A data analysis microcomputer package (DAMP) for biomedical signals.

The advent of cheap, powerful microcomputer systems makes the analysis of data via sophisticated techniques available to the personnel who are non-specialists in computing systems. The DAMP package described here is intended for use on personal computers and has therefore been written in BASIC for portability. The analysis techniques are powerful, comprising algorithms to perform sample-data generation, plotting displays, digital data filtering, auto-correlation functions, fast Fourier transforms and autoregressive modelling. The last technique contains a number of options including the display of z-plane plots, frequency response of the model, residual plotting and auto-correlation of the residuals. Illustrative results are shown from psychological mood data and rat locomotor activity. The package is designed both to instruct a user in the techniques of spectral analysis, and also to provide a range of methods for investigating time and frequency behaviour of biomedical data.     

Removal of power-line interference from the ECG: a review of the subtraction procedure

Background  

Modern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem.     

Detection of Salmonella spp. in milk by using Felix-O1 bacteriophage and high-pressure liquid chromatography

A method is described whereby the presence of less than five salmonellae was detected per milliliter of milk within 24 h of sample collection. Salmonellae were removed from milk by means of electropositive large-pore filters. Eluates from the filters were analyzed for the presence of Salmonella spp. by Felix-O1 bacteriophage and high-pressure liquid chromatographic techniques. The method gave only a positive response when salmonellae were present in the milk. Of the serotypes and strains of Salmonella spp. tested, Salmonella dublin (10 strains), Salmonella typhimurium (5 strains), Salmonella anatum, Salmonella krefeld, and Salmonella saint-paul gave positive responses. One strain of Salmonella agona (three strains tested) and three strains of Salmonella enteritidis (seven strains tested) were not detectable by the method described herein.     

Detection of Salmonella spp. in milk by using Felix-O1 bacteriophage and high-pressure liquid chromatography.

A method is described whereby the presence of less than five salmonellae was detected per milliliter of milk within 24 h of sample collection. Salmonellae were removed from milk by means of electropositive large-pore filters. Eluates from the filters were analyzed for the presence of Salmonella spp. by Felix-O1 bacteriophage and high-pressure liquid chromatographic techniques. The method gave only a positive response when salmonellae were present in the milk. Of the serotypes and strains of Salmonella spp. tested, Salmonella dublin (10 strains), Salmonella typhimurium (5 strains), Salmonella anatum, Salmonella krefeld, and Salmonella saint-paul gave positive responses. One strain of Salmonella agona (three strains tested) and three strains of Salmonella enteritidis (seven strains tested) were not detectable by the method described herein.     

Noninvasive motion ventilation (NIMV): a novel approach to ventilatory support.

A motion platform was developed that oscillates an animal in a foot-to-head direction (z-plane). The platform varies the frequency and intensity of acceleration, imparting periodic sinusoidal inertial forces (pG(z)) to the body. The aim of the study was to characterize ventilation produced by the noninvasive motion ventilator (NIMV) in animals with healthy and diseased lungs. Incremental increases in pG(z) (acceleration) with the frequency held constant (f = 4 Hz) produced almost linear increases in minute ventilation (VE). Frequencies of 2-4 Hz produced the greatest VE and tidal volume (VT) for any given acceleration between +/-0.2 and +/-0.8 G. Increasing the force due to acceleration produced proportional increases in both transpulmonary and transdiaphragmatic pressures. Increasing transpulmonary pressure by increasing pG(z) produced linear increases in VT, similar to spontaneous breathing. NIMV reversed deliberately induced hypoventilation and normalized the changes in arterial blood gases induced by meconium aspiration. In conclusion, a novel motion platform is described that imparts periodic sinusoidal acceleration forces at moderate frequencies (4 Hz) to the whole body in the z-plane. These forces, when properly adjusted, are capable of highly effective ventilation of normal and diseased lungs. Such noninvasive ventilation is accomplished at airway pressures equivalent to atmospheric or continuous positive airway pressure, with acceleration forces less than +/-1 G(z).     

Digital IIR filters design using differential evolution algorithm with a controllable probabilistic population size

Design of a digital infinite-impulse-response (IIR) filter is the process of synthesizing and implementing a recursive filter network so that a set of prescribed excitations results a set of desired responses. However, the error surface of IIR filters is usually non-linear and multi-modal. In order to find the global minimum indeed, an improved differential evolution (DE) is proposed for digital IIR filter design in this paper. The suggested algorithm is a kind of DE variants with a controllable probabilistic (CPDE) population size. It considers the convergence speed and the computational cost simultaneously by nonperiodic partial increasing or declining individuals according to fitness diversities. In addition, we discuss as well some important aspects for IIR filter design, such as the cost function value, the influence of (noise) perturbations, the convergence rate and successful percentage, the parameter measurement, etc. As to the simulation result, it shows that the presented algorithm is viable and comparable. Compared with six existing State-of-the-Art algorithms-based digital IIR filter design methods obtained by numerical experiments, CPDE is relatively more promising and competitive.     

