RESUMO
Cardiac function can be assessed from displacement measurements in imaging modalities from nuclear medicine Using positron emission tomography (PET) image sequences with Rubidium-82, we propose and estimate the total Kinetic Energy Index (KEf) obtained from the velocity field, which was calculated using 3D optical flow(OF) methods applied over the temporal image sequence. However, it was found that the brightness of the image varied unexpectedly between frames, violating the constant brightness assumption of the OF method and causing large errors in estimating the velocity field. Therefore total brightness was equalized across image frames and the adjusted configuration tested with rest perfusion images acquired from individuals with normal (n=30) and low (n=33) cardiac function. For these images KEf was calculated as 0.5731±0.0899 and 0.3812±0.1146 for individuals with normal and low cardiac function respectively. The ability of KEf to properly classify patients into the two groups was tested with a ROC analysis, with area under the curve estimated as 0.906. To our knowledge this is the first time that KEf has been applied to PET images.
Assuntos
Transferência de Energia/fisiologia , Ventrículos do Coração/diagnóstico por imagem , Interpretação de Imagem Assistida por Computador/métodos , Tomografia por Emissão de Pósitrons/métodos , Volume Sistólico , Função Ventricular Esquerda/fisiologia , Humanos , Imageamento Tridimensional/métodos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
After removal of the fast N-type inactivation gate, voltage-sensitive Shaker (Shaker IR) K channels are still able to inactivate, albeit slowly, upon sustained depolarization. The classical mechanism proposed for the slow inactivation observed in cell-free membrane patches--the so called C inactivation--is a constriction of the external mouth of the channel pore that prevents K(+) ion conduction. This constriction is antagonized by the external application of the pore blocker tetraethylammonium (TEA). In contrast to C inactivation, here we show that, when recorded in whole Xenopus oocytes, slow inactivation kinetics in Shaker IR K channels is poorly dependent on external TEA but severely delayed by internal TEA. Based on the antagonism with internally or externally added TEA, we used a two-pulse protocol to show that half of the channels inactivate by way of a gate sensitive to internal TEA. Such gate had a recovery time course in the tens of milliseconds range when the interpulse voltage was -90 mV, whereas C-inactivated channels took several seconds to recover. Internal TEA also reduced gating charge conversion associated to slow inactivation, suggesting that the closing of the internal TEA-sensitive inactivation gate could be associated with a significant amount of charge exchange of this type. We interpreted our data assuming that binding of internal TEA antagonized with U-type inactivation (Klemic, K.G., G.E. Kirsch, and S.W. Jones. 2001. Biophys. J. 81:814-826). Our results are consistent with a direct steric interference of internal TEA with an internally located slow inactivation gate as a "foot in the door" mechanism, implying a significant functional overlap between the gate of the internal TEA-sensitive slow inactivation and the primary activation gate. But, because U-type inactivation is reduced by channel opening, trapping the channel in the open conformation by TEA would also yield to an allosteric delay of slow inactivation. These results provide a framework to explain why constitutively C-inactivated channels exhibit gating charge conversion, and why mutations at the internal exit of the pore, such as those associated to episodic ataxia type I in hKv1.1, cause severe changes in inactivation kinetics.
Assuntos
Ativação do Canal Iônico/efeitos dos fármacos , Ativação do Canal Iônico/fisiologia , Canal de Potássio Kv1.4/efeitos dos fármacos , Canal de Potássio Kv1.4/metabolismo , Tetraetilamônio/farmacologia , Sítio Alostérico/efeitos dos fármacos , Sítio Alostérico/fisiologia , Animais , Citoplasma/metabolismo , Eletrofisiologia , Transferência de Energia/fisiologia , Feminino , Canal de Potássio Kv1.4/genética , Potenciais da Membrana , Camundongos , Oócitos , Potássio/metabolismo , Bloqueadores dos Canais de Potássio/metabolismo , Bloqueadores dos Canais de Potássio/farmacologia , Domínios e Motivos de Interação entre Proteínas/efeitos dos fármacos , Domínios e Motivos de Interação entre Proteínas/genética , Relação Estrutura-Atividade , Tetraetilamônio/metabolismo , Termodinâmica , Xenopus laevisRESUMO
BACKGROUND: Information regarding kinetic changes associated with walking speed is important for identifying alterations in locomotor disorders caused by pathological processes, as opposed to those arising solely from altered speeds. METHODS: Fourteen healthy subjects were assessed walking at both natural and imposed cadences of 60, 80, and 120 steps/min. A 3D motion analysis system, force platforms, and related software were used to obtain kinematic and kinetic data. Net joint powers were calculated across cycles and the area under the positive and negative phases of the power curves provided the mechanical work generated and absorbed at the hip, knee, and ankle. The relative contributions to the total positive and negative work across the four cadences were calculated for each joint. ANOVAs followed by planned contrasts were used to assess the effects of laterality, joint, and cadence. FINDINGS: Power and mechanical work, as well as the contributions of individual joints to the total energy generated and absorbed, were shown to be influenced by walking cadence, independent of laterality. The ankle, knee, and hip contributions to the total limb generation and absorption at the lowest cadence were 53%, 21%, and 26%, and at the highest cadence, the corresponding values were 34%, 33%, and 33%, respectively. INTERPRETATION: Power and mechanical work, as well as the contributions of individual joints to the total energy generated and absorbed, were shown to be influenced by the walking cadence, independent of laterality. These findings will be helpful for identifying walking strategies and adaptations in populations with gait disorders.
