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Biomedical subjects

J J Dowling

Publications and source records attributed to J J Dowling.

At least 19 recordsLinked to original sources
PubMed2006

An investigation into the deformable characteristics of the human foot using fluoroscopic imaging.

BACKGROUND: To determine the behaviour of the human foot during in vivo loading and unloading. METHODS: Fluoroscopic imaging was used to investigate the movement of the bones and 13 skin markers during loading and unloading for the medial aspect of the left foot. A foot-pressure measuring system was compared with a force plate used to gather kinetic information, simultaneously. Four male and two female subjects performed three tasks that mimicked jumping, walking, and sprinting. Two-dimensional vector displacements were calculated between bone landmarks over time. Foot rigidity was assessed by a 5 mm length variability threshold determined as the difference between the third and first quartiles of the data set. FINDINGS: The displacement between the first metatarso-phalangeal joint and distal aspect of the calcaneous varied more than the 5 mm threshold. A new foot model was developed which included three rigid segments joined together by hinge joints located at the first metatarso-phalangeal joint and between the anterior talus and navicular. The comparison between skin mounted markers and bone landmarks yielded a range of correlation slopes close to 1.00 for both the x- and y-directions. Foot pressure and force plate comparisons were promising (%RMS(error) approximately 10%) for the vertical ground reaction forces but not so for the centres of pressure (%RMS(error) up to 50%). INTERPRETATION: A multi-segment foot model is required to better represent the behaviour of a human foot. No consistent skin marker movement was determined. Better pressure distribution devices need to be developed to determine more accurate foot kinetics. Precise foot kinematics are required in order that accurate ankle moments and reaction forces be determined for the purpose of assessing foot and ankle function.

Biomechanical Phenomena↗
PubMed2005

In vivo assessment of elbow flexor work and activation during stretch-shortening cycle tasks.

The purpose of this study was to use an electromyography (EMG) based muscle model to investigate the performance enhancement of stretch-shortening cycle (SSC) tasks at different elbow flexion-extension velocities. A torque motor was used to oscillate the forearms of seven healthy male subjects (23-40 years) during SSC and non-SSC contractions at four frequencies of movement (.58, 1.5, 2.4 and 3.3Hz) over a range of 105 degrees -162 degrees of elbow extension. The torque was integrated as a function of joint angle to yield the work produced by the elbow flexors. The elbow flexors were transcutaneously stimulated with a voltage equivalent to 60% maximum voluntary isometric contraction torque for 4s at 50Hz. EMG of the elbow flexors and extensors was recorded from the biceps and triceps respectively. The processed EMG was used to drive a Hill based model to predict the torque of the elbow flexors. Results indicate that muscle work increases from non-SSC to SSC trials. Work decreases for SSC and non-SSC trials with increasing velocity. The simulated constant activation muscle model predicted work well for all trials and conditions, indicating muscle model accuracy. The EMG driven model predicted well for all non-SSC trials, but significantly underestimated the work for SSC tasks, suggesting that the contractile component is directly involved in optimising muscle work during SSC tasks.

Adult↗
PubMed2005

Ballistic muscle mechanisms determined using an EMG-driven model.

The purpose of this study was to determine the mechanisms responsible for improving ballistic elbow extension. In doing so, an electromyography (EMG)-driven model was developed to predict the actual triceps torque so that the model parameters between subjects could be compared. Thirty-two subjects performed maximum isometric trials at 60 degrees , 90 degrees and 120 degrees of elbow extension to determine torque-angle relations. Dynamic elbow extension trials were then performed against relative loads of 0%, 20%, 40%, 60% and 80% and absolute loads of 1.1 and 2.2 kg. These trials were used to determine the torque-angular velocity relation for each subject. The model predicted the triceps torque during the unloaded, 1.1 and 2.2 kg trials with an average r = 0.964 and an average root mean square error of 4.34 Nm. As a result of the good predictions, a forward dynamics approach was used to substitute different neuro-muscular mechanisms of a poor performance with those from an individual that displayed a superior performance. Performance was shown to improve when these modifications were made. Therefore, the EMG-driven model was capable of modeling the actual muscle torque which allowed for the identification of areas of weakness of a poor performance. A prescription for improvement was identified, albeit artificially, on an individual basis. The next stage is to determine which specific interventions can accomplish those theoretically proposed.

