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Biomedical subjects

A J Hodgson

Publications and source records attributed to A J Hodgson.

At least 19 recordsLinked to original sources
PubMed2005

Correlating motor performance with surgical error in laparoscopic cholecystectomy.

BACKGROUND: Analysis of motor performance in minimally invasive surgery (MIS) is a new field with applications in surgical training, surgical simulators, and robotics. Force/torque and derivatives of tool tip position (velocity, acceleration, and jerk) are examples of measures of motor performance (MMPs). Few studies have measured MMPs or have correlated MMPs with surgical performance during MIS on humans. The objectives of this study were to determine the feasibility of a novel multimodal system to quantify MMPs in laparoscopic cholecystectomy and to attempt to correlate MMPs with the magnitude of error as a measure of surgical performance. METHODS: Novice and expert surgeons performed laparoscopic cholecystectomies in two groups of three patients each. MMPs were obtained using a combination of optical and electromagnetic tool tip tracking and a force/torque sensor on a modified Maryland dissector. Error scores for laparoscopic cholecystectomy were calculated using a previously validated system. Novice and expert measurements were compared, and correlations were made between error scores and MMPs. RESULTS: Error scores were similar between novices and experts. Novice surgeons had a significantly greater mean velocity (566 +/- 83 vs 85 +/- 32 mm/s, p = 0.006) and acceleration (2,600 +/- 760 vs 440 +/- 174 mm/s2, p = 0.050) compared to expert surgeons. Force (16.5 +/- 4.6 vs 18.3 +/- 6.0 N, p = 0.829), position (121 +/- 25 vs 135 +/- 72 mm, p = 0.863), and jerk (19,600 +/- 7,410 vs 2,430 +/- 367 mm/s3, p = 0.138) were similar between groups. A positive correlation was found in novice surgeons between error score and jerk (Pearson correlation, 0.999; p = 0.035). CONCLUSIONS: It is feasible to quantify MMPs in laparoscopic cholecystectomy. Novice and expert surgeons can be differentiated by MMPs; moreover, there may be a positive correlation between jerk and error score in novice surgeons.

Adult↗
PubMed2003

Influence of interaction force levels on degree of motor adaptation in a stable dynamic force field.

Studies have shown that the point-to-point reaching movements of subjects seated in a dark, rotating room demonstrate errors in movement trajectories and endpoints, consistent with the direction of the Coriolis force perturbations created by room rotation. Adaptation of successive reaches and the presence of postrotation aftereffects have indicated that subjects form internal models of the Coriolis field dynamics in order to make appropriate movement corrections. It has been argued that these findings are inconsistent with predictions of peripheral stabilization assumed in equilibrium-point models of motor control. A possibility that has been raised, however, is that the Coriolis field findings may in fact stem from changes in control commands elicited due to the magnitude and destabilizing nature of the Coriolis perturbations. That is, it has been suggested that a perturbation threshold exists, below which central reactions are not necessary in order to maintain movement stability. We tested the existence of a perturbation threshold in normal-speed reaching movements. Twelve normal human subjects performed non-visually guided reaching movements while grasping a robotic manipulandum. The endpoints and trajectory deviations of their movements were measured before, during, and after a position-dependent force field (similar to a Coriolis field in terms of the time history of applied forces) was applied to their movements. We examined the responses to a range of perturbation field strengths from small to considerable. Our experimental results demonstrated a substantial adaptation response over the entire range of perturbation field magnitudes examined. Neither the amount of adaptation after 5 trials nor after 25 trials was found to change as disturbance magnitudes decreased. These findings indicate that there is an adaptive response even for small perturbations; i.e., threshold behavior was not found. This result contradicts the assertion that peripheral stabilization mechanisms enable the central controller to ignore small details of peripheral or environmental dynamics. Our findings instead point to a central dynamic modeler that is both highly sensitive and continually active. The results of our study also showed that subjects were able to maintain baseline pointing accuracies despite exposure to perturbation forces of sizeable magnitude (more than 7 N).

