Biomedical subjects

K M Bennett

Publications and source records attributed to K M Bennett.

At least 19 recordsLinked to original sources

PubMed2001

A four-year experience with patient individualized heparin and protamine dosing using the Hemochron RxDx system.

Cardiac surgical case histories, collected over 4 years at Huntsville Hospital in Alabama, were reviewed for 2,293 patients. Patients were separated into two dosing groups for both heparin and protamine, hospital empirically dosed and Hemochron RxDx dosed. Review of the heparin dosing information found that incomplete data were collected for 47 patients, leaving 2,246 patients eligible to be evaluated for heparin dose comparison. Both RxDx recommended and empirically calculated doses were recorded, as well as the actual dose given. Of the 2,246 patients, 1671 were administered heparin according to the RxDx calculated dose, and the remaining 575 patients were dosed according to the hospital's empirical protocol. The average RxDx calculated heparin dose was 17% greater then the empirically calculated heparin dose (350 U/kg) (p < .001). Anticoagulation to target ACT (480 sec) was achieved in 92% of the patients dosed according to the RxDx recommended dose; whereas, in the empirically dosed patient group only 80% of the patients reached the target ACT after initial heparin bolus dose. Incomplete protamine dosing data was recorded for 336 patients, leaving a total of 1,957 patients available for protamine dose evaluation. All patients had an RxDx protamine calculation, empirical protamine calculation, and actual amount of protamine dosed recorded. Of the 1,953 patients, 1,764 were dosed according to the RxDx recommended dose, with the remaining 189 patients dosed empirically (1 mg protamine/100 U of heparin). In both the RxDx and the empirical groups, 96% of the patients returned to baseline following initial protamine infusion. The overall RxDx dose (293 mg) was 16% lower than the average empirical dose (348 mg). The RxDx system has been shown to be an effective method for determining patient-specific dosing for both heparin and protamine. This long-term clinical experience demonstrates the consistency and reliability of patient maintenance using this individualized dosing system, which has been shown, in other independent evaluations, to lead to improved patient outcomes.

Analysis of Variance↗

PubMed2000

The reach-to-grasp movement in Parkinson's disease before and after dopaminergic medication.

The aim of the present study was to assess the effects of dopaminergic medication on the organisation of the reach-to-grasp movement in Parkinson's disease. A three-dimensional kinematic system (ELITE, B/T/S Italy) was used to record reach-to-grasp movements to objects of either small (0.7 cm) or large (8 cm) diameter placed at a reaching distance of either 20 or 30 cm. Vision of the reaching limb and target was also manipulated. Parkinson's disease participants (N = 14) were assessed in 'OFF' (12 h without medication) and 'ON' (1-2 h post-administration of medication) states. In the 'ON' state, movement duration and the time spent in arm deceleration were significantly less than in the 'OFF' state. The amplitudes of peak reaching velocity, acceleration and deceleration were all higher in the 'ON' than in the 'OFF' state. Further, in the 'ON' state, the acceleration profile no longer exhibited small irregular adjustments, the number of significant correlations between parameters measured from the transport and manipulation components was greater, and the movement was more direct in both the mediolateral horizontal and vertical planes. These results indicate that dopaminergic medication is of benefit in reducing bradykinesia and in fine-tuning kinematic parameterisation of a selected reach-to-grasp action.

Adult↗

PubMed2000

Interference from distractors in reach-to-grasp movements.

Descriptions of interference effects from non-relevant stimuli are extensive in visual target detection and identification paradigms. To explore the influence of features of non-relevant objects on reach-to-grasp movements, we instructed healthy normal controls to reach for and pick up a cylinder (target) placed midsagittally 30 cm from the starting position of the hand. In Experiment 1, the target was presented alone, or accompanied by a narrower, wider, or same-size distractor positioned to the left or right of the target. In Experiment 2, the target was presented alone or accompanied by a distractor, which was slanted at a different orientation to the target. Reflective markers were placed on the wrist, thumb, and index finger of the right hand, and infra-red light-detecting cameras recorded their displacement through a calibrated 3-dimensional working space. Kinematic parameters were derived and analysed. Consistent changes in the expression of peak velocity, acceleration, and deceleration were evident when the distractor was narrower or wider than the target. The impact of the orientation of the distractor, conversely, was not marked. We discuss the results in the context of physiological findings and models of selective attention.

