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T Drew

Publications and source records attributed to T Drew.

At least 19 recordsLinked to original sources
PubMed1999

Calcium channel activation and self-biting in mice.

The L type calcium channel agonist (+/-)Bay K 8644 has been reported to cause characteristic motor abnormalities in adult mice. The current study shows that administration of this drug can also cause the unusual phenomenon of self-injurious biting, particularly when given to young mice. Self-biting is provoked by injecting small quantities of (+/-)Bay K 8644 directly into the lateral ventricle of the brain, suggesting a central effect of the drug. Similar behaviors can be provoked by administration of another L type calcium channel agonist, FPL 64176. The self-biting provoked by (+/-)Bay K 8644 can be inhibited by pretreating the mice with dihydropyridine L type calcium channel antagonists such as nifedipine, nimodipine, or nitrendipine. However, self-biting is not inhibited by nondihydropyridine antagonists including diltiazem, flunarizine, or verapamil. The known actions of (+/-)Bay K 8644 as an L type calcium channel agonist, the reproduction of similar behavior with another L type calcium channel agonist, and the protection afforded by certain L type calcium channel antagonists implicate calcium channels in the mediation of the self-biting behavior. This phenomenon provides a model for studying the neurobiology of this unusual behavior.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1999

Kinetic and energetic patterns for hindlimb obstacle avoidance during cat locomotion.

The safe control of walking over different terrains requires appropriate adaptations in the dynamic and kinematic limb patterns. To date, the study of locomotor dynamics in the cat has been confined to level, unobstructed walking. The present study extends the work of Lavoie et al. by applying linked segment analyses to estimate muscle contributions to torque and mechanical power at the hindlimb joints of two female cats during both unobstructed walking and obstacle avoidance. Data during obstacle avoidance were analyzed both when the hindlimb led in clearance and was farthest from the obstacle, and when it trailed in clearance and was closest or near to the obstacle. It was found that, in both the Far and Near obstructed conditions, the cats cleared the obstacles primarily by increasing the knee flexor torque already used during unobstructed gait. Contributions from the hip and ankle muscle groups were more variable. There was more emphasis on the hip extensors in mid to late stance, and the hip flexors generated a small amount of energy at paw-lift in the Far condition. In the Near condition, the hip extensors were employed to control hip flexion. We suggest that hip flexor generation power in mid-swing contributes to the clearance of the upcoming obstacle in the Far condition while, in the Near condition, hip flexion advances the already extended limb ahead of the obstacle. The ankle was actively dorsiflexed in the Near condition but was maintained in extension in the Far condition. The emphasis on active knee flexor control by the cat to avoid obstacles, as well as the dependence of ankle control on obstacle proximity, is similar to strategies seen for humans. However, the knee flexor strategy is innate to the cat's normal level walking control, whereas in humans active knee flexion at toe-off requires a reorganization from level, non-obstructed gait.

Adaptation, Physiological↗
PubMed1999

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex.

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex. To determine the extent to which the rubrospinal tract is capable of modifying locomotion in the intact cat, we applied microstimulation (cathodal current, 330 Hz; pulse duration 0.2 ms; maximal current, 25 microA) to the red nucleus during locomotion. The stimuli were applied either as short trains (33 ms) of impulses to determine the capacity of the rubrospinal tract to modify the level of electromyographic (EMG) activity in different flexors and extensors at different phases of the step cycle or as long trains (200 ms) of pulses to determine the effect of the red nucleus on cycle timing. Stimuli were also applied with the cat at rest (33-ms train). This latter stimulation evoked short-latency (average = 11.8-19.0 ms) facilitatory responses in all of the physiological flexor muscles of the forelimb that were recorded; facilitatory responses were also common in the elbow extensor, lateral head of triceps but were rare in the physiological wrist and digit extensor, palmaris longus. Responses were still evoked in most muscles when the current was decreased to near threshold (3-10 microA). Stimulation during locomotion with the short trains of stimuli evoked shorter-latency (average = 6.0-12.5 ms) facilitatory responses in flexor muscles during the swing phase of locomotion and, except in the case of the extensor digitorum communis, evoked substantially smaller responses in stance. The same stimuli also evoked facilitatory responses in the extensor muscles during swing and produced more complex effects involving both facilitation and suppression in stance. Increasing the duration of the train to 200 ms modified the amplitude and duration of the EMG activity of both flexors and extensors but had little significant effect on the cycle duration. In contrast, whereas stimulation of the motor cortex with short trains of stimuli during locomotion had very similar effects to that of the red nucleus, increasing the train duration to 200 ms frequently produced a marked reset of the step cycle by curtailing stance and initiating a new period of swing. The results suggest that whereas both the motor cortex and the red nucleus have access to the interneuronal circuits responsible for controlling the structure of the EMG activity in the step cycle, only the motor cortex has access to the circuits responsible for controlling cycle timing.

