Biomedical subjects

S R Jackson

Publications and source records attributed to S R Jackson.

At least 37 records · Page 2Linked to original sources

PubMed1999

Pathological perceptual completion in hemianopia extends to the control of reach-to-grasp movements.

The neuropsychological phenomenon of blindsight is observed when patients who are cortically blind exhibit residual visual processing capabilities for stimuli presented within their scotoma to which they are otherwise unaware. Cortically blind patients may also exhibit the phenomenon of pathological visual completion in which, paradoxically, they can become aware of a complete visual stimulus even when a significant portion of that stimulus falls within their blind hemifield. In this study, the ability of a blindsight patient (G.Y.) to use visual information to control reach-to-grasp movements to static objects presented within his blind hemifield was investigated. The results indicate that while G.Y. was insensitive to variations in object size when reaching for objects presented entirely within his blind hemifield, his ability to accurately grasp objects located within his blind field was vastly improved if part of the object to be grasped extended into his seeing hemifield. This finding demonstrates that visual awareness can facilitate the visuomotor processing of object form within G.Y.'s apparently blind field, and suggests that the primary deficit in blindsight may be an impairment of visual consciousness rather than an absolute loss of visual function.

Adult↗

PubMed1999

The selection and suppression of action: ERP correlates of executive control in humans.

A key aspect of higher cortical function is the ability to selectively withhold or suppress action where appropriate. To examine the time course of executive control we used dense-sensor EEG recording techniques to study event-related electrical potentials (ERPs) during a visual 'go/no-go' task. We show that during both go and no-go trials there is a positive deflection in the ERP, which develops over posterior parietal sensors approximately 350 ms (P300) after the onset of a conditional visual stimulus, but is selectively suppressed during no-go trials. We also show that this modulation of the parietal P300 is preceded by a negative deflection in the ERP recorded over frontal cortex (N2), which is apparent only for no-go trials. We suggest that this signal provides an electrophysiological marker in man for the decision to withhold the execution of a motor response.

Adult↗

PubMed1999

Adult presentation of a tracheoesophageal fistula with co-existing laryngeal cleft.

Congenital posterior laryngeal clefts are rare anomalies, being first described by Richter in 1792, and first operated upon successfully by Pettersson in 1955. Most clefts present within the first few months of life, with only a few cases being documented as presenting in adulthood. We present the case of a 50-year-old lady presenting with a previously undiagnosed posterior laryngeal cleft with an associated tracheoesophageal fistula. The defect was graded as 2 on the Benjamin and Inglis classification system of posterior laryngeal clefts. Following a literature review, we believe that our patient is the oldest to present with this congenital defect.

Female↗

PubMed1999

Attention for action: coordinating bimanual reach-to-grasp movements.

Theories of attention have frequently pointed to the finding that there is a significant performance decrement ('cost') to responding to two different objects concurrently. However, much of the research aimed at investigating how attention is 'divided' in such circumstances has adopted response time (RT) as the measure of interest. In this paper we investigate how attention is 'divided' during the execution of concurrent motor responses, by studying bimanual reach-to-grasp movements directed towards two separate target objects. Furthermore, a key aspect of our study is that each hand is required to perform either the same action (congruent reaches) or a different action (incongruent reaches). Thus in Expt 1 we manipulated the movement amplitude of each hand, while in Expt 2 we manipulated object size. The results of this study suggest that while there is an overall cost associated with carrying out two movements simultaneously, kinematic measures are unaffected by whether the actions required of each hand are the same (congruent) or different (incongruent). The problem of executing incongruent bimanual movements appears to be solved by synchronizing each limb to a common movement duration, while movement velocity and grip aperture are independently scaled. These findings are discussed in relation to theories developed to explain the coordination of the reach-and-grasp phases of unimanual prehension, and in the context of recent theories of attention for action.

Adult↗

PubMed1998

In situ calibration of miniature sensors implanted into the anterior cruciate ligament part I: strain measurements.