Adaptation, Physiological↗
PubMed2002

Biomechanics of reaching: clinical implications for individuals with acquired brain injury.

PURPOSE: Outline the biomechanics of reaching both in healthy individuals and in individuals with acquired brain injury (ABI), and to discuss the clinical implications for using valid biomechanical models to assess reaching. METHODS: A review of current literature, including a MEDLINE search using keywords of reaching, ABI, stroke, biomechanics and motor control. RESULTS: Current assessments of the upper extremity in ABI are focused on single-joint characteristics of range of motion, strength and spasticity. However, reaching is a functional multijoint task requiring interjoint coordination in addition to feedback and feedforward control to position the hand optimally at a desired location so that it may interact with the environment. From the literature, biomechanical measures of reaching such as movement time, movement distance and interjoint coordination have been shown to discriminate changes to hand path quality following brain injury. These measures have also been shown to correlate with measures of sensorimotor function (e.g. Fugl-Meyer) in the upper extremity. CONCLUSIONS: Further development of reliable and valid multi-joint biomechanical evaluations is required, particularly for natural and goal-oriented reaching movements. The biomechanical assessment of reaching in ABI can provide an understanding of the specific deficits in physiological structures or motor planning underlying altered reaching ability, assist in the evaluation of new therapies, and characterize the recovery process following ABI.

Arm↗
PubMed2001

Automated high-frequency posture sampling for ergonomic assessment of laparoscopic surgery.

BACKGROUND: Despite widespread acknowledgement that strain injuries do occur to surgeons, ergonomic assessments in minimally invasive surgery are comparatively rare. Current assessment techniques rely on labor-intensive manual recording techniques, so there is a need for an automated system. METHODS: We used an optoelectronic measurement system to make postural measurements at frequencies of ~5 Hz and then converted these measurements to ergonomic stress scores using a modified Rapid Upper Limb Assessment (RULA) method. RESULTS: We successfully recorded postures at least once per second during 96% of the time the surgeon was performing tissue manipulation tasks. We found that the ergonomic stress scores were comparatively high throughout the procedure, particularly for the wrist. CONCLUSION: An automated high-frequency postural measurement system is feasible for making ergonomic assessments in an intraoperative setting. Such a system will also be a critical component in validating surgical simulations for use in training and credentialing surgeons and in designing and evaluating equipment.

Biomechanical Phenomena↗
PubMed1999

Polypyrrole-heparin composites as stimulus-responsive substrates for endothelial cell growth.

Heparin is a potent anticoagulant which can be immobilized on biomaterial surfaces to increase their hemocompatability. In the present work, we have electrochemically synthesized composites comprising heparin and the electrically conducting polymer polypyrrole. The incorporation and exposure of heparin were controlled by varying key conditions of polymer synthesis (i.e., applied current and synthesis time). The resulting composite polymers were electroactive after synthesis and the amount of heparin exposed in the polymer could be increased (up to threefold) by switching the polymers from their oxidized to reduced states. Polymer reduction was achieved by either application of negative potentials (-0.4 to -0.7 V for 90 s) or exposure to aqueous reductant (0.1M sodium dithionite for 30 min). Heparin-polypyrrole composites remained stable after autoclaving, displaying no significant loss of electroactivity, and had a shelf life of at least 2 years postautoclaving. Finally, the composites were found to be excellent substrates for the growth of human endothelial cells.

Biocompatible Materials↗
PubMed1999

The effects of physical constraints in laparoscopic surgery.