Adult↗

PubMed1999

Sudden and gradual presentation of distractor objects: differential interference effects.

In solving the selection-for-action problem, it is believed that attentional mechanisms enable dominance of target over non-target objects. However, under some conditions, information from non-target objects "interferes" with the action to a relevant target. We investigated the possibility that this interference may result when the irrelevant object activates a specific subset of visuomotor pathways. Participants reached to grasp three-dimensional stimuli while actively attending to a nearby flanker object. The means by which the flanker was presented was manipulated. This relevant object was illuminated either abruptly or gradually. The parvocellular pathway in early visual processing is equally activated in both conditions. The magnocellular pathway is strongly activated by abrupt presentation and weakly activated with gradual presentation of the flanker object. Kinematics of the reach-to-grasp action to the target showed signs of interference only in the sudden illumination condition. This suggests a dissociation between dorsal and ventral cortical streams in terms of relevance for action. Our data suggests that this effect is not due to early visual-pathway differences, but instead reveals a property of a transient object-based visual attention mechanism.

Adult↗

PubMed1999

Covert orienting and focusing of attention in children with attention deficit hyperactivity disorder.

Performance on the covert visuo-spatial attentional functions of orienting and focusing by a group of ADHD children (n = 20) was compared to that of age and sex-matched control children. In Experiment 1, responses were given to cued targets at valid and invalid locations. In Experiment 2, responses were given to targets presented in small, medium-sized or large visual field locations. For both experiments, the hypotheses that reaction times of ADHD children would be greater than those of control children and that performance would be asymmetrical, were supported. For Experiment 1, ADHD children showed bilaterally greater 'benefits' from having directed attention to the cued location and greater 'costs' in having to relocate the attentional focus than controls. In Experiment 2, the hypothesis that the function of focusing attention by ADHD children may show breakdown in the usual pattern of an increase in reaction time with focus area was partly supported by the finding of similar reaction times to targets presented in medium-sized and large regions of the left visual hemifield. These results have been interpreted as reflecting a stronger anchorage of attention by ADHD children upon a cued location and an inability to shift covert attention easily to an alternative location. The breakdown of the focusing function suggests adoption of similar time response sets across focus area size by the more compromised right hemisphere.

Attention↗

PubMed1998

Upper limb movement differentiation according to taxonomic semantic category.

The size or shape of an object, its perceptual features, determine the patterning of an arm and hand action involving that object. Little is known about the role played by the taxonomic semantic attributes of an object for perceptuomotor processing. In this study we investigated whether the semantic relationship between two target stimuli influences the kinematics of a bilateral reach-to-grasp action. The results showed that reach-to-grasp movements preceding the action of putting living-thing pairs together were faster, and showed earlier settings of reach and grasp temporal parameters, than movements involving pairs of non-living things. It is hypothesized that this reflects the recruitment of different categorical perceptuomotor pathways.

Adult↗

PubMed1998

Gender and longitudinal changes in physical activities in later life.

OBJECTIVES: to describe gender differences in levels of, and longitudinal changes in, habitual physical activity among older people. DESIGN: longitudinal study. PARTICIPANTS: sub-groups of survivors (with sample sizes dependent on the availability of complete datasets, ranging from 303-344) assessed on three occasions: 1985, 1989 and 1993 in Nottingham, UK. All were 65 years and over in 1985. METHODS: descriptive presentation (median and range values) of quantitative longitudinal data by gender across five activity categories assessed in a recall-based questionnaire. MAIN OUTCOME MEASURES: participation in walking, shopping, indoor, outdoor and leisure activities. RESULTS: while levels of indoor and outdoor activities were marked by decline for both sexes, gender differentials were maintained over the 8 years of the study, with women showing higher levels of activity participation indoors and men showing higher levels of activity participation outdoors. In levels of walking/shopping activity, however, there was evidence of gender differentials reducing over time. CONCLUSIONS: within these cohorts of older people traditional gender roles continue to exert a strong influence on levels and types of habitual physical activity well into later life. In some areas of activity, however, temporal changes provide some evidence of gender convergence consistent with late-life transitions in marital status and dependency.