The goals of this study were to (a) evaluate the differential variable reluctance transducer as an instrument for measuring tissue strain in the anteromedial band of the anterior cruciate ligament, (b) develop a series of calibration curves (for simple states of knee loading) from which resultant force in the ligament could be estimated from measured strain levels in the anteromedial band of the ligament, and (c) study the effects of knee flexion angle and mode of applied loading on output from the transducer. Thirteen fresh-frozen cadaveric knee specimens underwent mechanical isolation of a bone cap containing the tibial insertion of the anterior cruciate ligament and attachment of a load cell to measure resultant force in the ligament. The transducer (with barbed prongs) was inserted into the anteromedial band of the anterior cruciate ligament to record local elongation of the instrumented fibers as resultant force was generated in the ligament. A series of calibration curves (anteromedial bundle strain versus resultant force in the anterior cruciate ligament) were determined at selected knee flexion angles as external loads were applied to the knee. During passive knee extension, strain readings did not always follow the pattern of resultant force in the ligament; erratic strain readings were often measured beyond 20 degrees of flexion, where the anteromedial band was slack. For anterior tibial loading, the anteromedial band was a more active contributor to resultant ligament force beyond 45 degrees of flexion and was less active near full extension; mean resultant forces in the range of 150-200 N produced strain levels on the order of 3-4%. The anteromedial band was also active during application of internal tibial torque; mean resultant forces on the order of 180-220 N produced strains on the order of 2%. Resultant forces generated by varus moment were relatively low, and the anteromedial band was not always strained. Mean coefficients of variation for resultant force in the ligament (five repeated measurements) ranged between 0.038 and 0.111. Mean coefficients of variation for five repeated placements of the strain transducer in the same site ranged from 0.209 to 0.342. Insertion and removal of this transducer at the anteromedial band produced observable damage to the ligament. In our study, repeatable measurements were possible only if both prongs of the transducer were sutured to the ligament fibers.

Aged↗

PubMed1998

In situ calibration of miniature sensors implanted into the anterior cruciate ligament part II: force probe measurements.

The arthroscopically implantable force probe transducer, which measures the effects of local ligament fiber tension, was inserted into the anteromedial band of the anterior cruciate ligament after measurements with the differential variable reluctance transducer were completed in Part I of this study. The overall goals in Part II remained the same, with additional experiments included to determine the sensitivity of output voltage from the transducer to medial-lateral placement of the device within the anteromedial band and to depth of placement within a given insertion hole. Calibration curves of output voltage from the arthroscopically implantable force probe transducer versus resultant force in the ligament were generated during a separate series of knee-loading experiments identical to those performed in Part I. The output voltage for a given probe placement was highly sensitive to the depth of implantation into the anteromedial band. When the probe was completely buried within the ligament, voltage outputs were often sporadic or absent even though surface fibers had clearly developed tension. When the probe was only partially inserted into the hole, such that the end of the probe was slightly proud to the surface, voltage output was significantly higher as the device measured tension in the superficial fibers. Voltage outputs for proud placement were always significantly higher than corresponding voltages for deep placements for all test conditions. With proud placements, voltage outputs were not sensitive to small deviations in medial-lateral position within the anteromedial band. Mean coefficients of variation for output voltage (four repeated placements of the probe into the same central hole) ranged from 0.156 to 0.359 (deep and proud insertions). Output voltage from the probe generally followed the pattern of resultant force in the ligament during passive knee extension. For anterior tibial loading, the contribution of deep fibers to resultant force did not depend on the knee flexion angle at which the test was conducted; the contribution of superficial fibers was greatest beyond 45 degrees of flexion and least at full extension. The contributions of the anteromedial band to resultant force in the ligament were not significantly different between the three modes of loading (anterior tibial force, internal tibia torque, and varus moment) at either 0 or 10 degrees of flexion; this was true for both superficial and deep fibers. We found it necessary to secure the probe within the insertion site using a suture (for both deep and proud placements) to obtain repeatable readings. Puncturing the anteromedial band clearly produced tissue damage; the insertion hole often produced a permanent plane of cleavage in the anteromedial band. However, this tissue damage did not alter the overall ability of the ligament to generate resultant force.