Elbow Joint↗
PubMed2002

Are intestinal helminths a risk factor for non-typhoidal Salmonella bacteraemia in adults in Africa who are seropositive for HIV? A case-control study.

In Africa, invasive, non-typhoidal Salmonella (NTS) infections are a common but life-threatening complication in adults who are seropositive for HIV. The high prevalence of human infection with intestinal helminths which penetrate the gut could explain the greater importance of NTS bacteraemia in Africa compared with that in industrialized countries. If helminth infection is a major risk factor for NTS it would provide a locally relevant, public-health target. Intestinal helminth carriage in 57 HIV-positive patients with NTS bacteraemia (the cases) was compared with that in 162 HIV-positive controls who were similar to the cases in terms of age, sex, urban dwelling and socio-economic factors. The prevalence of helminth infection, 29% overall, was lower among the cases (18%) than among the controls (33%), giving a crude odds ratio of 0.40 [with a 95% confidence interval (CI) of 0.21-0.9] and an adjusted odds ratio (aOR) of 0.79 (CI = 0.4-1.8). Five (9%) of the cases and 12 (7%) of the controls were infected with nematodes which penetrate the gut (Ascaris lumbricoides and/or Strongyloides stercoralis). The aOR for infection with these penetrating worms, corrected for age, sex, urban dwelling and phase of study, was 1.40 (CI = 0.4-4.5). The present results do not exclude the possibility that helminths play a role in invasive NTS infections, but are not consistent with helminths being a sufficient risk factor in this population to be a public-health target. Anthelmintics are unlikely to have a major impact on preventing NTS bacteraemia in patients diagnosed HIV-positive in Africa.

AIDS-Related Opportunistic Infections↗
PubMed2001

Subcellular localisation of the X protein in HBV infected hepatocytes.

Hepatitis B virus X protein (HBx) is a multifunctional protein that exerts its effects primarily by acting as a transcriptional transactivator of viral and multiple host cell genes. HBx is thought to be essential for maintaining viral replication and has been implicated in the development of hepatocellular carcinoma in patients chronically infected with hepatitis B virus. Very little is known about its functional mechanisms and although interactions with several nuclear and cytoplasmic proteins have been demonstrated in vitro, there is no clear consensus as to where HBx localises in infected hepatocytes. In this study, the expression and intracellular distribution of HBx were examined in human liver biopsies using an anti-HBx rabbit polyclonal antiserum. HBx was detected in a high proportion (69%) of samples from patients with chronic HBV infection. Detection of HBx correlated with the absence of cirrhosis and the presence of serum e-antigen. HBx was detected predominantly in the cytoplasm; however, it was also found in the nuclei of up to 20% of positively stained hepatocytes, either exclusively nuclear or localised both in the nucleus and cytoplasm within the same cell. Furthermore, the intracellular distribution of HBx was analysed in transfected Huh-7 cells by confocal microscopy, using the monoclonal antibody 16F1. In these experiments, a substantial nuclear detection was confirmed in a significant proportion of HBx expressing cells. The data indicate a high functional significance of nuclear HBx, consistent with the concept that transactivation may involve interactions with nuclear proteins.

Adult↗
PubMed1999

Role of mechanical power estimates in the O2 cost of walking in children with cerebral palsy.

UNLABELLED: It has been established in able-bodied children that traditional biomechanical descriptors of gait such as stride length or stride frequency do not fully account for the differences seen in the energy cost of locomotion noted with age. Hence, measures of total body mechanical power output have been adopted to explain these differences. PURPOSE: The aim of this study was to estimate the ability of this mechanical power calculation to explain the variability in the metabolic energy cost of treadmill walking in children with spastic cerebral palsy (CP). METHODS: Thirteen subjects volunteered for the study. One group consisted of eight (6 male, 2 female) children with CP (age 12.2 +/- 2.7 yr). The second group consisted of five (4 male, 1 female) able-bodied controls (age 13.4 +/- 2.8 yr). The treadmill walking protocol consisted of one 4-min stage at 0% grade, 3 km x h(-1). Infrared markers were placed on 12 anatomical landmarks and data were collected using the OPTOTRAK motion analysis system over a 5-s time period during the last 30 s of the 4-min stage. On-line oxygen consumption VO2 measurements were obtained throughout using the Beckman Horizon Metabolic Cart. RESULTS: Relative VO2 (mL x kg(-1) x min(-1)) was significantly (P < 0.05) different between the two groups (CP: 16.6 +/- 6.5 vs control: 10.2 +/- 1.2). Simple linear regression analysis demonstrated that mechanical power measurements, incorporating transfers of energy between and within adjacent body segments, accounted for 87.2% of the total variability noted in VO2 for the children with CP, compared with only 2.4% in the able-bodied subjects. CONCLUSIONS: The results indicate that mechanical power differences explain the majority of the variability noted in VO2 in children with CP at a submaximal walking speed.

