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1.
Biometrics ; 69(3): 741-7, 2013 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-23859366

RESUMO

We present an application of mechanistic modeling and nonlinear longitudinal regression in the context of biomedical response-to-challenge experiments, a field where these methods are underutilized. In this type of experiment, a system is studied by imposing an experimental challenge, and then observing its response. The combination of mechanistic modeling and nonlinear longitudinal regression has brought new insight, and revealed an unexpected opportunity for optimal design. Specifically, the mechanistic aspect of our approach enables the optimal design of experimental challenge characteristics (e.g., intensity, duration). This article lays some groundwork for this approach. We consider a series of experiments wherein an isolated rabbit heart is challenged with intermittent anoxia. The heart responds to the challenge onset, and recovers when the challenge ends. The mean response is modeled by a system of differential equations that describe a candidate mechanism for cardiac response to anoxia challenge. The cardiac system behaves more variably when challenged than when at rest. Hence, observations arising from this experiment exhibit complex heteroscedasticity and sharp changes in central tendency. We present evidence that an asymptotic statistical inference strategy may fail to adequately account for statistical uncertainty. Two alternative methods are critiqued qualitatively (i.e., for utility in the current context), and quantitatively using an innovative Monte-Carlo method. We conclude with a discussion of the exciting opportunities in optimal design of response-to-challenge experiments.


Assuntos
Biometria/métodos , Modelos Estatísticos , Potenciais de Ação , Animais , Simulação por Computador , Coração/fisiopatologia , Hipóxia/fisiopatologia , Análise dos Mínimos Quadrados , Modelos Cardiovasculares , Método de Monte Carlo , Dinâmica não Linear , Coelhos , Análise de Regressão , Biologia de Sistemas/estatística & dados numéricos
2.
bioRxiv ; 2020 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-32676592

RESUMO

In only a few months, the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a global pandemic, leaving physicians, scientists, and public health officials racing to understand, treat, and contain this zoonotic disease. SARS-CoV-2 has made the leap from animals to humans, but little is known about variations in species susceptibility that could identify potential reservoir species, animal models, and the risk to pets, wildlife, and livestock. While there is evidence that certain species, such as cats, are susceptible, the vast majority of animal species, including those in close contact with humans, have unknown susceptibility. Hence, methods to predict their infection risk are urgently needed. SARS-CoV-2 spike protein binding to angiotensin converting enzyme 2 (ACE2) is critical for viral cell entry and infection. Here we identified key ACE2 residues that distinguish susceptible from resistant species using in-depth sequence and structural analyses of ACE2 and its binding to SARS-CoV-2. Our findings have important implications for identification of ACE2 and SARS-CoV-2 residues for therapeutic targeting and identification of animal species with increased susceptibility for infection on which to focus research and protection measures for environmental and public health.

3.
Science ; 208(4439): 53-5, 1980 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-7361105

RESUMO

The magnetic field of the action potential from an isolated frog sciatic nerve was measured by a SQUID magnetometer with a novel room-temperature pickup coil. The 1.2 x 10(-10) tesla field was measured 1.3 millimeters from the nerve with a signal-to-noise ratio of 40 to 1.


Assuntos
Potenciais de Ação , Magnetismo , Condução Nervosa , Animais , Anuros , Nervo Isquiático/fisiologia
4.
Science ; 290(5492): 791-5, 2000 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-11052940

RESUMO

The ejection of material from Mars is thought to be caused by large impacts that would heat much of the ejecta to high temperatures. Images of the magnetic field of martian meteorite ALH84001 reveal a spatially heterogeneous pattern of magnetization associated with fractures and rock fragments. Heating the meteorite to 40 degrees C reduces the intensity of some magnetic features, indicating that the interior of the rock has not been above this temperature since before its ejection from the surface of Mars. Because this temperature cannot sterilize most bacteria or eukarya, these data support the hypothesis that meteorites could transfer life between planets in the solar system.


Assuntos
Exobiologia , Marte , Meteoroides , Cristalização , Magnetismo , Temperatura
5.
Science ; 198(4322): 1159-62, 1977 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-929192

RESUMO

A unipositional lead system has been developed to record the human magnetic heart vector and to permit comparison with the electric heart vector recorded with a conventional Frank lead system. Recordings made in five normal subjects showed a remarkably consistent relation between the electric and magnetic heart vectors. However, the angle between electric heart vector R and T waves was markedly different from the magnetic heart vector R-T angle. In addition, recordings made in two patients with bundle branch block showed a different relation between the electric and magnetic heart vectors compared to normal subjects. These data support the hypothesis that magnetic measurements have a different sensitivity to some components of cardiac activation compared with body surface potential measurements.


