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Voltage gated ion channels activate in response to step changes in voltage but slowly inactivate even though the voltage is maintained. It has been proposed that part of the channel forms a ball tethered to a chain and inactivation occurs when this ball binds to a site blocking the pore of the channel. The authors derived the statistical properties of this model so that it can be quantitatively tested...
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Stretch-activated ion channels (SACs) in myocytes isolated from neonatal rats were studied in cell-attached patches. Stretch was applied to cell-attached patches by suction (5-20 mm Hg) in the recording pipet. Stretch caused the triggering of action potentials that were recorded in cell-attached patches as biphasic action currents (ACs). The significance of a temporal correlation between SAC open...
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Electric-field-induced surface traction (surface force density) within the red blood cell (RBC) membrane was examined. The RBC was modeled as a spheroid with a membrane of finite thickness. Surface traction within the RBC was derived using Maxwell's stress tensor. The derivation results suggested that both a compressive force and a net outward pushing force were acting on the RBC membrane. The interaction...
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A simplified model of cranial exposure to 60-Hz electromagnetic fields is developed and analyzed. The physiological mechanisms surrounding exposure effects in the central regions of the brain, and pertinence to this model, are described. The simplified model is based on three concentric spherical shells representing the skull, grey matter, and white matter of the head. Approximated boundary conditions...
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Digitized X-ray angiograms of the left ventricle were clustered using a weighted Euclidean distance criterion with the constraint that the pixels in a cluster are spatially coherent. A three-dimensional feature space was used: position along x and y coordinates and image intensity. The spatial coherence constraint is based upon the belief that pixels within a cluster should be coherent in a spatial...
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A novel thresholding method to separate the myocardium of correct thickness from a sequence of two-dimensional echocardiograms is presented. The threshold is made adaptive by maintaining a constant wall width ratio throughout the image sequence. The width ratio is computed at an interactively indicated wall section where the wall width is known a priori. The method is well suited for detecting the...
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The author provides a review of the subjects of positron emission tomography (PET) and magnetic resonance imaging (MRI) cardiac imaging. The physics behind both types of systems is examined, followed by a summary of the topics, and typical papers, regarding each system. A list of references obtained regarding the correlation of the different imaging modalities is provided.<<ETX>>
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Monte Carlo techniques have been used to study and optimize a two-dimensional detector array system for high-resolution positron emission tomography (PET) that consists of an 8*4 matrix of BGO crystals coupled to four photomultipliers. This allows dense packing of small scintillation crystals and their optical coupling to a smaller number of photomultiplier tubes. The design included optimizing the...
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In previous work, tracking of isophase lines in a structured light pattern projected on the human face was used to acquire the 3-D coordinates of the face in real time (1/30th of a second) (see K. Cheung and M.D. Fox, Proc. IEEE EMBS 11th Ann. Conf., p.1655-6, June 1989). In the present work, the author automated tracing of an isophase line to achieve submillimeter 3-D resolution. In contrast to work...
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The Hurst coefficient H can be interpreted as a measure of the texture contained within an image. In this work, the analysis of texture is applied to bone sections in an attempt to quantify calcification. Because the bone structure is generally nonisotropic, a radially oriented implementation of a maximum likelihood estimator for the Hurst coefficient H is proposed to determine a directionally dependent...
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An oxygen measurement system using the phase delay of ultrasonic waves has been developed. The error estimation for the sequence of data acquisition and processing and the analysis of updated data are presented here. The actually measured and the estimated errors are compared as a final step to verify the system performance. The actually measured errors were close to or even less than the estimated...
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A Rhesus monkey model has been developed that makes it possible to investigate physiological rhythms and circadian effects on performance in an integrated framework. Body temperature and animal activity are of great importance in the study of circadian rhythms. To monitor a free-ranging monkey's temperature, a telemetry system is used. Monkey activity is measured using strain-gage transducers mounted...
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The effect of exercise on optical properties of the limb is of interest when the optical properties can be related to changes at depth within the limb. Such information may suggest ways in which noninvasive optical methods can be used to monitor exercise. In the present study, a source-detector arrangement was connected to a computer for collection of data at approximately 7-s intervals during sitting,...
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An instrument for constant current iontophoretic transdermal drug delivery was designed, prototyped, and preliminarily tested in the New Zealand white rabbit. This flexible device has been designed to synthesize several constant current output waveshapes of selectable magnitude, frequency, and duty cycle. The output waveforms include the conventional DC and monophasic pulsed DC, as well as two novel...
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An attempt was made to attain a better understanding of the autonomic effects involved in the motion sickness stimulation of the heart. An attempt was made to monitor the vagal activity in ten NASA volunteers undergoing motion stimulation. The heart rate spectrum was adopted as the technique which noninvasively allows the quantitative measurements of vagal tone by assessing the amount of heart rate...
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Changes in electroencephalogram (EEG) were analyzed at different levels of halothane anesthesia. Five experiments were carried out on mongrel dogs. Four channels of EEG data were recorded, at different anesthetic levels. A tenth-order autoregressive (AR) model was used to represent the EEG signal. The AR model parameters were used as input to a three-layer perceptron feedforward neural network, and...
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A least squares algorithm is presented which uses one weight for phase shift correction per reference input for adaptive noise canceling with one or multiple reference inputs. The method uses an iterative gradient search procedure which assumes that phase shifts between inputs are small compared to the frequency of meaningful, correlated, periodic noise components. In a simulation in which the primary...
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A system has been developed for multineuronal studies through a single extracellular microelectrode. This system is used to detect and study the behavior of local neuronal nets, formed by the dendritic appendages of tectral cells in the superficial tectum of the frog. The system consists of a software package for visual stimulation, spike detection, and classification, calculation of cross-correlograms...
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Three circuits are described as an initial step toward implementing an analog VLSI-based backpropagation neural network. One of these circuits is the connectivity matrix for a fully connected five-input perceptron. The second is a summer circuit that immediately computes total backpropagated error. The third is a triggerable processor that optimizes a given synaptic weight with respect to backpropagated...
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The single-layer feedforward neural network (FFNN) in conjunction with the backpropagation training algorithm (BPTA) is used for electrocardiogram (ECG) classification. It has been observed that, for such a problem, the values of the input weights are closely related to the input training set. An implication of this observation is that, rather than choosing initially random weights for the BPTA, one...