Animals↗
PubMed1998

Total radiated power, infrared output, and heat generation by cold light sources at the distal end of endoscopes and fiber optic bundle of light cables.

BACKGROUND: Skin burns and ignition of drapes have been reported with the use of cold light sources. The aim of the study was to document the temperature generated by cold light sources and to correlate this with the total radiated power and infrared output. METHODS: The temperature, total radiated power, and infrared output were measured as a function of time at the end of the endoscope (which is inserted into the operative field) and the end of the fiber optic bundle of the light cable (which connects the cable to the light port of the endoscope) using halogen and xenon light sources. RESULTS: The highest temperature recorded at the end of the endoscope was 95 degrees C. The temperature measured at the optical fiber location of the endoscope was higher than at its lens surface (p < 0.0001). At the end of the fiber optic bundle of light cables, the temperature reached 225 degrees C within 15 s. The temperature recorded at the optical fiber location of all endoscopes and light cables studied rose significantly over a period of 10 min to reach its maximum (p <0.0001) and then leveled off for the duration of the study (30 min). The infrared output accounted only for 10% of the total radiated power. CONCLUSIONS: High temperatures are reached by 10 min at the end of fiber optic bundle of light cables and endoscopes with both halogen and xenon light sources. This heat generation is largely due to the radiated power in the visible light spectrum.

Cold Temperature↗
PubMed1998

Computer-controlled endoscopic performance assessment system.

We have devised an advanced computer-controlled system (ADEPT) for the objective evaluation of endoscopic task performance. The system's hardware consists of a dual gimbal mechanism that accepts a variety of 5.0-mm standard endoscopic instruments for manipulation in a precisely mapped and enclosed work space. The target object consists of a sprung base plate incorporating various tasks. It is covered by a sprung perforated transparent top plate that has to be moved and held in the correct position by the operator to gain access to the various tasks. Standard video endoscope equipment provides the visual interface between the operator and the target-instrument field. Different target modules can be used, and the level of task difficulty can be adjusted by varying the manipulation, elevation, and azimuth angles. The system's software is designed to (a) prompt the surgeon with the information necessary to perform the task, (b) collect and collate data on performance during execution of specified tasks, and (c) save the data for future analysis. The system was alpha and beta tested to ensure that all functions operated correctly.

Endoscopy↗
PubMed1998

Improved control of gas humidity in neonatal intensive care ventilators.

Difficulties experienced by nursing staff in controlling humidity in neonatal intensive care ventilators are shown to originate in the use of a single control, namely a heater, to condition two parameters, namely temperature and humidity, at the inlet to the inspiratory tube. It is shown that better control can be achieved by separating the gas flow through the humidifier into two streams, only one of which is humidified. It is proposed that the temperature along most of the inspiratory tube should be maintained about 3-5 degrees C higher than the target delivery temperature. This eliminates the risk of condensation in the tube, a second commonly occurring problem in existing systems. It is shown why the control of ventilator systems should be based on absolute humidity, not relative humidity, even though the latter may be preferred for monitoring purposes.

Humans↗
PubMed1998

Corticoreticular pathways in the cat. I. Projection patterns and collaterization.

