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Biomedical subjects

A Z Khan

Publications and source records attributed to A Z Khan.

At least 19 recordsLinked to original sources
PubMed2006

Proprioceptive guidance of saccades in eye-hand coordination.

The saccade generator updates memorized target representations for saccades during eye and head movements. Here, we tested if proprioceptive feedback from the arm can also update handheld object locations for saccades, and what intrinsic coordinate system(s) is used in this transformation. We measured radial saccades beginning from a central light-emitting diode to 16 target locations arranged peripherally in eight directions and two eccentricities on a horizontal plane in front of subjects. Target locations were either indicated 1) by a visual flash, 2) by the subject actively moving the handheld central target to a peripheral location, 3) by the experimenter passively moving the subject's hand, or 4) through a combination of the above proprioceptive and visual stimuli. Saccade direction was relatively accurate, but subjects showed task-dependent systematic overshoots and variable errors in radial amplitude. Visually guided saccades showed the smallest overshoot, followed by saccades guided by both vision and proprioception, whereas proprioceptively guided saccades showed the largest overshoot. In most tasks, the overall distribution of saccade endpoints was shifted and expanded in a gaze- or head-centered cardinal coordinate system. However, the active proprioception task produced a tilted pattern of errors, apparently weighted toward a limb-centered coordinate system. This suggests the saccade generator receives an efference copy of the arm movement command but fails to compensate for the arm's inertia-related directional anisotropy. Thus the saccade system is able to transform hand-centered somatosensory signals into oculomotor coordinates and combine somatosensory signals with visual inputs, but it seems to have a poorly calibrated internal model of limb properties.

Adult↗
PubMed2005

Optic ataxia errors depend on remapped, not viewed, target location.

Optic ataxia is a disorder associated with posterior parietal lobe lesions, in which visually guided reaching errors typically occur for peripheral targets. It has been assumed that these errors are related to a faulty sensorimotor transformation of inputs from the 'ataxic visual field'. However, we show here that the errors observed in the contralesional field in optic ataxia depend on a dynamic gaze-centered internal representation of reach space.

Adult↗
PubMed2003

Spontaneous splenic rupture--a rare complication of amyloidosis.

We present a case of spontaneous rupture of the spleen, an uncommon complication of systemic amyloidosis. Amyloid deposition leading to capsular distension and increased vascular fragility is thought to predispose the spleen to rupture spontaneously.

Amyloidosis↗
PubMed2003

Ocular kinematics and eye-hand coordination.

Eye-hand coordination is complicated by the fact that the eyes are constantly in motion relative to the head. This poses problems in interpreting the spatial information gathered from the retinas and using this to guide hand motion. In particular, eye-centered visual information must somehow be spatially updated across eye movements to be useful for future actions, and these representations must then be transformed into commands appropriate for arm motion. In this review, we present evidence that early visuomotor representations for arm movement are remapped relative to the gaze direction during each saccade. We find that this mechanism holds for targets in both far and near visual space. We then show how the brain incorporates the three-dimensional, rotary geometry of the eyes when interpreting retinal images and transforming these into commands for arm movement. Next, we explore the possibility that hand-eye alignment is optimized for the eye with the best field of view. Finally, we describe how head orientation influences the linkage between oculocentric visual frames and bodycentric motor frames. These findings are framed in terms of our 'conversion-on-demand' model, in which only those representations selected for action are put through the complex visuomotor transformations required for interaction with objects in personal space, thus providing a virtual on-line map of visuomotor space.

Biomechanical Phenomena↗
PubMed2002

Visuomotor transformations for eye-hand coordination.

