Search PubMed⌕ Search

Biomedical subjects

S Akselrod

Publications and source records attributed to S Akselrod.

108 records · Page 6Linked to original sources
PubMed1986

The effects of varying lengths and powers of CO2 laser pulses transmitted through an optical fiber on atherosclerotic plaques.

We have studied the changes induced in atherosclerotic arteries by a CO2 laser beam delivered through a silver halide optical fiber. We found that the crater depth and diameter correlate with the total energy delivered and with the mode of delivery. Short-duration high-power pulses caused shallower and narrower craters and less damage to the arterial wall compared to the same energy delivered as low-power pulses of long duration. Thus, high-power pulses for short periods may be an effective and safe procedure for evaporization of atherosclerotic plaques.

Arteriosclerosis↗
PubMed1986

Rhythm of sounds produced by larvae of the oriental hornet Vespa orientalis: spectral analysis.

In the hornet nest of the species Vespa orientalis, there is transmission of information by acoustic means between the larvae and the adults. The rhythmic pattern of the sounds produced by the larvae was recorded and spectrally analyzed for rhythm frequencies by use of the Fast Fourier Transform. The frequency of the "larval activity duration till cessation" was 0.018 Hz whereas the interval between two successive sound productions ranged from 0 to 1.0 Hz. The possible significance of precise signaling by the larvae towards efficient communication in colonies of social insects is discussed.

Animals↗
PubMed1986

Analysis of heart rate and respiratory patterns in sudden infant death syndrome victims and control infants.

Retrospective analyses of patterns of breathing and heart rate variability obtained by visual inspection and spectral analysis of ECG and respiratory activity have provided markers associated with subsequent death in a referred population of infants at high risk for sudden infant death syndrome (SIDS). Such markers include breathing patterns characterized by excessive apneic pauses and periodic breathing, heart rate spectra characterized by increased low frequency oscillations, and respiratory activity spectra characterized by a widened "bandwidth" during regular breathing. To test whether such measurements could distinguish SIDS cases and randomly selected controls from a population study the data from 10 cases and 100 age-matched control subjects were analyzed blind. The code was disclosed after completion of the analysis. We found that none of the markers served to distinguish the SIDS cases from the controls in the population at large. This observation may indicate important physiological differences between infants destined to die in the referred high risk population and infants who die of SIDS at large. The possible reasons for our inability to identify the group of SIDS in the general population, as compared to the group of deaths in the referred high risk group are: (1) different disease processes in the two groups, (2) difference responses to the same disease process in the two groups, (3) a response reflecting the psychosocial setting of the referred high risk population, (4) methodological differences between this and previous studies. We conclude that these markers are not of value in screening the population at large.

Heart Rate↗
PubMed1985

Cross-correlation technique for arrhythmia detection using PR and PP intervals.

A combined, cross-correlation procedure for computerized arrhythmia detection is presented. It enables the classification of a wide range of arrhythmia and is based upon the determination of both P and QRS waves. The electrocardiogram (ECG) signal is recorded from external leads, digitized (10 bits of resolution) at 1.28 kHz and processed with a CDC 6600 computer. A normal beat is stored as a reference signal and the onsets of the P wave and the QRS complex are measured for determining the PR, PP, and RR intervals. The combined cross-correlation procedure is carried out between the template and each successive ECG waveform over two time intervals, the first of which includes the P wave and the second, the QRS complex. Prior to this correlation procedure each of the ECG waveforms is filtered through a nonrecursive digital bandpass filter (10 and 100 Hz for low and high cutoff frequencies, respectively). The cross-correlation functions are then calculated by means of a cross spectrum and Fast Fourier Transform algorithm. The maximum value of the normalized cross-correlation function and the time shift providing that value are searched for, allowing (1) determination of the similarity between the present beat and the normal reference beat, allowing for the discrimination of abnormal P and QRS shapes; (2) accurate measurement of the RR, PP, and PR intervals of this subsequent waveform. Applying this method enables a reliable detection of a wide variety of arrhythmia.

Arrhythmias, Cardiac↗
PubMed1985

Hemodynamic regulation: investigation by spectral analysis.