Assuntos
Bloqueio Cardíaco/fisiopatologia , Coração/fisiologia , Magnetismo , Eletrocardiografia , Coração/fisiopatologia , Humanos
6.
Biophys J ; 95(8): 4057-67, 2008 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-18676656

RESUMO

The PI3K/PTEN pathway, as the regulator of 3'-phosphoinositide (3'-PI) dynamics, has emerged as a key regulator of chemoattractant gradient sensing during chemotaxis in Dictyostelium and other cell types. Previous results have shown 3'-PIs to be important for regulating basal cell motility and sensing the direction and strength of the chemoattractant gradient. We examined the chemotaxis of wild-type cells and cells lacking PTEN or PI3K1 and 2 using analytical methods that allowed us to quantitatively discern differences between the genotype's ability to sense and efficiently respond to changes in gradient steepness during chemotaxis. We found that cells are capable of increasing their chemotactic accuracy and speed as they approach a micropipette in a manner that is dependent on the increasing strength of the concentration gradient and 3'-PI signaling. Further, our data show that 3'-PI signaling affects a cell's ability to coordinate speed and direction to increase chemotactic efficiency. Using to our knowledge a new measurement of chemotactic efficiency that reveals the degree of coordination between speed and accuracy, we found that cells also have the capacity to increase their chemotactic efficiency as they approach the micropipette. Like directional accuracy and speed, the increase in chemotactic efficiency of cells with increased gradient strength is sensitive to 3'-PI dysregulation. Our evidence suggests that receptor-driven 3'-PI signaling regulates the ability of a cell to capitalize on stronger directional inputs and minimize the effects of inaccurate turns to increase chemotactic efficiency.


Assuntos
Quimiotaxia/efeitos dos fármacos , Dictyostelium/citologia , Dictyostelium/efeitos dos fármacos , Fosfatidilinositóis/farmacologia , Animais , Simulação por Computador , Genótipo , Transdução de Sinais/efeitos dos fármacos , Fatores de Tempo
7.
J Microsc ; 232(1): 1-6, 2008 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-19017196

RESUMO

We report a novel method for obtaining simultaneous images from multiple vantage points of a microscopic specimen using size-matched microscopic mirrors created from anisotropically etched silicon. The resulting pyramidal wells enable bright-field and fluorescent side-view images, and when combined with z-sectioning, provide additional information for 3D reconstructions of the specimen. We have demonstrated the 3D localization and tracking over time of the centrosome of a live Dictyostelium discoideum. The simultaneous acquisition of images from multiple perspectives also provides a five-fold increase in the theoretical collection efficiency of emitted photons, a property which may be useful for low-light imaging modalities such as bioluminescence, or low abundance surface-marker labelling.


Assuntos
Microscopia de Fluorescência/métodos , Microscopia/métodos , Manejo de Espécimes/métodos , Animais , Dictyostelium/ultraestrutura , Imageamento Tridimensional/métodos , Organelas/ultraestrutura
8.
J Gen Physiol ; 98(5): 1043-61, 1991 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-1765761

RESUMO

Recent advances in the technology of recording magnetic fields associated with electric current flow in biological tissues have provided a means of examining action currents that is more direct and possibly more accurate than conventional electrical recording. Magnetic recordings are relatively insensitive to muscle movement, and, because the recording probes are not directly connected to the tissue, distortions of the data due to changes in the electrochemical interface between the probes and the tissue are eliminated. In vivo magnetic recordings of action currents of rat common peroneal nerve and extensor digitorum longus (EDL) muscle were obtained by a new magnetic probe and amplifier system that operates within the physiological temperature range. The magnetically recorded waveforms were compared with those obtained simultaneously by conventional, extracellular recording techniques. We used the amplitude of EDL twitch force (an index of stimulus strength) generated in response to graded stimulation of the common peroneal nerve to enable us to compare the amplitudes of magnetically recorded nerve and muscle compound action currents (NCACs and MCACs, respectively) with the amplitudes of electrically recorded nerve compound action potentials (NCAPs). High, positive correlations to stimulus strength were found for NCACs (r = 0.998), MCACs (r = 0.974), and NCAPs (r = 0.998). We also computed the correlations of EDL single motor unit twitch force with magnetically recorded single motor unit compound action currents (SMUCACs) and electrically recorded single motor unit compound action potentials (SMUCAPs) obtained with both a ring electrode and a straight wire serving as a point electrode. Only the SMUCACs had a relatively strong positive correlation (r = 0.768) with EDL twitch force. Correlations for ring and wire electrode-recorded SMUCAPs were 0.565 and -0.366, respectively. This study adds a relatively direct examination of action currents to the characterization of the normal biophysical properties of peripheral nerve, muscle, and muscle single motor units.


