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Biomedical Engineering, IEEE Transactions on

Issue 10 • Date Oct. 1993

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Displaying Results 1 - 13 of 13
  • Algorithm to control "effect compartment" drug concentrations in pharmacokinetic model-driven drug delivery

    Page(s): 993 - 999
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    In most computer-controlled pharmacokinetic model-driven drug infusion pumps, simulation of a linear compartmental pharmacokinetic model is used to compute the rate of intravenous drug infusion required to achieve setpoint central compartment (plasma) drug concentrations. For many drugs, it has been suggested that it is the drug concentration in a hypothetical "effect" compartment, rather than in the plasma, that should be manipulated to achieve maximum control over pharmacologic action. Controlling the effect compartment drug concentration is algorithmically more difficult than controlling the central compartment drug concentration because of the time delay between administration of drug into the central compartment and its subsequent appearance in the effect compartment. The authors present a model-based dosing algorithm for use in pharmacokinetic model-driven drug infusion devices that target the theoretical effect compartment drug concentration. View full abstract»

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  • A linear time-varying model of force generation in skeletal muscle

    Page(s): 1000 - 1006
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    A model of isometric force production by skeletal muscle was developed in which the response to each stimulus in a train was described by a critically damped, linear second-order system. The parameters describing the system were constrained to be constant within an interstimulus interval, but were allowed to vary between interstimulus intervals. The ability of this model to match experimental data, and the time variation in the parameters (low-frequency gain and natural frequency) required to do so were examined in soleus and plantaris muscles of the cat stimulated by synchronous whole-nerve stimulation. The model produced good fits across firing rates from twitch to tetanus for slow and fast muscle, rested and fatigued muscle, and maximal and submaximal stimulation. Both gain and natural frequency generally varied smoothly and predictably under all conditions. Gain increased at intermediate stimulation rates and in potentiated muscle, and decreased with fatigue and submaximal stimulation. Natural frequency was higher in fast muscle, and decreased with stimulation rate and fatigue. This modeling approach may provide a useful alternative to current models of skeletal muscle force, as its implementation is simple and it can describe force under conditions (fatigue, potentiation) where the muscle dynamics change with time. View full abstract»

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  • Stability and control of a frontal four-link biped system

    Page(s): 1007 - 1018
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    A conceptual model, for studying the involvement of the central nervous system (CNS) in the performance of lateral swaying movements is described. The model is based on a four-link planar biped that approximates gross human locomotion in the frontal plane. The viscoelastic function of the musculoskeletal system provides a linear controller for the system. Such an intrinsic controller can effectively duplicate simple well-learned tasks in the absence of higher level CNS feedback. This hypothesis is supported by comparing the proposed controller with two neurophysiologically involved linear decoupling schemes. Reference trajectories for swaying commands are recorded from experiments conducted in the Gait Analysis Laboratory of the Ohio State University Hospitals. These reference trajectories are inputs to all three controllers. The viability of intrinsic feedback scheme in the execution of swaying tasks is demonstrated via comparison of responses from the three controllers. View full abstract»

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  • Fatigue compensation of the electromyographic signal for prosthetic control and force estimation

    Page(s): 1019 - 1023
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    During a sustained muscle contraction, the amplitude of electromyographic (EMG) signals increases and the spectrum of the EMG signal shifts toward lower frequencies. These effects are due to muscular fatigue and can cause problems in the control of myoelectric prostheses and in the estimation of contraction level from the EMG signal. It has been well known that the fatigue effects can be explained by the conduction velocity changes during the fatigue process and by the idea that the conduction velocity is linearly proportional to the median frequency of EMG signals. Hence the fatigue process can be monitored by measuring the median frequency. A fatigue compensation preprocessor has been developed. It uses the widely accepted power spectrum density model of EMG signals that contains the conduction velocity as a measure of fatigue. It was verified that the preprocessor scales down the amplitude of the fatigued EMG signal and decompresses the spectrum. Hence, the preprocessor eliminates the increase in amplitude and the shift in frequency and enables consistent EMG signals to be used to control prostheses. View full abstract»

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  • Sensory nerve recording for closed-loop control to restore motor functions

