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Biomedical Engineering, IEEE Transactions on

Issue 3 • Date March 1997

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Displaying Results 1 - 12 of 12
  • The design of a ferrofluid magnetic pipette

    Page(s): 129 - 135
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    An electromagnetic pipette using a ferrofluid was designed to sample liquid volumes smaller than 0.2 μl. Submicroliter sample sizes are desirable for reducing the amount of costly reagents and reducing sample requirement for large-scale analysis. The pipette consists of four electromagnets arranged such that air-gaps are aligned to accommodate a tube. A light-hydrocarbon-based ferrofluid is contained in the tube and acts as a plunger. The position of the ferrofluid in the tube was controlled to within 0.2 mm by combining adjacent air-gap magnetic fields. The position of the ferrofluid as a function of time and magnetic pressure as a function of position was measured in one electromagnet air-gap from the device. Maximum pressure measured was 770 Pa which corresponds to a maximum velocity of 0.9 cm/s. The assembled pipette weighs approximately 25 g, and it measures 4 cm long, 1 cm wide, and 3 cm high. View full abstract»

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  • A triaxial accelerometer and portable data processing unit for the assessment of daily physical activity

    Page(s): 136 - 147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB)  

    The present study describes the development of a triaxial accelerometer (TA) and a portable data processing unit for the assessment of daily physical activity. The TA is composed of three orthogonally mounted uniaxial piezoresistive accelerometers and can be used to register accelerations covering the amplitude and frequency ranges of human body acceleration. Interinstrument and test-retest experiments showed that the offset and the sensitivity of the TA were equal for each measurement direction and remained constant on two measurement days. Transverse sensitivity was significantly different for each measurement direction, but did not influence accelerometer output (<3% of the sensitivity along the main axis). The data unit enables the on-line processing of accelerometer output to a reliable estimator of physical activity over eight-day periods. Preliminary evaluation of the system in 13 male subjects during standardized activities in the laboratory demonstrated a significant relationship between accelerometer output and energy expenditure due to physical activity, the standard reference for physical activity (r=0.89). Shortcomings of the system are its low sensitivity to sedentary activities and the inability to register static exercise. The validity of the system for the assessment of normal daily physical activity and specific activities outside the laboratory should be studied in free-living subjects. View full abstract»

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  • Wavelength selection for low-saturation pulse oximetry

    Page(s): 148 - 158
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (218 KB)  

    Conventional pulse oximeters are accurate at high oxygen saturation under a variety of physiological conditions but show worsening accuracy at lower saturation (below 70%). Numerical modeling suggests that sensors fabricated with 735 and 890 nm emitters should read more accurately at low saturation under a variety of conditions than sensors made with conventionally used 660 and 900 nm band emitters. Recent animal testing confirms this expectation. It is postulated that the most repeatable and stable accuracy of the pulse oximeter occurs when the fractional change in photon path lengths due to perturbations in the tissue (relative to the conditions present during system calibration) is equivalent at the two wavelengths. Additionally, the penetration depth (and/or breadth) of the probing light needs to be well matched at the two wavelengths in order to minimize the effects of tissue heterogeneity. At high saturation these conditions are optimally met with 660 and 900 nm band emitters, while at low saturation 735 and 890 nm provide better performance. View full abstract»

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  • A real-time microprocessor QRS detector system with a 1-ms timing accuracy for the measurement of ambulatory HRV

    Page(s): 159 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (178 KB)  

    The design, test methods, and results of an ambulatory QRS detector are presented. The device is intended for the accurate measurement of heart rate variability (HRV) and reliable QRS detection in both ambulatory and clinical use. The aim of the design work was to achieve high QRS detection performance in terms of timing accuracy and reliability, without compromising the size and power consumption of the device. The complete monitor system consists of a host computer and the detector unit. The detector device is constructed of a commonly available digital signal processing (DSP) microprocessor and other components. The QRS detection algorithm uses optimized prefiltering in conjunction with a matched filter and dual edge threshold detection. The purpose of the prefiltering is to attenuate various noise components in order to achieve improved detection reliability. The matched filter further improves signal-to-noise ratio (SNR) and symmetries the QRS complex for the threshold detection, which is essential in order to achieve the desired performance. The decision for detection is made in real-time and no search-back method is employed. The host computer is used to configure the detector unit, which includes the setting of the matched filter impulse response, and in the retrieval and postprocessing of the measurement results. The QRS detection timing accuracy and detection reliability of the detector system was tested with an artificially generated electrocardiogram (EGG) signal corrupted with various noise types and a timing standard deviation of less than 1 ms was achieved with most noise types and levels similar to those encountered in real measurements. A QRS detection error rate (ER) of 0.1 and 2.2% was achieved with records 103 and 105 from the MIT-BIH Arrhythmia database, respectively. View full abstract»

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  • Linear and nonlinear ARMA model parameter estimation using an artificial neural network

    Page(s): 168 - 174
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    Addresses parametric system identification of linear and nonlinear dynamic systems by analysis of the input and output signals. Specifically, the authors investigate the relationship between estimation of the system using a feedforward neural network model and estimation of the system by use of linear and nonlinear autoregressive moving-average (ARMA) models. By utilizing a neural network model incorporating a polynomial activation function, the authors show the equivalence of the artificial neural network to the linear and nonlinear ARMA models. They compare the parameterization of the estimated system using the neural network and ARMA approaches by utilizing data generated by means of computer simulations. Specifically, the authors show that the parameters of a simulated ARMA system can be obtained from the neural network analysis of the simulated data or by conventional least squares ARMA analysis. The feasibility of applying neural networks with polynomial activation functions to the analysis of experimental data is explored by application to measurements of heart rate (HR) and instantaneous lung volume (ILV) fluctuations. View full abstract»

