RESUMO
PURPOSE: Based on the critical power (Pc or critical force; Fc) concept, a recent mathematical model formalised the proportional link between the decrease in maximal capacities during fatiguing exercises and the amount of impulse accumulated above Fc. This study aimed to provide experimental support to this mathematical model of muscle fatigability in the severe domain through testing (i) the model identifiability using non-exhausting tests and (ii) the model ability to predict time to exhaustion (tlim) and maximal force (Fmax) decrease. METHODS: The model was tested on eight participants using electrically stimulated adductor pollicis muscle force. The Fmax was recorded every 15 s for all tests, including five constant tests to estimate the initial maximal force (Fi), Fc, and a time constant (τ). The model's parameters were used to compare the predicted and observed tlim values of the incremental ramp test and Fmax(t) of the sine test. RESULTS: The results showed that the model accurately estimated Fi, Fc, and τ (CI95% = 2.7%Fi and 9.1 s for Fc and τ, respectively; median adjusted r2 = 0.96) and predicted tlim and Fmax with low systematic and random errors (11 ± 20% and - 1.8 ± 7.7%Fi, respectively). CONCLUSION: This study revealed the potential applications of a novel mathematical formalisation that encompasses previous research on the critical power concept. The results indicated that the model's parameters can be determined from non-exhaustive tests, as long as maximal capacities are regularly assessed. With these parameters, the evolution of maximal capacities (i.e. fatigability) at any point during a known exercise and the time to exhaustion can be accurately predicted.
RESUMO
Desde hace décadas se sabe que al colocar un electrodo cerca de la ventana redonda de la cóclea es posible registrar potenciales cocleares en respuesta a estímulos sonoros, tales como el potencial microfónico coclear o el potencial de acción compuesto del nervio auditivo. Sin embargo, hace algunos años, se ha descrito que al posicionar un electrodo en el nicho de la ventana redonda en animales de experimentación y en ausencia de estimulación acústica, se obtiene actividad eléctrica aparentemente aleatoria y no desencadenada por estímulo. Esta actividad eléctrica se ha denominado ruido eléctrico de ventana redonda (RWN, por su sigla en inglés Round Window Noise) y representaría la descarga espontánea de fibras del nervio auditivo. La técnica para su registro es similar a la utilizada en la electrococleografía para obtener potenciales cocleares en humanos. Esta señal se distingue del ruido eléctrico no biológico por tener un peak en su poder espectral centrado en torno a los 900 Hz. La amplitud de esta banda de frecuencia se correlaciona con la sensibilidad auditiva en la región basal de la cóclea, entre los 12 a 30 kHz en cobayos y gatos. El RWN se ha estudiado a través de estimulación acústica y bloqueo farmacológico, logrando caracterizar sus propiedades electrofisiológicas para desarrollar modelos de estudio con aplicación clínica.
For decades, it has been known that placing an electrode near the round window niche allows the recording of cochlear potentials in response to auditory stimuli, such as the cochlear microphonic potential and the compound action potential of the auditory nerve. However, some years ago, it was discovered, that by positioning an electrode in the round window niche of experimental animals, and in the absence of acoustic stimulation, apparently random electrical activity is obtained. This electrical activity is called round window electrical noise (RWN) and represents the spontaneous discharge of auditory nerve fibers. The recording technique is similar to that used in electrocochleography in humans. This bioelectrical signal is distinguished from that of non-biological electrical noise, as it has a power spectral peak centered around 900 Hz. The magnitude of this frequency peak is correlated with hearing sensitivity in the basal region of the cochlea, between 12 to 30 kHz in guinea pigs and cats. The RWN has been characterized using sound stimulation or pharmacologic suppression, and its electrophysiological properties could be used to develop models of auditory nerve function with possible clinical application.
Assuntos
Humanos , Janela da Cóclea/fisiologia , Potenciais de Ação/fisiologia , Nervo Coclear/fisiologia , Audiometria de Resposta EvocadaRESUMO
El tracto olivo-coclear medial ha sido ampliamente estudiado en animales de experimentación y clínicamente en humanos. Se ha sugerido que una de sus funciones se relaciona con la discriminación del habla en presencia de ruido de fondo. Actualmente no se cuenta con estudios sistemáticos de las posibles correlaciones entre el efecto de supresión eferente y el rendimiento en tareas de discriminación de habla en ruido. Por lo anterior, en nuestro laboratorio estamos investigando los valores del efecto de supresión y cómo estos pueden relacionarse con tareas de discriminación del habla. En el presente artículo se reportan los resultados de un estudio piloto en esta materia. Un grupo de 45 sujetos adultos y auditivamente normales fueron estudiados. Los procedimientos incluyeron emisiones otoacústicas transientes, efecto de supresión de las emisiones otoacústicas transientes, reflejos acústicos ipsi y contralaterales (para las frecuencias 0.5, 1, 2 y 4 KHz) y la prueba de HINT. No se encontraron diferencias estadísticamente significativas para el efecto de supresión eferente entre ambos oídos. Por otra parte, no se observaron correlaciones entre la amplitud del efecto de supresión y los valores obtenidos en la prueba de HINT para las subpruebas de habla en ruido. Se discuten los hallazgos encontrados y la necesidad de futuras investigaciones.
The medial olivo-cochlear bundle has been widely studied in experimental animals and clinically, in human subjects. It has been suggested that one of the functions of this bundle relates to the discrimination of speech in the presence of background noise. No systematic studies of possible associations between the efferent suppression of otoacustic emissions (OAEs) and performance on speech-in-noise tasks has been carried out. For this reason, we are investigating the amplitude of the efferent suppression of OAEs and how this may be associated with performance on speech-in-noise tasks. The results of a pilot study on this topic are addressed in this manuscript. A total of 45 normal-hearing adult subjects were studied. Transient-evoked OAEs (TEOAEs), the efferent suppression of TEOAEs, ipsi and contralateral acoustic reflexes (0.5, 1, 2, and 4 HHz) were obtained and the hearing-in-noise-test (HINT) was administered to all the subjects selected. No significant differences were found in the efferent suppression of TEOAEs between ears. No significant correlations between results for the efferent suppression of TEOAEs and those for the HINT were found. These results and the need for further research are discussed.