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Bioengineering Conference, 1989., Proceedings of the 1989 Fifteenth Annual Northeast

Date 27-28 March 1989

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Displaying Results 1 - 25 of 117
  • Proceedings of the Fifteenth Annual Northeast Bioengineering Conference (Cat. No.89-CH2689-8)

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    Freely Available from IEEE
  • Effects of rapid onset acceleration on cephalic pulsatile blood volume impedance waveforms in humans

    Page(s): 129 - 130
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    Electrical impedance plethysmographic measurements of the relative changes in cephalic pulsatile blood volume (rheoencephalography, or REG) have been performed clinically for many years. REG indices provide information about cerebral vascular resistance (CVR). The technique has been used to noninvasively monitor real-time cephalic pulsatile blood volume changes in humans exposed to acceleration stress in the head-to-foot direction (+Gz) on the Naval Air Development Center (NADC) human centrifuge. Changes in the REG waveform occurring with increasing +Gz load have been characterized View full abstract»

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  • Data length effects on the coherence estimate of EEG

    Page(s): 93 - 94
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    The coherence functions between EEGs (electroencephalograms) collected from the hippocampal subfield CA1 and dentate is reexamined by conventional (periodogram) and autoregressive (AR) approaches to study the effects of different data lengths on the performance of these approaches and the variation of the resultant magnitude squared coherence (MSC) and phase coherence estimates. The MSC and phase coherence obtained from the autoregressive method are smoother and demonstrate lower standard deviation than the results obtained by the classical approach. In general, the standard deviation of the MSC and the phase coherence decreases as data length increases, and the standard deviation of the AR method is less than that of the periodogram. The results indicate that for applications in which computational speed is not critical, the multichannel autoregressive model provides a coherence estimate that is smoother and exhibits lower standard deviation than the conventional periodogram approach View full abstract»

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  • Post-repolarization refractoriness in the ventricular muscle

    Page(s): 7 - 8
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    The authors extend an experimental model to a two-dimensional analysis of post-repolarization refractoriness (PRR) and ventricular arrhythmias. The rectifying potassium channel in the plateau phase of the model plays a major role in the near-synchronous repolarization in the normal tissue. With changes in the time constant of inactivation of inward currents and with the concentration changes in calcium and potassium ion, the action potential duration can be seen to be affected adversely. This, coupled with the poor cellular communication observed, affects the slow recovery of subthreshold currents, leading to PRR View full abstract»

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  • Further results utilizing the MRE principle in inverse electrocardiography

    Page(s): 229 - 230
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    The authors explore two linearized implementations of the application of a frequency-domain method, the minimum relative entropy (MRE) reconstruction principle, to the inverse problem in electrocardiography. These methods reconstruct the power spectrum of each epicardial signal, in contrast to most methods that have been applied to this problem, which operate in the time domain of the data using regularization techniques and minimizing squared error. The least-squares methods have important weaknesses for clinical applications. Simulations and comparisons are carried out using canine epicardial data and an accurate model of the human torso taken from CT (computerized tomography) scans View full abstract»

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  • Time-of-flight PET with BaF2

    Page(s): 109 - 110
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    The available TOFPET (time-of-flight positron-emission tomography) scanners with BaF2 have a TOF resolution of about 500 ps. The possible reasons for this can be several, including spread in the time of arrival of photons to the photocathode, transit time spread in the photomultiplier, jitter in the timing from the discriminator and the time-to-digital converters, and systematic channel-to-channel shifts. The authors have developed a Monte Carlo program to study the contribution of each of these effects to the TOF results. They simulate the interactions of 511 KeV gammas with the detector (Compton and photoelectric absorption), the emission and propagation of UV light in the crystal, and the pulse formation in the photomultiplier. The time spread due to each effect is calculated, as well as the time spread due to all these effects combined. Experimental evidence indicates that the length of the crystal has a strong effect on the light collection time spread, both due to reflections and to the exponential distribution of interaction points inside the crystal. To quantify the length effect, the authors calculated the FWHM (full-width half maximum) of the time of production of the first photoelectron on the photocathode View full abstract»

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  • Projection processing for improved resolution and noise suppression of reconstructed images of computer tomography