In order to provide guidelines for the development and evaluation of advanced laparoscopic instrumentation (including teleoperated devices), we assessed the impact of constrained motion on surgeons' ability to perform standardized pick-and-place and suturing tasks when using an emulation of a perfectly transparent teleoperator under direct, binocular vision. The surgeons' performance when using the emulator represents an upper bound on performance using any conceivable teleoperator with one-to-one force and motion scaling. Our analysis examines the mean differences in task completion time between three open tool configurations and two laparoscopic tool configurations with various degrees of freedom (DOFs). Fifteen laparoscopic surgeons participated in the study. We show that avoiding reversed hand and tool motions and adding DOFs significantly improves suturing performance. In the pick-and-place task, avoiding the reversed motions also improves performance, but adding DOFs to an open tool configuration does not. For both tasks, subjects who use open tools constrained to four DOF complete their tasks in approximately 38% less time than when using standard four-DOF laparoscopic tools. The marginal benefit to overall surgical time of adding two additional degrees of freedom is likely to be small (approximately 2%), although surgeons may then feel confident in attempting more difficult procedures.

Analysis of Variance↗
PubMed1999

Human endothelial cell attachment to and growth on polypyrrole-heparin is vitronectin dependent.

Composite materials comprised of the electrically conducting polymer, polypyrrole, with a variety of biologically active molecules, e.g. proteins or polysaccharides, are emerging as a novel class of "smart" biomaterials. In the present work we have studied the utility of a heparin-polypyrrole composite as a substrate for human umbilical vein endothelial cell (HUVEC) growth. We found that the polymer composites were well suited to support cell attachment and growth; displaying low surface hydrophobicity (water contact angle of approximately 20 degrees ) and roughness, Rq of approximately 10-12 nm. Doubling times for HUVEC on heparin-polypyrrole were greater than observed for gelatin-coated tissue culture polystyrene (44 and 36 h, respectively), however, the cells did proliferate to cover the polymer in an even monolayer. The initial mechanism of attachment and subsequent proliferation of HUVEC on heparin-polypyrrole was critically dependent on the presence of the serum adhesion glycoprotein vitronectin. Polymers that were composed of polypyrrole and sodium nitrate were more hydrophobic than heparin-polypyrrole and they did not support HUVEC growth. Given the relative ease with which these polymer composites can be electrochemically synthesized, the diverse range of cellular "signal agents", e.g. growth factors, that can be incorporated within them, and the high degree of control that can be achieved in the release-surface exposure of these agents, we suggest that polypyrrole composites could serve a useful role as "smart" biomaterials in the near future.

Journal Article↗
PubMed1995

Lowering hospital charges in the trauma intensive care unit while maintaining quality of care by increasing resident and attending physician awareness.

OBJECTIVE: The goal of this study was to determine if trauma intensive care unit (TICU) charges could be reduced through informal daily bedside resident-attending physician discussions regarding relative patient costs of diagnostic and therapeutic alternatives. DESIGN: This was a prospective pre- and postinterventional study. SETTING: The study took place in a TICU in a level I, community-based, university-affiliated teaching hospital. PATIENTS: Ninety-one consecutive patients were admitted to the TICU during a 6-month period. MATERIALS AND METHODS: The TICU charges were tracked over two consecutive 3-month periods. The first 3 months served as control. No attempt was made to alter cost of care, and residents were unaware that a study was in progress. During the ensuing 3-month period, attendings explicitly discussed with residents relative costs of diagnostic and therapeutic interventions in an attempt to lower charges. Composition of the surgical trauma team remained constant throughout the study. MEASUREMENT AND MAIN RESULTS: The median and mean age, Injury Severity Score, intensive care unit length of stay, and sex ratio were not statistically different between the two study groups. Total median daily charges of the postintervention group were reduced over the control group by $818/intensive care unit day (p = 0.0002). The major categories in which charges were reduced included medications ($151/day, p = 0.003), laboratory tests ($120/day, p = 0.072), chest x-ray films ($61/day, p = 0.001), respiratory therapy ($185/day, p = 0.21), and miscellaneous charges ($141/day, p = 0.055). Mortality rates and number of major complications were not statistically different between groups. CONCLUSIONS: Increased awareness of cost factors and specific attempts to achieve patient cost reduction resulted in a demonstrable decrease in daily TICU charges, without compromising the quality of care.

Adult↗
PubMed1994

A proposed etiology for tourniquet-induced neuropathies.