Assuntos
Magnetismo , Neurônios Motores/fisiologia , Contração Muscular/fisiologia , Músculos/inervação , Músculos/fisiologia , Fibras Nervosas/fisiologia , Potenciais de Ação/fisiologia , Animais , Condutividade Elétrica/fisiologia , Estimulação Elétrica , Masculino , Junção Neuromuscular/fisiologia , Ratos , Ratos Endogâmicos
9.
Med Biol Eng Comput ; 43(1): 85-93, 2005 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-15742724

RESUMO

Biomagnetic measurements are increasingly popular as functional imaging techniques for the non-invasive assessment of electrically active tissue. Although most currently available magnetometers utilise only one component of the vector magnetic field, some studies have suggested the possibility of obtaining additional information from recordings of the full magnetic field vector. Three projection techniques were applied to different biomagnetic signals for analysis of the three orthogonal components of the vector magnetic field. Vector magnetic fields obtained from fetal cardiac activity were projected into evenly spaced directions around a unit sphere. The vector magnetic field recorded from multiple intestinal current sources with independent temporal frequencies was then projected. Finally, an external reference signal from an invasive electrode was used to project the recorded vector magnetic fields due to gastric electrical activity. In each case, it was found that the information obtained by examination of the projected magnetic field vectors gave superior clinical insight to that obtained by analysis of any single magnetic field component.


Assuntos
Eletrodiagnóstico/métodos , Campos Eletromagnéticos , Processamento de Sinais Assistido por Computador , Animais , Feminino , Coração Fetal/fisiologia , Trato Gastrointestinal/fisiologia , Humanos , Gravidez , Diagnóstico Pré-Natal/métodos , Coelhos
10.
Neurogastroenterol Motil ; 15(5): 475-82, 2003 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-14507349

RESUMO

We recorded the vector magnetogastrogram (MGG) due to gastric electrical activity (GEA) in normal rabbits using a Superconducting QUantum Interference Device (SQUID) magnetometer and measured the degree of correlation of the MGG with 24 channels of serosal electrodes. The vector magnetometer allows us to non-invasively record three orthogonal magnetic field components and project the recorded magnetic field vector into arbitrary directions. We optimized the magnetic field vector direction to obtain the highest possible correlation with each serosal electrode recording. We performed a vagotomy and examined spatial and temporal changes in the serosal potential and in the transabdominal magnetic field. We obtained spatial information by mapping the recorded signals to the electrode positions in the gastric musculature. Temporal evidence of uncoupling was observed in spectral analyses of both serosal electrode and SQUID magnetometer recordings. We conclude that non-invasive recordings of the vector magnetogastrogram reflect underlying serosal potentials as well as pathophysiological changes following vagotomy.


Assuntos
Magnetismo , Complexo Mioelétrico Migratório/fisiologia , Vagotomia , Nervo Vago/fisiologia , Animais , Fenômenos Eletromagnéticos , Masculino , Coelhos
11.
Eur J Pharmacol ; 417(1-2): 131-40, 2001 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-11301068