This paper summarizes and compares the projection patterns and the receptive fields of cortical neurons in areas 4 and 6 that project to the pontomedullary reticular formation (PMRF). A total of 326 neurons were recorded in area 4 and 129 in area 6 in four awake, unrestrained cats that were chronically implanted with arrays of electrodes in the PMRF and the pyramidal tract (PT). In area 4, 47% of the neurons projected to the caudal PT but not to the PMRF (PTNs); 19% were activated only from the PMRF [corticoreticular neurons (CRNs)], whereas 27% were activated from both the PT and the PMRF (PTN/CRNs). More PTN/CRNs conducted at velocities >20 m/s (82%) than did CRNs (23%). In area 6, only 19% of the neurons were identified as PTNs, 12% were PTN/CRNs and 31% were CRNs; a further 38% could not be activated from either structure. Collateral branches within the PMRF conducted at maximum velocities of 20 m/s (average = 6.5 m/s). No significant differences in the conduction velocities of the collateral branches were found either between fast and slow PTNs or between area 4 and area 6 neurons. A large proportion of neurons in area 4 (85/173, 49%) were activated by passive manipulation of the more distal, contralateral forelimb, with approximately equal numbers being classed as PTNs, PTN/CRNs and CRNs. Most neurons in area 6 for which a receptive field could be found were excited by lightly touching or tapping the face and neck; a receptive field could not be determined for 39% of the area 6 neurons compared with only 5% of those in area 4. Finally, there was evidence that neurons in quite widespread areas of the pericruciate cortex, including both areas 4 and 6 projected onto similar, restricted regions of the PMRF. The fact that the cortical projection from area 4 to the PMRF includes a high percentage of fast PTNs with a receptive field on the distal forelimb is consistent with the view that this projection may serve to integrate movement and the dynamic postural adjustments that accompany them. The fact that the cortical projection from area 6 to the PMRF is primarily from slow PTNs with receptive fields on the face, neck and back is consistent with a role for this cortical area in adjusting the general posture of the animal on which movements are superimposed.

Animals↗
PubMed1998

Corticoreticular pathways in the cat. II. Discharge activity of neurons in area 4 during voluntary gait modifications.

We propose that the descending command from area 4 that is responsible, in part, for the change in limb trajectory required to step over an obstacle in one's path also plays a role in triggering the anticipatory postural modifications that accompany this movement. To test this hypothesis, we recorded the discharge characteristics of identified classes of corticofugal neurons in area 4 of the cat. Neurons were identified either as: pryamidal tract neurons (PTNs) if their axon projected to the caudal pyramidal tract (PT) but not to the pontomedullary reticular formation (PMRF); as corticoreticular neurons (CRNs) if their axon projected to the PMRF but not to the PT; and as PTN/CRNs if their axon projected to both structures. Altogether, the discharge properties of 212 corticofugal neurons (109 PTNs, 66 PTN/CRNs, and 37 CRNs) within area 4 were recorded during voluntary gait modifications. Neurons in all three classes showed increases in their discharge frequency during locomotion and included groups that increased their discharge either during the swing phase of the modified step, during the subsequent stance phase, or in the stance phase of the cycle preceding the step over the obstacle. A slightly higher percentage of CRNs (39%) discharged in the stance phase prior to the gait modification than did the PTNs or PTN/CRNs (20% and 17% respectively). In 37 electrode penetrations, we were able to record clusters of 3 or more neurons within 500 micro(m) of each other. In most cases, PTN/CRNs recorded in close proximity to PTNs had similar receptive fields and discharged in a similar, but not identical, manner during the gait modifications. Compared with adjacent PTNs, CRNs normally showed a more variable pattern of activity and frequently discharged earlier in the step cycle than did the PTNs or PTN/CRNs. We interpret the results as providing support for the original hypothesis. We suggest that the collateral branches to the PMRF from corticofugal neurons with axons that continue at least as far as the caudal PT provide a signal that could be used to trigger dynamic postural responses that are appropriately organized and scaled for the movements that are being undertaken. We suggest that the more variable and earlier discharge activity observed in CRNs might be used to modify the postural support on which the movements and the dynamic postural adjustments are superimposed.