Pneumatic tourniquets are used in limb surgery to provide a bloodless operating field, but they can also cause nerve injuries. These injuries are thought to be mechanically induced, although no previous work has quantified such a mechanism. This paper hypothesizes that axial compression of the nerve leads to damage at the nodes of Ranvier and presents simulation results based on this hypothesis which are in substantial agreement with clinical observations.

Evaluation Studies as Topic↗
PubMed1994

Considerations in applying dynamic programming filters to the smoothing of noisy data.

Dynamic programming techniques are useful in smoothing and differentiating noisy data signals according to an optimization criterion and the results are generally quite robust to noise spectra different from that assumed in the construction of the filter. If the noise properties are sufficiently different, however, the generalized cross-validation function used in the optimization can exhibit either multiple minima or no minima other than that corresponding to an insignificant amount of smoothing; in these cases, the smoothing parameter desired by the user typically does not lie at the global minimum of the generalized cross-validation function, but at some other point on the curve which can be identified heuristically. I present two cases to demonstrate this phenomenon and describe what measures one can take to ensure that the desired smoothing parameter is obtained.

Algorithms↗
PubMed1990

Cholera toxin B-gold, a retrograde tracer that can be used in light and electron microscopic immunocytochemical studies.

The purpose of this study was to test whether a new retrograde tracer, the B subunit of cholera toxin conjugated to colloidal gold particles (CTB-gold), was taken up and transported by neurons in the central nervous system of the rat. Retrograde transport of CTB-gold was assessed from axon terminals, from damaged nerve fibers, and from axons of passage. For light microscopy, CTB-gold was visualized by silver intensification; for electron microscopy, sections were silver-intensified with or without subsequent gold toning. Retrogradely transported CTB-gold was detected in neurons after survival times of 12 hours to 42 days and appeared as black punctate deposits in perikarya and proximal dendrites at the light microscope level. Ultrastructurally, the deposits were usually associated with lysosomes. Injections of CTB-gold into the caudal ventrolateral medulla or into the lateral horn of the spinal cord gave small well-defined injection sites and resulted in retrograde labelling in medullary neurons in the same locations as similarly placed injections of wheat germ agglutinin-horseradish peroxidase. When injected into the superior cervical ganglion, CTB-gold was transported to nerve cell bodies in the spinal cord, but application of CTB-gold to the cut cervical sympathetic trunk did not label neurons in the spinal cord. Injection of CTB-gold into the nodose ganglion retrogradely labelled neurons in the dorsal motor nucleus of the vagus and the nucleus ambiguus. CTB-gold was not transported anterogradely from injections sites within the medulla. Nerve fibers and cell bodies containing neuropeptides, monoamines, or neurotransmitter-synthesizing enzymes were readily immunostained after silver intensification of retrogradely transported CTB-gold. Immunoreactivity for neuropeptides and enzymes was also demonstrated ultrastructurally after silver intensification and gold toning. These results show that CTB-gold is retrogradely transported from nerve terminals and fibers of passage but not from damaged axons. CTB-gold gives well-localized injection sites and persists in neurons for weeks. Transported CTB-gold is easily visualized and its detection is compatible with light and electron microscopic immunocytochemistry. These properties make CTB-gold a valuable tool for studying the connectivity and neurochemistry of pathways in the central nervous system.

Animals↗
PubMed1988

Monoclonal alkaline phosphatase-anti-alkaline phosphatase (APAAP) complex: production of antibody, optimization of activity, and use in immunostaining.

