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Biomedical subjects

P J McCullagh

Publications and source records attributed to P J McCullagh.

At least 19 recordsLinked to original sources
PubMed2003

Structure data entry using graphical input: recording symptoms for multiple sclerosis.

Structured Data Entry provides flexible and efficient input to the computer-based patient record. We have utilized the SDE approach to build a prototype interface for recording common symptoms associated with Multiple Sclerosis (MS). The software provides both graphical input and output, to facilitate efficient data entry and monitoring of data. Graphical input is transformed to textual information, which is stored in a database in a hierarchical tree structure. Pain management in MS may be achieved by careful monitoring of the symptom in response to treatment. Pain location is selected on a body image and severity and other attributes represented using a graphical visual analog scale, leading to more convenient input and a less ambiguous coding than is achievable with narrative text alone. This approach could provide an objective means of monitoring the progress of the disease and management of the symptoms. The intuitive interface may also facilitate self-monitoring.

Computer Graphics↗
PubMed2001

Paradigms for recording cognitive brain electrical activity.

Human event-related potentials reflect cognitive processing, and are normally elicited by external events, such as acoustic sounds or visual stimuli. As such they provide an opportunity to study normal and abnormal brain function noninvasively, at sub-second resolution. Advances in multimedia technology permit specialists in informatics and neuropsychology to co-operate in the design and implementation of paradigms, which influence ERP components. The paper illustrates the progression from standard paradigms such as the auditory oddball, which can be used to study memory update through to contingent negative variation and three condition, visual paradigms which can be used to study cognitive and emotional responses. Data from a study investigating the comparative processing of target pictures and words illustrate how external stimuli influence the later cognitive potentials.

Brain Mapping↗
PubMed1999

WWW as a teaching resource for introductory medical informatics in primary care.

This pro and contra report assesses the current state of the WWW as a teaching aid for Medical Informatics, using the experience gained from the delivery of a module to a heterogeneous group of health workers enrolled in an MSc/PgDip in Primary Care. The students were expected to act as both information consumers in a directed bibliographic retrieval task and information providers for Primary Care. The students' perceptions as to the usefulness and local relevance of current resources on the world wide web (WWW) are discussed.

Curriculum↗
PubMed1999

Multimedia stimulation for psychophysiological investigation.

This paper describes a multimedia approach to sensory stimulation in psychophysiological studies. High resolution colour images are presented to a subject by a Delphi stimulus program, controlled by a data acquisition system which concurrently records cognitive Event Related Potentials from the subject. The acquisition PC is linked to the stimulus PC using serial communications and requests slide material using a character based protocol. The sound card in the data acquisition system can present concurrent complex auditory stimuli for multimedia experiments.

Acoustic Stimulation↗
PubMed1997

Influence of gamma-irradiation sterilization and temperature on the fracture toughness of ultra-high-molecular-weight polyethylene.

Surface damage of the tibial plateau components of knee prostheses made from medical grade ultra-high-molecular-weight polyethylene (UHMW-PE) has been attributed to delamination wear caused by a fatigue fracture mechanism. It has been proposed that factors such as component design and method of sterilization contribute to such failure mechanisms. Understanding the fracture behaviour of UHMW-PE is therefore critical in optimizing the in vivo life-span of total joint components. The elastic-plastic fracture toughness parameter J was consequently determined for a commercial UHMW-PE at ambient and body temperatures, before and after gamma-irradiation sterilization in air at a minimum dose of 29 kGy. Both ductile stability theory and experimental data suggest that cracks propagate in a stable manner, although stability is affected by the sterilization process. Sterilization with gamma-irradiation results in a loss in fracture toughness JIc of 50% and a decrease in tearing modulus (Tm) of 30%. This dramatic reduction could result in a 50% decrease in the residual strength of the components, maximum permissible crack size under service loading and service life (assuming flaws such as fusion defects exist). The time required for a crack to grow from its original size to the maximum permissible size could be decreased by 30%, resulting in earlier failure. In terms of the design of joint replacement components the critical factor to envisage is the design stress level, which should be halved to account for the irradiation process. A scanning electron microscope study reveals that the material fails in layers parallel to the fracture surface.