Animals↗
PubMed1997

Organization of the projections from the pericruciate cortex to the pontomedullary brainstem of the cat: a study using the anterograde tracer Phaseolus vulgaris-leucoagglutinin.

The anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) was used to study the distribution and density of the projections that originate from four identified subdivisions of the pericruciate cortex (namely, the forelimb and hind limb representations of area 4, area 6a beta, and area 6a gamma) and that terminate in the pontomedullary brainstem in the cat. Injections of PHA-L in all areas of the pericruciate cortex labelled numerous fibers and their terminal swellings in the brainstem. The major target regions of all four cortical areas were the pontine nuclei and the pontomedullary reticular formation (PMRF). Injections into both the forelimb and hind limb representations of area 4 and into area 6a beta resulted in a dense pattern of terminal labelling in restricted regions of the medial and lateral parts of the ipsilateral pontine nuclei. The labelling following the area 6a beta injection was spatially distinct from that seen following the area 4 injections. Injections into the forelimb representation of area 4 as well as into area 6a beta and 6a gamma resulted in the labelling of numerous terminal swellings bilaterally in the PMRF; in contrast, there were few labelled terminal swellings in the PMRF following injections into the hind limb representation of area 4. Terminal swellings on individual corticoreticular fibers were far less densely aggregated than those in the pontine nuclei. The dense pattern of innervation to restricted regions of the pontine nuclei supports previous suggestions that the corticopontine projections retain a high degree of topographical specificity that could be used in the control of discrete voluntary movements. In contrast, the more diffuse pattern of the projections to the PMRF may facilitate the selection and activation of the complex postural patterns that accompany voluntary movement.

Animals↗
PubMed1997

Organization of the projections from the pericruciate cortex to the pontomedullary reticular formation of the cat: a quantitative retrograde tracing study.

Dextran-amines were used as retrograde tracers to investigate the organization of cortical projections to different cytoarchitectonic regions of the pontomedullary reticular formation of the cat. Injections into the nucleus reticularis pontis oralis resulted in labelling of neurones in the proreus cortex and area 6a beta of the premotor cortex, with little labelling in the motor cortex (area 4). This labelling was predominantly ipsilateral to the injection site. In contrast, injections into the nucleus reticularis pontis caudalis (NRPc), nucleus reticularis gigantocellularis (NRGc), and nucleus reticularis magnocellularis (NRMc) resulted in bilateral labelling--primarily in areas 6a beta, 6a gamma, and in the rostromedial region of area 4--with little labelling in the proreus cortex. In general, the cortical projections to the caudal NRGc and the NRMc were larger than those to the NRPc. More than 25% of the total projections to each of the latter three reticular regions arose from the medial part of area 4. Labelling in the hindlimb regions of area 4 was largest following the NRMc injections and smallest after injections in the NRPc. The projections to the NRPc originated from more medial parts of areas 4 and 6 than did the projections to the caudal region of the NRGc. These results suggest that areas 4 and 6 may be able to differentially activate different regions of the pontomedullary reticular formation depending on the movement that is made and perhaps also on the context of that movement.

Animals↗
PubMed1997

Establishment of serial persistent infections with bovine viral diarrhoea virus in cattle and sheep and changes in epitope expression related to host species.

A pestivirus was transmitted by contact from a persistently infected (P.I.) bullock to pregnant sheep. This resulted in the birth of P.I. lambs, one of which in turn was able to transmit virus by contact to pregnant cattle. Two of these animals gave birth to P.I. calves, from one of which the virus was again transmitted by contact with pregnant sheep, leading to another generation of P.I. lambs. The expression of one or more epitopes on the E2 glycoprotein of the viruses isolated from this series of alternate cattle-sheep transmissions appeared to depend on the host species. Thus, several monoclonal antibodies which bound strongly to, and neutralised, viruses isolated from the bovine hosts, failed to bind or neutralise in the case of sheep isolates. The viral consensus sequences of the E2 gene as well as parts of the 5' untranslated region and of the Npro and capsid genes were compared between the different isolates. This revealed a high degree of genetic stability. However, a single codon change at amino acid position 9 of the E2 gene correlated with and was able to cause the loss of particular epitopes.

