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PubMed1976

A simple electronic circuit for simulation of pharmacokinetic processes.

A simple electronic circuit is constructed for simulation of the theoretical curves associated with single and multiple dosing kinetics. The output is an analog device which generates plasma concentration curves versus time, consistent with the assumption in a one-compartment open model with rapid intravenous injection or first-order absorption. Potentiometer settings offer variations in dosing schedules, distribution volumes as well as in absorption and elimination rate constants. All details are made from standard electronic components. The device can be used in teaching of the elements of pharmacokinetics.

Computers, Analog↗

PubMed1975

E1A calculating unit for the determination of the peak measured contraction velocity of the contractile elements.

An analog calculating unit is described, which is able to differentiate the left ventricular pressure and divide dP/dt by P, where P is the absolute pressure value. The parameter dP/dt/P is called the peak measured velocity (Vpm) with the dimension s(-1). The unit has an appropriate accuracy for division, three ranges and easy to handle calibration steps. The time constants for the various ranges are 40, 8 and 4 ms.

Computers, Analog↗

PubMed1983

A duration matching method for the measurement of jitter in single fibre EMG.

A new microprocessor method for on-line measurement of jitter in SFEMG is described. The method is based on a duration matching procedure: automatic detection of the repetitive occurrence of two single fibre potentials with stable durations and time-locked to one another. During the investigation of a motor unit a potential pair is accepted or rejected for the determination of jitter on the basis of the potential durations and the interpotential interval; the time criteria are set by the first potential pair measured. The measuring device consists of a microprocessor and an analog interface; it is small and can be connected to any EMG equipment. Compared with the methods previously described the duration matching method (a simple pattern recognition procedure) has the following advantages: the measurement during activation of several motor units is faster and more reliable; the 'technical jitter' is smaller, which allows a more accurate determination of the normal range. Consequently, the method yields values of physiological jitter which are significantly smaller than those previously described.

Computers, Analog↗

PubMed2002

[Digital vs. analog hearing aids for children. Is there a method for making an objective comparison possible?].

Until now, the assumed benefits of digital hearing aids are reflected only in subjective descriptions by patients with hearing aids, but cannot be documented adequately by routine diagnostic methods. Seventeen schoolchildren with moderate severe bilateral symmetrical sensorineural hearing loss were examined in a double-blinded crossover study. Differences in performance between a fully digital hearing aid (DigiFocus compact/Oticon) and an analogous digitally programmable two-channel hearing aid were evaluated. Of the 17 children, 13 choose the digital and 4 the analogous hearing aid. In contrast to the clear subjective preferences for the fully digital hearing aid, we could not obtain any significant results with routine diagnostic methods. Using the "virtual hearing aid," a subjective comparison and speech recognition performance task yielded significant differences. The virtual hearing aid proved to be suitable for a direct comparison of different hearing aids and can be used for double-blind testing in a pediatric population.

Child↗

PubMed1980

Resonant response of a neural model and of Limulus ommatidia to double frequency stimulation.

Signals which are the sum of two sinusoids of frequencies v1 and v2 are used to stimulate: i) an electronic analog of the leaky integrator neural model, ii) the visual neurons of the Limulus lateral eye. This makes it possible to investigate the resonant amplification of the impulse density modulation for v1 + v2 which approaches the free-run discharge rate; this resonance is predicted by the Volterra series representation of the leaky integrator (Poggio and Torre, 1977). The resonant responses obtained look very similar for the simulated discharge and for the experimental one.

Animals↗

PubMed2002

Combined feedback-feedforward active noise-reducing headset--the effect of the acoustics on broadband performance.

Active noise-reducing headsets that employ analog feedback control and provide good broadband attenuation are commercially available for a wide range of applications. Recent studies have explored the integration of an adaptive digital feedforward controller with the analog feedback controller to provide additional attenuation of periodic noise components. This paper presents an experimental study of such a combined control system, but with both feedback- and feedforward controllers attenuating broadband noise. Good performance is demonstrated in a reverberant sound field, while under direct sound-field conditions the attenuation performance of the feedforward controller is shown to be dependent on head position. The paper concludes with an analysis of the forward path delay showing how the passive attenuation mechanism improves broadband performance.

Computers↗

PubMed2001

Protein folding simulation with solvent-induced force field: folding pathway ensemble of three-helix-bundle proteins.

