Is phrenic nerve conduction affected in patients with difficult-to-treat asthma? / A neurocondução do nervo frênico está alterada na asma de difícil controle?

ABSTRACT Objective The aim of this study was to obtain data on phrenic neuroconduction and electromyography of the diaphragm muscle in difficult-to-treat asthmatic patients and compare the results to those obtained in controls. Methods The study consisted of 20 difficult-to-treat asthmatic patients compared with 27 controls. Spirometry, maximal inspiratory and expiratory pressure, chest X-ray, phrenic neuroconduction and diaphragm electromyography data were obtained. Results The phrenic compound motor action potential area was reduced, compared with controls, and all the patients had normal diaphragm electromyography. Conclusion It is possible that a reduced phrenic compound motor action potential area, without electromyography abnormalities, could be related to diaphragm muscle fiber abnormalities due to overload activity.

RESUMO Objetivo O objetivo do presente estudo foi obter dados da neurocondução do frênico e exame com agulha do diafragma em pacientes com asma de difícil controlee comparar com um grupo normal. Métodos O estudo consiste em realizar radiografia de tórax, espirometria, pressão máxima inspiratória e expiratória, neurocondução do nervo frênico e eletromiografia do músculo diafragma em 20 pacientes asmáticos de difícil controle e comparar com 27 controles. Resultados Encontramos redução da área do potencial de ação muscular composto do nervo frênico e a eletromiografia do musculo diafragma estava normal em todos os pacientes. Conclusão É possível que a redução da área do potencial de ação muscular composto do nervo frênico nos pacientes com asma de difícil controle associado a eletromiografia normal do músculo diafragma esteja relacionada as alterações da fibra muscular do mesmo devido à sobrecarga de atividade.

Effectiveness of diaphragmatic stimulation with single-channel electrodes in rabbits / Efetividade da estimulacao diafragmatica com eletrodos monocanais em coelhos

Every year, a large number of individuals become dependent on mechanical ventilation because of a loss of diaphragm function. The most common causes are cervical spinal trauma and neuromuscular diseases. We have developed an experimental model to evaluate the performance of electrical stimulation of the diaphragm in rabbits using single-channel electrodes implanted directly into the muscle. Various current intensities (10, 16, 20, and 26 mA) produced tidal volumes above the baseline value, showing that this model is effective for the study of diaphragm performance at different levels of electrical stimulation.

A cada ano um grande número de pessoas perde a função do diafragma tornando-se dependentes de ventilação mecânica. As principais causas são o trauma raquimedular da região cervical e as doenças neuromusculares. Desenvolvemos um modelo experimental para avaliar o desempenho da estimulação elétrica do diafragma em coelhos com eletrodos monocanais implantados diretamente neste músculo. Foram aplicadas diferentes intensidades de correntes (10, 16, 20 e 26 mA), as quais geraram volumes correntes acima dos valores basais, mostrando que este modelo é eficaz para estudar o desempenho do diafragma sob diferentes tipos de estimulação elétrica.

Tres casos de parálisis diafragmática: utilidad del estudio electromiográfico / Three cases of diaphragmatic paralysis: the utility of electromyographic studies

La parálisis diafragmática (PD) es poco frecuente en pediatría y su adecuado manejo es importante por el potencial compromiso respiratorio. La PD es sospechada por la radiografía de tórax y confirmada por la ultrasonografía. Ultimamente la electromiografía (EMG) ha mostrado utilidad en la evaluación funcional del diafragma y del nervio frénico (NF), en especial a lo que se refiere a su pronóstico y reversibilidad. Objetivo: Reportar la utilidad de la EMG en 3 pacientes con PD. Pacientes y Método: Caso 1, lactante con PD bilateral secundaria a enfermedad neuromuscular adquirida y distrés respiratorio, la EMG mostró denervación y se indicó ventilación permanente. Caso 2: lactante con PD derecha secundaria a cirugía del plexo braquial, el seguimiento electromiográfico permitió tratamiento conservador. Caso 3: preescolar portadora de cardiopatia compleja, PD bilateral post cirugía cardiaca y dependencia de ventilación mecánica (VM), se realizó plicatura diafragmática bilateral, presentó recidiva, necesitó nueva plicatura izquierda por amplitud muy disminuida en la respuesta diafragmática al estudiar conducción de NF. Conclusión: La EMG determinó la disfunción del NF y permitió una conducta conservadora en estos pacientes evitando la cirugía. Sugerimos que la EMG es una herramienta útil en el estudio de pacientes con PD y en la determinación de su conducta terapéutica.

Electrophysiological and ultrastructural analysis of the neuromuscular blockade and miotoxicity induced by the Micrurus nigrocinctus snake venom

Micrurus nigrocinctus is the most abundant coral snake in Central America. The venom of this specie induced a concentration-dependent (10-20 mug/ml) depolarization in the isolated mouse phrenic nerve-diaphragm preparations incubated ate 37 degree. D-Tubocurrarine (10 mug/ml) and alpha betaungarotoxin (3-5 mug/ml) were able to partially protect against the depolarization induced by the venom (10 mug/ml), suggesting the involvement of subsynaptic cholinergic receptors. This venom (10 mug/ml) also increased the frequency and amplitude of miniature end-plate potentials (mepps) during the first 10-20 min of incubation. Subsequently, the mepps progressively decreased and disappeared after 60 min. These responses were accompanied by ultrastructural changes involving the nerve terminals, the subsynaptic junctional folds and the muscle mitochondria. The synaptic gutter was shallow and, very often, "shrunken" terminal with omega-shaped axolemmal identations and a decreased number of synaptic vecicles were present. A common finding was the presence of numerous finger-like, membrane-bounded bodies interposed between the terminal and the Schwann cells or postsynaptic sarcolemma. The preincubation of the venom with specific antivenom or the incubation of the preparations at room temperature (24-26 degree) reduced the number and intensity of the ultrastructural alterations. The last finding suggests the involvement of a enzymatic process, probably a phospholipase A2, present in the venom. There was a good correlation between the electrophysiological and ultrastructural effects induced by the venom which allow us to conclude that M. nigrocinctus venom has a presynaptic action in the initial stages of intoxication followed by sub- and postsynaptic effects, the last being the most important cause of neuromuscular blockade. A direct action of the venom on muscle fibers may also contributes to the irreversible blockade.