Animals↗
PubMed1997

Technology for Psychomotor Skills Testing in Endoscopic Surgery.

Psychomotor research is essential for aptitude-based selection of surgical trainees and sound surgical practice. Two microprocessor-controlled psychomotor testers were developed to evaluate psychomotor skills related to endoscopic surgery. Dundee Endoscopic Psychomotor Tester (DEPT) measures single-handed performance in an endoscopic environment and therefore it can be used to evaluate differing abilities between the right and left hand. Advanced Dundee endoscopic Psychomotor Tester (ADEPT) measures two-handed performance, and consequently it can be used to assess coordinated bimanual endoscopic manipulations. Psychomotor testers provide real-time objective scoring systems that have several aspects of face validity to real endoscopic environment. Studies on medical students have confirmed that objective evaluation of task performance in an endoscopic field is feasible and have documented differences in psychomotor abilities between subjects.

Journal Article↗
PubMed1997

Psychomotor skills for endoscopic manipulations: differing abilities between right and left-handed individuals.

OBJECTIVE: The objective of this study was to compare the psychomotor aptitudes relevant to endoscopic manipulations between right-handed and left-handed subjects. SUMMARY BACKGROUND DATA: There has been little research on the psychomotor performance in relation to minimal access surgery and there are no psychomotor tests to evaluate aspects of psychomotor abilities relevant to endoscopic manipulations. METHODS: A microprocessor-controlled psychomotor tester was developed for objective evaluation of endoscopic performance. The task involved negotiating ten target holes with a probe under videoscopic imaging. Subjects consisted of two groups of 10 medical students: right- and left-handed. After a prestudy familiarization session, each subject performed two test runs with one hand, followed by two runs with the other hand. These test runs were repeated 1 week later. The outcome measures were the total execution time, force on backplate, angular deviations, error rate, and first-time accuracy. RESULTS: A significant difference in the error rate and first time accuracy was observed between subjects (p < 0.001 and p < 0.001, respectively) and between the dominant and nondominant hands (p < 0.001 and p < 0.025, respectively), with no significant change with practice. Right-handed subjects performed better with either hand in terms of error rate (p < 0.001) and first time accuracy (p < 0.001). Practice improved the execution time (p < 0.001) and the degree of angular deviations (p < 0.02). CONCLUSIONS: Right-handed subjects perform less errors and exhibit better first time accuracy. The parameters that improve with practice reflect the positive effect of training, whereas others, such as errors rate and first time accuracy which do not, reflect innate abilities.

Endoscopy↗
PubMed1996

Responses of medullary reticulospinal neurones to stimulation of cutaneous limb nerves during locomotion in intact cats.

The present study was designed to determine whether the transmission of cutaneous afferent information from the limbs to the medullary reticular formation is phasically modulated during locomotion. Experiments were carried out in three chronically prepared, intact cats in which nerve cuff electrodes were placed, bilaterally, on the superficial radial and the superficial peroneal nerves. Thirty-seven reticulospinal neurones (RSNs) were identified by stimulation of their axons in the lumbar spinal cord (L2); 29 of 37 of these were recorded with the cat at rest, 28 of 37 during locomotion and 20 of 37 both at rest and during locomotion. Low-threshold stimulation of the cutaneous nerves evoked excitatory responses in the majority of RSNs both at rest and during locomotion. In the 28 of 37 RSNs recorded during locomotion, it was possible to record the evoked response to stimulation of all four limb nerves, giving a total of 184 tested cases [RSNs tested x number of nerves stimulated x phase of stimulation (swing or stance)]. The responses of most RSNs to cutaneous stimulation were modulated in a phase-dependent manner during locomotion. The maximal responses in most, but not all, cases were obtained during the swing phase of the limb that was stimulated and were largely independent of the discharge pattern of the cell. We interpret this result as indicating that the efficacy of transmission of the afferent information is determined more by the excitability of the spinal relay neurones than by the level of excitability of the RSNs in the brainstem. It is suggested that the base discharge pattern of RSNs might be largely determined by their central afferent input, while peripheral afferent inputs would primarily serve to modify the RSN discharge pattern in response to perturbations.

