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PubMed1987

A first step quantification by correlation techniques of the variability in some time intervals measured on the Politecnico/Ca' Granda VCG Database On Young Normal Subjects.

The unevident variability during a 30-min period on intervals measured once every cardiac cycle was investigated by correlation techniques implemented on a digital computer, on normal healthy subjects from the "Politecnico/Ca' Granda VCG Database On Young Normal Subjects". Our most important conclusions are as follows: Generally each time series, related to the many interval values measured, shows that its variability is different from that of the R-R intervals. In particular Bazzett's formula, which provides the widely used "corrected QT interval", has to be amended.

Algorithms↗
PubMed1983

Osmotic response of individual cells during freezing. II. Membrane permeability analysis.

An analytical model is presented to simulate the freezing of individual yeast cells. In addition the model is solved numerically on a digital computer to obtain values for cell volume as a function of temperature, based on the thermal protocol during freezing, and the transport parameters of the cell membrane. The numerical procedure was modified to enable values for the membrane hydraulic permeability reference coefficient, Lpg, and activation energy, ELp, to be deduced by nonlinear analysis of complementary experimental data (10). It was observed that the apparent values of both Lpg and ELp increase with cooling rate, from Lpg = 0.0116 micrometer 3 micrometers-2 atm-1 min-1 and ELp = 19.4 kJ mol-1 for 9 degrees K/min to Lpg = 2.11 micrometers 3 micrometer-2 atm-1 min-1 and ELp = 101 kJ mol-1 for 35 degrees K/min. The deduced permeabilities fall within the range of values determined in a prior study by Levin (6). Analysis with the model also indicates that the turgor pressure exerts a negligible effect on yeast exposed to freezing stress.

Cell Membrane Permeability↗
PubMed1983

Osmotic response of individual cells during freezing. I. Experimental volume measurements.

The osmotic response of yeast to freezing was measured as a function of cooling rate and degree of extracellular supercooling. Thirteen experimental trials were conducted on a cryomicroscope in which incremental size changes of individual cells were recorded photographically, and the corresponding volume variations were measured using a digital computer image analysis algorithm. Plots were obtained of normalized cell volume as a function of temperature. Cellular dehydration during freezing was progressively inhibited with increasing values of cooling rate and extracellular supercooling. Normalized cell volume changes were not a function of the relative initial cell size. A constant volume plateau occurred for conditions under which intracellular ice formation was expected.

Cell Membrane↗
PubMed1977

Automatic detection and localization of epileptic foci.

A new method of automatic EEG analysis (ASD or automatic non-stationarity detection) derived from a parametric EEG model (autoregressive filter model) and based on inverse filtering, has been applied to scalp and subdural EEGs of epileptic patients. By this method it was possible to detect the occurrence of transient non-stationarities such as paroxysmal patterns of activity (spikes, spike-and-waves) characteristic of inter-ictal EEGs. The ASD has been implemented in a general purpose digital computer. The method allows: (a) statistical evaluation of paroxysmal patterns; (b) multi-channel analysis, where the interrelationships of different derivations are quantified and displayed by means of a clinically useful spatial map. The application of the ASD method to scalp and subdural EEGs, simultaneously recorded, has revealed that a number of transient non-stationarities detected in the scalp by the program yet not by visual inspection, coincide with clear paroxysmal patterns in subdural derivations. In this way conventional definitions of characteristic paroxysmal patterns at the scalp are put in question. Identical conclusions regarding the localization of an epileptogenic zone in 4 patients were obtained either using the conventional methods of recording electro-clinical seizures in EEGs of long duration or applying the ASD method to short EEG epochs (100 sec long, at most).

Computers↗
PubMed1978

Signal to noise ratio and response variability measurements in single trial evoked potentials.

Techniques were developed for measurement of signal to noise ratio and response variability in single trial evoked potentials. These techniques were extended and verified using a digital computer simulation of signal plus noise trials. When applied to real data the measures appear to have high reliability and to demonstrate that human evoked potentials are more variable than would be expected from background noise variation alone. Empirical equations are presented which can be applied to existing single trial EP data to estimate both signal-to-noise ratio and its expected variance.