We propose a coarse-grained model of proteins that take into account solvent effects and apply it for simulating folding of a three-helix-bundle protein. The energy functional form, refined from our previous work (Takada et al., J Chem Phys 1999;110:11616-11629), tries to closely imitate real physico-chemical interactions. In particular, the hydrogen bond that depends on local dielectric constant, the helix capping effect, and side-chain entropic effects are included. With use of the model, we simulate folding of the GA module of an albumin binding domain, 1prb(7-53), finding most trajectories reach at the native topology within 1 micros. In the simulation, helices 1 and 3 are mostly formed earlier accompanied by non-specific collapse, while second helix is intrinsically less stable and is formed with the help of tertiary contacts at later stage. We compute an analog of the transition state ensemble and compare it with those of other three-helix-bundle proteins. The transition state of 1prb(7-53) includes a few specific tertiary contacts of C terminus of helix 3 with the loop region between helices 1 and 2. This resembles, but is not equivalent to, an early formed region of fragment B of staphylococcal protein A, but is quite different from the folding transient structures of a de novo designed three-helix-bundle peptide.

Albumins↗

PubMed1995

Update on the analysis of the need for pediatric surgeons in the United States.

UNLABELLED: Accurate estimations of pediatric surgical manpower needs are necessary if this specialty is to avoid the consequences of under- or oversupply, and reasonable decisions must be made relative to the number of training programs needed. METHODS: Fifteen, 10, and 5 years ago, pediatric surgeons (PSs) in 62 standard metropolitan statistical areas (SMSAs) having a population of at least 200,000 were asked to estimate the number of PSs needed in their localities. A computer program analogous to the SOSSUS program was designed to project the number of PSs that would result from various numbers of trainee graduates per year. The program has been updated for comparison. Known input data included the present number and age of PSs, age range of trainees, current US population projections to the year 2025, and the average retirement age. RESULTS: These PSs estimated that 88 additional PSs are needed in the next 10 years. Currently, 26 programs in the United States graduate an average of 24 trainees per year, and six programs in Canada graduate six trainees per year. The previous projection indicated that 20 trainees per year would result in 525 PSs in 1993, and the actual number is 559; so the figures indicate that 27 or 28 PSs are entering practice each year. The apparent increase in numbers is related to entry of Canadian trainees primarily, and a few others, into practice. The current computer projection indicates that 20 graduate trainees per year would result in an absolute increase of 0.55% per year, and 25 per year would result in an increase of 1.43% per year, to 2020, while the increases in the US population would be 1.02% per year for all ages and 0.52% for 0 to 15 year olds. If all programs currently being considered for approval are certified, as many as 36 trainees per year--or 7 times the rate of the 0-15-year population increase--will result. CONCLUSION: Although an average of 20 graduates per year entering practice would keep pace with the pediatric population, 25 to 27 graduates per year--or 3.5 to 4 times the rate of the 0- to 15-year population increase--can be accommodated now into the current system of delivery of pediatric surgical care on the basis of estimated need. Many more graduates than this would create an excess of surgeons before long.

Canada↗

PubMedDate not supplied

Automated analog-to-digital conversion of graphical cardiotocographic records.

The system described, VISC, has as its aim the acquisition and subsequent digitization of monodimensional cardiotocographic signals. These signals can originate in any type of hospital cardiotocographic register, as well as in a book of uterine activity (UA) or fetal heart rate (FHR) signals. VISC consists of a set of algorithms to identify the fetal heart rate signal, although it can be used with minor corrections to work on any continuous curve. Some of the problems that may arise, such as signal loss and presence of noise, are discussed to illustrate the proposed method. The program is integrated into a wider environment, whose main nucleus is the NST-EXPERT expert system, for the diagnosis of fetal well-being, the recommendation of therapeutical plans and the prognosis of immediate neonatal states.

Algorithms↗

PubMed1977

Phonoangiography by autocorrelation.

Phonoangiography, as a noninvasive quantitative analysis of arterial bruits, was conducted just prior to standard invasive radiographic angiography in 135 patients. Sound records from 162 carotid arteries were analyzed with a new processing technique employing a high speed analog acoustic analyzer, the autocorrelator. In 18 arteries with carotid stenosis, a correlation coefficient of 0.87 resulted between phonoangiographic diameter predictions and radiographic diameter estimates. Bruit analysis identified two patients with patent lumen diameters, but tortuous carotid vessels. One hundred thirty-three carotid arteries had no bruits that could be analyzed, but angiograms showed no extracranial stenosis. Four arteries from which bruits could not be analyzed were found to be totally occluded. Carotid phonoangiography appears applicable in approximately one of seven patients now requiring angiography of head and neck vessels. When applicable, phonoangiography is significantly correlated with angiographic findings.

Adult↗

PubMed1997

Effect of septal perforations on measures of nasal resistance.