Assuntos
Articulação do Tornozelo/fisiologia , Transferência de Energia/fisiologia , Marcha/fisiologia , Articulação do Quadril/fisiologia , Articulação do Joelho/fisiologia , Perna (Membro)/fisiologia , Esforço Físico/fisiologia , Caminhada/fisiologia , Simulação por Computador , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Modelos BiológicosRESUMO
The electrical characteristics of the sparks produced between the active electrode and the biological tissue during electrosurgical procedures have been experimentally investigated. The results have shown that the minimum voltage required to initiate a spark depends on the applied voltage polarity resulting in electrosurgical voltage asymmetry. This voltage asymmetry is capable of producing dc levels that can result in tissue electrostimulation or direct current burns as discussed in this paper. The experimental setup and the conditions, under which the results have been obtained, including the techniques used to improve experimental reproducibility, are reported in detail.
Assuntos
Eletrocirurgia/instrumentação , Eletrocirurgia/métodos , Transferência de Energia/fisiologia , Músculo Esquelético/fisiologia , Músculo Esquelético/cirurgia , Radiometria/métodos , Animais , Campos Eletromagnéticos , Análise de Falha de Equipamento , Técnicas In Vitro , Doses de Radiação , SuínosRESUMO
Intensive poultry production generates over 100,000 t of litter annually in West Virginia and 9 x 10(6) t nationwide. Current available technological alternatives based on thermophilic anaerobic digestion for residuals treatment are diverse. A modification of the typical continuous stirred tank reactor is a promising process being relatively stable and owing to its capability to manage considerable amounts of residuals at low operational cost. A 40-m3 pilot plant digester was used for performance evaluation considering energy input and methane production. Results suggest some changes to the pilot plant configuration are necessary to reduce power consumption although maximizing biodigester performance.
Assuntos
Archaea/fisiologia , Bactérias Anaeróbias/fisiologia , Reatores Biológicos/microbiologia , Transferência de Energia/fisiologia , Esterco/microbiologia , Metano/metabolismo , Esgotos/microbiologia , Modelos Biológicos , Projetos PilotoRESUMO
The International Commission on Radiological Protection intends to revise the organ and tissue equivalent dose conversion coefficients published in various reports. For this purpose the mathematical human medical internal radiation dose (MIRD) phantoms, actually in use, have to be replaced by recently developed voxel-based phantoms. This study investigates the dosimetric consequences, especially with respect to the effective male dose, if not only a MIRD phantom is replaced by a voxel phantom, but also if the tissue compositions and the radiation transport codes are changed. This task will be resolved by systematically replacing in the mathematical ADAM/GSF exposure model, first the radiation transport code, then the tissue composition and finally the phantom anatomy, in order to arrive at the voxel-based MAX/EGS4 exposure model. The results show that the combined effect of these replacements can decrease the effective male dose by up to 25% for external exposures to photons for incident energies above 30 keV for different field geometries, mainly because of increased shielding by a heterogeneous skeleton and by the overlying adipose and muscle tissue, and also because of the positions internal organs have in a realistically designed human body compared to their positions in the mathematically constructed phantom.
Assuntos
Transferência de Energia/fisiologia , Modelos Biológicos , Proteção Radiológica/métodos , Radiometria/métodos , Medição de Risco/métodos , Adulto , Simulação por Computador , Feminino , Humanos , Internacionalidade , Masculino , Especificidade de Órgãos , Prótons , Doses de Radiação , Proteção Radiológica/normas , Radiometria/normas , Eficiência Biológica Relativa , Reprodutibilidade dos Testes , Medição de Risco/normas , Fatores de Risco , Sensibilidade e Especificidade , Fatores SexuaisRESUMO
Calor é um subproduto da transformação de energia, em suas diversas formas, durante a síntese e a utilização do ATP. Nos animais homeotérmicos, o calor derivado das funções biológicas - estando o organismo em repouso e à temperatura ambiente - é utilizado para manter o organismo próximo a 37ºC. Essa termogênese obrigatória está associada à ineficiência termodinâmica intrínseca mitocondrial, derivada da presença de proteínas desacopladoras (UCPs, uncoupling proteins). Durante a exposição ao frio, o organismo é capaz de gerar mais calor através da termogênese facultativa, por processos que também envolvem UCPs. Os hormônios tireóideos influenciam diretamente a expressão da UCP-1 e, indiretamente, a expressão das UCP-2 e UCP-3. Além disso, também aceleram o turnover de várias reações ou vias metabólicas cíclicas que levam a maior gasto de ATP e produção de calor.