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Biomedical subjects

M J Wright

Publications and source records attributed to M J Wright.

At least 19 recordsLinked to original sources
PubMed1999

Limitation of ankle range of motion in survivors of acute lymphoblastic leukemia: a cross-sectional study.

BACKGROUND: The purpose of this study was to evaluate and determine the factors related to active and passive dorsiflexion range of motion (DF-ROM) in survivors of acute lymphoblastic leukemia (ALL), which is the most obvious impairment of musculoskeletal function in such children. PROCEDURE: The subjects included 54 survivors of ALL treated on Dana-Farber Cancer Institute protocols and 54 comparable healthy children. Bilateral active and passive DF-ROM were measured with the knee extended. RESULTS: The survivors of ALL had significantly less active and passive DF-ROM (6.4 vs. 16.8, 10.5 vs. 18.8 degrees, respectively, P < 0.001) than the comparison children. Weight for age at the time of assessment and change in height during treatment showed significant negative correlations with DF-ROM. Length of time-off treatment was not associated with DF-ROM. CONCLUSIONS: Multiple regression analyses identified the variables of age at diagnosis and gender as significant predictors of both DF-ROM measures following treatment. Children diagnosed at a younger age and females were at greater risk for restricted DF-ROM. Close monitoring and preventative therapy programs for this complication are warranted for children, especially young girls receiving treatment for ALL.

Adolescent↗
PubMed1999

Visual discrimination of direction changes based upon two types of angular motion.

We address the question of how the visual system analyses changes in direction. Using plaid stimuli, we define type O direction changes which entail a change in the orientations of the plaid components, and type V direction changes in which the orientations of the components remain constant, relative to the observer but their relative speeds change. Lower thresholds for discriminating type O and type V direction changes were compared. Type O thresholds for clockwise/anticlockwise direction change were very low (0.2-0.5 degree), were resistant to directional noise, and showed a low-pass relationship with drift velocity. Type V thresholds on the other hand were higher (1-5 degrees), and exhibited a bandpass relationship with drift velocity. Type O direction changes gave low thresholds at short inter-stimulus intervals (ISI) (< 160 ms) and higher thresholds (successive orientation discrimination) at long ISI (240 ms-12.8 s). Type V thresholds, on the other hand, exhibited no short-range process and performance at short ISI, was no better than for successive direction discrimination at long ISI. A two-stage rotary motion model is sufficient to explain the discrimination of type O direction changes and results rule out a model based on velocity discrimination. For type V direction changes, a two-stage mechanism is insufficient and results are consistent with a minimum of three computational stages.

Humans↗
PubMed1999

Low thrombogenicity of polyethylene glycol-grafted cellulose membranes does not influence heparin requirements in hemodialysis.

Heparin is the most commonly used anticoagulant for hemodialysis despite potentially serious side effects. Polyethylene glycol-grafted cellulose (PGC) membranes produce less activation of the coagulation cascade than cuprophane membranes. Anecdotally, we found some patients required a surprisingly low level of anticoagulation using these membranes. We compared the anticoagulant requirement of the PGC membrane with that of the cuprophane membrane in this randomized, prospective, crossover study. Sixty-three patients were randomized to treatment using either membrane, and heparin administration was progressively reduced to the lowest dose that prevented visible clotting in excess of that normally encountered. Patients underwent dialysis at this dose for 1 month, after which the heparin requirement and Kt/Vurea (1.162 x ln [urea pre/urea post]) were assessed. This process was then repeated for each patient using the other membrane, and the results were compared. Heparin administration during dialysis was reduced from a mean loading dose of 29.0 +/- 9.4 to 1.5 +/- 3.2 IU/kg for both membranes and a mean maintenance infusion of 14.0 +/- 6.7 to 0.77 +/- 1.6 IU/kg/h for both membranes (both P < 0.0001 v full anticoagulation; no difference between membranes). The Kt/Vurea was not significantly altered. Forty-six patients with PGC and 45 patients with cuprophane membranes underwent dialysis successfully without heparin during dialysis, and the other patients were using considerably reduced doses. Aspirin and warfarin had no effect on the heparin requirement. These results do not support the theory that PGC membranes have a lower anticoagulant requirement than cuprophane membranes; however, they suggest that dialysis can be performed successfully with much smaller anticoagulant doses than are currently in common use.

Anticoagulants↗
PubMed1998

Long-term gross motor performance following treatment for acute lymphoblastic leukemia.