We investigated the hypothesis that beat-to-beat variability in hemodynamic parameters reflects the dynamic interplay between ongoing perturbations to circulatory function and the compensatory response of short-term cardiovascular control systems. Spontaneous fluctuations in heart rate (HR), arterial blood pressure, and respiration were analyzed by spectral analysis in the 0.02- to 1-Hz frequency range. A simple closed-loop model of short-term cardiovascular control was proposed and evaluated in a series of experiments: pharmacological blockades of the parasympathetic, alpha-sympathetic, beta-sympathetic, and renin-angiotensin systems were used to open the principal control loops in order to examine changes in the spectral pattern of the fluctuations. Atrial pacing was used to examine blood pressure variability in the absence of HR variability. We found that respiratory frequency fluctuations in HR are parasympathetically mediated and that blood pressure fluctuations at this frequency result almost entirely from the direct effect of centrally mediated HR fluctuations. The sympathetic nervous system appears to be too sluggish to mediate respiratory frequency variations. Low-frequency (0.02-0.09 Hz) fluctuations in HR are jointly mediated by the parasympathetic and beta-sympathetic systems and appear to compensate for blood pressure fluctuations at this frequency. Low-frequency blood pressure fluctuations are probably due to variability in vasomotor activity which is normally damped by renin-angiotensin system activity. Blockade of the alpha-adrenergic system, however, does not significantly alter low-frequency blood pressure fluctuations.

Animals↗
PubMed1984

Fluctuations in T-wave morphology and susceptibility to ventricular fibrillation.

Susceptibility of the ventricles to fibrillation has been related to the degree of spatial inhomogeneity in the repolarization process. We studied the pattern of beat-to-beat fluctuations in ventricular repolarization processes in order to determine whether a relationship also exists between the temporal variability of ventricular repolarization and susceptibility to ventricular fibrillation. We used the morphology of the T-wave recorded in surface and epicardial leads as a measure of the ventricular repolarization process. The Ventricular Fibrillation Threshold (VFT) was used as the standard measure of cardiac susceptibility to fibrillation. In dog experiments, T-wave morphologic indices were computed on 1,024 sequential beats. Histogram, autocorrelation and power spectrum analyses were performed on the sequence of T-wave morphologic indices. A series of 27 experiments were performed on 20 dogs in which VFT was reduced by several different interventions--hypothermia, tachycardia and coronary artery ligation. For all three interventions we observed the same characteristic change in the pattern of T-wave morphology fluctuations. In particular, we found that as the VFT was reduced, a pattern of T-wave alternans developed. This pattern was generally not detectable by visual inspection of the ECG. It was, on the other hand, easily quantified in terms of a T-wave alternans index (TWAI) which we computed from the power spectrum of the T-wave fluctuations. In 26 of the 27 experiments, measured VFT decreased (p less than .001); in 20 of these experiments the TWAI computed from the surface ECG increased (decreased) when VFT decreased (increased) (p less than .01). In 17 experiments epicardial electrograms were recorded. In 16 of these experiments VFT decreased (p less than .001). In 16 of these 17 experiments TWAI computed from the epicardial ECG increased (decreased) when the VFT decreased (increased) (p less than .001). We conclude that statistical analysis of fluctuations in ECG complex morphology may provide a sensitive probe of ventricular vulnerability to fibrillation.

Animals↗
PubMed1984

Sudden infant death syndrome: abnormalities in short term fluctuations in heart rate and respiratory activity.

In order to test the hypothesis that a defect in cardiorespiratory regulation contributes to death of infants from sudden infant death syndrome (SIDS), we analyzed the power spectra of heart rate and respiratory activity during 256-sec epochs of quiet sleep. Data were obtained from pneumogram recordings performed for 12 h at night on eight infants who subsequently died from SIDS and 22 age-matched control infants. We computed the heart rate and respiratory power spectra from a single epoch on each infant using an algorithm developed for an 8085 microprocessor system dedicated to this investigation. There was no statistically significant difference between SIDS and controls based on mean respiratory and heart rates. Spectral analysis revealed enhancement of low frequency power in the 0.02 to 0.1 Hz band in the heart rate power spectrum in the SIDS group compared to control (p less than 0.002) and dispersion in respiratory frequency as determined by the respiratory band width (p less than 0.00001). These data suggest that a predisposition to SIDS manifests itself in an abnormal pattern of fluctuations in heart rate and respiratory activity.

Female↗
PubMed1981

Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control.

Power spectrum analysis of heart rate fluctuations provides a quantitative noninvasive means of assessing the functioning of the short-term cardiovascular control systems. We show that sympathetic and parasympathetic nervous activity make frequency-specific contributions to the heart rate power spectrum, and that renin-angiotensin system activity strongly modulates the amplitude of the spectral peak located at 0.04 hertz. Our data therefore provide evidence that the renin-angiotensin system plays a significant role in short-term cardiovascular control in the time scale of seconds to minutes.

Angiotensins↗
PubMed1980

Does rigidity in structure of muscarinic agonists and antagonists reflect drug specificity?