Aged↗

PubMed1998

The influence of initial hand posture on the expression of prehension parameters.

This paper describes the transport and grasp kinematic parameters associated with four initial hand postures (palm flat and thumb against the hand, palm flat and thumb extended laterally, index and thumb in opposition, and index and thumb in opposition and elbow flexed 90 degrees). A group of healthy adult subjects reached for and picked up a wooden dowel placed midsagittally, at one of three distances (20 cm, 25 cm and 30 cm). The initial posture of the hand and arm altered transport (peak velocity and peak negative acceleration) as well as grasp (peak angle and time to peak angle) parameters, particularly when the elbow was flexed 90 degrees. The pattern of results was reproduced in a pointing paradigm. The findings are discussed in the context of joint space models of reaching.

Acceleration↗

PubMed1998

Admission of bone marrow transplant recipients to the intensive care unit: outcome, survival and prognostic factors.

The role of ICU support in BMT patients is controversial. In an era of constrained resources, the use of prognostic factors predicting outcome may be helpful in identifying patients who are most likely (or unlikely) to benefit from this intervention. We attempted to define the survival of patients admitted to ICU following autologous or allogeneic BMT and to identify those factors important in determining patient outcome. A retrospective study of all adult BMT recipients admitted to intensive care over a 6 year study period was performed to determine overall and prognostic indicators of poor outcome. Pre-treatment, pre-ICU admission and ICU admission data were analyzed to identify factors predicting long-term survival. 116 patients were admitted to ICU on 135 separate occasions with the primary reasons for admission being respiratory failure (66%), sepsis associated with hypotension (10%), and cardiorespiratory failure (8%). No pre-ICU characteristics were predictive of survival. Univariate analysis identified the number of support measures required, the need for ventilation or hemodynamic support, the APACHE II score, the year of ICU admission and the serum bilirubin as significant predictors of post-discharge survival. On multivariate analysis the year of ICU admission, the need for hemodynamic support and the serum bilirubin remained significant. The APACHE II score significantly underestimated survival in the 46% of patients with scores less than 35, and could only be used to predict 100% mortality when it exceeded 45. Twenty-three percent of all BMT patients admitted to the ICU and 17% of ventilated patients survived to hospital discharge. Of the 27 patients surviving to leave hospital, 16 remain alive with a median follow-up of 4.2 years and a mean Karnofsky performance status of 90. Although mortality in BMT recipients admitted to ICU is high our results indicate that intensive care support can be lifesaving and that the outcome in patients requiring ventilation and ICU support may not be as poor as has been previously reported. No single variable was identified which could be used to predict futility but patients requiring both hemodynamic support and mechanical ventilation, and those with an APACHE II score greater than 45 have a very poor prognosis and are unlikely to benefit from lengthy ICU support.

Adolescent↗

PubMed1997

Grip force scaling after hemispatial neglect.

Spatial neglect has been explained as an impairment in the representation of extrapersonal space. One account suggests that representations of extrapersonal space are spatially compressed following neglect. In support of this view it has been demonstrated that neglect patients systematically underestimate the size of stimuli presented in their left hemifield. In the current study we investigated this phenomena by obtaining an indirect measure of perceived object size - the scaling of grip force during prehension. We demonstrate for the first time that neglect patients show increased levels of grip force for objects presented in their left hemifield. This finding is discussed with reference to a proposed distinction between visual processing used for object recognition, and visual processing used to guide action.

Aged↗

PubMed1997

A prospective, randomized trial comparing continuous bladder drainage with catheterization at abdominal hysterectomy.

OBJECTIVE: To compare the infection rate and post-operative morbidity between in-dwelling urinary catheterization and 'in-out' catheterization at the time of routine total abdominal hysterectomy. PATIENTS AND METHODS: The study comprised 100 patients who were blindly randomized to have either an indwelling Foley catheter or an 'in-out' catheterization at the time of surgery. Follow-up data on the retention of urine, urinary symptoms and infection were obtained. RESULTS: Of the 95 patients with complete data, 36% of those undergoing in-out catheterization had urinary retention after operation, requiring bladder emptying, compared with 4% of those receiving an indwelling catheter (P < 0.001). In addition, 29% of the catheterized group had urinary tract bacteriuria compared with 13% of the uncatheterized group (P < 0.025). CONCLUSION: This randomized controlled trial showed that in-out urinary catheterization at the time of routine abdominal hysterectomy was associated with a significantly higher incidence of post-operative urinary retention compared with in-dwelling catheterization, and may have implications for long-term bladder function.