Adolescent↗
PubMed1997

Ballistic movement performance in karate athletes.

Nine male karate athletes and 13 untrained men did maximal voluntary isometric (MVC) and ballistic elbow extension actions, the latter unloaded (L0) and against a load equal to 10% MVC (L10). The karate group achieved greater (P < 0.05) isometric (32%) and ballistic action peak torque with L0 (30%) and L10 (40%). With L10 the ratio of ballistic action to isometric action, peak torque was 13% greater in the karate group, indicating a load specific training adaptation. With L0 the corresponding ratio did not differ significantly between groups. Ballistic action peak rate of torque development (51%, 51%) and peak acceleration (15%, 9%) with L0 and L10, respectively, were greater in the karate group. In contrast, peak velocity and movement time did not differ significantly between groups. Electromyographic recordings of agonist triceps and antagonist biceps were made during the isometric and ballistic actions. Since ballistic actions (L10) were initiated from a preloaded condition, the occurrence and duration of premovement agonist depression were monitored. In ballistic actions there were no group differences in agonist activation, the ratio of ballistic to isometric action agonist activation, or antagonist coactivation. Premovement agonist depression occurred infrequently in both groups, with no group differences. It is concluded that karate athletes have enhanced elbow extension ballistic performance, but it could not be related to amplified agonist activation, altered antagonist activation, or more frequent occurrence of agonist premovement depression.

Acceleration↗
PubMed1997

The use of electromyography for the noninvasive prediction of muscle forces. Current issues.

Suitably processed electromyographic (EMG) signals can be combined with Hill-type musculoskeletal models to noninvasively achieve estimations of individual muscle forces. This method has particular advantages over other methods for the assessment of a given performance. The purpose of this review is to report on the current issues facing the human movement scientist who wishes to extend the kinetic information yielded by linked segment models to the kinetics of individual muscles. Such an extension is necessary when considering co-contraction of antagonistic muscles, the role of bi-articular muscles, co-ordination, movement efficiency or bone-on-bone forces. Currently, linked segment models have not been successfully extended to individual muscle forces for diagnostic purposes by using the EMG approach or any other approach. Most models have been designed for a specific purpose and have only been evaluated over a narrow range of movement conditions. More generalised models will require greater complexity and possibly more extensive calibration or an increased number of specific inputs or greater computational effort. This review shows the promise of the EMG approach and presents the challenges, as well as the strategies, that should enable more general, accurate and precise estimates of individual muscle forces.

Animals↗
PubMed1996

Role of cocontraction in the O2 cost of walking in children with cerebral palsy.

UNLABELLED: A major movement related limitation for children with spastic cerebral palsy (CP) is the compromised gait pattern, which may explain their excessive energy cost of locomotion. The aims of this study were to determine differences in the O2 cost of locomotion between children with CP (7 males, 2 females; 12.7 +/- 2.8 yr) and able-bodied controls (7 male, 1 female; 13.6 +/- 2.1 yr) and to assess the contribution that cocontraction of agonist and antagonist muscles had upon the elevated O2 cost seen in children with CP versus able-bodied controls. The treadmill submaximal walking protocol consisted of 2 x 4 min intermittent stages at 3 km.h-1 and 90% of the predetermined fastest walking speed (FWS) at 0% grade. Electromyographic data were collected during the final minute of each bout from vastus lateralis and hamstrings (thigh) and tibialis anterior and soleus (lower leg). Significant (P < 0.05) differences were noted at 3 km.h-1 for mass-relative VO2. (CP: 16.6 +/- 6.5 vs control: 10.2 +/- 1.2 ml.kg-1.min-1), % VO2max (CP: 53.5 +/- 26.0 vs CONTROL: 22.5 +/- 4.93) and heart rate (CP: 143 +/- 41 vs CONTROL: 91 +/- 14 beats.min-1). Thigh and lower leg muscle cocontraction accounted for 51.4% and 42.8%, respectively, of the variability in VO2 for the subjects with CP at 3 km.h-1. These results suggest that cocontraction is a major factor responsible for the higher energy cost of walking seen in children with CP.