BACKGROUND: The primary purpose of this descriptive study was to determine the long-term effects of cancer treatment in childhood on musculoskeletal function and gross motor skills. PROCEDURE: Musculoskeletal and gross motor function were assessed in a cohort of 36 survivors of acute lymphoblastic leukemia (ALL) seen in a pediatric tertiary care referral centre, compared to 36 age and gender matched comparison subjects. Basic gross motor skills were assessed using dimensions D: standing, and E: walking, running, and jumping of the Gross Motor Function Measure (GMFM). Strength, balance, and running speed and agility were assessed using the Bruininks-Oseretsky Test of Motor Proficiency (BOTMP). Hand grip strength and ankle dorsiflexion range of motion were also measured. Findings in the children with ALL were compared by dependent (paired) t-tests to those in age and gender matched children. RESULTS: The GMFM scores for standing were 98.7% and for walking, running, and jumping were 99% of normal. The mean standard scores for the BOTMP were significantly lower than those of the comparison group: strength 11.5 vs. 19.4, balance 9.4 vs. 15.5, and running speed and agility 9.9 vs. 16.6. The ALL subjects had less hand grip strength 156.3 vs. 190.2, and less ankle dorsiflexion 7.5 vs. 16.1 degrees than the comparison group. The survivors of childhood leukemia were able to perform most basic gross motor functions. However, musculoskeletal impairment was evident and levels of motor proficiency were significantly poorer than those of age and gender matched children. CONCLUSIONS: Programs to promote physical activity and limit disability may improve gross motor function and increase overall quality-of-life in survivors of leukemia in childhood.

Adolescent↗
PubMed1998

beta-Galactosidase staining following intracoronary infusion of cationic liposomes in the in vivo rabbit heart is produced by microinfarction rather than effective gene transfer: a cautionary tale.

The myocardium is a potential target for the expression of exogenous genes to treat inherited and acquired diseases. Although adenovirus-mediated gene transfer has resulted in high-level gene transfer in vivo via direct intramyocardial injection and via a percutaneous intra-arterial route, the time-course of gene expression is limited by host immune responses. It was the aim of this study to test whether cationic liposome-mediated gene transfer, which does not suffer from the aforementioned problems, was feasible in the adult rabbit myocardium via a percutaneous transluminal approach. Doses of plasmid DNA encoding lacZ from 200-800 micrograms complexed to cationic liposomes resulted in X-gal conversion at day 3 with associated myocardial damage. We hypothesised that the damage was associated with macro-aggregates of cationic liposomes-DNA occluding the microcirculation. When such aggregates were excluded no X-gal conversion was seen in vivo. In order to show that X-gal conversion occurs in areas of infarction in the myocardium we caused closed chest infarction by deploying a platinum micro-embolisation coil in the circumflex coronary artery. At day 3 X-gal conversion was observed in the territory supplied by the occluded artery. Thus, microinfarction causes the false positive appearance of gene transfer when using a lacZ reporter gene.

Animals↗
PubMed1997

Coherence and motion transparency in rigid and nonrigid plaids.

Under a wide range of conditions, stimuli composed of two superimposed grating components with unequal rotation velocities (differing in sign and/or magnitude) gave a striking percept of a single, coherent, nonrigidly deforming plaid surface. Conversely, component angular velocities of the same sign and magnitude yielded rigidly rotating plaids. Rigidity and motion coherence were shown to be independent percepts, and coherent plaids were categorised unambiguously as rigid or nonrigid. Coherence and motion transparency were found to depend upon the relative orientation of components, and polar plots showed two lobes of high coherence for narrow intercomponent angles. There was a slight tendency for plaids with unequal component rotations to appear less coherent, but this was nonsignificant, once the effect of intercomponent angle was taken into account. Changes in the relative spatial frequency of components, relative contrast of components, and repeated presentation produced equivalent effects on coherence for rigid and nonrigid types of plaid motion. Manipulation of the terminators in the display by making the aperture diameters for the two component gratings unequal reduced coherence and increased transparency. The effect was the same for rigid and nonrigid plaids. Coherence in rigid and nonrigid plaids thus depends primarily on local processes and there is no strong interaction between rigidity and coherence.

Humans↗
PubMed1997

Firearm injury in Orleans parish: a 24-month perspective.

This study is a retrospective review of all gunshot wounds treated at Charity Hospital, the Orleans Parish designated trauma center, for the 24-month period from November 1993 to November 1995. Its purpose was to define the magnitude of firearm injury in the parish and the impact on the health care system. One-thousand-six-hundred-sixty-nine gunshot wounds were analyzed. Most involved African-American males. Twenty percent were fatal. Two-thousand-forty-three emergent operations were performed. Ten percent of surviving patients had some permanent disability, 6% required institutional care. In 760 patients, initial hospital charges totaled $5,153,516. Extrapolation of these figures to the entire group yields an initial hospital cost of $11,317,392. Transport by the "911" system and in-house trauma team activation were required in most patients. In summary, firearm injury poses a serious economic problem and is a substantial drain on health care providers and their resources.

Adolescent↗
PubMed1996

A biologically plausible model of early visual motion processing. I: theory and implementation.

A model of local image encoding is described which explicitly incorporates quantitative data about the number density, bandwidth and receptive field organisation of neurons involved in motion detection. The model solves the problem of extracting local velocity on the basis of inputs tuned to spatiotemporal frequency and sensitive to contrast. The spatiotemporally tuned, opponent motion filters are followed by a compressive non-linearity and comprise a first stage. The inter-stage signals are interpreted as those from single neurons and the second stage is modelled as a neural-network layer. The second stage uses semilinear units and models the effect of lateral, on-centre off-surround, intra-layer connections. Characterisation of the first stage leads to a clarification of the concept of the psychophysical 'channel' and its relation to physiological data. The quantitative parametrisation of the model allows the simulation of several psychophysical phenomena which are reported in a companion paper.

Fourier Analysis↗