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L Niles

Publications and source records attributed to L Niles.

11 recordsLinked to original sources
PubMed1992

Improved techniques for measuring muscle fiber conduction velocity.

Cross-correlation (CCT) and dip analysis (DAT) are accepted techniques for estimating muscle fiber conduction velocity (MFCV). In the DAT, the product of the power spectrum of the conducted EMG times a cosine function of the MFCV is added to and inseparable from the noise power spectrum. The inclusion of the noise power is the weakness of the DAT. We propose and evaluate 2 new techniques that directly estimate the cosine function and, hence, the MFCV, avoiding the noise power: (1) The power-modulating-component (PMC), which equals the real part of the cross-power-spectrum of the EMG signal divided by its magnitude; and (2) The power spectrum of the PMC (PMCP). We recorded intramuscular from 229 biceps in isometric maximum voluntary contraction. The EMG signals were analyzed by the 4 techniques, and the results were compared in pairwise design (sign-tests and t tests) for quality and bias. The PMC surpassed the DAT (P less than 0.00005); both the CCT and PMCP performed equally well and better than the DAT and the PMC (P less than 0.00005). Also, the new techniques were superior with simulated EMG. In many cases only the PMCP worked. We conclude that the new techniques are valuable in supplementing the others, and most likely will enhance clinical use of MFCV estimations.

Electromyography↗
PubMed1992

Muscle fiber conduction velocity and mean power spectrum frequency in neuromuscular disorders and in fatigue.

This study investigated the relation of muscle fiber conduction velocity (MFCV) to difference power spectrum mean frequency (MF), their fatigue trends, and differences between their values and their fatigue trends in various neuromuscular disorders. Electromyographic interference pattern was recorded inside the biceps in continuous isometric maximal voluntary contractions. Each subject was encouraged to pull for as long as possible. Fatigue was calculated as percent of time to complete inability to sustain contraction. The MFCV was computed by cross-correlation. The MF was computed by differencing, windowing, FFT, squaring of coefficient, and repeat averaging. There were 33 healthy, 86 polyneuropathic, 28 myasthenic, 13 myotonic, and 32 myopathic patients. Both MFCV and MF changed significantly with fatigue--the MFCV linearly, while the MF in a markedly nonlinear fashion. Both were found to be insensitive to the end stages of muscle fatigue--the MFCV did not change its slope toward complete fatigue, and the MF did not change at all beyond the 40% fatigue point. A statistically sound fatigue regression equation was derived for each, and a nonlinear equation was found to best describe their relationship. Neither MFCV nor its fatigue changes were found to be significantly different across the neuromuscular disorders. The MF, however, was found to be significantly different in some neuromuscular disorders in both its average values and fatigue trends. This study showed, in contrast to the literature, a nonlinear relationship between MFCV and MF. It also shows that neither the MFCV nor the MF had reasonable diagnostic power on its own; however, the MF was very promising to serve as an adjunct to other variables.

Action Potentials↗
PubMed1992

Involvement of multiple sulfhydryl groups in melatonin signal transduction in chick brain.

To gain insight into the molecular mechanism underlying melatonin binding and signal transduction in the chick brain, we have investigated the role of -SH groups, using a sulfhydryl alkylating reagent N-ethylmaleimide (NEM). At least two -SH groups are involved in the formation of the receptor-G protein complex: one is sensitive to and the other relatively insensitive to NEM. Alkylation of the sensitive group selectively abolishes high affinity binding of 2-[125I]iodomelatonin ([125I]MEL), similar to the effect induced by GTP, thus leading to a complete loss of sensitivity to nucleotides. Modification of both groups causes a marked reduction in binding capacity. Agonists with high affinity, but not other compounds with low affinity for the melatonin receptor, protect against alkylation by NEM. GTP gamma s does not significantly alter the reactivity of -SH groups towards NEM, but agonist-protected receptors remain sensitive to this nucleotide. Moreover, NEM pretreatment blocks the inhibitory effect of melatonin on forskolin-stimulated adenylate cyclase activity in chick brain. These data suggest that the -SH group modulating agonist affinity may lie within the coupling domain between the receptor and G protein but outside of the GTP binding site. In addition, sulfhydryl groups are essential for melatonin binding and signal transduction in chick brain.

Adenylyl Cyclases↗
PubMed1991

A novel and sensitive radioreceptor assay for serum melatonin levels.

A simple and sensitive radioreceptor assay (RRA) has been developed to measure melatonin levels in serum. The assay is based on competition between 2-[125I]iodomelatonin ([125I]MEL) and melatonin for binding to high-affinity binding sites in chick forebrain. To measure the amount of melatonin present in a serum sample, it was extracted with dichloromethane and added to the assay medium. The percentage inhibition of radioligand binding in the presence of the extracted serum was determined and compared to the percent displacement by known amounts of melatonin in a standard curve. There was little or no cross-reactivity with other structurally related compounds. The sensitivity of the assay is approximately 1.5pg/0.15 mL and the intra- and inter-assay variations are approximately 8%. Since the RRA results are comparable to that of an established radioimmunoassay (RIA), it provides a sensitive and rapid alternative to the more time consuming RIA.