Adolescent↗
PubMed1996

Cocontraction and phasic activity during GAIT in children with cerebral palsy.

Simultaneous activity of agonist and antagonistic muscles during a task is known as cocontraction. The primary aim of the present study was to use a cocontraction index (CI) to quantify differences in EMG activity between a group of CP and control children at two different walking speeds. The secondary aim was to compare the amount of time the muscles were activated ("on" thresholds) between the groups. Seventeen subjects volunteered for the study. One group consisted of 9 (7M, 2F) children with CP (age 12.7 +/- 2.8 years, mean +/- SD). The second group consisted of 8 able-bodied controls (7M, 1F). The discontinuous submaximal treadmill walking protocol had two 4min stages at 0% gradient. Speeds selected were 3 km.h-1 and 90% of the pre-determined fastest walking speed (FWS). Two sites of CI were measured from the EMGs of tibialis anterior and soleus (leg) and vastus lateralis and hamstrings (thigh). Significantly (p < 0.05) higher CI values were noted for the CP subjects compared to the controls, irrespective of speed or cocontraction site and there was a significant (p < 0.05) increase in CI values with increased walking speed for both CP and control subjects. Phasic analyses for 5% max EMG and 10% max EMG "on" thresholds demonstrated significant (p < 0.05) main effects for group (CP subjects had a longer time period of muscle activation than controls) and speed (muscles were active longer at 90% FWS than 3 km.h-1). The precise mechanisms by which cocontraction contributes toward abnormal gait and wasted mechanical energy require further research incorporating both electromyographic and kinematic analysis.

Adolescent↗
PubMed1995

Seven protein tyrosine phosphatases are differentially expressed in the developing rat brain.

Regulation of protein function through tyrosine phosphorylation is critical in the control of many developmental processes, such as cellular proliferation and differentiation. Growing evidence suggests that tyrosine phosphorylation also regulates key events in neural development. Although a large body of data has demonstrated that protein tyrosine kinases play an important role in neural development, much less is known about their counterparts, protein tyrosine phosphatases (PTPases). Using polymerase chain reaction (PCR) with degenerate primers and a neonatal rat cortex cDNA library, we have identified seven PTPases expressed in the developing rat brain. Four of these are transmembrane PTPases: LAR, LRP, RPTP gamma, and CPTP1. Three are nonreceptor PTPases: PTP-1, P19-PTP, and SHP. Northern hybridization analysis demonstrates that only CPTP1 is preferentially expressed in neural tissues, whereas the others are found abundantly in nonneural tissues as well as in the brain. Within the embryonic and early postnatal brain, the seven PTPases have overlapping, yet unique, distributions. For example, LAR mRNA is highly expressed by both proliferating and postmitotic cells in the cerebral cortex at embryonic day 17 and in all layers of the cortex at postnatal day 4. In contrast, RPTP gamma mRNA is expressed by postmitotic neurons in the embryo and predominantly by neurons in the superficial layers of the postnatal cortex. Several of the PTPases examined here are expressed at very high levels in the embryonic cortical plate and postnatal neocortex, including the subplate and subventricular zone. The spatial and temporal regulation of PTPase gene expression suggests that these PTPases have important roles in signal transduction during early neuronal differentiation and neural development.

Animals↗
PubMed1995

Force-length, torque-angle and EMG-joint angle relationships of the human in vivo biceps brachii.

The relationships of EMG and muscle force with elbow joint angle were investigated for muscle modelling purposes. Eight subjects had their arms fixed in an isometric elbow jig where the biceps brachii was electrically stimulated (30 Hz) and also in maximum voluntary contraction (MVC). Biceps EMG and elbow torque transduced at the wrist were recorded at 0.175 rad intervals through 1.75 rad of elbow extension. The results revealed that while the torque-length relationship displayed the classic inverted "U" pattern in both evoked and MVC conditions, the force-length relationship displayed a monotonically increasing pattern. Analyses of variance of the EMG data showed that there were no significant changes in the EMG amplitudes for the different joint angles during evoked or voluntary contractions. The result also showed that electrical stimulation can effectively isolated the torque-angle and force-length relationships of the biceps brachii and that the myoelectric signal during isometric contraction is uniform regardless of the length of the muscle or the joint angle.

