Decomposition of surface EMG signals

This report describes an early version of a technique for decomposing surface electromyographic (sEMG) signals into the constituent motor unit (MU) action potential trains. A surface sensor array is used to collect four channels of differentially amplified EMG signals. The decomposition is achieved by a set of algorithms that uses a specially developed knowledge-based Artificial Intelligence framework. In the automatic mode the accuracy ranges from 75 to 91%. An Interactive Editor is used to increase the accuracy to > 97% in signal epochs of about 30-s duration. The accuracy was verified by comparing the firings of action potentials from the EMG signals detected simultaneously by the surface sensor array and by a needle sensor. We have decomposed up to six MU action potential trains from the sEMG signal detected from the orbicularis oculi, platysma, and tibialis anterior muscles. However, the yield is generally low, with typically < or = 5 MUs per contraction. Both the accuracy and the yield should increase as the algorithms are developed further. With this technique it is possible to investigate the behavior of MUs in muscles that are not easily studied by needle sensors. We found that the inverse relationship between the recruitment threshold and the firing rate previously reported for muscles innervated by spinal nerves is also present in the orbicularis oculi and the platysma, which are innervated by cranial nerves. However, these two muscles were found to have greater and more widespread values of firing rates than those of large limb muscles.     

Alteration in α- and β- adrenoceptor profile of rabbit-knee-joint blood vessels due to chronic inflammation

Experiments were performed to investigate the nature of α- and β-adrenoceptors in blood vessels supplying the posterior capsule of the chronically inflamed rabbit knee joint, and results were compared to the finding from previous experiments on the normal and acutely inflamed joint to assess any alteration which may occur in the adrenoceptor profile due to the chronic inflammation process. Electrical stimulation of the posterior articular nerve resulted in vasoconstriction that was completely blocked by phentolamine. This constrictor response was almost equally inhibited by prazosin and yohimbine. The dose–response curves to close intraarterial injection of α-adrenoceptor agonists showed a rank-order potency of adrenaline = clonidine = phenylephrine. The adrenaline dose–response curve was shifted to the right by administration of α-antagonists with a rank-order potency of phentolamine = prazosin = yohimbine. At this stage of experiments, there was an equal response of α₁- and α₂- adrenoceptors in blood vessels of the chronically inflamed rabbit knee joint. In another group of animals, the neurally mediated vasodilatation, which appeared after administration of phentolamine, was completely blocked by propranolol and was reduced significantly by ICI118551, but the effect of atenolol was not significant. The dose–response curve to close intraarterial injection of β-adrenoceptor agonists showed a rank-order potency of: isoprenaline > salbutamol > dobutamine. The isoprenaline dose–response curve was shifted to the right by administration of β-antagonists with rank-order potency of propranolol > ICI118551 > atenolol. These experiments showed a greater β₂-adrenoceptor response than β₁-adrenoceptor response in chronically inflamed rabbit-knee-joint blood vessels. Overall, compared to previous experiments on normal joint in which α₂- and β₁-adrenoceptor responses predominated, and in acutely inflamed joint in which an equal α₁/α₂ and β₁/β₂ response was shown, in chronically inflamed joint the sympathetic constriction response was returned toward normal. No more α-adrenoceptor shift had happened, and the shift of β₁ to β₂ response continued.     

Posterior semicircular canal dehiscence following endolymphatic sac surgery

Posterior semicircular canal dehiscence is a rare otologic entity that presents with third window signs and symptoms. Petrous apex cholesteatoma, fibrous dysplasia, high riding jugular bulb, and eosinophilic granuloma have been reported to be associated with posterior semicircular canal dehiscence. Here we report a case of development of posterior semicircular canal dehiscence following an endolymphatic sac surgery for the first time. Laryngoscope, 2012.