Adult↗
PubMed1979

Automated detection of EEG artifacts during sleep: preprocessing for all-night spectral analysis.

This paper describes a simple artifact detection algorithm which can be used when large amounts of EEG data are to be automatically processed via spectral analysis techniques in a general purpose digital computer, and visual inspection of each EEG epoch becomes an impossible task. The technique is based on a chi-square (chi(2)) goodness-of-fit test to a Gaussian distribution (CSQ), and it was applied to EEG epochs each 30 sec long. This test proved to be very sensitive to non-stationarities in the EEG amplitude distribution for a particular epoch, and it produced a large value for the chi(2) coefficient when an artifact was present. EEG epochs that gave rise to chi(2) coefficients of value larger than a heuristically determined minimum were discarded from further analysis. The above technique enabled efficient data reduction and reliable automatic off-line processing of 50 nights of sleep EEG via spectral techniques.

Action Potentials↗
PubMed1981

Some methods to study information transmission through multi-channel neuronal systems.

Methods are proposed to isolate nearly simultaneous events or events with specific time relations to each other from two (or more) stimulus or spike trains. The methods can be implemented by means of a digital computer, but were implemented here with simple electronic hardware to present an alternative. The usefulness of these methods is demonstrated on data from cat experiments in which the influences of several motor units activated in parallel upon muscle spindle discharge patterns were studied by use of poststimulus time histograms (PSTHs). The contractions of one motor unit can interfere with the effects of others on muscle spindle discharges. In order to show this conditioning influence quantitatively, the integral of the PSTH is shown graphically as a function of the time interval between contractions of two motor units. These methods may help to elucidate some features of interactions between parallel neuronal channels bearing on the problem of the kind of information and how the latter is transmitted through complex multichannel systems.

Animals↗
PubMed1982

Human pulvinar units, spontaneous activity and sensory-motor influences.

Unit activity was recorded from the pulvinar nucleus (Pu) in human patients undergoing stereotaxic surgery. Thirty-six units (12 isolated and 12 pairs recorded with the same microelectrode) with a signal-to-noise ratio greater than 5, a stable amplitude, and a sustained discharge rate for more than 1 min, were selected for processing. The following functions were calculated with a digital computer to characterize discharge patterns: interval, autocorrelation and peristimulus time histograms for spikes, cross-correlation histograms between spikes of a pair, and autocorrelation functions and averages of the EEG. In spontaneous conditions, about half of the units fired in rhythmic bursts at the same or half the frequency of the Pu EEG. Most non-rhythmic units showed a "Poisson-like' interval histogram indicating a random firing pattern. Some non-rhythmic units revealed a periodic cross-correlation with the rhythmic Pu EEG, indicating that spikes tend to fire at a preferred phase of the rhythm. About half of the units showed phasic firing rate changes during voluntary movements. In most cells a discharge rate increase was observed. One unit also responded to passive movements of the fingers. Of the neurons tested, 2 out of 3 showed firing rate modulation during voluntary movements of the jaw as well as of the contralateral hand. The above units also increased the impulse rate after visual stimulation. Convergence of the effects of voluntary movements, and visual and auditory stimulation, was demonstrated in one unit. These results indicate the participation of the Pu in sensory-motor integrative functions.

Acoustic Stimulation↗
PubMed1988

Automatic real-time analysis of human sleep stages by an interval histogram method.

A new interval histogram method for automatic, all-night sleep stage scoring, simulated on a digital computer, is described. The system consists of a 2-step analysis. The first step is recognition of elementary patterns in EEG, EOG and EMG, and the second step is the determination of sleep stages based on these parameters. Correlation of this method with power spectral analysis of the dominant EEG patterns during each sleep stage supported the reliability of the first step analysis. Overall agreement (89.1%) between the computer and human judges was only 3% less than the agreement (92.1%) among the scorers, indicating considerable reliability of the second step. The primary areas of disagreement that arose in the identification of sleep stages occurred with stages 1, 2 and REM. To improve scoring accuracy, the system may require epoch sequence information. The profile of the elementary parameters of the EEG signals clearly illustrated the cyclic nature of these activities throughout the night. The alpha and delta 2 waves clearly separated the awake state from sleep stages. Beta 2 can discriminate stages 1 and REM from stage 2, and the best indicator for distincting stage 1 from REM was muscle activity. Sigma and spindles were prominent during stage 2 sleep. Both delta 2 and high voltage delta waves distinguished stage 3 from stage 4. On the other hand, delta 1 was evenly distributed and seemed to be common to all sleep stages.