RESUMO

Stretch-activated ion channels have been identified as transducers of mechanoelectric coupling in the heart, where they may play a role in arrhythmogenesis. The role of the cytoskeleton in ion channel control has been a topic of recent study and the transmission of mechanical stresses to stretch-activated channels by cytoskeletal attachment has been hypothesized. We studied the arrhythmogenic effects of stretch in 16 Langendorff-perfused rabbit hearts in which we pharmacologically manipulated the microtubular network of the cardiac myocytes. Group 1 (n=5) was treated with colchicine, which depolymerizes microtubules, and Group 2 (n=6) was treated with taxol, which polymerizes microtubules. Stretch-induced arrhythmias were produced by transiently increasing the volume of a fluid-filled left ventricular balloon with a volume pump driven by a computer-controlled stepper motor. Electrical events were recorded by a contact electrode which provided high-fidelity recordings of monophasic action potentials and stretch-induced depolarizations. The probability of eliciting a stretch-induced arrhythmia increased (0.22+/-0.11 to 0.62+/-0.19, p=0.001) in hearts treated with taxol (5 microM), whereas hearts treated with colchicine (100 microM) showed no statistically significant change. We conclude that proliferation of microtubules increased the arrhythmogenic effect of transient left ventricle diastolic stretch. This result indicates a possible mode of arrhythmogenesis in chemotherapeutic patients and patients exhibiting uncompensated ventricular hypertrophy. The data would indicate that the cytoskeleton represents a possible target for antiarrhythmic therapies.


Assuntos
Arritmias Cardíacas/fisiopatologia , Colchicina/farmacologia , Paclitaxel/farmacologia , Tubulina (Proteína)/metabolismo , Disfunção Ventricular/fisiopatologia , Animais , Arritmias Cardíacas/etiologia , Colchicina/metabolismo , Ventrículos do Coração/fisiopatologia , Hemodinâmica/fisiologia , Técnicas In Vitro , Microtúbulos/efeitos dos fármacos , Microtúbulos/metabolismo , Paclitaxel/metabolismo , Ligação Proteica , Coelhos , Estresse Mecânico , Disfunção Ventricular/etiologia
12.
J Biomed Opt ; 4(2): 200-7, 1999 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23015205

RESUMO

Optical imaging of cardiac transmembrane potential in dye-stained tissue is an emerging technique in cardiac electrophysiology. Despite its widespread application to studies of isolated hearts, it has been applied traditionally to recording only a single view that presents the potential distribution of a fraction of the cardiac surface. This poses a significant limitation in studying whole heart electrophysiology, particularly when large-scale phenomena such as fibrillation and defibrillation are of interest. We have developed a panoramic imaging system based on a high-speed charge-coupled device camera with a maximum imaging speed of 335 frames/s at 128×64 pixels/frame. Our system provides one front view and two back mirror views of isolated hearts, thus extending optical imaging capabilities to record from the entire three dimensional heart surface with only one camera. © 1999 Society of Photo-Optical Instrumentation Engineers.

13.
Med Phys ; 7(4): 297-306, 1980.
Artigo em Inglês | MEDLINE | ID: mdl-7393156

RESUMO

Because the magnetic susceptibility of the heart and the intracardiac blood is substantially greater than that of the surrounding lung tissue, the periodic redistribution of blood and tissue during the cardiac cycle will alter an externally applied magnetic field. These magnetic field changes can be detected by a magnetometer outside the body and have been termed magnetic susceptibility plethysmography (MSPG) signals. This paper presents a theoretical analysis of the MSPG technique. A single moving sphere model is used to explain the susceptibility induced field changes and the detection of the MSPG signals. The susceptibility distribution within the thorax and a more detailed model of the heart are then used to predict the MSPG waveform. Several other contributions to the MSPG signal are analyzed. This model has demonstrated that the time dependence of certain MSPG components closely resembles that of the total heart volume while other components have waveforms similar to the displacement of the cardiac center of mass. The magnitude and direction of the MSPG field has been shown to depend on the location of the field point, the volume change of the heart, and the motion of the heart's center of mass. It has also been shown that 90% of more of the MSPG signal recorded near the heart but outside the body will be produced by cardiac volume changes. For these reasons, the MSPG technique may provide a noninvasive method of measuring changes both in total cardiac volume and in the position of the cardiac center of mass throughout the cardiac cycle.


Assuntos
Cardiografia de Impedância , Magnetismo , Pletismografia de Impedância , Humanos , Matemática , Modelos Biológicos
14.
Med Phys ; 7(4): 307-14, 1980.
Artigo em Inglês | MEDLINE | ID: mdl-7393157

RESUMO

The magnetic susceptibility of the heart and the intracardiac blood is substantially greater than that of the surrounding lung tissue. The periodic redistribution of blood and tissue during the cardiac cycle will thus alter an externally applied magnetic field. These magnetic field changes can be detected by a magnetometer outside the body, and have been termed magnetic susceptibility plethysmography (MSPG) signals. A differential magnetometer, a liquid helium dewar, and a superconducting persistent-current magnet have been developed to detect the x component of the MSPG signal. The theoretical analysis of this instrument is presented to understand the spatial sensitivity of an MSPG susceptometer with a nonuniform magnetizing field. Preliminary measurements are shown to be in fair agreement with the model calculations. Several possible improvements of the technique are discussed.