The present work is an attempt to elucidate: (1) whether highly rigid structural analogs of acetylcholine are still capable of activating the muscarinic receptor; (2) whether such analogs, be they agonists or antagonists, discriminate among the various ACh-mediated functions, thereby providing a tool for the study of a possible receptor heterogeneity; (3) whether structural rigidity is a significant factor in the kinetics of drug-receptor interaction. To this end, we investigated some properties of drugs in the spiro-(1,3-dioxolane-4,3')-quinuclidine system (SDQ) which embodies the muscarinic pharmacophore in a framework of utmost rigidity. Wherever possible, these properties were compared with those of a closely related but more flexible analog. Variation in effect between members of a rigid-flexible pair or among drugs of varying rigidity is considered to reflect varying affinities towards various sites of action. 2-Methyl-spiro-(1,3-dioxolane-4,3')-quinuclidine (AF-30) is a weak but selective muscarinic agonist. It can be viewed as a highly rigid version of 3-acetoxyquinuclidine (3-AcQ) and it can be used as a probe for detection of heterogeneity among muscarinic receptors. AF-30 is equipotent with 3-AcQ in causing tremors (mice), but has 1/17th the activity of 3-AcQ in the guinea-pig ileum, 1/30th in lowering blood pressure (cats) and 1/10th in inducing analgesia (mice). 2-Diphenylmethyl-spiro(1,3-dioxolane-4',3)-quinuclidine (AF-41) and 2.2-diphenyl-spiro-(1,3-dioxolane-4,3')-quinuclidine (AF-32 are potent antagonists and possess KD values in the same range as those of the more flexible congener 3-diphenylacetoxy-quinuclidine (AF-43) and atropine (0.6--2 nM) but with koff = 0.1 msec-1 (AF-41) and koff = 1 msec-1 (AF-43) (carp atrium). Thus, duration of drug action of drug action at the receptor is a function of structural rigidity in the drug molecule, termination of action being fastest with the flexible molecules. Differences in rigidity among various antagonists also find expression in an unequal distribution of potencies in various tests; thus the rigid antagonists differentiate between two central effects in mice, viz., prevention of oxotremorine-induced tremors and fall from the rotating rod by a factor of 1:20 (especially AF-41 versus AF-43), whereas the more flexible antagonists (AF-43, atropine or even 3-quinuclidinyl-benzilate) do not show such as a selectivity. The existence of heterogenous muscarinic receptors can be inferred from data presented. Both theoretical and practical implications are discussed.

Acetylcholine↗
PubMed1979

Offset rate of action of muscarinic antagonists depends on their structural flexibility.

Time course measurements of the action of muscarinic antagonists were performed in the spontaneously beating carp atrium. Several high affinity drugs, which embody the quinuclidine structure were examined. The structural flexibility of these molecules was reflected in the dissociation of the drugs from the muscarinic receptor. The dissociation of rigid drugs was very much prolonged as compared to flexible drugs of the same affinity.

Acetylcholine↗
PubMed1979

Electromechanical noise in atrial muscle cells of the carp: a possible ionic feed-back mechanism.

1. Spontaneous electrical fluctuations (+/- 0.2-0.4 mV) were recorded in 'quiescent' atrial fibres of the carp. 2. The noise decreased in acetylcholine, small hyperpolarization and EGTA. 3. The noise increased (to +/- 1-2 mV) and became more synchronous in K+-free Ringer and in ouabain. 4. Large voltage fluctuations (+/- 1-2 mV) were accompanied by a fine mechanical tremor, indicating intracellular [Ca2+] fluctuations. 5. Spectral analysis showed a clear resonant frequency at about 1 Hz, indicating that the noise cannot result from the random switching of independent ionic channels. 6. We propose that the intracellular [Ca2+] and the membrane K+-conductance are involved in a feed-back loop which can oscillate and produce the electromechanical noise. The frequency of oscillation is determined by the relatively slow diffusion of Ca2+ from the intracellular reservoir to the surface membrane.

Animals↗
PubMed1977

Electro-mechanical noise in atrial muscle fibres of the carp.

Steady membrane voltage fluctuations have been observed in atrial muscle fibres of the carp. These voltage fluctuations produce minute mechanical escillations, as revealed by an interference contrast microscope. The steady voltage fluctuations may be related to abnormal automaticity in the heart.

Animals↗
PubMedDate not supplied

Contrast echocardiographic quantification of regional myocardial perfusion: validation with an isolated rabbit heart model.