Adult↗

PubMed1997

Detection of glove puncture and skin contamination during caesarean section.

Measures that can be taken to reduce exposure to potentially infected body fluids are of particular relevance in obstetric and gynaecological surgery due to high rates of glove puncture and relatively higher prevalence of human immunodeficiency virus seropositivity in the obstetric age group. We describe the use of a simple electronic device that alarms following puncture of surgical gloves or the creation of a fluid bridge between surgeon and patient. Further exposure to potentially infected body fluids is thus prevented. This present study was performed in the context of caesarean section, but the application of the technique to gynaecological procedures is appropriate.

Cesarean Section↗

PubMed1996

Changes in metabolism of collagen in genitourinary prolapse.

BACKGROUND: Genitourinary prolapse is a common problem, the pathophysiology of which is unknown. METHODS: We analysed vaginal-epithelial tissue from premenopausal women with genitourinary prolapse and compared them with controls. FINDINGS: We found that genitourinary prolapse is associated with a reduction in total collagen content and a decrease in collagen solubility. Both intermediate intermolecular cross-links and advanced glycation cross-links were increased in prolapse tissue. Collagen turnover, as indicated by matrix metalloproteinase activity, was up to four times higher in prolapse tissue. Collagen-type ratios, mature cross-link pyridinoline and total elastin content were similar in both prolapse and control tissues. Increased collagenolytic activity causes loss of collagen from prolapse tissue. INTERPRETATION: Based on these findings, we have identified a probable mechanism for genitourinary prolapse. Development of agents to inhibit collagenolytic activity may help in the treatment of this condition.

Adult↗

PubMed1996

Visuomotor functions of the lateral pre-motor cortex.

Recent studies have provided new insights into the visuomotor functions of the dorsal and ventral regions of the lateral pre-motor cortex. Anatomical and physiological investigations in non-human primates have demonstrated that these regions have differing patterns of cortical connectivity and distinctive neuronal responses. Brain-imaging techniques and lesion studies have begun to probe the functions of homologous regions in humans.

Animals↗

PubMed1996

Glandular lesions of the cervix-cytological and histological correlation.

In this retrospective review we assessed the frequency with which atypical glandular cells in cervical smears predict cervical glandular lesions. Asymptomatic patients (n=34) with one or more smears showing atypical glandular cells aand subsequent histopathological assessment were studied. Independent cytological and histological review was undertaken. Cytological review confirmed atypical glandular cells in 29 cases, 17 of which had coexisting squamous dyskaryosis. Histological review of these 29 cases revealed glandular neoplasia in 13 (45%) and microglandular hyperplasia (MEH) in an additional four (14%). Initial reporting had underestimated the prevalence of glandular neoplasia.

Adenocarcinoma↗

PubMed1996

Detection of urinary incontinence during ambulatory monitoring of bladder function by a temperature-sensitive device.

OBJECTIVES: To determine whether the difference between urinary and perineal temperatures is sufficient to allow registration of incontinent episodes by detection of temperature change alone. To design and assess the use of a diode-based temperature-sensitive device in the detection of episodes of urinary incontinence in long-term ambulatory monitoring (LTAM) studies. SUBJECTS AND METHODS: Perineal temperature recordings were made in 46 women during various activities. A temperature-sensitive device consisting of six IN4148 diodes, spanning 5 cm, and a nearby reference negative diode, was placed in a light perineal pad and attached to a portable amplifier/digitizer and recorder. The performance of the device was determined by comparison with increases in pad weight in 51 incontinent and 23 continent control subjects. RESULTS: A sufficient temperature differential existed between perineal and urinary temperature during all activities except being seated with crossed legs. Incontinence was reliably detected by the temperature-sensitive device. The device had a sensitivity of 95.2% and a specificity of 90.6% compared to a pad test. CONCLUSIONS: This temperature-sensitive device offers a new method for detecting urinary incontinence during LTAM studies. It can be fitted in an unobtrusive perineal pad and has a higher sensitivity and specificity for the detection of incontinence when compared to a pad test. It may also be used as a marker of voiding in ambulatory studies not employing an integrated voiding channel.