OBJECTIVE: The purpose of this investigation was to determine the effect of septal perforations on posterior and anterior rhinomanometric measures of nasal resistance in an analog model. DESIGN: The data were analyzed using a repeated-measures ANOVA. Nasal resistance was the dependent variable, while type of rhinomanometry, septal perforation size, and position of resistance (proximal vs. distal) were nominal scale independent variables. PARTICIPANTS: The analog model used in this study was similar to that described by Warren and Devereux (1966), except that the nasal cavities of the model were modified to create septal perforations. OUTCOME MEASURES: The main dependent measure was nasal resistance. RESULTS: An Important finding of this investigation was that septal perforations resulted in large differences (> 3 cm H2O/L/sec) between posterior and anterior nasal resistance values in the bilateral proximal resistor condition. CONCLUSIONS: Anterior rhinomanometry may underestimate true nasal resistance when a septal perforation is present, because the septal perforation prevents accurate measurement of nasopharyngeal pressure. Posterior rhinomanometric measures should accurately reflect nasal resistance despite septal perforations, because the perforation does not invalidate the estimate of nasopharyngeal pressure.

Adult↗

PubMed1975

The central arterial pulses. Experiments on a hybrid model of the heart and the arterial system.

In order to examine the contours of central aortic and coronary flow pulses as well as those of pressure and flow pulses along the aorta, a hybrid model of the arterial system and the heart was designed. The digitally programmed model of the aortic system is an inhomogeneous transmission line with adjustable reflection factors at the end and at three intermediate locations. For the reflection factor at the entrance different values may be chosen for the ejection time and the diastole. The influence of a stenosis and of frequency-independent damping may be examined. The model of the ventricle is the analog solution of a system consisting of an internal isometric pressure source and an internal resistance and capacitance. The model of the coronary artery is the analog solution of a windkessel model of the system. The digital and analog models are interlocked by AD and DA converters. All programs can be executed in real time. The characteristic contour of the aortic flow is determined by the relation between the internal impedance of the ventricle and the magnitude of the characteristic impedance of the aorta. Furthermore, the influence of reflections within the arterial system is shown to be quite remarkable. Natural pressue pulses can be simulated by the model under normal and pathological conditions including aortic coarctation. The contour of the left coronary artery flow is determined on the one hand by the fraction of the ventricular pressure which acts as a counterpressure at the site of the peripheral resistance, and by the time constant of the coronary windkessel on the other hand.

Aorta, Thoracic↗

PubMed1975

On-line identification of sensory systems using pseudorandom binary noise perturbations.

A technique of on-line identification of linear system characteristics from sensory systems with spike train or analog voltage outputs was developed and applied to the semicircular canal. A pseudorandom binary white noise input was cross-correlated with the system's output to produce estimates of linear system unit impulse responses (UIRs), which were then corrected for response errors of the input transducers. The effects of variability in the system response characteristics and sensitivity were studied by employing the technique with known linear analog circuits. First-order unit afferent responses from the guitarfish horizontal semicircular canal were cross-correlated with white noise rotational acceleration inputs to produce non-parametric UIR models. In addition, the UIRs were fitted by nonlinear regression to truncated exponential series to produce parametric models in the form of low-order linear system equations. The experimental responses to the white noise input were then compared with those predicted from the UIR models linear convolution, and the differences were expressed as a percent mean-square-error (%MSE). The average difference found from a population of 62 semicircular canal afferents was relatively low mean and standard deviation of 10.2 +/- 5.9 SD%MSE, respectively. This suggests that relatively accurate inferences can be made concerning the physiology of the semicircular canal from the linear characteristics of afferent responses.

Animals↗

PubMed1999

Belt worn control system and battery for the percutaneous model of the Jarvik 2000 heart.

A belt worn controller and lithium-ion battery pack have been developed for use with the initial clinical trials of the Jarvik 2000 heart. Patient interface considerations, safety, and simplicity were major design inputs for the system. The controller was developed using all analog technology to avoid difficulties with electromagnetic interference (EMI), to minimize susceptibility to electrostatic discharge, and to avoid the need for software validation. Manual control of pump speed is accomplished by a patient operated knob, according to physician instructions for rest and exercise for each individual patient. The system includes alarms and indicators which show the following: the amount of remaining battery charge, if the battery is low and needs replacement, the power in watts being consumed, if the power consumed is above 15 W, if the pump is running below the selected speed setting, and if the pump stops. The control box, curved to be worn on the belt, is only 2.5 inches high for comfort when sitting. The battery pack, also form fitted for patient comfort, weighs just over 1 1/2 pounds and supplies 65 W-h of energy storage, sufficient to run the device for over 8 h at nominal load.

Computers, Analog↗

PubMed2000

Modeling alternation to synchrony with inhibitory coupling: a neuromorphic VLSI approach.