    Page(s): 111 - 112
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    A nonlinear digital filtering technique (median filtering) is suggested for processing the projections to reduce error without the distortion introduced by linear filtering. The rationale for the application of these filters is discussed. To compare the effectiveness of linear filtering and median filtering, computer simulations and further experiments are suggested. It is expected that median filters have potential to improve image quality beyond that of linear filtering, particularly for edge reproduction View full abstract»

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  • Three-dimensional reconstruction of the craniofacial surface with stereopair images

    Page(s): 115 - 116
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    A simple method is described for adding texture to the relatively smooth surface of the human face by projecting fine textural patterns drawn on transparency. Experiments show that these fine patterns can improve the accuracy of cross-correlation data and thus the accuracy of surface height calculated from such cross correlation. The average percent error of height determination on a face phantom improved from 79% without a projected pattern to 18% with such a pattern, or a 438% improvement View full abstract»

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  • Optimal adjustment of the atrio-aortic left ventricular assist device (AA-LVAD)

    Page(s): 69 - 70
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    The authors document a protocol for optimal timing of the LVAD based on reduced heart oxygen consumption. Timing is studied using a closed-loop analog model of the heart, vascular system, and the LVAD. Results indicate that the pump should begin ejection immediately after the close of the aortic valve and that the pump filling pressure should pump set to a value which produces maximum filling of the pump and maximum ventricular unloading. The optimization of the pump ejection pressure is a trade-off between left-ventricular O2 and stroke volume and mean arterial pressure View full abstract»

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  • Quantitative determination of cardiac function based on 3-D geometrical analysis

    Page(s): 13 - 14
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    A novel ventricular analytical procedure for 3-D reconstruction of the left ventricle (LV) is utilized to define quantitatively the 3-D shape by a size-independent individual geometric cardiogram (GCG). Individual vectors can then be grouped to define the characteristic shape of the normal heart and the pathological state. Shape, wall thickness, and stress were found to be sensitive to regional infarction. Magnetic resonance image (MRI) data of ischemic dogs and cine-computed tomography analysis of patients with clinically defined diseased LV verify the power of this procedure to identify pathological shape changes. The convenient application of shape analysis is demonstrated by MRI studies of hypertrophy under hypotension for a period of 23 weeks View full abstract»

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  • Using signal processing techniques for DNA sequence comparison

    Page(s): 173 - 174
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    The most widely used algorithm for the comparison of two sequences of DNA are O(m×n) on the lengths, m and n, of the sequences been compared. The authors present a comparison algorithm that is O(nlog n) on the length, n, of the longer sequence. This algorithm uses techniques developed for rapid comparison of two discrete signals, in particular, cross-correlation using the fast Fourier transform (FFT). The authors treat the DNA as a discrete signal with each nucleotide base represented by a single point in the signal. There are only four possible values that the signal can assume which they represent by one of four complex numbers. The comparison is made by performing a cross correlation between one signal and the complex conjugate of the other. Any significant peak in the resulting signal indicates a strong similarity between the two sequences. The authors present the results of comparison of two strains of the human immunodeficiency virus and of human and simian immunodeficiency viruses. Their results suggest that this technique is a powerful method for comparing very long sequences of DNA View full abstract»

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  • A nonlinear spectrum compression algorithm for the hearing impaired

    Page(s): 21 - 22
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    A technique is proposed for increasing the speech intelligibility of persons with profound sensorineural hearing loss. The processing is based on a modification of the chirp-z transform that allows for nonlinear sampling along an arbitrary contour of the z-plane. Although the theory allows the nonlinear sampling to be arbitrary, an example showing that it is appropriate for nonlinear spectrum compression to aid the hearing-impaired is given. Samples are linearly spaced along the unit circle for a specified low-frequency segment; beyond the break-point the samples are nonlinearly spaced, perhaps spiraling inward to enhance spectral peaks, with the spacing width increasing with increasing frequency following an exponential function. A standard inverse DFT of these frequency samples returns the spectrum-compressed sequence. Processing of continuous speech requires windowing and processing of data in a manner similar to the short-time Fourier transform (STFT). The authors present the theoretical basis for, and development of, the algorithm View full abstract»

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  • EKG waveform recognition procedure

    Page(s): 225 - 226
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    A fast, accurate, and robust EKG (electrocardiogram) waveform-recognition algorithm has been developed for a personal computer. The method uses the convolution of raw EKG data with one or more sample EKG waveform templates as a recognition signal. Recognition occurs when the convolution exceeds a user-defined reference level. This level can depend on the history of the recognition signal as well as on other physiological data View full abstract»

