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Biomedical subjects

J F Jabre

Publications and source records attributed to J F Jabre.

At least 19 recordsLinked to original sources
PubMed1997

Hazardous waste and neurobehavioral effects: a developmental perspective.

This paper summarizes the findings gleaned from detailed clinical examinations of three groups of residents who were exposed to trichloroethylene in well water. Also summarized are diagnostic findings for peripheral neuropathy. A detailed description of the neuropsychological test results is included, as well as a summary of domain-specific findings and diagnostic outcomes. A high rate of cognitive deficits of the type seen in patients with central nervous system dysfunction attributable to solvent exposure was seen. In addition, there was a clear developmental trend: subjects who were younger at the time of TCE exposure showed deficits in a larger variety of cognitive realms than did subjects who had already reached adulthood by the time of exposure. In particular, language deficits were seen in the younger, but not older, exposed subjects.

Adolescent↗
PubMed1997

The volitional unit: a functional concept in cortico-motoneuronal connections in humans.

We used the EMG precision decomposition technique to resolve complex EMG signals and derive information about the firing times of a family of motor units (MUs) and the force they produce. The active units shared a common behavior among their firing rates, a concept described by DeLuca et al. and termed the 'common drive'. This 'common' behavior was extracted as the average of the firing rates of MUs and found to track the subject's force trajectory. In this paper, we propose the existence of functional cortico-motoneuronal connections which provide for a large number of combinations between affector cortical motoneurons (CMNs) and effector spinal motoneurons (SMNs) for the generation of a purposeful movement. We argue that these connections provide the essential link between volition and movement and function as a 'volitional unit' which consists of the CMNs, the SMNs and the anatomical and interneuronal connections between them.

Adult↗
PubMed1997

Classification of back muscle impairment based on the surface electromyographic signal.

A surface electromyographic (EMG) procedure for classifying muscle impairments in persons with low back pain (LBP) is described. The procedure was studied using a device, the Back Analysis System (BAS), to acquire and process EMG signals from six bilateral muscle sites during sustained isometric contractions designed to progressively fatigue the lower back. Back muscle impairment was determined on the basis of the different ways in which the EMG median frequency parameters change as a function of contraction duration and muscle site. The article describes a series of studies that have been useful in developing an automated procedure for identifying back muscle impairment by comparing individual test results to a normative database. To date, the research results have produced multivariate discriminant functions that have identified two muscle impairment categories associated with deconditioning and imbalances secondary to LBP. We have found that the functions can distinguish individuals with and without LBP with an accuracy of approximately 90%. Other studies are described in which the technique is applied to monitoring changes in muscle performance capability that occur following rehabilitation for LBP. Many of our findings here are also compared to the results of independent studies by others using similar procedures. The need for further research and development of the technique to improve its clinical applicability is also described.

Diagnosis, Computer-Assisted↗
PubMed1996

The demonstration of the size principle in humans using macro electromyography and precision decomposition.

We set out to study the relationship between a motor unit's size and firing rates and its recruitment threshold and recruitment order. The data were collected from the first dorsal interosseous muscle of 11 normal subjects and analyzed using the precision decomposition and macro electromyography techniques. Our study showed that the recruitment order of a motor unit varies directly with its recruitment threshold (P<0.00005) and that there is a progressive increase in the macro potential size of successively recruited motor units (P=0.002). The firing rates of motor units vary inversely with their recruitment order (P=0.006), the smaller, earlier recruited units consistently reaching higher firing rates than the larger, later recruited units. This study conforms the existence of a size principle of motor unit recruitment in humans and reveals the interactions between a motor unit's size and its firing rate properties.

Adult↗
PubMed1995

Correlates of motor unit size, recruitment threshold, and H-reflex jitter.

The aim of this research was to study the neurophysiology of the anterior horn cell (AHC) using single-fiber EMG (SFEMG) study of the flexor carpi radialis (FCR) H-reflex. Twelve men and 7 women, ages 20-80 years, were studied. The mean H-jitter was 138 +/- 59 microseconds. H-jitter increased with age (while the M-jitter did not) and was greater in men than in women. There was a direct correlation between the H-jitter and H-latency which was used as an indirect measure of the AHC's size. Given that small AHCs have a higher input resistance than large ones, the H-jitter can be used as an indirect indicator of the AHC's input resistance and therefore its size. When subjects fell asleep, the H-jitter increased over tenfold the baseline value, raising the possibility of an alternative, oligosynaptic pathway. H-reflex jitter studies provide a useful clinical neurophysiological tool for the study of AHC physiology.

Adult↗
PubMed1992

The spectrum of concentric macro EMG correlations. Part I. Normal subjects.

Using a concentric macro electrode, both the concentric and macro action potentials of a motor unit were analyzed for duration, area, and amplitude. Eighty-six different motor units were analyzed from the tibialis anterior muscle in 10 normal subjects. The aim of this work was to compare concentric and macro action potential measurements of the same motor unit. The study revealed significant correlations between concentric and macro samples, with the concentric potential's area correlating better with the macro potential than its amplitude. This shows that the 10 to 15 muscle fibers studied by the concentric electrode serve as a good sample of the motor unit as a whole. We briefly review the technique used in concentric macro EMG, as well as describe the methods used for collecting and comparing both concentric and macro action potentials.

Action Potentials↗
PubMed1992

The spectrum of concentric macro EMG correlations. Part II. Patients with diseases of muscle and nerve.