Adolescent↗
PubMed1989

24 hour continuous tremor quantification based on EMG recording.

A new method is described that allows continuous quantification of parkinsonian and essential tremor over a period of up to 24 h on the basis of surface EMG recording from antagonistic forearm muscles. Tremor extraction from EMG data and all other calculations are performed on a digital computer. The occurrence, intensity and frequency of tremor are calculated. The data evaluation is fully automatic, including quality control and elimination of artifacts. Since tremor changes considerably over a 24 h period, long-term quantification gives more reliable data to study diurnal variations and to control the effects of medical treatment on tremor. As an additional advantage tremor recording is not restricted to a laboratory environment. Tremor can be monitored under everyday conditions and in the presence of moderate voluntary EMG activity.

Electromyography↗
PubMed1983

Opposing effects of apomorphine on pain in rats. Evaluation of the dose-response curve.

The effect of apomorphine on a supraspinally mediated response to pain was studied after subcutaneous administration of 10 different doses (25 micrograms/kg up to 10 mg/kg). Depending on the dose given, apomorphine was found to induce opposing effects on pain, so that low doses, 25-100 micrograms/kg, dose-dependently increased the sensitivity to pain. This effect then gradually declined in potency with increasing doses and high doses induced antinociception. The data therefore suggest that the net effect recorded involves the sum of responses from at least two functional systems. Using the Hill equation and the digital computer program NONLIN, we have dissociated the observed effect into two components, each having its particular dose-response characteristics: low doses having an ED50 value of 36 micrograms/kg produced hyperreactivity to pain, and high doses having an ED50 of 465 micrograms/kg (in the absence of hyperalgesia) induced antinociception.

Animals↗
PubMed1984

Changes in thalamic nociception resulting from morphine- and meperidine-dependence in rats.

Rats were injected with progressively increasing doses of morphine or meperidine during a period of 3 to 40 days. From this colony of animals individual rats were used at 3- to 4-day intervals for electrophysiologic experiments to analyze the activity of nociceptive neurons in the somesthetic thalamus. After an i.p. injection of chloralose-urethane and the appropriate preparation for a stereotaxic microelectrode penetration of the thalamus, a nociceptive neuron was identified in the nucleus ventralis posterolateralis by its unique spacing of spike potentials emitted in response to pricking the foot with a pin. In addition to the short-latency response that formed a high activity peak on poststimulus time histograms, spikes following the stimulus up to 500 ms also formed activity peaks. Single-pulse stimulation of the sciatic nerve evoked the same response as pinpricks, but innocuous stimuli (pin shielded with a piece of cork) evoked a response without the late activity peaks. Only neurons that exhibited this differential response were regarded as nociceptive. Their response and spontaneous activity were accumulated separately on a digital computer. Following this, naloxone was infused i.v. and the computer accumulations were repeated. It was found that during naloxone-precipitated narcotic withdrawal, innocuous stimuli evoked responses indicative of pain; the nociceptive system was sensitized. Furthermore, a small dose or morphine or meperidine heightened the sensitization. This action of the narcotic agents was reversed by 5-hydroxytryptophan, which assisted the narcotics in suppressing pain in morphine- or meperidine-dependent rats but had no demonstrable effect in control animals. The spontaneous tonic activity of the nociceptive neurons of the somesthetic thalamus was high in rats exhibiting narcotic dependence. Naloxone decreased the count, but not to the value of the control animals. The sensitization of nociception can be explained by a decreased action of a neural pathway that descends from the periaqueductal gray matter via the nucleus raphe magnus to the spinal cord and there blocks the excitation of the spinothalamic tract cells by A-delta and C fibers. The mechanisms that increase the spontaneous activity of the thalamic nociceptive neurons remain unclear.