Biocompatible Materials↗
PubMed1996

Effects of batch to batch variations and test methodology on degree of crystallinity and melting temperature of UHMW-PE as measured by differential scanning calorimetry.

The thermal and structural analysis of a total 22 batches from three medical grade ultrahigh molecular weight polyethylene (UHMW-PE) resins was determined using the DSC method. Batch to batch variations of approximately 5% were obtained for the melting temperature and the degree of crystallinity. The variations correlated both to the changes caused by gamma-irradiation sterilization and subsequent aging, and to the differences in DSC results obtained from various laboratories on materials believed to exhibit essentially similar clinical performances. Varying the sample weight from 4.4 to 27.1 mg resulted in a significant relative increase of 5% in the degree of crystallinity. The study shows that the standard double melting/recrystallisation procedure for DSC evaluation produces variations in the melting behaviors of approximately the same magnitude as those indicated by batch lot or sterilization/aging.

Calorimetry, Differential Scanning↗
PubMed1996

Effect of counterface material on the characteristics of retrieved uncemented cobalt-chromium and titanium alloy total hip replacements.

A number of total hip components explanted at revision with bearing surfaces in either cobalt-chromium-molybdenum alloy or titanium-6% aluminium-4% vanadium alloy were examined and compared to contemporaneously manufactured but unused items; particular attention was paid to the bearing surfaces which were examined visually, by low-power microscopy, scanning electron microscopy (SEM), confocal microscopy, white light interferometry, laser profilometry and conventional stylus profilometry. The cobalt alloy heads maintained their surface finish well over periods up to 12 years. The titanium implants became badly damaged over much shorter periods although even badly scratched heads continued to meet the current standards for titanium alloy heads. Analysis showed that the damage to the titanium alloy heads was not a random but a well-defined process of scarring of a consistent size created by abrasion with small particles of bone. These damaged heads had the potential to wear the matching UHMWPE components rapidly creating large amounts of polymer debris. The finding that measurement of these damaged heads is within current standards raises concerns as to whether current standards incorporate fully the requirements for clinical performance.

Alloys↗
PubMed1995

Biomechanics and design of shoulder arthroplasty.

Since the introduction by Neer in 1973 of the metal-on-plastic unconstrained total shoulder replacement, unfortunately there have been no long-term clinical follow-up reports. Short- to mid-term information (less than ten years) indicates good to excellent clinical results in approximately 90 per cent of cases. While this early experience is encouraging, much attention has been focused on lucencies of the glenoid component, which although they may not predispose to failure, have led to considerable design activity. The humeral component has also advanced in design, with modularity of the head in particular providing greater intra-operative flexibility. State-of-the-art instrumentation, borrowing key features found beneficial to hip and knee joint replacement, is an important advancement in contemporary systems. The aim of this paper is to position shoulder arthroplasty in relation to biomechanical considerations and recommendations from clinical experience.

Activities of Daily Living↗
PubMed1994

PC software library for the production of auditory stimuli in cognitive event-related potential experiments.

Software which provides an interface to the features of the Sound Blaster Pro card for the IBM PC using MS-DOS is described. The library may be called from a Turbo Pascal version 6 program. It permits tones of specified frequency (500 Hz-8 kHz in increments of 500Hz) and aversive noise to be turned on and off by a controlling program, during cognitive event-related potential paradigms. Tones are synthesized by hardware and noise is replayed from memory using the digital sound processor. The library provides the appropriate level of abstraction for the programmer designing such paradigms, by hiding the detail of the register level. It provides a model for programming the card in other high level languages and may be augmented to provide more complex stimuli, such as short segments of speech or music. The card when controlled by the library provides a versatile and cost effective alternative to an audiometer in the electrophysiological laboratory.

Cognition↗
PubMed1992

Quality of the surface finish of the head of the femoral component and the wear rate of the socket in long-term results of the Charnley low-friction arthroplasty.