In the second part of this study we investigate the correlations between the concentric and conmac action potentials in motor units of individuals with diseases of muscle and nerve. We studied 86 myopathic and 86 neurogenic motor units and compared their concentric and conmac action potentials. In the patients with myopathy, we found that the concentric motor unit action potential's (MUAP) area correlates strongly with the conmac potential, even better than in normals, while its amplitude correlates less. In the neurogenic group, we found that both the concentric MUAP's area and amplitude correlated very well with their conmac counterpart, more so than in normals. Thus, in pathology, as in normals, measuring the concentric MUAP's area in addition to its amplitude adds to the diagnostic sensitivity of motor unit potential measurements. These findings are discussed in light of the known dynamic and architectural motor unit changes which take place in the myopathic and neurogenic motor unit.

Action Potentials↗
PubMed1992

An investigation of a workplace cluster of Bell's palsy.

We undertook a study to confirm the existence of an apparent cluster of Bell's palsy in an industrial plant ("W4"), and to test etiologic hypotheses regarding chemical exposures, immune suppression, and infectious etiologies. Cases were enumerated by questionnaire. Employees with a history of Bell's palsy ("cases") were invited to participate in a study that included medical history, T cell studies, viral and Lyme disease serologies, and blink reflex studies. Thirty-three unaffected volunteers from W4 and 32 from a comparison building were also tested. Extensive environmental studies were carried out in W4, evaluating infectious, chemical, and radiation exposures. The lifetime incidence of self-reported Bell's palsy was 11.6/10,000 person-years (P-Y) in W4 and 2.4 cases/10,000 P-Y in the comparison building (RR = 4.8, P < .05); the comparison rate was similar to that reported in previous population studies. When restricted to cases occurring after the onset of work, the W4 incidence was 29.2 cases/10,000 P-Y, compared to 4.8 cases/10,000 P-Y in the comparison building (RR = 6.1, P < .05). The cases and noncases did not differ with respect to clinical histories or infectious disease titers. The W4 noncases had small but significant decreases in T lymphocyte (1974 +/- 86 vs 2291 +/- 103) and CD4 (1083 +/- 318 vs 1459 +/- 494) counts compared to the remote noncases. The cases had significantly prolonged RR1, LR1, and LFC values compared to both groups of noncases. No medical or environmental factors were identified that could explain an excess of disease.

Age Factors↗
PubMed1991

Concentric macro electromyography.

Concentric EMG electrodes can record from a few (10 to 15) muscle fibers of a motor unit (MU). Macro EMG, is able to record from the majority of muscle fibers in the MU. The macro EMG electrode uses a single fiber action potential (SFAP) on one channel to trigger the time locked cannula (macro) response on the other channel. To study the concentric motor unit action potential (MUAP), alongside the macro potential, we built a needle electrode combining concentric and macro recording surfaces. The study of 240 motor units in 10 healthy subjects with the single fiber (SF macro) and concentric macro (conmac) electrodes revealed no significant differences between macro potentials areas and amplitudes obtained with either electrode. The ability to study a small and a large section of the motor unit simultaneously offers insights into the local or global nature of motor unit changes not otherwise available to the electromyographer. It also reveals which concentric parameters correlate best with the macro potential and, can even be of great help with the newer EMG signal decomposition techniques; by identifying each motor unit by its concentric and macro waveform simultaneously, it will allow for the "marking" of these motor units helping to reduce the risk of their misclassification when the concentric MUAP is used alone.

Action Potentials↗
PubMed1989

Stimulation SFEMG in myasthenia gravis.

The diagnostic usefulness of single-fiber electromyography (SFEMG) in the diagnosis of neuromuscular transmission disorders is well established. Increased jitter is one of the earliest indications of abnormality. In patients with severe weakness, tremor, or altered consciousness, performance of the study is difficult because of the degree of cooperation needed. We studied five patients and eight normal subjects with voluntary and stimulation SFEMG techniques. Our results, in search of normal values and changes with pathology, revealed differences in the values of jitter and the percentage of abnormal fibers between both techniques. The mean consecutive difference (MCD) is smaller (on average 30% less), and the percentage of abnormal fibers is lower (on average 10% less) with the stimulation technique. These differences are largely explained by the jitter measurement of one endplate with the stimulation technique versus two endplates with the voluntary. They may also be related, however, to the difference in motor unit populations sampled with each technique.

Aged↗
PubMed1989

Single-fiber EMG study of the flexor carpi radialis H reflex.

Late responses were studied in the flexor carpi radialis muscle by surface-recording and single-fiber electromyography. By single-fiber studies we were able to distinguish 2 distinct components. One was an H reflex obtained without a preceding M response and with a stimulus response jitter of about 100 musec; its latency was shortened and jitter decreased with the Jendrassik maneuver. The other was an F wave always preceded by an M response and with a stimulus response jitter of under 50 musec; its jitter and latency are unaffected by the Jendrassik maneuver. At the single-fiber level it was possible to determine the rate of occurrence of individual H reflexes and F responses for a given number of surface-applied stimuli. The H reflex had a very high rate of occurrence (up to 97%), whereas the F wave occurred very infrequently (less than 2% of the time). Using the H reflex rate of occurrence in conjunction with the maximal surface H/M amplitude ratios allowed us to determine the proportion of alpha motor neurons which participate in the H-reflex generation. The study of H-reflex jitter gives an estimate of the central synaptic jitter and effectiveness of the spatial and temporal summation of type 1a fiber inputs on the motor neurons.

Adolescent↗
PubMedDate not supplied

Surface recording of the H-reflex of the flexor carpi radialis.

Although the H-reflex of the triceps surae is used routinely in nerve conduction studies of the lower extremities, doubt still exists concerning the H-reflex in the upper extremities. The H-reflex of the flexor carpi radialis is easily obtainable and can be recorded by a simple nerve conduction technique detailed in this communication.

Adolescent↗