A mouse monoclonal antibody, FMC55 (an IgG1), to alkaline phosphatase was prepared and evaluated in immunostaining. Clones producing antibody to alkaline phosphatase were selected using a micro-ELISA which identified antibodies forming active soluble complexes (APAAP) with the enzyme. Conditions that influenced the formation of the complex were investigated by using a quantitative assay in which the complex was captured by a bridging anti-mouse antibody. The ratio of FMC55 to enzyme had a major influence on the activity of the complex. Although all complexes had some activity, those that contained excess antibody had reduced ability to bind to anti-mouse antibody because of competition with excess unlabeled antibody. The optimal complex was formed with 3 micrograms of FMC55 per unit of enzyme. This complex contained neither free enzyme nor free antibody. The molecular weight by gel permeation chromatography was 600,000, giving a composition of two enzyme and two antibody molecules or one enzyme and three antibody molecules. The size of the complex was not altered by adding excess antibody or excess enzyme. Immunoblotting showed that FMC55 bound only to the Mr 140,000 homodimeric form of alkaline phosphatase. The APAAP complex was used in combination with biotin-streptavidin-peroxidase reagent to detect two antigens labeled with two different mouse monoclonal antibodies in the same tissue preparation.

Alkaline Phosphatase↗
PubMed1987

Antigen expression during early human granulocyte development studied with immuno-electron microscopy.

Expression of the hapten fucosyl-N-acetyllactosamine was correlated with ultrastructural development in human granulocyte precursors using the monoclonal antibody FMC 10 with immunogold techniques. The antigen was detectable from the myeloblast/early neutrophilic promyelocyte stage onwards and was associated with striking development of the rough endoplasmic reticular system. In addition, low levels of labelling were seen on monocytes, eosinophils and some basophil precursors. Contraction and alignment of the cisternae of the rough endoplasmic reticulum during the promyelocyte stage of neutrophilic differentiation gave the appearance of a plasma cell. However, on closer examination it was apparent that true plasma cells did not react with this antibody.

Antibodies, Monoclonal↗
PubMed1986

The relationship between GABA immunoreactivity and labelling by local uptake of [3H]GABA in the striate cortex of monkey.

An antiserum to GABA was used in the macaque monkey to determine whether neurons that accumulate exogenously applied [3H]GABA in vivo are also immunoreactive for GABA. Following the injection of [3H]GABA into different laminae of striate cortex in two untreated animals and in one animal treated with amino-oxyacetic acid, selective accumulation of the labelled amino acid was demonstrated in perikarya by autoradiography. Radiographically labelled neurons (n, 519) and their unlabelled neighbours were tested in consecutive 0.5 micron thick sections by immunocytochemistry for GABA immunoreactivity. Injection of [3H]GABA did not increase the number of neurons showing GABA immunoreactivity. On the contrary many of the cells that accumulated [3H]GABA were immunonegative. These neurons were mostly located in layers IVC and VA following [3H]GABA injection into layers II-III, and in layers upper III and II following injection into layers V and VI. A comparison of the position of these neurons with known local projection patterns in the striate cortex of monkey suggests that GABA-immunonegative neurons may nevertheless become labelled by [3H]GABA if most of their local axon terminals fall within the injection site. The interlaminar projection of GABA-immunopositive neurons, which probably contain endogenous GABA, could be deduced from the position of the [3H]GABA injection site that leads to their autoradiographic labelling. Although the present study confirmed our previous results on the interlaminar connections of neurons that accumulate [3H]GABA, it demonstrated that [3H]GABA labelling alone may not be a sufficient criterion to assess the GABAergic nature of neurons in the striate cortex of monkey.

Animals↗
PubMed1985

Identified axo-axonic cells are immunoreactive for GABA in the hippocampus and visual cortex of the cat.

Chandelier or axo-axonic cells (AACs) are specialized interneurons terminating on the axon initial segments of pyramidal neurons. Two AACs have been localized by Golgi impregnation, one in the CA1 region of the hippocampus and one in the visual cortex of cat, for structural analysis and for the identification of their transmitter. They had 323 and 268 terminal bouton rows, respectively, probably making synapses with an equal number of initial segments. The distribution of the dendrites of the hippocampal cell was strikingly similar to that of pyramidal cells suggesting a similar input. Using an antiserum to GABA and postembedding GABA-immunocytochemistry, developed for Golgi-impregnated neurons, both cells were found to be GABA-immunoreactive. The strategic location of their synapses and the presence of GABA in AACs suggest that in normal cortical tissue they play a major role in GABA-mediated inhibition.

Animals↗