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Biomedical subjects

K L Cummins

Publications and source records attributed to K L Cummins.

18 recordsLinked to original sources
PubMed1987

Speech distortion measures for hearing aids.

Advances in digital technology and the associated introduction of new forms of distortion led us to investigate supplementary measures of electroacoustic distortion for hearing aids. Mathematical techniques were used to formulate a working model in which the hearing aid acts as a time varying linear filter. This model embodies an approach to separating distortion into perceptually relevant and irrelevant categories. Digitized speech was converted to analog form, routed through a commercial hearing aid, and the output of the aid was redigitized and stored. For a given input signal, output speech waveforms were then compared to the model output and performance measures were derived. Distortion was plotted in three dimensions to permit interpretation with respect to time, frequency, and amplitude. These results provide a more comprehensive and general format for the analysis of hearing aid distortion.

Acoustics↗
PubMed1985

Electrical properties of commercial concentric EMG electrodes.

Five electrical characteristics--impedance, broadband noise generation, line interference sensitivity, signal distortion, and common-mode conversion--were measured in five electromyographic (EMG) concentric needle electrodes (CNEs) from each of six commercial manufacturers. Untreated CNEs showed considerable variation in impedance and broadband noise characteristics, both within and among manufacturers. Electrolytic treatment reduced impedances by a factor between 1.5 and 4.0, and lessened within-manufacturer variability. Average post-treatment impedances at 100 Hz ranged from 31 to 436 kOhms, reflecting in part the range of core surface areas. Treatment also reduced the broadband noise to the level of the instrumentation noise for all but the highest impedance CNEs. Distortion and common-mode conversion were negligible for the lowest impedance CNEs. Line interference from a nearby power cord was completely suppressed only by those CNEs with fully shielded cables, and then only when the electromyographer also was grounded; there was no measurable benefit when the shield was driven, as opposed to grounded. We conclude that there are consistent differences in the properties of CNEs from different manufacturers, reflecting differences in materials, design, and construction; electrolytic treatment temporarily improves the performance of all CNEs, and tends to lessen the differences among them, most likely through a surface electrochemical effect; and both active and passive cable shields are effective in reducing extraneous line interference.

Electrochemistry↗
PubMed1983

Studies of diabetic polyneuropathy using conduction velocity distribution (DCV) analysis.

The distributions of nerve fiber conduction velocities (DCVs) derived from the median nerves of 29 adult diabetic patients (mean age, 52.1 +/- 12.3 years) with mild or no symptoms or signs of polyneuropathy were compared with DCVs from 34 age-appropriate normal subjects. Ten patients (34%) had normal findings (type A DCVs). In the 19 patients (66%) with abnormal DCVs, defined as 10% or more of the DCV area falling outside the normal 95% confidence limits, two distinct patterns of DCV alteration were observed: type B DCVs (11 patients) showed reduced DCVmax, DCVmean, and DCVpeak, together with reduced DCVrange (narrow profile); whereas type C DCVs (8 patients) had reduced DCVmax, DCVmean, DCVpeak, and DCVmin, with normal DCVrange (broad profile). It is proposed that type C DCV represents a more advanced form of type B and that both reflect selective dysfunction of the fastest conducting (presumably largest-diameter) fibers in the nerve trunk. DCVmax was consistently greater than conventional measures of "maximal" CV in all patient subgroups. Patients with abnormal DCVs had higher incidence of mild neuropathic symptoms (15 of 19 versus 4 of 10, p less than 0.01) and greater insulin dependence (11 of 19 versus 1 of 10, p less than 0.001). Serial studies in 10 patients showed, at most, small degrees of change in conduction properties over relatively short intervals (1 to 9 months).

Action Potentials↗
PubMed1982

Modulation of axonal excitability mediated by surround electric activity: an intra-axonal study.

Intra-axonal recordings were obtained in vitro from frog sciatic nerve axons. Adjusting whole nerve stimulation current to just subthreshold for the impaled axon elicited triphasic threshold changes in that axon. Threshold changes were determined by direct intra-axonal current application. Graded subthreshold depolarizations were present in many axons during the passage of action potentials in surrounding axons. When nerve branches were stimulated and axon recordings were obtained from the main nerve trunk, both branches, the one that activated the impaled axon and the one that did not, elicited threshold changes in the impaled axon. These data indicate on a cellular level that impulse activity in an intact nerve bundle can modulate the excitability of adjacent nonactivated fibers.

Animals↗
PubMed1982

Conduction velocity distributions of the human median nerve: comparison of methods.

We have estimated the distribution of conduction velocities (DCV) of large myelinated fibers in the median nerves of 10 normal subjects and a patient with amyotrophic lateral sclerosis (ALS) who had a de-efferented hand, using three different computer-based methods: a 2CAP method, which tests both motor and sensory nerve fibers; and 2MAP and CMAP methods, which test only the alpha motor fibers. The magnitudes of the parameters DCVmax, DCVmean, DCVpeak, and DCVrange all were very similar in the two motor estimations, but all were significantly higher (P less than 0.001 in each case) in the mixed nerve estimates; the differences presumably represent the properties of the faster-conducting sensory fiber population. The 2CAP DCV from the de-efferented nerve resembled those from normal mixed nerve. Compared with DCV analysis, conventional measures of maximal motor and sensory CV were found to be relatively poor indices of the conduction properties of their respective large, myelinated, nerve fiber populations.

Adult↗
PubMed1981

Nerve fiber conduction velocity distributions: studies of normal and diabetic human nerves.