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  • Time-varying identification of the neuromuscular system. I. Human joint dynamics

    Page(s): 147 - 148
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    A time-varying system identification technique has been developed to track abrupt changes in system characteristics using ensemble input and output records. No a priori assumptions are required regarding the system structure, form of the nonstationary, or input characteristics. A simulation study has shown the method to be capable of tracking the time course of changes in human ankle-joint dynamics associated with an abrupt change in the level of voluntary activation. The method has proved to be robust in the presence of noise View full abstract»

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  • Stability analysis of an output feedback controller for the Penn State electrical ventricular assist device

    Page(s): 71 - 72
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    The development of a controller which minimizes the energy consumption of the implanted electric ventricular assist device (EVAD) and remains stable for the duration of the implantation is considered. The EVAD model has four state variables, only one of which is measurable in vivo. An output feedback control law that utilizes the single available state and minimizes the EVAD's energy consumption has been derived. The inclusion of the output feedback gain in the model results in a time-varying plant for which stability has to be proved. The EVAD is a pulsatile device which operates in a periodic manner. By recognizing this periodic nature, the time-varying model can be transformed into a linear time-invariant model that describes the periodic values of the system states. This linear time-variant model is used for determining whether the output feedback control law can meet the necessary and sufficient conditions for asymptotic stability View full abstract»

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  • Syntax and semantics of languages for medical information processing

    Page(s): 189 - 190
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    A set of suggestions is presented by the authors to IEEE committees working to standardize medical data communications between devices and host computers (IEEE P1073) and among host computers (IEEE P1157). The authors' model is intended to be a formal logic for the conceptual schema, and does not specify any particular implementation. They give a syntax in terms of abstract data records linked by pointers and also a semantics based on naive category theory View full abstract»

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  • Experiments with lateral inhibition in two-dimensional photoreceptor arrays

    Page(s): 181 - 182
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    The process known as lateral inhibition has been observed in many sensory systems from a wide range of biological organisms. Regarded as a crucial step in preprocessing sensory information, it has been recreated in the form of two-dimensional arrays of visual receptor cells. Lateral inhibition (LI) is applied by two different means on arrays of pixels in two different configurations. One method is a dynamic algorithm that it applied to a 25-cell rectangular array. A second, static method is used on a nineteen-cell hexagonal array. Both circuits were implemented in VLSI using 3 μm CMOS technology View full abstract»

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  • Biological time-series analysis via a fast orthogonal search

    Page(s): 149 - 150
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    Advantages of time-series analysis are described and illustrated by the fast orthogonal search method. The method can be used to approximate biological time-series data by a parsimonious sinusoidal series model or representation. The component frequencies in this model need not be commensurate nor integral multiples of the fundamental frequency corresponding to the record length. The method achieves economy of representation by finding the most significant frequencies first. In simulations, the author shows that the method really copes with missing or unequally-spaced data, and is capable of five to eight time the frequency resolution of a conventional Fourier-series analysis View full abstract»

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  • Measurements of vascular wall O2 consumption following increased potassium

    Page(s): 245 - 246
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    Vascular wall tissue PO2 was measured with recessed cathode microelectrodes (tip diameters <5 μm) in either strips or perfused segments of rabbit abdominal aortas (n=10). When bathed by saline with low K+ (4 mEq/L) oxygenated at 20 kPa, the minimum wall PO2 was 6.65±1.56 (S.E.) kPa for seven aortic strips and 10.38±0.54 kPa for 16 measurements in three perfused aortic segments. Biphasic PO2 increased significantly above control by +0.91±0.21 kPa (p<0.05), decreasing below control within 1 min in most cases. After 3 min, PO2 decreased significantly below control by -0.72±0.24 kPa (p<0.05). O2 disappearance rates measured after stopping flow to perfused segments were significantly faster (p<0.001) after relatively small changes in K+ (4 to 7 mEq/L) with little further increase at higher K+ up to 30 mEq/L. The data are consistent with elevated O2 consumption as K+ increases. Perfused aortic segments had much greater metabolic changes than aortic strips for similar K+ increases View full abstract»

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  • Vestibular contributions to the information processing rate of the head/neck complex