Activities of Daily Living↗

PubMed1998

Customary physical activity and gender as precursors for late life personal disturbance.

OBJECTIVES: To examine whether customary physical activity (CPA) and gender are precursors for personal disturbance in later life. DESIGN: The study was part of a longitudinal study, with data collected in 1985 and 1989. Measures of CPA were obtained in men and women who by 1989 had developed elevated levels of personal disturbance. A case-control design was used: the cases were matched with controls on their 1985 levels of personal disturbances, gender and age. METHODS: Levels of personal disturbance were measured using the Symptoms of Anxiety and Depression (SAD) Scale. CPAs were assessed using five continuous and two discrete measures of physical activity, including indoor productive activity, outdoor productive activity and flexibility. The cases were 26 women and 11 men and the controls were 26 women and 11 men. RESULTS: Both CPA and gender were found to be precursors for later elevated personal disturbance. Specifically, indoor and outdoor productive activity and activities requiring flexibility were precursors for elevated personal disturbance. The effects of gender were even more specific: a main effect for gender was found for indoor productive activity (women doing more than men); and an interaction effect was observed between personal disturbance and gender for outdoor productive activity (the difference between depressed and non-depressed men is greater than between depressed and non-depressed women). CONCLUSIONS: The study found that both CPA and gender were precursors for elevated levels of personal disturbance. However, the effects of both CPA and gender were quite specific.

Activities of Daily Living↗

PubMed1998

The effect of unilateral posteroventral pallidotomy on the kinematics of the reach to grasp movement.

OBJECTIVE: To assess postoperative effects of unilateral posteroventral pallidotomy on the organisation of upper limb movement. METHODS: A three dimensional kinematic system (ELITE, B/T/S/ Italy) was used to record reach to grasp movements to objects of either small (0.7 cm) or large (8 cm) diameter placed at a reaching distance of either 20 or 30 cm. Four patients with Parkinson's disease were assessed in "off" (12 hours without medication) and "on" (1 hour after administration of medication) preoperatively and postoperatively. RESULTS: Duration of the movement and the time spent in arm deceleration were significantly reduced after surgery. However, movement patterning according to object size was adversely affected. Postoperatively, all four patients showed an abnormal pattern of a longer movement duration, and three showed a longer time of reaching arm deceleration, for reach to grasp movements to the large object than for those to the small object. CONCLUSION: Posteroventral pallidotomy seems to be beneficial in reducing bradykinesia of upper limb movements but may have "costs" to movement patterning, particularly for reach to grasp movements to objects of differing sizes. This study raises interesting questions about the role of the globus pallidus interna in coordinating stimulus bound visual information with appropriate motor patterning.

Aged↗

PubMed1997

A longitudinal study of wellbeing in widowed women.

Changes in mental and physical health, morale and social functioning were assessed in a random sample of elderly women widowed during the course of an 8-year study, compared with never-married and still-married controls. The sample as a whole showed age-related declines in mental and physical health. As a function of ageing there were increases in personal disturbance and in physical health problems and declines in both morale and social engagement. However, over and above these age-related changes the windows showed significant changes in mental health. There were decreases in morale after widowhood, followed by slight increases in morale in the longer term. Similarly, there were increases in personal disturbance following widowhood, with slight decreases later. The results confirm that, even after several years, widowhood has differential effects on wellbeing and morale.

Activities of Daily Living↗

PubMed1997

The bilateral reach-to-grasp movement of Parkinson's disease subjects.