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  • A dynamic neuromuscular model for describing the pendulum test of spasticity

    Page(s): 175 - 184
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    Both dynamic and static thresholds, as well as the gain in the stretch reflex loop, affect the sensitivity of motoneurons to muscle stretch. How the variation in each parameter will influence the mechanical behavior of patients with spasticity is not well understood because of the difficulty in experimentally isolating individual parameters. A neuromuscular dynamic model, based on the pendulum test of spasticity, has been developed to study the specific contribution of individual parameter abnormalities in stretch reflex loops to the observed mechanical abnormalities. The model contains detailed nonlinear dynamics of muscle force generation and stretch reflexes. A computer simulation of the model indicates that the stretch reflex thresholds and the gain have different influences on the leg swing in the pendulum test of spasticity. Individual changes in the static stretch reflex threshold, in the dynamic threshold, or in the gain can not stimulate the whole spectrum of spasticity severity. When simultaneous changes in all three parameters of the stretch reflex loop occur, a small variation of the gain coupled with changes in both static and dynamic thresholds can produce increasing severity of spasticity as the thresholds further decrease. The model is also successful in simulating the effect of posture changes on spasticity. View full abstract»

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  • Closed-loop drug infusion for control of heart-rate trajectory in pharmacological stress tests

    Page(s): 185 - 195
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    The diagnosis of coronary artery disease (CAD) is an important task in the management of cardiology patients. Recently, the use of pharmacological stress testing has become available as an alternative to exercise stress testing (ETT). A new system (device-drug combination) was developed specifically for the diagnosis of coronary artery disease. The system uses a novel catecholamine, arbutamine, which is infused intravenously to increase heart rate (HR) and cardiac contractility in order to evoke signs of ischemia. The development of a closed-loop control algorithm for the delivery of this drug and a pharmacodynamic (PD) model representing the HR response to arbutamine infusions are presented. Model parameters are estimated from clinical data on normal volunteers and patients. Based on this mathematical model, a rule-based control algorithm is designed. The structure of the control algorithm is discussed and testing of the algorithm based on simulations and animal and human trials are summarized. Results from clinical trials shows that the algorithm controls the HR increase according to a selected trajectory. The automated delivery of the drug can provide the cardiologist with an efficient, effective, and safe method for administering a pharmacological stress test. View full abstract»

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  • Sensitivity distributions of EEG and MEG measurements

    Page(s): 196 - 208
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    It is generally believed that because the skull has low conductivity to electric current but is transparent to magnetic fields, the measurement sensitivity of the magnetoencephalography (MEG) in the brain region should be more concentrated than that of the electroencephalography (EEG). It is also believed that the information recorded by these techniques is very different. If this were indeed the case, it might be possible to justify the cost of MEG instrumentation which is at least 25 times higher than that of EEG instrumentation. The localization of measurement sensitivity using these techniques was evaluated quantitatively in an inhomogeneous spherical head model using a new concept called half-sensitivity volume (HSV). It is shown that the planar gradiometer has a far smaller HSV than the axial gradiometer. However, using the EEG it is possible to achieve even smaller HSVs than with whole-head planar gradiometer MEG devices. The micro-superconducting quantum interference device (SQUID) MEG device does have HSVs comparable to those of the EEG. The sensitivity distribution of planar gradiometers, however, closely resembles that of dipolar EEG leads and, therefore, the MEG and EEG record the electric activity of the brain in a very similar way. View full abstract»

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  • Determination of the red blood cell ability to traverse cylindrical pores

    Page(s): 209 - 212
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    An expression relating the red blood cell (RBC) volume and membrane surface area to the pore minimum radius/maximum length which the cell is able to traverse is derived. The application of this analytical model to design/specification of filters for RBC deformability evaluation is presented. The passage of the RBC's through relatively long (10 μm or more) submicron radii pores, which the developed model demonstrates, is also discussed. View full abstract»

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  • Efficient computation of amplitude and phase maps in nuclear medicine equilibrium-gated cardiac studies

    Page(s): 213 - 215
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    The Goertzel algorithm is proposed as a method to obtain the first harmonic coefficient of time activity curves from equilibrium gated cardiac studies. The coefficients are used to produce functional images. The algorithm achieves an important reduction in the number of operations and memory accesses needed to compute the coefficients. View full abstract»

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  • Estimation of slowly changing components of physiological signals

    Page(s): 215 - 220
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB)  

    A method for the estimation of slowly changing components of physiological signals is presented in this communication. The method is based on a sequential approximation of slowly changing components by a low-order polynomial function. The polynomial coefficients are obtained by minimizing the distance between the expected zero crossing density (ZCD) value of the fast components of the physiological signal and the estimated ZCD value of these components. The method has been tested and preliminary results were satisfactory. View full abstract»

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  • The electrical conductivity of human cerebrospinal fluid at body temperature

    Page(s): 220 - 223
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    The electrical conductivity of human cerebrospinal fluid (CSF) from seven patients was measured at both room temperature (25°C) and body temperature (37°C). Across the frequency range of 10 Hz-10 kHz, room temperature conductivity was 1.45 S/m, but body temperature conductivity was 1.79 S/m, approximately 23% higher. Modelers of electrical sources in the human brain have underestimated human CSF conductivity by as much as 44% for nearly two decades, and this should be corrected to increase the accuracy of source localization models. 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