Diagnostic system for studying generation of subterahertz radiation during beam-plasma interaction in the GOL-3 facility

The design principles and construction of the subterahertz radiometric spectral systems developed for the GOL-3 facility are described. The spectral systems are designed according to the quasi-optical scheme and use multilayer filters based on frequency-selective surfaces. The design and manufacturing technology of such elements are discussed. The results of measuring subterahertz radiation of plasma at the frequency close to the double plasma frequency are presented.     

High-speed digital microscopy

High-speed imaging is an ideal technique to accurately resolve the temporal and spatial characteristics of rapid events at either the molecular or cellular level. In this article, the digital imaging techniques used to simultaneously acquire transillumination phase-contrast images, at 240 images s(-1) (high-speed), to characterize ciliary beat frequency, and fluorescence images, at 30 images s(-1) (fast), to measure intracellular calcium concentration ([Ca2+]i), are described. With this technique, a precise correlation between the changes in ciliary beat frequency with changes in [Ca2+]i can be made. Simultaneous imaging is achieved by using different wavelengths of light to form the phase-contrast and fluorescent images and selectively directing these light wavelengths to different cameras with dichroic mirrors and bandpass filters. High-speed images compatible with standard video recording equipment are obtained by prematurely resetting the raster scan of a CCD camera with additional vertical synchronization pulses. The fast [Ca2+]i images are determined using the ratiometric dye fura-2 and a recording technique that monitors rapid changes in fluorescence at a single wavelength and uses intermittent reference images for calibration.     

Real time microprocessor-based 50 Hz notch filter for ECG

High performance analogue notch filters are difficult to realize in practice. Their real time digital counterparts, when implemented on an inexpensive microprocessor with no additional hardware, also have limitations of their own. To overcome these limitations, we have developed a new type of 50 Hz notch filter with its poles close to the zeros of the transfer function 1 + Z^−N. This new type of digital notch filter can be used for suppression of 50 Hz noise in the ECG. The filter is simple to design and easy to implement on most 8-bit microprocessors. It has a high execution speed, low analogue to digital noise, low recursive noise and good frequency response with no overshoot or ringing. It is capable of suppressing 50 Hz noise by at least 40 db. Its finite bandwidth of 4 Hz causes about 2% attenuation on the QRS peak, which is acceptable for almost all practical applications. One possible drawback is that multiple notches occur at higher frequencies. However, this has hardly any effect on the ECG because of the limited notch bandwidth.     

A low frequency active filter with plug-in tuning impedances.

A new approach to the construction of low frequency (1 Hz -- 20 kHz) active filters, based on the application of a pair of IC operational amplifiers forming a separate module and a plug-in unit containing RC tuning circuits, is described. The electronic circuits and the design of the filters are presented with all details.     

Determination of bacterial number and biomass in the marine environment.

Three techniques for the measurement of bacterial numbers and biomass in the marine environment are described. Two are direct methods for counting bacteria. The first employs an epifluorescence microscope to view bacteria that have been concentrated on membrane filters and stained with acridine orange. The second uses a transmission electron microscope for observing replicas of bacteria that are concentrated on membrane filters. The other technique uses Limulus amebocyte lysate, an aqueous extract from the amebocytes of the horseshoe crab, Limulus polyphemus, to quantitate lipopolysaccharide (LPS) in seawater samples. The biomass of gram-negative (LPS containing) bacteria was shown to be related to the LPS content of the samples. A factor of 6.35 was determined for converting LPS to bacterial carbon.     

Determination of bacterial number and biomass in the marine environment.

Three techniques for the measurement of bacterial numbers and biomass in the marine environment are described. Two are direct methods for counting bacteria. The first employs an epifluorescence microscope to view bacteria that have been concentrated on membrane filters and stained with acridine orange. The second uses a transmission electron microscope for observing replicas of bacteria that are concentrated on membrane filters. The other technique uses Limulus amebocyte lysate, an aqueous extract from the amebocytes of the horseshoe crab, Limulus polyphemus, to quantitate lipopolysaccharide (LPS) in seawater samples. The biomass of gram-negative (LPS containing) bacteria was shown to be related to the LPS content of the samples. A factor of 6.35 was determined for converting LPS to bacterial carbon.     

DIGITAL FILTERS IN AUDITORY PHYSIOLOGY

ABSTRACT

In auditory research, the manipulation of signals by filtering with analog electronic filters plays an important role. Recently, digital filters that compute signal modifications in realtime became available. They can mimic all functions of analog filters, and additionally make possible new experimental concepts.

This tutorial paper introduces the concept of digital filters by using analogies from acoustics. Even complex acoustical environments can be simulated with digital filters, as they allow the programming of almost arbitrary frequency and phase responses.     