Female↗

PubMed1996

The continence control pad--a new external urethral occlusion device in the management of stress incontinence.

OBJECTIVE: To assess the use of an external urethral occlusion pad (the continence control pad, CCP) in the management of stress incontinence. PATIENTS AND METHODS: Nineteen women (median age 47 years, range 36-72) complaining of stress incontinence were taught to use the CCP. The patients were assessed during the week before, and again after using the CCPs for 2 weeks, by urinary diaries, pad-tests and a review of their symptoms. RESULTS: Use of the CCP was associated with a cure or improvement in 17 women, as assessed by the number of incontinent episodes per week. There was a significant decrease in both the number of incontinent episodes (P < 0.001) and pad-test leakage (P = 0.002) when using the CCP. Minor difficulties in placement and removal were described in a minority of women. CONCLUSION: The CCP offers a simple, non-invasive treatment for women complaining of stress incontinence. The short-term success rate was better than that with other conservative methods of treatment, is independent of the general practitioner and safe. It is a promising home-based method of managing stress incontinence.

Adult↗

PubMed1995

Are non-relevant objects represented in working memory? The effect of non-target objects on reach and grasp kinematics.

The role of visual information and the precise nature of the representations used in the control of prehension movements has frequently been studied by having subjects reach for target objects in the absence of visual information. Such manipulations have often been described as preventing visual feedback; however, they also impose a working memory load not found in prehension movements with normal vision. In this study we examined the relationship between working memory and visuospatial attention using a prehension task. In this study six healthy, right-handed adult subjects reached for a wooden block under conditions of normal vision, or else with their eyes closed having first observed the placement of the target. Furthermore, the role of visuospatial attention was examined by studying the effect, on transport and grasp kinematics, of placing task-irrelevant "flanker" objects (a wooden cylinder) within the visual field on a proportion of trials. Our results clearly demonstrated that the position of flankers produced clear interference effects on both transport and grasp kinematics. Furthermore, interference effects were significantly greater when subjects reached to the remembered location of the target (i.e., with eyes closed). The finding that the position of flanker objects influences both transport and grasp components of the prehension movement is taken as support for the view that these components may not be independently computed and that subjects may prepare a coordinated movement in which both transport and grasp are specifically adapted to the task in hand. The finding that flanker effects occur primarily when reaching to the remembered location of the target object is interpreted as supporting the view that attentional processes do not work efficiently on working memory representations.

Adult↗

PubMed1995

The internal control of action and Parkinson's disease: a kinematic analysis of visually-guided and memory-guided prehension movements.

This paper reports two experiments which examined the effects of Parkinson's disease (PD) upon the sensorimotor mechanisms used to control prehension movements. Transport and grasp kinematics for visually-guided and memory-guided prehension movements were examined in healthy control subjects and compared against those of patients with idiopathic PD. Two research questions were addressed: (1) Are patients with PD particularly susceptible to distraction by non-relevant objects? (2) Are patients with PD especially reliant on external feedback when executing goal-directed actions? The results indicated that the patient group were no more susceptible to distraction by non-relevant objects than the control group. In contrast, the patients with PD were shown to be significantly impaired when executing memory-guided reaches. Furthermore, the deficits exhibited by the PD group on memory-guided reaches were confined solely to those markers associated with the transport component of the prehension movement. That is, while both controls and patients with PD widened their grip aperture on memory-guided trials, the magnitude of this adjustment was comparable across the two groups. The implications of these findings for theories of visuomotor processing in sufferers of PD and the control of prehension movements more generally are discussed.

Aged↗