The performance of simultaneous movements is said to be disrupted in Parkinson's disease, yet there are some indications that this dysfunction is less evident for bilateral inter-limb actions, as opposed to unilateral simultaneous actions. Focussing specifically upon natural actions, this study uses a three-dimensional kinematics system (ELITE) to assess the movement kinematics of a bilateral non-homologous reach-to-grasp action. The target device consisted of a large cylinder (diameter 8 cm) to which a handle (diameter 0.8 cm) was attached. The task was to reach and grasp the cylinder with one hand (gross grasp) while reaching to grasp the handle with the contralateral hand (precision grasp). Overall the results indicated that Parkinson's disease subjects, like controls, showed independent and appropriate kinematic parameterization of each limb. For example, and as a reflection of task precision requirements, the time taken to decelerate upon the item to be grasped was longer for the limb grasping the handle than for the limb grasping the cylinder. Subtle indications of compensatory mechanisms, in response to left upper limb inadequacies of Parkinson's disease subjects, were suggested by findings of an earlier timing of maximum hand grip aperture for the left than for the right hand, and adjustments to the final transport phase of the left arm under bilateral conditions. It is proposed that left-right hand differences are more evident with basal ganglia dysfunction, but that these differences are compensated for by CNS mechanisms so that natural non-homologous reach-to-grasp actions are performed in a functional, coordinated and appropriate manner.

Adult↗

PubMed1996

How perceived object dimension influences prehension.

A kinematic study assessed the effects of the perceived dimensions of an object upon the patterning of a prehension movement involving that object. If an apple was perceived as two-dimensional, subjects utilized a large precision grip between the index finger and thumb. If the apple was perceived as three-dimensional, whole hand prehension involving all the digits was utilized. A visual perturbation from perceived two-dimensional to three-dimensional at movement onset resulted in a transition from the 2D precision grip pattern to the 3D whole hand prehension. These results suggest that visual mechanisms for interpreting the dimension of an object directly influence motor selection pathways, and do not necessarily access a three-dimensional central nervous system representation of the object.

Acceleration↗

PubMed1996

Three-dimensional covert attentional functions in Parkinson's disease subjects.

This study assessed the ability of mildly affected Parkinson's disease (PD) subjects (n = 16) to perform attentional cognitive tasks within a three-dimensional object. A hollow cube was displayed on a computer screen and the subject was required to respond as quickly as possible to the highlighting of one of the cube angles by pressing the spacebar of the keyboard. Prior to the appearance of this imperative stimulus, the same ("valid" trials) or an alternative ("invalid" trials) angle was highlighted. For the invalid trials this meant that the subject oriented attention to the cued angle but, on imperative stimulus appearance, was unexpectedly required to redirect attention to another angle, which could be on a different cube face to that which had been cued. For one experimental session the cube was stationary, that is, object-centred and viewer-centred coordinates of a cube angle corresponded. For another session, the cube rotated such that the viewer-centred coordinates of an angle changed between appearance of the cue and appearance of the stimulus, but the angle's object-centred coordinates remained constant. The finding of lower reaction times for the valid than for the invalid trials, even when the cube was rotating, indicated that PD subjects could operate attention using an object-centred coordinate system. However, PD subjects showed exaggerated reaction times when the stimulus appeared in a cube face that was opposite to, rather than the same as, that of the invalidly cued angle. It is suggested that this reflects a dysfunction in the grouping of the structural components of the whole object at an attentional level.

Attention↗

PubMed1996

Corticomotoneuronal contribution to the fractionation of muscle activity during precision grip in the monkey.

1. During independent finger movements, the intrinsic muscles of the hand show a fractionated pattern of activity in which the timing and amplitude of electromyographic (EMG) activity varies considerably from one muscle to another. It has been suggested that, in the macaque monkey, corticomotoneuronal (CM) cells that produce postspike facilitation (PSF) of EMG in these muscles contribute to this fractionation. To test this hypothesis, we have investigated the relationship between the pattern of PSF exerted by a CM cell and the pattern of activity shown by the cell and by its target muscles. 2. The activity of 15 identified CM cells was recorded from two monkeys that performed a precision grip task. Spike-triggered averaging of rectified EMG during the hold period of this task showed that each cell produced PSF in at least two intrinsic hand muscles. 3. Segments of data were selected from the initial movement period of the task in which the EMG activity in one target muscle was substantially greater than that of the other, and the mean firing rate of each CM cell was determined for these periods. 4. CM cells showed bursts of activity in the movement period. Most of them (13/15) had a significantly (P < 0.001) higher firing rate when one of its target muscles was more active than the other. For nine of these cells (identified as set A), this muscle was the one receiving the larger PSF. In four cases (set B), the reverse was true. Two cells (set C), which produced PSF of equal size in their target muscles, showed no change in firing rate across the periods of fractionated EMG activity. 5. All set A and set B cells fired at significantly (P < 0.001) higher rates during the movement period, in association with fractionation of EMG activity, than in the hold period, in which a cocontracted pattern of muscle activity was observed. 6. There were pronounced differences in the strength of PSF exerted by the CM cells on their target muscles during the fractionation periods. One CM cell exerted PSF of a muscle during one period of fractionation, but postspike suppression of the same muscle during the other period. 7. It is suggested that changes in the firing rate of a CM cell and in the degree of facilitation it exerts could both contribute to the fractionation of activity in its target muscles. Cells of set A appear to be specifically recruited in a manner that directly reflects the pattern of facilitation they exert on the sampled target muscles. These results may explain why the CM system is so important for the performance of relatively independent finger movements.