A minicomputer program for automatic saccade detection and linear analysis of eye movement systems using sine wave stimulus

A FORTRAN IV program is described, which may be run interactively or in batch and which allows a user to obtain the frequency response amplitude ratio and phase resulting from the linear analysis of an eye movement system using sine wave stimuli. The response (eye position) signal may contain components contributed by the saccadic eye movements. The program can digitize analog signals and store data on a magnetic tape. With the aid of digital filters, the program can detect saccades without requiring any input parameters from the user. The program interpolates the saccade interval using a method of least square curve fitting with a sine wave. The interpolation is relatively noise immune and works well regardless of the stimulus frequencies and the width of a saccade interval. Moreover, the program can handle long duration of signals such as 90 min of data which covers about 5 cycles of a 0.001 Hz sine wave signal. Sample runs for the cases of 0.001 and 0.1 Hz are given. The resident driver and the overlayable segments of the program have been implemented on a DEC (Digital Equipment Corp.) LAB-11 minicomputer (PDP 11/20).     

A reflectance spectrophotometer-surface fluorometer suitable for monitoring changes in hemoprotein spectra and fluorescence of flavins and nicotinamide nucleotides in intact tissues

A spectrophotometer-fluorometer was constructed for simultaneous measurement of reflectance spectrum changes and surface fluorescence of intact tissues and organs. The apparatus employs monochromators for dual-wavelength spectrophotometry and optical filters for fluorometry. Three light beams are time-shared by a novel type of modulator to hit the same area of the tissue to be measured. The analog circuitry was controlled by a digital logic circuitry clocked by an optically derived frequency based on the angular velocity of the rotating light modulator and produced a maximum of three sets of differences in the parameters measured. The optical design has the advantage of allowing the use of monochromators rather than filters in a multichannel apparatus. The electronics accept a wide range of light modulation frequencies without difficulties in the phasing of the detector gates, so that signal sampling can be optimized for the recording of fast and slow phenomena. The apparatus was used successfully for the simultaneous monitoring of the mitochondrial redox state and tissue oxygenation in isolated perfused rat hearts.     

Power-line interference cancellation in ECG signals

The efficiency of notchfilters and a subtraction procedure for power-line interference cancellation in electrocardiogram (ECG) signals is assessed. In contrast with the subtraction procedure, widely used digital notch filters unacceptably affect QRS complexes. The procedure eliminates interferences of variable amplitude and frequency. The frequency modulations are overcome by adaptive synchronized sampling. Initially, this is accomplished by current hardware power-line frequency measurement. Because this approach is impossible in battery-supplied and some computer-aidd devices, a software measurement of the power-line interference period is developed.     

Robust optimization of total joint replacements incorporating environmental variables.

Direct search techniques for the optimal design of biomechanical devices are computationally intensive requiring many iterations before converging to a global solution. This, along with the incorporation of environmental variables such as multiple loading conditions and bone properties, makes direct search techniques infeasible. In this study, we introduced new methods that are based on the statistical design and analysis of computer experiments to account efficiently for environmental variables. Using data collected at a relatively small set of training sites, the method employs a computationally inexpensive predictor of the structural response that is statistically motivated. By using this predictor in place of the simulator (e.g., finite element model), a sufficient number of iterations can be performed to facilitate the optimization of the complex system. The applicability of these methods was demonstrated through the design of a femoral component for total hip arthroplasty incorporating variations in joint force orientation and cancellous bone properties. Beams on elastic foundation (BOEF) finite element models were developed to simulate the structural response. These simple models were chosen for their short computation time. This allowed us to represent the actual structural response surface by an exhaustive enumeration of the design and environmental variable space, and provided a means by which to validate the statistical predictor. We were able to predict the structural response and the optimal design accurately using only 16 runs of the computer code. The general trends predicted by the BOEF models were in agreement with previous three-dimensional finite element computer simulations, and experimental and clinical results, which demonstrated that the important features of intramedullary fixation systems were captured. These results indicate that the statistically based optimization methods are appropriate for optimization studies using computationally demanding models.     

The assessment of the mutagenic potential of vehicle engine exhaust in the Ames Salmonella assay using a direct exposure method

A method for the assessment of the mutagenic activity of vehicle engine exhaust in the Ames assay is described in which the bacterial strains used (TA98 and TA98/DNP) are exposed to the freshly produced engine exhaust using a "Cassella' slit sampler. The method is found to be effective both in the presence and absence of metabolic activation, using Aroclor-1254-induced rat liver S9 fractions. A comparison is made between the direct exposure method and the standard methods involving the collection of particulate samples on glass fibre filters and the testing of various extracts of these samples. Possible uses of the direct exposure testing method are suggested and the effect of sampling techniques on the results obtained in the Ames assay is also discussed.     

A general solution for the time delay introduced by a low-pass Butterworth digital filter: An application to musculoskeletal modeling

Low-pass Butterworth digital filters are commonly used in biomechanics-related research. In general, the input signal is filtered in the forward and reverse directions so that a temporal shift in the output signal does not occur. There are times, however, when introducing a specific time delay is an important consideration when modeling a physiological event. Filtering the data in the forward direction only can be used as an efficient method to account for a specific time delay. Specific delays are possible by carefully selecting the filter order and cut-off frequency. The purpose of this paper is to present the analytical formulation of a general solution for the time delay introduced by a low-pass Butterworth digital filter.