Afferent Pathways↗
PubMed1996

A microprocessor-controlled psychomotor tester for minimal access surgery.

BACKGROUND: There is little reported information on psychomotor performance in relation to minimal access surgery (MAS). METHODS: A microprocessor-controlled endoscopic psychomotor tester (the Dundee Endoscopic Psychomotor Tester-DEPT) has been developed to evaluate psychomotor aspects of MAS. Experiments were conducted on 20 medical undergraduates to evaluate accuracy and reliability of the tester. RESULTS: The study demonstrated a significant difference between subjects (p < 0.01). It also identified three individuals who enacted 16, 22, and 40 errors while the majority (85%) sustained less errors with a median of 4.5. CONCLUSIONS: DEPT provides a standard, reproducible, objective real-time scoring system. It identifies individuals who cannot adjust to endoscopic viewing and therefore manipulate from endoscopic images.

Clinical Competence↗
PubMed1996

A numerical model of an intensive care ventilator-humidifier system.

Current intensive care ventilator-humidifier systems neither monitor nor adequately control inspired gas humidity. Problems of low delivered humidity and condensation within ventilator circuitry are commonly encountered. To help to address these problems, a numerical model of a complete ventilator-humidifier-patient intensive care system has been developed. The model, based on a finite difference technique, can predict pressures, flow-rates, temperatures and relative humidities at discrete points throughout the system. A comparison of numerical predictions and measurements in a real system is reported. A strong qualitative agreement is demonstrated in all cases studied, and a good quantitative agreement is obtained in most cases. It is concluded that such models could be used to assess methods of controlling ventilator-humidifier systems to prevent the occurrence of condensation. Similar models could be developed for other medical gas delivery systems.

Biomedical Engineering↗
PubMed1996

A comparison of treadmill locomotion in adult cats before and after spinal transection.

1. The aim of this study was to document the kinematics and the electromyographic activity recorded from several muscles during treadmill locomotion in the same cat (N = 4), before and after spinalization by using a chronic implantation method. Because identical experimental and control conditions were used, it was possible to establish similarities and differences in the timing and amplitude of the muscular activity and kinematics under the intact and spinal conditions in the same animal. The data presented in this paper were collected when the cats had fully recuperated a stable locomotor pattern, walking at a constant speed of approximately 0.4 m/s. 2. The adult spinal cats retained many of the general locomotor features and electromyographic (EMG) characteristics seen before transection. However, there were also important differences. 3. There was a reduction in the step length that was principally due to the forward placement of the paw at the onset of the stance. Similarly, there was a decrease in the step cycle duration which was attributed to a reduction of both the stance and swing phases. 4. The overall angular excursions of the hip, knee, and ankle were generally similar, although joints were sometimes more flexed at all phases of the step cycle. In contrast, the overall excursions of the metatarsophalangeal joints was much greater in all four cats after spinalization due to a paw drag during the initial portion of the swing phase that exaggerated the plantarflexion. 5. There was an increase in the EMG amplitude of the flexor muscles at two of three joints (i.e., hip, knee, and ankle) in each cat after spinalization. The change in the EMG amplitude of the extensors did not appear to be as consistent as that observed in the flexor muscles. When looking at each cat individually, the postspinalization extensor activity decreased at two of three joints in two cats, whereas the opposite was true for the other two cats. 6. There was a delay in the onset of the knee flexor (semitendinosus) activity while the ankle dorsiflexor (tibialis anterior) activity started earlier with respect to the beginning of the swing phase. The onset of hip flexors was somewhat more variable. This change in the timing of flexor activity was most probably responsible for the paw drag at the onset of the swing phase. 7. The present results reveal that despite the few differences, the spinal cord and the hindlimbs afferents are capable of generating very good locomotor patterns with almost normal kinematics and EMG characteristics.

Animals↗