We have assessed the clinical applicability of a previously described new method for analyzing the distribution of conduction velocities (DCV) in peripheral nerve. Surface-recorded median sensorimotor compound action potentials (CAPs) were found to contain contributions from classes of fibers conducting between 25 and 80 m/sec in the elbow-to-axilla segment. Test-retest correlation coefficients ranged from 0.91 to 0.98. Increasing stimulus intensity recruited additional fiber activity into the CAP with relative preferential activation of faster-conducting fibers at lower stimulus levels. Changes in limb temperature altered the conduction velocity of all fiber classes 4% per degree Celsius. A comparison of fiber diameter distribution and DCVs in a normal sural nerve gave a correlation of 0.70 over the range of 7 to 12 mu. Diabetic patients with minimal or no clinical polyneuropathy showed varying degrees of DCV shift toward the slower conduction velocities, sometimes even in the face of normal conventional nerve conduction studies. These findings indicate that the DCV may be considered the electrophysiological counterpart--not equivalent--of the fiber diameter distribution, with the capacity to distinguish subtle differences in conduction properties of normal and diseased human nerves.

Adult↗
PubMed1981

Nerve conduction velocity distributions: a method for estimation based upon two compound action potentials.

A model was presented describing the nerve-bundle CAP in terms of its constituent SFAPs. The model has a general structure capable of accommodating a large variety of specific assumptions regarding the nature of the CAP. Using this model, several techniques were presented for estimating the DCV of a nerve bundle. One method, refered to as the 2CAP method, was presented in detail. This method does not require explicit knowledge of the SFAP waveshapes in order to yield an estimate of the DCV, but does require that the CAP be recorded at two sites along the course of the nerve. In order to evaluate the clinical utility of the 2CAP method of DCV analysis, the following factors were studied: reproducibility, sensitivity to temperature and stimulus intensity, and variation within a normal population. The results indicate that the 2CAP method, when controlled for stimulus intensity and temperature, provides a reproducible measure of nerve function with the capacity to distinguish subtle differences in conduction properties of normal human nerves. Further application of this technique to patients with diabetes mellitus indicates that the DCV can demonstrate subtle electrophysiologic abnormality, even in patients with normal conventional nerve conduction studies. Although DCV analysis cannot accurately characterize all types of nerve abnormalities (such as focal nerve lesions), it will likely become a tool for earlier detection and more accurate diagnosis of many nerve diseases, and provide a key to the better understanding of the dynamics of nerve growth, development, damage, healing, and response to treatment.

Action Potentials↗
PubMed1980

Use of cerebral evoked potentials to evaluate spinal somatosensory function in patients with traumatic and surgical myelopathies.

Cerebral somatosensory evoked potentials (SEP's) were elicited by electrical stimulation of the median nerve in the arm (SEPA) and of the posterior tibial nerve in the leg (SEPL) in 23 patients with incomplete localized lesions (including traumatic injuries, neoplasms, vascular malformations and infarcts) of the low cervical, thoracic, or lumbar spinal cord. In eight of 46 attempts (left and right sides), SEPL could not be recorded. Of the remaining 38 sides, spinal somatosensory conduction velocity (SSCV, indirectly estimated) was abnormally slow (less than 35 m/sec) in 20, and the amplitude of SEPL relative to SEPA (L:A ratio) was abnormally low (less than 0.5) in 20 (p less than 0.001 in each case, compared to normal controls). All three criteria yielded a combined 72% incidence of abnormality, correlating best with impairment of joint position sense. Serial postoperative studies in four cases documented an increase in the SSCV and L:A ratio following spinal decompression. These results demonstrate that the latency and amplitude characteristics of the cerebral SEP's from arm and leg permit quantitative evaluation of the functional status of the spinal somatosensory system.

Adult↗
PubMed1979

Nerve fiber conduction-velocity distributions. I. Estimation based on the single-fiber and compound action potentials.

A method is described for estimating the distribution of nerve-fiber conduction velocities in a nerve bundle. This method is based on a detailed general model of the nerve bundle compound action potential, which is characterized as a weighted sum of delayed single-fiber action potentials. The non-iterative estimation method is applied to two examples taken from existing literature, demonstrating the similarity of conduction velocity and fiber diameter distributions, sensitivity of the estimate to variations in important model parameters, and applicability to the differentiation of normal and abnormal nerve function.

Action Potentials↗
PubMed1979

Nerve fiber conduction-velocity distributions. II. Estimation based on two compound action potentials.

A method is presented for estimating nerve fiber conduction velocity distributions from non-invasive measurements of the compound action potential at two distinct locations separated by a known distance along the nerve bundle. This method is based on a model of the compound action potential as a weighted sum of delayed single-fiber action potentials, but does not require explicit knowledge of the single-fiber action potential wave shapes in order to yield a unique estimate of the conduction velocity distribution. Illustrative examples are presented from normal and diseases nerves. This method appears to have clinical applications in the electrophysiological assessment of peripheral nerve function.

Action Potentials↗
PubMed1978

Electrophysiological localization of central somatosensory lesions in patients with multiple sclerosis.

Somatosensory evoked potentials (SEPs) and selected indices of peripheral nerve function were compared in 30 multiple sclerosis (MS) patients and 15 normal controls. A high incidence of delayed SEP onset was observed in the MS patients, correlating with sensory loss--particularly of joint position and vibration sense. Using a method for deriving an indirect estimate of spinal cord conduction velocity, the longitudinal level of the sensory disturbance could in many cases be localized either to the spinal or to the supraspinal segment (or both) of the somatosensory pathway. Abnormally low spinal conduction velocity correlated with clinical judgements of spinal cord malfunction, but abnormalities were encountered also in some cases with no clinical evidence of myelopathy. Electrophysiological studies can contribute to the assessment of patients with suspected MS by demonstrating conduction abnormalities in specific segments of the somatosensory pathway.

Adolescent↗