Animals↗
PubMed1991

Muscle fiber conduction velocity: dip analysis versus cross correlation techniques.

Among the various techniques in use for computing Muscle Fiber Conduction Velocities (MFCV) the Cross Correlation (CCT) and the Dip Analysis (DAT) Techniques are the most similar to each other. The CCT has been applied to intramuscular and surface EMG recordings, while the DAT has been applied to surface recording only. On theoretical grounds the CCT carries higher signal to noise ratio than the DAT and therefore should be preferred over the latter. This study was designated to test and proved the above for intramuscular recording at maximal contractions with real data. In this study 240 subjects had their biceps EMG Interference Pattern recorded intramuscularly at maximal isometric contraction with two concentric needle electrodes separated one cm from one another along and parallel to the muscle fibers. The recording period lasted for 5.84 seconds. One hundred and sixty nine subjects (70%) showed distinct peaks in their cross correlograms, while only in 20 subjects (8%) were dips discernible by DAT. While most peaks in the CCT were high, clear and distinct most dips were shallow and blurred; also, there were only three cases where dips were detected on the DAT but no peaks were detected on the CCT while there were 152 cases where the CCT was superior to the DAT. This study verifies the superiority of the CCT over the DAT in this specific paradigm. Discussed are suggestions on how to improve the DAT by recording and displaying each lead power spectra separately prior to the differential amplifications of the EMG sinal from the two channels.

Adolescent↗
PubMed1978

Preoperative cervical dilatation with 15(S)15-methyl PGF2alpha methyl ester pessaries.

A clinical trial comparing two vaginal dose schedules of 15(S)15-methyl prostaglandin F2alpha (PGF2alpha) methyl ester (4 or 6 mg) for preoperative dilatation of the cervix is described. The trial included 28 patients at 8-12 weeks' gestation. Vaginal pessaries containing either 1.0 mg (15 patients) or 1.5 mg (13 patients) of the prostaglandin analogue were administered every 3 hours (maximum, 4 doses). The success rates for the two groups were 93% and 100%, respectively. Sixty percent of the patients aborted before the planned vacuum aspiration. Minor side effects, primarily vomiting and diarrhea, occurred in approximately 80% of the cases and were more prominent with the higher dose pessary. It is concluded that the vaginal administration of 15(S)15-methyl PGF2alpha methyl ester is highly effective for preoperative dilatation of the cervix before suction curettage abortion.

Abortion, Therapeutic↗
PubMedDate not supplied

Second trimester abortion with prostaglandin F2 alpha.

A clinical trial comparing 40-mg and 50-mg, intraamniotic dose schedules of prostaglandin F2 alpha (PGF2 alpha) is described. The trial included 48 patients at 15-20 weeks' gestation, with 20 receiving a 40-mg dose of PGF2 alpha and 28 receiving a 50-mg dose of PGF2 alpha. The success rates for the two groups were 85% and 93%, respectively. All nulliparous patients who had 50 mg of PGF2 alpha and all multiparous patients who had 40 mg of PGF2 alpha aborted within the 48-hour trial period. The mean induction-to-abortion interval with the 50-mg dose was two hours shorter than that with the 40-mg dose. All patients who had 40 mg of PGF2 alpha over 16 weeks' gestation aborted within the trial period. In patients who had 50 mg of PGF2 alpha, the period of gestation did not influence the induction-to-abortion interval. Minor side effects, primarily vomiting or diarrhea, were observed in 65% and 93% of the patients who had 40-mg and 50-mg doses, respectively. We conclude that intraamniotic administration of 50 mg of PGF2 alpha successfully induces midtrimester abortion in nulliparous patients, whereas a 40-mg dose suffices for multiparous women.

Abortion, Induced↗
PubMedDate not supplied

EMG interference pattern power spectrum analysis in neuro-muscular disorders.

One hundred sixty six subjects, who had clinically proven Neuromuscular (NM) diagnoses and 37 normal controls, had their biceps muscle EMGs, recorded in sustained isometric maximum voluntary contraction (MVC). The EMG signals were repeatedly transformed into power spectra (PS). The PS were then analysed by various statistical methods. The statistical analyses showed an overall significant difference in power between the sexes but only in the Dysschwannian Neuropathy group and no differences due to age; a very highly significant fatigue trend that manifests, to a different extent, in all frequency bands; the groups were significantly different from one another in both total power and in band-specific power, and to differ in their responses to fatigue. These analyses showed that based on PS alone discriminant analysis can separate the cases into only two significantly different groups: normal controls could not be separated from neuropathies, but both were significantly different from Myasthenia Gravis and myopathies. The statistical analysis highlighted as important the use of separate PS frequency bands and the use of a fatigue paradigm for separating the various NM disorders--showing Group-by-Fatigue; Group-by-Band and Group-by-Band-by-Fatigue interactions to be highly significant. All the above mentioned significant features, though, resulted in a low predictive (diagnostic) value by discriminant analysis and even worse by clustering techniques.

Adult↗