We developed an analog very large-scale integrated system of two mutually inhibitory silicon neurons that display several different stable oscillations. For example, oscillations can be synchronous with weak inhibitory coupling and alternating with relatively strong inhibitory coupling. All oscillations observed experimentally were predicted by bifurcation analysis of a corresponding mathematical model. The synchronous oscillations do not require special synaptic properties and are apparently robust enough to survive the variability and constraints inherent in this physical system. In biological experiments with oscillatory neuronal networks, blockade of inhibitory synaptic coupling can sometimes lead to synchronous oscillations. An example of this phenomenon is the transition from alternating to synchronous bursting in the swimming central pattern generator of lamprey when synaptic inhibition is blocked by strychnine. Our results suggest a simple explanation for the observed oscillatory transitions in the lamprey central pattern generator network: that inhibitory connectivity alone is sufficient to produce the observed transition.

Animals↗

PubMed1975

Lyapunov Redesign of Model Reference Adaptive Control System for long term ventilation of lung.

A lyapunov redesign of Model reference adaptive control system for a long term, automatically regulated, ventilatory system is presented. A fixed resistance-capacitance RC analog lung model is used to generate a desirable (reference response) alveolar pressure. The instantaneous difference in alveolar pressures between the patient and its model is fed to an adaptive controller. The controller is designed to adjust the patient's inflating pressure in such a way as to reduce the instantaneous difference in the alveolar pressures to zero. The adaptive control system described can be implemented provided the patient's alveolar pressure is continuously measurable. Unfortunately, this measurement is impossible to realize; therefore, a method to estimate the continuous alveolar pressure of the patient is to be developed. This estimation is achieved indirectly from the identification process of the patient's respiratory parameter. The same Lyapunov redesign is used in this identification process. Digital simulation of the control of the patient's inflating pressure and the identification process, as well as the simulation of the combined system, were performed. The result has demonstrated the ability of this adaptive system to perform in a fast and stable manner.

Airway Resistance↗

PubMedDate not supplied

A comparison of digital and analog methods of Doppler spectral analysis for quantifying flow.

Ultrasonic methods can be used for calculating flow when the mean Doppler frequency is representative of spatial average velocity. We have examined the capabilities of two commercially available methods of Doppler spectral analysis for providing measurements of spatial average velocity and flow. In a steady state flow model, Doppler audio spectra were recorded using a 5-MHz duplex scanner. Fast Fourier transform (FFT) spectral analysis was used to determine mean (M), mode (MO), and maximum (MAX) frequencies. An analog method (offset zero crossing detector = ZC) was used to determine root mean square (RMS) frequencies. The results of comparing Doppler flow estimates (QM, QMO, QMAX and QRMS) with direct flow measurements (n = 10; range = 128-1098 ml/min) were (1) QM = 0.67Q + 23 ml/min (SEE = 36 ml/min); (2) QMO = 0.96Q + 152 ml/min (SEE = 32 ml/min); (3) QMAX = 1.19Q + 171 ml/min (SEE = 23 ml/min); and (4) QRMS = 0.93Q + 76ml/min (SEE = 92 ml/min). Estimates of flow using M and RMS frequencies were adversely affected by experimental conditions likely to result in turbulence. We conclude that application of commercially available FFT determined M frequencies could result in significant errors in calculations of spatial average velocity and flow. Alternatively, FFT determined MO frequencies and ZC determined RMS frequencies resulted in accurate estimates of flow in this model. This study demonstrates the importance of evaluating the capabilities of commercially available methods of Doppler spectral analysis when using ultrasound for determining velocity and flow.

Blood Flow Velocity↗

PubMed2003

A manual slide rule for target-controlled infusion of propofol: development and evaluation.

UNLABELLED: We describe the development and evaluation of a simple slide rule that enables the bedside determination of the infusion rate for a particular target plasma concentration of propofol. The infusion rate to reach this target concentration at time (t) is the product of the target concentration, body weight, and a correction factor that depends on the time elapsed from the start of the initial infusion. Our target-controlled infusion (TCI) slide rule, constructed along this principle, performs the multiplications, analogous to the principle of the classical slide rule, as addition of logarithms. We calculated the percentage deviation of the predicted concentration obtained by STANPUMP versus predicted concentrations obtained using the infusion rates determined from the TCI slide rule. The evaluation using STANPUMP simulations showed, for a constant target concentration of 3 micro g/mL of propofol, a mean deviation of 4.05% (max, 6.97%) in the first 15 min and a mean deviation of 0.5% (max, 2.03%) between 16 and 300 min. The mean deviation after changing the target from 3 micro g/mL to 1, 2, 4, or 5 micro g/mL ranged from 1.15% to 17.76%. This pocket-sized TCI slide rule combines the advantages of minimal financial and technical cost with reasonable accuracy. IMPLICATIONS: We describe the development and evaluation of a simple slide rule that enables the bedside determination of the required infusion rate for a particular target plasma concentration. This pocket-sized target-controlled infusion slide rule combines the advantages of minimal financial and technical cost with reasonable accuracy.

Algorithms↗