In recent years the scientific community has come to appreciate that the early cortical representations for visually guided arm movements are probably coded in a visual frame, i.e. relative to retinal landmarks. While this scheme accounts for many behavioral and neurophysiological observations, it also poses certain problems for manual control. For example, how are these oculocentric representations updated across eye movements, and how are they then transformed into useful commands for accurate movements of the arm relative to the body? Also, since we have two eyes, which is used as the reference point in eye-hand alignment tasks like pointing? We show that patterns of errors in human pointing suggest that early oculocentric representations for arm movement are remapped relative to the gaze direction during each saccade. To then transform these oculocentric representations into useful commands for accurate movements of the arm relative to the body, the brain correctly incorporates the three-dimensional, rotary geometry of the eyes when interpreting retinal images. We also explore the possibility that the eye-hand coordination system uses a strategy like ocular dominance, but switches alignment between the left and right eye in order to maximize eye-hand coordination in the best field of view. Finally, we describe the influence of eye position on eye-hand alignment, and then consider how head orientation influences the linkage between oculocentric visual frames and bodycentric motor frames. These findings are framed in terms of our 'conversion-on-demand' model, which suggests a virtual representation of egocentric space, i.e. one in which only those representations selected for action are put through the complex visuomotor transformations required for interaction with actual objects in personal space.

Arm↗
PubMed2001

Ocular dominance reverses as a function of horizontal gaze angle.

Ocular dominance is the tendency to prefer visual input from one eye to the other [e.g. Porac, C. & Coren, S. (1976). The dominant eye. Psychological Bulletin 83(5), 880-897]. In standard sighting tests, most people consistently fall into either the left- or right eye-dominant category [Miles, W. R. (1930). Ocular dominance in human adults. Journal of General Psychology 3, 412-420]. Here we show this static concept to be flawed, being based on the limited results of sighting with gaze pointed straight ahead. In a reach-grasp task for targets within the binocular visual field, subjects switched between left and right eye dominance depending on horizontal gaze angle. On average, ocular dominance switched at gaze angles of only 15.5 degrees off center.

Adult↗
PubMed2001

Early experience with laparoscopic radical gastrectomy for advanced gastric cancer.

Use of the laparoscopic approach for the management of gastric cancer is still in the developmental phase. The authors present their experience with laparoscopic radical gastrectomy for advanced gastric cancer. Between September 1997 and August 1999, four laparoscopic gastrectomies for gastric carcinoma were performed on two male and two female patients (mean age, 61.5 years). One D2 total radical gastrectomy and three D2 subtotal distal gastrectomies were performed, using a totally laparoscopic approach. Mean operative time was 210 minutes. There were no intraoperative complications. All four patients recovered uneventfully from surgery and began oral feeding on the third postoperative day. Median postoperative stay was 7 days (range, 6-9). All patients were alive 8 months to 3 years after the operation, with no cancer recurrences. This series shows that laparoscopic radical gastrectomy for moderately advanced cancers can produce good results in terms of safety and oncologic adequacy.

Adenocarcinoma↗
PubMed2001

Clinical audit: can we improve further?

Clinical audit is an important tool for comparing one's practice against existing standards. The authors have analysed the Junior Doctor's understanding of audit by performing a survey and questionnaire from 146 trainees, SpRs and SHOs from nine hospitals. The study showed that 107 (72.8%) performed audit and among those who performed audit, 52 (48.6%) experienced difficulty in obtaining data. This study highlights the importance of support needed to encourage the junior doctors to participate in audit programmes.

Adult↗
PubMed1997

Investigation of multiple dose citalopram on the pharmacokinetics and pharmacodynamics of racemic warfarin.

AIMS: An open, controlled, randomized, crossover study was conducted in healthy males to assess the possible occurrence of a pharmacokinetic/pharmacodynamic interaction between warfarin and the selective serotonin re-uptake inhibitor citalopram. METHODS: Twelve subjects received a single 25 mg dose of racemic warfarin either alone or on Day 15 of a 21-day oral dosing regimen of 40 mg citalopram daily. Blood samples for pharmacokinetic analysis were obtained over a 168 h period after warfarin dosing. The degree of anticoagulation was assessed by the prothrombin time. RESULTS: Citalopram produced no change in the pharmacokinetics of (R)- and (S)-warfarin, indicating that citalopram does not alter the metabolism of warfarin mediated via CYP1A2, CYP3A4 and CYP2C9. Citalopram coadministration resulted in a statistically significant increase in the maximum prothrombin time (R(max); by 1.6 +/- 3.0 s) and the area under the prothrombin time-time curve (AUC(PT); by 5.0 +/- 5.7%). The 90% confidence intervals for R(max) and AUC(PT) ratios (citalopram + warfarin/warfarin alone) were 1.01-1.10 and 1.03-1.07, respectively. CONCLUSIONS: The small increase in prothrombin time observed in this study with coadministration of citalopram and warfarin is not considered to be of importance in the clinical setting.

