did not have the form predicted under the assumption that the direction of motion of the pattern could be discriminated using the motion of either of its two component gratings. Finally, an elaborated version of the Adelson and Movshon [(1982) Nature, 300, 523-525] two-stage model, in which noise affects the two stages fails to predict the performance in identifying the pattern motion of the plaid pattern, except for 1 c/deg low contrast plaids. These results suggest that when 2-D patterns contain moderately high contrasts or high spatial frequencies observers may use other attributes, instead of, or in addition to Fourier components, to analyse their 2-D motion.

Discrimination, Psychological↗

PubMed1993

The age of infection with varicella-zoster virus in St Lucia, West Indies.

Sera from an age-stratified sample of 1810 people from the Caribbean island of St Lucia were tested for antibodies against varicella-zoster virus. The results indicate that very few infections occur in childhood, which agrees with clinical survey data from other tropical countries, but contrasts with the observed high case rate in children in temperate countries. The alternative hypotheses which may explain these results are discussed, and it is suggested that high ambient temperatures interfere with the transmission of the virus. Irrespective of the cause, the pattern of varicella incidence observed has important implications for any vaccination policy adopted in tropical countries.

Adolescent↗