    Page(s): 201 - 202
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    The authors assess the applicability of Fitts' law for the prediction of head movement time in healthy university males. Another central issue is addressed; namely, the effect that the presence of onboard sensors in the head (i.e. the vestibular system and the visual system) has on the information processing capability of the head/neck complex. It was found that the information processing rages (the inverse of the regression slope parameter in Fitts' equation) for each subjects's head movement ranged from 4 to 8 b/s. In the overall regression equation, the information processing rate for the experimental head movement was 7 b/s. This rate is much less than that of the extremities during reciprocal tapping tasks. Explanations for this difference are offered View full abstract»

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  • Anisotropy of human coronary artery intima

    Page(s): 205 - 206
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    There is extensive evidence that the acute phase of myocardial infarction frequency involves fissuring of the intima of epicardial coronary arteries. The fissures have been found postmortem generally at the sites of atheromatous plaques containing lipid. Pathological evidence suggest that the fracture occurs before death, with a thrombus growing in the pocket of the plaque as well as in the lumen of the vessel. Mechanical measurements have been made in uniaxial testing of human coronary artery intima segments. The fracture stresses measured are in the range of those computed in whole vessel walls, for which measured mechanical properties of tissues have been assigned, under pressure achieved within the physiological range, after the stress-intensifying effects of local lipid plaques have been incorporated View full abstract»

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  • Breathing modulates fetal heart rate

    Page(s): 233 - 234
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    To assess the modulation of fetal heart rate (FHR) by breathing movements, the authors investigated the relationship between FHR and fetal breathing rate (FBR). FHR was obtained from the R-R interval of the EKG and FBR from the burst-burst interval of the diaphragmatic electromyogram (EMG). The R-R intervals of EKG and burst-burst interval of the diaphragmatic EMG were determined using a template recognition method. These data were then analyzed in both the frequency and time domains. Frequency analysis was carried out using the linear prediction method with the optimum order. It is confirmed that fetal breathing movements modulate fetal heart-rate variability View full abstract»

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  • Visual-vestibular interaction during rotation about the Earth horizontal axis

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    Summary form only given. Seven human subjects were tested for visual-vestibular interaction (VVI) in a constant-velocity Earth horizontal axis (EHA) yaw rotation. This so-called barbecue-spit rotation provides an angular acceleration pulse to the horizontal semicircular canals and a constantly rotating gravity vector to the otolith organs. The subjects were tested with their eyes open in the dark (EOD), while fixating on a target rotating with them (FIX), and while counting stationary optokinetic stripes (VVR). The magnitude parameters for the canal mediated response (AMP) and those of the otolith mediated response (MOD and BIAS) were measured in each of the VVI conditions. In the VVR paradigm, AMP values were slightly below those of EOD. Averaged over all subjects, MOD values were greater for the VVR paradigm than that of the EOF paradigm. The FIX results suggest that canal and otolith mediated vestibular responses are suppressed using a small-angle fixation target in a similar way. The VVR results suggest that the gain of the otolith mediated parameters of BIAS and MOD may increase by a factor of nearly four when subjected to an illuminated surround View full abstract»

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  • Intraocular lens optical quality testing

    Page(s): 47 - 48
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    The possibility that problems relating to the optical quality of manufactured intraocular lenses (IOLs) may require regulatory attention is addressed. Based on the American National Standard for Ophthalmics-Intraocular Lenses-Optical and Physical Requirements (ANSI Standard Z80.7-1984), the US Food and Drug Administration (FDA) will soon be ready for conformance testing of IOLs. A description is given of the current IOL test setup, some of the test parameters to be addressed, and future outlook of this IOL test program View full abstract»

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  • Determination of the mechanical losses of the Penn State electrical ventricular assist device

    Page(s): 67 - 68
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    The Penn State electric ventricular assist device (EVAD) consists of a brushless DC electric motor, rollerscrew, pusher plate, pump chamber, and valves. The authors analyze the mechanical linkage of the EVAD and quantify the dissipated energy of the rollerscrew and the supporting bearings. Their analysis sheds further light on the physical phenomenon undertaken in transforming the rotary motion of the armature into a linear motion of the pusher plate. Understanding this phenomenon enables them to construct a better mathematical model of the device, which can be used for identifying the possible modifications that will increase the efficiency of future EVAD designs View full abstract»

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