Animals↗

PubMed1995

Reorganization of prehension components following perturbation of object size.

This study provides a kinematic comparison of the response of 12 older persons (ages 60-70) and 12 young persons (ages 20-26) to a perturbation of object size during a reach-to-grasp movement. For 80 out of 100 trials, each participant reached to grasp an illuminated cylinder of either small or large diameter (0.7 and 8.0 cm, respectively). For 20 out of 100 trials, a visual perturbation occurred at movement onset. This perturbation consisted of a switch of illumination from 1 to the other cylinder. For the switch from large to small cylinder, participants changed the distal grasp from whole-hand prehension to precision grip. For the opposite switch, participants changed from precision grip to whole-hand prehension. The older participants successfully adapted to these perturbations but showed a more conservative approach. Generally the approach time as the hand neared the object was prolonged, and the coordination between transport and manipulation components was maintained when comparing perturbed with nonperturbed trials. Young participants showed a more flexible pattern with a decrease or loss of temporal coupling between the components. It is hypothesized that the more rigid movement pattern of older participants to unanticipated motor requirements could be a contributory factor to the higher incidence of accidents for this group.

Adult↗

PubMed1995

Habitus and hip fracture revisited: skeletal size, strength and cognition rather than thinness?

In a prospective study, 50 consecutive women with fractured hips were compared for body mass, skeletal size, handgrip strength and the 12-point information/orientation CAPE score with 50 age-matched women who had never broke their hips. Women were excluded from both groups if they lived in institutions or were severely disoriented. Although weight and skeletal size were significantly lower in the patients than in the controls, weights when corrected for skeletal size were not significantly different. Handgrip was significantly lower in the cases than in the controls. Both handgrip strength and CAPE score were significant correlates of hip fracture in multiple regression analysis. After exclusion of heavily dependent patients, hip fracture may be associated with reduced muscle strength rather than reduced body mass or fat.

Aged↗

PubMed1995

Covert visuospatial attentional mechanisms in Parkinson's disease.

Orienting and focusing of attention were assessed in 32 Parkinson's disease and 32 control subjects. No differences were found in the covert orienting of attention, suggesting that the Parkinson's disease subjects of the current study were not impaired in the ability to orient attention towards an expected source of stimulation. However, with the process of modulating the attentional focus or of managing more than one attentional task, dysfunction in Parkinson's disease subjects became apparent. The observed results are explained in terms of deficits in the relationship between task-related distribution of attentional resources and time efficiency of processing.

Attention↗

PubMed1995

The drinking action of Parkinson's disease subjects.

Using the ELITE system, a kinematic analysis was performed of the upper limb drinking action of nine Parkinson's disease patients and nine control subjects. The aim was to use a natural task to investigate the reported Parkinson's disease dysfunction in the performance of simultaneous and sequential movements. Subjects were required to reach 28 cm, grasp a half-filled glass and then take a sip of water. Dysfunction for simultaneous movements was supported by the finding that, in both absolute and relative terms, Parkinson's disease subjects often began to open the hand later than control subjects. Dysfunction for sequential movements was supported by the finding that Parkinson's disease subjects often showed a pause between the first ('reach-grasp') and second ('take-to-lips') parts of the drinking action. Despite these delays and pauses, the proportional organization of the action was similar for both groups. This suggested that Parkinson's disease subjects were able to compensate for the problem in activating the different components of the drinking action. The results are discussed in relation to the influence of the abnormal basal ganglia input to cortical motor regions.

Adult↗