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Biomedical subjects

J Cadwell

Publications and source records attributed to J Cadwell.

8 recordsLinked to original sources
PubMed1996

A new method using neuromagnetic stimulation to measure conduction time within the cauda equina.

Using principles derived from electric field measurements and studies of phrenic nerve in vitro, neuromagnetic stimuli in humans were predicted to excite selective low threshold sites in proximal and distal cauda equina. Physical models, in which induced electric fields were recorded in a segment of human lumbosacral spine immersed in a saline filled tank, supported this prediction. Conclusions from the model were tested and confirmed in normal human subjects. Ipsilateral motor evoked potentials were elicited in lower limb muscles and striated sphincters by magnetic coil (MC) stimulation of both proximal and distal cauda equina. Over proximal cauda equina a vertically oriented MC junction and cranially directed induced current elicited a newly identified compound muscle action potential (CMAP). The F response latency and lack of attenuation when the target muscle was vibrated suggest that the proximal response is a directly elicited M response arising near or at the rootlet exit zone of the conus medullaris. Over distal cauda equina, lumbar roots were optimally excited by a horizontally oriented MC junction, and sacral roots by an approximately vertically oriented MC junction, eliciting CMAPs with similar appearance but shorter latency consistent with the known intrathecal lengths of the lower lumbar and sacral nerve roots. The induced current was usually most effective when directed towards the spinal fluid filled thecal sac. Normal subjects showed stable CMAP onset latencies elicited at proximal and distal cauda equina despite wide variation in amplitude. Thus, cauda equina conduction time can be directly calculated. This new method may improve the detection and classification of peripheral neuropathies affecting lower limbs and striated sphincters.

Adult↗
PubMed1993

The use of a cap-shaped coil for transcranial magnetic stimulation of the motor cortex.

A cap-shaped coil is introduced as a superior design for inducing transcranial magnetic motor evoked potentials for spinal cord monitoring. Evaluation of the magnetic characteristics of the cap coil showed higher induced electrical fields at and below the depth of the cortical surface, compared to a 9-cm, butterfly-shaped coil. Twenty normal adults were stimulated with the cap coil and a 9-cm round coil in three positions. Compound muscle action potentials were recorded from the left and right abductor digiti minimi and anterior tibialis muscles. The cap coil induced potentials with higher intensities and lower variability between consecutive stimuli. The cap coil was also more able to simultaneously induce motor evoked potentials from the four muscles studied. This coil design should provide superior means of inducing transcranial magnetic motor evoked potentials in multiple muscles.

Arm↗
PubMed1991

Optimizing magnetic stimulator design.

Optimal magnetic stimulation depends on application and design. The best design generates the desired depolarization current in the desired area with acceptable current speed. Power and cooling requirements, electrical and mechanical safety, stimulus rate, reliability, and ease of use are additional considerations. By understanding the interactions among these requirements, suitable choices are made. Magnetic stimulation requires moving enough charge through an electrically sensitive tissue to depolarize it reliably. Usually there is a need to depolarize a delimited volume of tissue and to repeat the depolarization at convenient intervals. A good design achieves the focality and speed needed for the application. Since the applications for magnetic stimulation are varied, however, the designs for the stimulators also will be different, and defining the application (or applications) is, therefore, a requirement for optimization.

Electric Conductivity↗
PubMed1990

Focal magnetic coil stimulation reveals motor cortical system reorganized in humans after traumatic quadriplegia.

A figure of '8' magnetic coil (MC) was used to stimulate focally the motor cortex of two adult, traumatic quadriplegics and three normal adults. The two patients were injured approximately 2 years previously and had intense physiotherapy, including biofeedback training of biceps and deltoid muscles, respectively, which were the most caudal muscles spared. The focal MC elicited compound motor action potentials (CMAPs) from these muscles from a much wider area of scalp than in the normal subjects. Latency of biceps and deltoid CMAPs were inversely related to CMAP amplitude. A reorganization of the motor cortical projection system is inferred, in which areas normally eliciting digit movements instead activate muscles in quadriplegics just above the spinal level. The reorganization applies also to the central sense of movement normally elicited by focal frontal cortex stimulation. Possible mechanisms of the reorganization and an implication for rehabilitation are discussed.

Action Potentials↗
PubMed1990

Absence of HIV infection in blood donors with indeterminate western blot tests for antibody to HIV-1.

To determine whether apparently healthy persons who have had repeatedly reactive enzyme immunoassays and an indeterminate Western blot assay for antibody to the human immunodeficiency virus type 1 (HIV-1) are infected with HIV-1 or HIV-2, we studied 99 such volunteer blood donors in a low-risk area of the country. The subjects were interviewed about HIV risk factors. Coded blood specimens were tested again for HIV-1 antibody (by two different enzyme immunoassays, a Western blot assay and a radioimmunoprecipitation assay) and for HIV-2 antibody by enzyme immunoassay, for HIV-1 by the serum antigen test, for HIV-1 by culture, for human T-cell leukemia virus Type I or II antibody by enzyme immunoassay, and for sequences of HIV DNA by the polymerase chain reaction. Of the 99 blood donors, 98 reported no risk factors for HIV-1 infection; 1 donor had used intravenous drugs. After a median of 14 months (range, 1 to 30) from the time of the initial test, 65 subjects (66 percent) were still repeatedly reactive for HIV-1 antibody on at least one immunoassay. In 91 subjects (92 percent) the Western blot results were still indeterminate, whereas in 8 they were negative. No donor met the criteria for a positive Western blot assay for HIV-1, and none had evidence of HIV-1 or HIV-2 infection on culture or by any other test. We conclude that persons at low risk for HIV infection who have persistent indeterminate HIV-1 Western blots are rarely if ever infected with HIV-1 or HIV-2.

Adult↗
PubMed1990

Magnetoelectric stimulation of human motor cortex: normal values and potential safety issues in spinal cord injury.

Upon magnetoelectric stimulation (MES) of the motor cortex, maximal amplitude and minimal latency of compound muscle action potentials were recorded for four limbs in 20 able-bodied volunteers after ten sequential stimulations. The ratio of maximal cortical to maximal peripheral compound muscle action potential was calculated. Standard statistical parameters were calculated for values from each limb. A paired t-test revealed a statistically significant difference in lower extremity side-to-side amplitude. Regression analysis of patient height vs upper extremity and lower extremity latency demonstrated a strong correlation: r = .720 and r = .601, respectively. A pendulum model demonstrated that a miniscule amount of energy is imparted onto metallic fixation devices by the magnetic coil, but no significant paraspinal activity could be measured in any of five volunteers upon stimulation of the motor cortex. This study has established a normal MES data base that might be useful in evaluating spinal cord injured patients. It has also demonstrated that initial safety concerns about the use of MES in this population are likely unfounded.

Adult↗
PubMed1983

Determinants of community placement of institutionalized mentally retarded persons.

A systematic examination of the decision process used when deinstitutionalizing mentally retarded persons was undertaken to determine what criteria, if any, institutional review teams employed when making placement recommendations. A multivariate analysis of variance and a discriminant analysis revealed that demographic and Adaptive Behavior Scale (ABS) measures varied significantly with placement recommendations for skill development homes, group homes, small intermediate facilities, and large intermediate facilities. In general, higher functioning residents were placed in less restrictive settings. Specific differences among residents placed in skill development homes and group homes were examined. Implications for preparing institutionalized residents for community placement were drawn and directions for future research outlined.

Adaptation, Psychological↗