Adult↗
PubMed1996

Atovaquone has no effect on the pharmacokinetics of phenytoin in healthy male volunteers.

The potential pharmacokinetic interaction between atovaquone and phenytoin was investigated in 12 healthy male volunteers. Each volunteer received a single 600 mg oral dose of phenytoin in the two treatment periods. On one occasion phenytoin was taken alone and on the other pre-treatment with 2000 mg atovaquone taken as two doses of 1000 mg as a microfluidized suspension. The mean (+/- s.d.) peak plasma concentrations (Cmax), apparent total clearance (CL/F) and terminal half-life (t1/2) for phenytoin when administered alone were 10.6(1.8) mg 1(-1), 24.3 (7.7) ml min-1 and 25(8) h, respectively. When administered together with atovaquone, phenytoin Cmax, CL/F and t1/2,z were 10.9 (2.0) mg 1(-1), 23.8 ml min-1 and 24(6) h, respectively. There were no statistically significant differences in any of these plasma pharmacokinetic parameters. There were also no statistically significant differences in the fraction of circulating drug not bound to plasma protein or urinary excretion of 5-hydroxyphenyl-phenyl-hydantoin. In conclusion, there was no effect of atovaquone on the pharmacokinetics of phenytoin or its major metabolite after a single dose.

Adult↗
PubMed1995

Mothers' attitudes to children's chest infections in India.

Acute Respiratory Infections (ARIs) account for a very high morbidity and mortality amongst children in the developing countries. A knowledge, attitude and practice study in relation to the literacy status of mothers whose children suffered from ARI was conducted. A sample of 140 mothers who had 265 children were selected for the study. The majority of literate mothers (75%) had complete knowledge regarding management of ARI. Literacy alone was not the only factor responsible for developing a positive attitude and adopting correct practices during ARI. Mass media and health personnel played an equally important role. Most women (89.3%) had obtained their knowledge regarding ARI through media and paramedical staff. Most mothers (96.4%) were concerned about the health of their children when they suffered from episodes of ARI and the majority of them (87.2%) were worried because they felt that their children or contacts could be adversely affected. Nearly 72% of mothers took early action during an episode of ARI. The majority of the medical practitioners practised non-allopathic medicine but all of them were prescribing allopathic drugs. Most of the mothers (70%) had no problem in taking their children to the desired health centers when needed.

Acute Disease↗
PubMed1994

Absence of effect of ranitidine on blood alcohol concentrations when taken morning, midday, or evening with or without food.

OBJECTIVE: To investigate the effects of multiple dosing with ranitidine (300 mg four times a day) on the absorption of a moderate dose of alcohol (0.5 gm.kg-1), consumed postprandially or on an empty stomach at different times of day, and to investigate if coadministration of ranitidine affects psychomotor function. METHODS: Two double-blind, randomized, two-way crossover, and placebo-controlled studies were performed in a university research establishment. Study subjects were 36 (18 in each study) normal, healthy, nonalcoholic men aged from 25 to 48 years. Subjects received either 300 mg ranitidine four times a day or placebo for 8 days with oral alcohol (0.5 gm.kg-1) in the morning on day 4, at midday on day 6, and in the evening on day 8. Alcohol was consumed 45 minutes after standard meals and 30 minutes after ranitidine in the first study; it was consumed on an empty stomach 30 minutes after ranitidine in the second study. RESULTS: Maximum blood alcohol concentrations, area under the blood alcohol concentration--time curve, and time to maximum concentration were not significantly different during ranitidine coadministration compared with coadministration of placebo. This result held true for each time of day and for fed and fasting states. Similarly, ranitidine had no detectable effect on any of the results from tests of psychomotor function. CONCLUSION: Irrespective of the time of day, ranitidine has no statistically or clinically significant effects on blood alcohol profiles.

Absorption↗