Adult↗
PubMed1994

Are humans able to voluntarily elicit maximum muscle force?

Previous investigators have used electrical stimulation superimposed on voluntary efforts to show that humans are capable of maximum muscle activation. In the present study this notion was tested using the interpolated twitch technique enhanced by triggered averaging and doublet stimulation of the human biceps brachii. It was found that the decline in extra torque evoked by percutaneous stimulation with increasing levels of voluntary effort was nonlinear and that none of the twelve subjects was able to elicit a voluntary effort large enough to prevent extra torque of elbow flexion. The exponential nature of the declining extra torque indicated that an extrapolated maximum muscle force could be considerably larger than that to which subjects were able to elicit voluntarily.

Adult↗
PubMed1994

Pattern of expression of highly polysialylated neural cell adhesion molecule in the developing and adult rat striatum.

In rats, morphological and synaptic maturation of the striatum, a brain area involved in the control of movement and in cognitive behaviour, proceeds for several weeks postnatally. Little is known, however, about the molecular events associated with the final maturation of the striatum. In particular, there is little information on molecules playing a role in cell adhesion, a phenomenon of particular importance for neuronal development. We have examined the time course and topography of expression of the highly polysialylated form of the neural cell adhesion molecule in the rat striatum during postnatal development and in the adult, and compared it to growth-associated protein-43, a marker of axonal growth. As earlier during development [Aaron L. I. and Chesselet M.-F. (1989) Neuroscience 28, 701-710], immunolabelling for polysialylated neural cell adhesion molecule was very intense in the entire striatum at postnatal days 17-19. At postnatal days 21 and 22, loss of polysialylated neural cell adhesion molecule immunoreactivity in the caudal part of the striatum contrasted with the persistence of immunoreactivity at more rostral levels. Most of the striatum was devoid of polysialylated neural cell adhesion molecule immunoreactivity by postnatal day 25. At this age, as well as in the striatum of adult rats, immunolabelling was only observed along the ventricular edge of the striatum. In contrast to polysialylated neural cell adhesion molecule immunoreactivity, immunolabelling for growth-associated protein-43 had reached its adult pattern by postnatal day 17, indicating that polysialylated neural cell adhesion molecule persists beyond the period of major axonal growth. In the adult, an area of stronger growth associated protein-43 immunoreactivity overlapped with the region which retained immunoreactivity to polysialylated neural cell adhesion molecule. The results indicate that, in the developing rat striatum, the neural cell adhesion molecule remains highly sialylated not only during the ingrowth of cortical and nigral inputs but also during the formation of dendritic spine and synaptogenesis. Loss of polysialyated neural cell adhesion molecule occurs at the time of emerging spontaneous activity in cerebral cortex, and precedes the development of mature responses to cortical stimulation and adult membrane properties in a majority of striatal neurons.

Animals↗
PubMed1994

Relative cross-sectional areas of upper and lower extremity muscles and implications for force prediction.

The purposes of this investigation were to examine the reduction in variability when muscle size is expressed relative to a functional group and its effect on improving muscle force prediction. Fourteen subjects performed maximum voluntary contractions (MVC) of elbow flexion and knee extension and had CT scans taken of the thigh and upper arm. The variation of relative cross-sectional area (RCSA) was significantly lower than CSA (p < 0.01). No significant differences were found between male and female RCSAs. A method of predicting individual muscle forces based on an MVC and RCSA is presented that reduced prediction errors to a third of those predicted on the basis of CSA and a specific tension or stress value of muscle.

Adult↗
PubMed1991

Psychiatry and molecular genetics: a paradigm shift.

The late 20th century is witnessing an explosion of biomedical knowledge in the discipline of molecular genetics. In this regard many medical specialties will be transformed in terms of diagnosis and treatment. The technology and the recent clinical research in psychiatry is one of these.

Genetic Linkage↗
PubMed1984

Granulomatous hepatitis in Yersinia enterocolitica bacteraemia.

Bacteraemia caused by Yersinia enterocolitica was associated in a 60-year-old diabetic man with right upper-quadrant abdominal tenderness and abnormal liver function tests. Biopsy of the liver demonstrated granulomas with acute necrosis. To the authors' knowledge, this is the first report of granuloma formation in the human liver associated with this infection. Yersinia enterocolitica should therefore be added to the list of organisms associated with granulomatous hepatitis in human beings.

Biopsy↗