Assuntos
Cardiografia de Impedância , Magnetismo , Pletismografia de Impedância , Adulto , Cardiografia de Impedância/instrumentação , Humanos , Masculino , Pletismografia de Impedância/instrumentação
15.
J Clin Neurophysiol ; 8(2): 170-88, 1991 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-2050817

RESUMO

We review the fundamental origins of biomagnetic fields in terms of ionic currents flowing at the cellular level. Mathematical models provide the link between the macroscopic fields and the microscopic electrophysiological sources. The single cell view is then expanded to include more complex systems such as nerve and muscle bundles. We provide an overview of the two most promising methods to measure the magnetic fields from these systems, we discuss the capabilities and limitations of the techniques based on comparisons with conventional electric methods, and we show that the direct measurement of action currents and the ability to scan along nonuniform samples are of prime importance. We present a number of interesting applications for basic research under laboratory conditions, including measurements of the time course of electrophysiological changes following a crush injury to a nerve and the spatial and temporal dependence of action currents as they propagate away from the motor endplate zone of a single motor unit in skeletal muscle. We conclude by discussing the potential applications in the clinic, including the intraoperative assessment of neuroma-in-continuity and the long-term monitoring of nerve regeneration and degenerative neuromuscular disorders.


Assuntos
Axônios/fisiologia , Magnetismo , Músculos/fisiologia , Nervos Periféricos/fisiologia , Potenciais de Ação/fisiologia , Animais , Humanos , Íons , Ratos
16.
Am J Surg ; 167(6): 586-92, 1994 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-8209933

RESUMO

Intestinal ischemia is associated with changes of the basic electric rhythm (BER) of the small intestine. We hypothesized that these changes can be measured noninvasively using a superconducting quantum interference device (SQUID). After general anesthesia, a laparotomy was performed on 10 animals and the jejunum was placed in a nonmagnetic recording chamber containing Krebs' solution at 38 degrees C. Five animals had electrodes placed while five others were placed under the SQUID. Injection of thrombin into the mesenteric artery decreased blood flow (measured with a laser doppler flow-meter) 95% within 5 minutes. SQUID measurements showed significant decreases (P < 0.01 for all changes) in the frequency (15.5 +/- 0.3 to 8.9 +/- 0.2 cycles/min) and the propagation velocity of slow waves (3.5 +/- 0.2 to 1.9 +/- 0.3 sec). The changes in intestinal biomagnetic activity after ischemia were similar to the changes in electrical activity. The SQUID magnetometer is a reliable noncontact device that can detect early intestinal ischemia in animal models. We have recently recorded human small bowel biomagnetic activity using a SQUID magnetometer and believe further technical developments will permit the noninvasive diagnosis of mesenteric ischemia.


Assuntos
Intestinos/irrigação sanguínea , Intestinos/fisiopatologia , Isquemia/diagnóstico , Isquemia/fisiopatologia , Magnetismo , Animais , Modelos Animais de Doenças , Eletrofisiologia , Masculino , Coelhos , Fatores de Tempo
17.
Phys Med Biol ; 38(9): 1311-28, 1993 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-8415903

RESUMO

We report measurements of slowly varying magnetic field patterns close to fertilized eggs of the chicken Gallus domesticus during the first few days of incubation. These fields are generated by ionic currents within the egg that are associated with the development of the embryo. Since they are very weak (no greater than tens of pT) and vary over distances of a few millimetres, it has been necessary to develop specialized instrumentation and analysis techniques. We describe the use of high-spatial-resolution SQUID magnetometers to measure the field patterns and appropriate imaging algorithms to model the current sources responsible for producing the fields. Our results provide strong evidence for a distributed source in the extra-embryonic membranes. There is also indication of a more localized source within the embryo itself.