    Page(s): 1024 - 1031
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    A method is developed for using neural recordings to control functional electrical stimulation (FES) to nerves and muscles. Experiments were done in chronic cats with a goal of designing a rule-based controller to generate rhythmic movements of the ankle joint during treadmill locomotion. Neural signals from the tibial and superficial peroneal nerves were recorded with cuff electrodes and processed simultaneously with muscular signals from ankle flexors and extensors in the cat's hind limb. Cuff electrodes are an effective method for long-term chronic recording in peripheral nerves without causing discomfort or damage to the nerve. For real-time operation the authors designed a low-noise amplifier with a blanking circuit to minimize stimulation artifacts. They used threshold detection to design a simple rule-based control and compared its output to the pattern determined using adaptive neural networks. Both the threshold detection and adaptive networks are robust enough to accommodate the variability in neural recordings. The adaptive logic network used for this study is effective in mapping transfer functions and therefore applicable for determination of gait invariants to be used for closed loop control in an FES system. Simple rule-bases will probably be chosen for initial applications to human patients. However, more complex FES applications require more complex rule-bases and better mapping of continuous neural recordings and muscular activity. Adaptive neural networks have promise for these more complex applications. View full abstract»

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  • Quantitative in vivo measurements of inner ear tissue resistivities. I. In vitro characterization

    Page(s): 1032 - 1047
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    An in vivo resistivity measurement system, based on the 4-electrode reflection-coefficient technique that nondestructively measures the complex resistivity of cochlear tissues, is described. Details of the theory and instrumentation used for noninvasive measurement of resistivity are presented. In vitro experiments both characterize the accuracy of the proposed resistivity measurement system and establish general criteria for ensuring that a particular theoretical model accurately represents the experimentally measured geometry. 2 Idealized geometries (2-layer planar and 2-layer spherical) are measured experimentally; error analyses using experimental results describe the maximum error with which the experimental system noninvasively estimates resistivity from experimental reflection coefficient measurements. The precise accuracy of a noninvasive resistivity estimate depends on both the variability for experimentally measuring the reflection coefficient of a particular geometry and the average value of the measured reflection coefficient. For example, 2-point measurements of an in vitro 2-layer planar interface allow noninvasive estimation of complex resistivity with total errors of less than 1%. In addition to characterizing accuracy of resistivity estimates for different in vitro geometries, 2 general criteria were established. View full abstract»

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  • An alternative to the biomagnetic forward problem in a realistically shaped head model, the "weighted vertices"

    Page(s): 1048 - 1053
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    The "weighted vertices" (WV), an alternative in solving the biomagnetic forward problem (BFP) for a realistically shaped head (RSH) model are presented. This proposed approach differs from the others in the way some terms in the governing integral equations are defined. The effects that WV has on important issues such as the "auto solid angle" and "stability of equations" are discussed. Two variants of the WV approach, i.e., the "linear weight" and the "quadratic weight", have been developed, and comparison of results produced by these two approaches shows that the implementation of quadratic elements to evaluate the integral produces significant improvements. This study is done with a focus on magnetic rather than electric phenomena, so a homogeneous conductor has been used in the numerical example. However, the thoughts behind this proposed method can be easily extended for cases where inhomogeneous conductors are involved. Significant improvement in the accuracy of the forward problem has been observed by use of the WV approach. View full abstract»

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  • Electric-field-induced volume and membrane ionic permeability changes of red blood cells

    Page(s): 1054 - 1059
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    When an external electric field (EF) is applied to red blood cells (RBCs), the RBCs are observed to undergo a swelling action. The swelling may or may not lead to hemolysis, depending on the EF strength. An objective verification of this swelling is by measuring the RBC mean corpuscular volume (MCV). In this study, the RBC's were exposed to the appropriate EF strength to induce swelling, but caused minimal hemolysis. The MCV was measured. The change in the erythrocyte membrane ionic permeability as a result of the EF exposure was also determined, as an objective verification of presumed membrane conductance change concomitant with the swelling. The fluxes of cations K +, Na +, and Ca ++ and anion Cl - were measured. The results showed that red cell MCV was indeed increased after EF application. The EF also altered the membrane ionic conductance to allow ions to flow down their respective concentration gradient across the membrane. Without a counterbalancing ionic pressure gradient, hemoglobin colloidal pressure inevitably drew H 2O in, thus producing the observed swelling. View full abstract»

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  • Efficient electrode spacing for examining spatial organization during ventricular fibrillation

    Page(s): 1060 - 1066
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (729 KB)  