Four Charnley femoral stems, removed on average 20 years after implantation, were examined for the quality of surface finish of the head. The average roughness was 0.031 microns (range 0.008-0.102 microns) as compared with 0.019 microns (range 0.008-0.031 microns) for the current production models and 0.05 microns as recommended by the British Standard and the International Standards Organization. The average socket penetration rate was 0.022 mm/year and there was no radiological or operative evidence of socket loosening. The findings emphasize the importance of achieving and maintaining good surface finish of the head of the femoral component. A suggestion is also made that the orientation of the asperities may be important.

Bone Cements↗
PubMed1991

Variation in power spectral analysis of the EEG with gestational age.

Power spectral analysis (PSA) of the EEG was studied in healthy term and preterm neonates to establish the normal range with gestational age. Sixty healthy newborn infants from 26 to 41 weeks' gestation had PSA performed at 3 days of age. Five main frequency bands were studied: delta 1 (1 Hz or less), delta 2 (2-3 Hz), theta, alpha, and beta. A significant correlation was shown between absolute power in delta 1 and delta 2 with gestational age. Relative power of each frequency band, calculated as a percentage of the total power in each channel, also correlated with gestational age. A significant quadratic relationship between absolute power in the beta range and gestational age is described for the first time.

Electroencephalography↗
PubMed1991

Spectral edge frequency of the EEG in healthy neonates and variation with behavioural state.

Spectral edge frequency (SEF) of the EEG was studied in 51 healthy neonates to assess its value as a measure of cerebral maturation. SEF was calculated as the frequency below which 95% of the power in the power spectrum resides. Summated SEF (sSEF) of 4 EEG channels correlated significantly with gestational age (r = 0.83). sSEF varied with behavioural state and with EEG derivation. Intra- and interindividual variability were both greater in preterm compared to term babies. We conclude that SEF is a useful measure of cerebral maturation in the newborn and may have a role in studying stressed newborns.

Behavior↗
PubMed1990

Microcomputer based analysis of nystagmus eye movement.

An algorithm to assist in the computation of routine peripheral nystagmus slow phase velocity (SPV) has been implemented on an Apple based data acquisition system. Waveforms stored by the computer may be output to a dot matrix printer to complement conventional strip-chart recorder output. An estimate of SPV is available after each caloric session. Analysis modes range from a summarized output for inclusion in the clinical report to a detailed beat by beat report comprising waveforms, markers and tabulated results. Problematic signals, beyond the scope of the automatic analysis, may be inspected interactively using a software controlled cursor.

Algorithms↗
PubMed1989

Topographical brain electrical activity mapping on an IBM-compatible personal computer.

A new system for computing brain electrical activity maps on a standard IBM-compatible computer has been developed. The EEG is recorded using a CED1401 intelligent laboratory interface and stored in the computer; colour coded maps are generated using software developed in Turbo PASCAL and displayed on the EGA graphics screen. An acceptable computation time of 1.2 s for a 64 x 64 map displayed as a 128 x 128 pixel image has been achieved by incorporating assembly language routines and a maths coprocessor. The system may be readily upgraded as improved hardware becomes available and further software can be added. In addition to triggering auditory, visual and somatosensory stimulators, it provides the potential for the generation of complex stimuli for cognitive experiments by means of mass RAM and digital-to-analogue converters.

Brain Mapping↗
PubMed1986

A bioengineering analysis of human muscle and joint forces in the lower limbs during running.

A two-dimensional, dynamic bioengineering model of the lower limbs was developed in order to estimate muscle and joint forces present during running at 4.5 m s-1. Data were collected from four subjects using a force platform and cine film. Individual X-rays and anthropometric data from the lower limbs were utilized to produce accurate bone models of the subjects' legs. Electromyographic verification of the model was undertaken while a runner was undergoing treadmill running at 4.5 m s-1. Results indicate that peak muscle forces of 22 times subject body weight (22 BW) could be present in the quadriceps muscle group and 7 BW in the gastrocnemius. The anterior shin muscles were found to be active for the first 9% of stance phase only, and compressive loads of 33 BW were found in the knee joint. The relationship between these high forces in the lower limbs and running related injuries is discussed.

Adult↗