Assuntos
Embrião de Galinha/fisiologia , Campos Eletromagnéticos , Íons , Algoritmos , Animais , Embrião de Galinha/crescimento & desenvolvimento , Zigoto
18.
IEEE Trans Biomed Eng ; 41(3): 232-40, 1994 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-8045575

RESUMO

Numerical calculations simulated the response of cardiac muscle to stimulation by electrical current. The bidomain model with unequal anisotropy ratios represented the tissue, and parallel leak and active sodium channels represented the membrane conductance. The speed of the wavefront was faster in the direction parallel to the myocardial fibers than in the direction perpendicular to them. However, for cathodal stimulation well above threshold, the wavefront originated farther from the cathode in the direction perpendicular to the myocardial fibers than in the direction parallel to them, consistent with observations of a dog-bone-shaped virtual cathode made by Wikswo et al., Circ. Res. 68:513-530, 1991. The model showed that the virtual cathode size and shape were dependent upon both membrane and tissue conductivities. Increasing the peak sodium conductance or reducing the transverse intracellular conductivity accentuated the dog-bone shape, while the opposite change caused the virtual cathode to become more elliptical, with the major axis of the ellipse transverse to the fiber direction. A cathodal stimulus created regions of hyperpolarization that slowed conduction of the wavefront propagating parallel to the fibers. An anodal stimulus evoked a wavefront with a complex shape; activation originated from two depolarized regions 1 to 2 mm from the stimulus site along the fiber direction. The threshold current strength (0.5 ms duration pulse) for a cathodal stimulus was 0.048 mA, and for an anodal stimulus was 0.67 mA. When the model was modified to simulate the effect of electropermeabilization, which may be present when the transmembrane potential reaches very large values near the stimulating electrode, our qualitative conclusions remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)


Assuntos
Coração/fisiologia , Potenciais da Membrana/fisiologia , Modelos Cardiovasculares , Animais , Cães , Condutividade Elétrica , Estimulação Elétrica , Eletrofisiologia , Dinâmica não Linear , Valores de Referência , Canais de Sódio/metabolismo
19.
IEEE Trans Biomed Eng ; 41(10): 969-74, 1994 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-7959804

RESUMO

A digital simulation has been performed of an idealized, thin, 2-D cardiac slice in the chi-y plane. The slice is stimulated near the center and the resulting action potential propagates outward, developing a distribution of electrical current with nonzero curl. An anisotropic bidomain model is used for the calculation, with membrane physiology based upon either just fast sodium fluxes or the more complete Beeler-Reuter myocardial model. The electrical anisotropy, expressed as the ratio of longitudinal to transverse electrical conductivity, is much greater for the inner domain than for the outer one, and this results in current loops that develop ahead of and behind the wavefront and produce a Bz magnetic field of order 10(-9) T 1 mm above the tissue, similar to recent experimental observations on canine cardiac tissue slices. The fields exhibit a quatrefoil symmetry which can be distorted by nonuniformities in the tissue. The field from repolarization currents is larger by almost an order of magnitude than might be predicted from considerations of rate of change of voltage.


Assuntos
Simulação por Computador , Campos Eletromagnéticos , Coração/fisiologia , Modelos Cardiovasculares , Potenciais de Ação/fisiologia , Anisotropia , Condutividade Elétrica , Processamento de Imagem Assistida por Computador , Técnicas In Vitro
20.
IEEE Trans Biomed Eng ; 44(10): 948-57, 1997 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-9311164

RESUMO

We have developed a computationally simple model for calculating the magnetic-field strength at a point due to a single motor unit compound action potential (SMUCAP). The motor unit is defined only in terms of its anatomical features, and the SMUCAP is approximated using the tripole model. The distributed current density J is calculated within the volume defined by the motor unit. The law of Biot and Savart can then be cast in a form necessitating that J be integrated only over the region containing current sources or conductivity boundaries. The magnetic-field strength is defined as the summation of the contributions to the field made by every muscle fiber in the motor unit. Applying this model to SMUCAP measurements obtained using a high-resolution SUper Conducting Quantum Interference Device (SQUID) magnetometer may yield information regarding the distribution of action currents (AC's) and the anatomical properties of single motor units within a muscle bundle.


Assuntos
Magnetismo , Modelos Neurológicos , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Potenciais de Ação/fisiologia , Animais , Eletromiografia , Placa Motora/fisiologia , Fibras Musculares Esqueléticas/fisiologia , Condução Nervosa/fisiologia , Distribuição de Poisson , Ratos
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