Animals↗
PubMed1987

Effects of somatostatin on gallbladder emptying.

Because approximately 80% of reported patients with somatostatinomas have gallstones, this study was performed to determine the effects of exogenous somatostatin on gallbladder emptying responses to liquid and solid meals, direct cholinergic stimulation by bethanechol, indirect cholinergic stimulation by sham feeding, and intravenously administered octapeptide of cholecystokinin. Gallbladder emptying was quantitated using 99mTc-HIDA and a gamma-camera on line to a digital computer. Somatostatin, administered at a dosage of 7 micrograms/kg X h, prevented the gallbladder emptying responses to both test meals, sham feeding, and bethanechol. The maximal gallbladder emptying response to octapeptide of cholecystokinin at 5.0 ng/kg X min was reduced from 93.2% +/- 4.8% to 57.1% +/- 9.9% (p less than 0.01) and to octapeptide of cholecystokinin at 0.5 ng/kg X min from 91.3% +/- 5.3% to 14.8% +/- 4.2% (p less than 0.01). These findings suggest that somatostatin is a potent inhibitor of gallbladder emptying in humans. This may be an important factor in the development of gallstones in patients with somatostatinomas.

Adult↗
PubMed1975

Compound action potential and single acoustic nerve fibres activity generation: an equivalent neuron approach.

The peripheral acoustic system can be easily subdivided into three distinct subsystems: a mechanical one (middle ear and basilar membrane), the set of mechanical-to-neural transducers (the inner and outer hair cells) and the neural part. The functional behaviour of the external and middle ear is well known, but the processes concerned with the transduction of mechanical motion into neural activity are still under investigation. Actually the mechanism of transmission of information concerning acoustic stimuli to the central nervous pathways is not clearly known. On the basis of physiological knowledge, a mathematical model reproducing the pattern of activity of the acoustic nerve, in response to the most typical acoustic stimuli, is proposed. This has been simulated on a digital computer.

Action Potentials↗
PubMed1982

[Control of recruitment of muscle motor units by optimization of energy expenditure].

In order to vary the force it is exerting a muscle calls upon a variable number of motor elements (spatial mobilisation) and modulates the contraction frequency of each of the fibers (temporal mobilisation). We have studied the frequency distribution as a function of the strength developed and of the elongation of the muscle, as well as the number of fibers recruited. Based on a double approach, experimental and mathematical, we propose a function controlling this two-fold muscular mobilisation: the optimisation of the energy expenditure. In other words, to develop a particular force, the number of fibers called upon and the contraction frequencies of each of them are such that the quantity of energy required by the muscle is a minimum. The study is limited to voluntary isometric muscular contraction. Using optimization techniques, numerical results corresponding to the model's simulation has been obtained by using a digital computer.

Energy Metabolism↗
PubMed1983

Digital analysis of RR intervals for identification of cardiac arrhythmias.

This paper describes a digital computer program for the automated detection and classification of persistent cardiac rhythms. The algorithm is based on dynamic mathematical models and state estimation. The method is based on the use of RR interval data and the development of simple models that describe the sequential behavior of such intervals characteristic of different persistent rhythms. The method involves the calculation of sufficient statistics for the data. The method was tested on the actual rhythm data; it provides a rapid and accurate identification of persistent cardiac rhythms.

Arrhythmias, Cardiac↗
PubMed1994

Simulation of micropopulations in epidemiology: tutorial 1. Simulation: an introduction. A series of tutorials illustrated by coronary heart disease models.

This is the first in a series of tutorials concerning the simulation of micropopulation models for use in epidemiological research. The series emphasizes the techniques that are in use at the National Micropopulation Simulation Resource at the University of Minnesota. This initial series of tutorials uses chronic disease models, specifically coronary heart disease models, to illustrate the principles and methodologies employed. The series is intended for persons having some familiarity with electronic, digital computation and desiring to know more about a specific class of simulations, namely those that apply Monte Carlo techniques in the simulation of micropopulation models as a part of biomedical research. It is the author's hope that these tutorials will be particularly useful for students in medical informatics; they could also be of interest to professionals in both the computational and the biomedical sciences.

Chronic Disease↗