    Spatial organization has been observed during episodes of ventricular fibrillation (VF) by recording epicardial unipolar electrograms on a grid of electrodes. In such studies, the choice of spacing between electrodes is an important decision, affecting the resolution and the size of the domain to be studied. A basic tenet of sampling theory, the Nyquist criterion, states that an electrode spacing smaller than half the smallest significant wavelength is required to capture the important details of a spatially sampled process. The authors suggest a method to choose a practical interelectrode spacing by examining wavenumber power spectra of high-resolution VF data recorded from a square 11*11 array of electrodes spaced 0.28 mm apart. The plaque was sutured on the epicardium near the left ventricular apex in 7 anesthetized pigs. VF was induced with AC simulation. Unipolar extracellular electrograms were simultaneously recorded from each channel for 2 s after the induction of VF. Each signal was sampled in time at 1000 Hz. Wavenumber power spectra were calculated for 100 ms segments using the zero-delay wavenumber spectrum method, for a total of 140 power spectra. All spectra had dominant peaks at the origin and fell off rapidly with increasing wavenumber (decreasing wavelength). In all the spectra, every wavelength shorter than 1.4 mm contributed insignificant power. Furthermore, in 134 of 140 spectra (96%), insignificant power levels were associated with every wavelength shorter than 2.8 mm. These results suggest that, for unipolar extracellular electrodes, an intersensor spacing on the order of 1 mm is appropriate to study organization during early VF. View full abstract»

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  • Low-frequency Korotkoff signal analysis and application

    Page(s): 1067 - 1070
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    The low frequency (LF) components of the Korotkoff signal are recorded, analyzed, and applied in the derivation of blood pressure estimates. The LF components are found to be the dominant feature of the Korotkoff signal throughout the entire occlusive cuff deflation cycle, and a sharp rise in the energy of these components is found to correlate with the occurrence of systolic pressure. This feature is applied in 2 separate energy thresholding algorithms which produce estimates of systolic blood pressure which correlate well (r=0.907 and r=0.938) with those systolic pressure derived via the auscultatory technique. View full abstract»

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  • Real-time left ventricular volume of the canine heart from ultrasonic dimension data

    Page(s): 1070 - 1073
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB)  

    A real-time (instantaneous) system is presented to measure the dynamic volume of the left ventricle. This system uses the invasive measurement of long axis diameter, short axis diameter, and wall thickness of the cardiac left ventricle. Three pairs of pulse-transit ultrasonic dimension transducers are used to obtain these measurements. The dynamic volume was then found by applying these measurements to an ellipsoidal shell model of the left ventricle. It is possible to obtain on-site, real-time, continuous measurements of the left ventricular volume (LVV) by employing an electronic device which implements a corrected volume equation for the ellipsoidal shell model. The device's output is a calibrated estimation for the LVV. The function of the device is shown to compare well with other accepted measurements for the LVV. View full abstract»

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  • Tracking of changes in latency and amplitude of the evoked potential by using adaptive LMS filters and exponential averagers

    Page(s): 1074 - 1079
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    The adaptive LMS algorithm in combination with exponential averagers are compared to the use of exponential averagers only in tracking latency and amplitude changes in the evoked potential. The estimator is intended for use in applications where neurologic functions are monitored by detecting changes in the evoked potential. Two different structures of the estimator are evaluated and it is found that averaging before filtering is to be preferred. It is shown that the desired signal to the LMS-filter can have a rather low SNR with only mirror influence on the estimator performance. The estimator which combines an LMS filter and an exponential averager was shown to detect changes in latency faster than the estimator which uses a nonfiltered average. The LMS filter is shown to exhibit bias in the estimate of the evoked potential due to the fact that response and background spectra has overlapping frequency ranges. The bias seems not to affect the latency estimation while amplitude estimation was clearly affected. Simulations are performed with both white noise and EEG background. View full abstract»

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  • Power deposition properties of a travelling-wave applicator for interstitial hyperthermia

    Page(s): 1079 - 1081
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    An interstitial hyperthermia applicator is described that is capable of providing uniform heating over an extended range of depths. The applicator utilizes lossy two-wire transmission lines that are terminated in p-i-n diodes that may be biased on or off. A pair of these transmission lines within a single applicator allows a variety of symmetrical and asymmetrical patterns to be produced. Theoretical predictions of the applicator's performance are provided that are based on empirically determined transmission line characteristics. View full abstract»

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Aims & Scope

IEEE Transactions on Biomedical Engineering contains basic and applied papers dealing with biomedical engineering. Papers range from engineering development in methods and techniques with biomedical applications to experimental and clinical investigations with engineering contributions.

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Editor-in-Chief
Bin He
Department of Biomedical Engineering