Quantification of regional myocardial tissue blood flow (RMBF) based on contrast echocardiography has yet to be achieved. This study validated our recently proposed algorithm for quantification of RMBF with colored microspheres. Experiments were carried out in an isolated rabbit heart preparation (n = 11). Aortic root injections of perfluoropropane-filled albumin microsphere solution (FS069) and colored microspheres were performed at five levels of coronary flow achieved by altering perfusion pressure. During each injection of contrast material, consecutive end-diastolic images of the heart and an extracardiac reference chamber were acquired with a 7.5 MHz transducer and digitized. Time-intensity curves from the reference chamber and myocardial regions of interest, corresponding to the anatomic segments used for colored microsphere analysis, were analyzed for RMBF. Blood flow was calculated as the intravascular volume fraction (ratio of areas under myocardial and reference curves) divided by mean transit time (deconvolution of impulse response) and compared with those obtained with colored microspheres. Injections of FS069 resulted in highly reproducible enhancement of myocardial contrast. Analysis of time-intensity curves provided consistent measurements of RMBF (r = 0.91), which correlated highly with microsphere data (r = 0.84). The use of this new algorithm allows accurate quantification of RMBF in the isolated heart model. Further validation of this approach in an animal model with peripheral intravenous injections of contrast material will allow noninvasive clinical measurements of RMBF.

Albumins↗
PubMedDate not supplied

The effect of verapamil calcium antagonist on autonomic imbalance in migraine: evaluation by spectral analysis of beat-to-beat heart rate fluctuations.

Abnormalities in autonomic control have been documented in migraine even during the headache-free interval. It has long been recognized that spectral analysis of heart rate (HR) fluctuations can reflect the autonomic function, especially the sympathetic to parasympathetic balance. This technique is the basis for a quantitative approach to the investigation of migraine applied in the present study. A 24-hour Holter ECG recording was performed for each subject in a group of five migraine patients during the interheadache period. In addition, shorter 5-minute-long recordings of blood flow (BF) and blood pressure (BP) were made in these patients in both supine and standing positions. Short, 256-second subtraces were taken every 30 minutes along the 24-hour ECG signal and were submitted, as well as the BF and BP traces, to A/D conversion and computation of the power spectrum of fluctuations in HR, BF, and BP. Spectral analysis of fluctuations in these hemodynamic parameters was performed in the migraine patients before and during the treatment with verapamil and compared to that of a healthy control group. This procedure enabled us to assess the autonomic function, the sympathetic vs parasympathetic balance, and their response to a change in position, before and during calcium blockade. A characteristic autonomic abnormality is revealed in the group of untreated migraine patients in supine position: enhanced low frequency (LF) fluctuations reflecting increased sympathetic sensitivity during the inter-headache phase. An exaggerated sympathetic response is measured in the migraine patients during the transition from supine to standing position with a concomitant nonsignificant decrease in parasympathetic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Nonlinear filters applied on computerized axial tomography: theory and phantom images.

New nonlinear image processing techniques, in particular smoothing based on the understanding of the image, may create computerized tomography (CT) images of good quality using less radiation. Such techniques may be applied before the reconstruction and particularly after it. Current CT scanners use strong linear low-pass filters applied to the CT projections, reducing noise but also deteriorating the resolution of the image. The method in this study was to apply a weak low-pass filter on the projections, to perform the reconstruction, and only then to apply a nonlinear filter on the image. Various kinds of nonlinear filters were investigated based on the fact that the image is approximately piecewise constant. The filters were applied with many values of several parameters and the effects on the spatial resolution and the noise reduction were evaluated. The signal-to-noise ratio of a high-contrast phantom image processed were compared with the nonlinear filter, with the SNR of the phantom images obtained with the built-in CT linear filters in two scanning modes, the normal and the ultra high resolution modes. It was found that the nonlinear filters improve the SNR of the image, compared to the built-in filters, about three times for the normal mode and twice for the UHR scanning mode. The most successful filter on low-contrast phantom image was applied and it also seems to lead to promising results. These results seem to show that applying nonlinear filters on CT images might lead to better image quality than using the current linear filters.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMedDate not supplied

Association of silent ST-segment depression on one-hour ambulatory ECGs with exposure to industrial noise among blue-collar workers in Israel examined at different levels of ambient temperature--the CORDIS Study.

BACKGROUND: Epidemiologic studies on the effects of ambient temperature or industrial noise on the cardiovascular system have usually focused on blood pressure. However, the ambulatory ECG may be a sensitive instrument for evaluating transient changes in the myocardium associated with exposure to such environmental stressors. In particular, the presence of silent ST-segment depression would strongly suggest transient myocardial ischemia. AIM: To evaluate a possible association between exposure to ambient noise and temperature in the workplace and silent ST-segment depression on short-term ambulatory ECGs. METHODS: Between 1985 and 1987, approximately 6,000 factory workers in Israel were examined in the framework of the CORDIS study. Each worker underwent ambulatory ECG monitoring for one hour. Measurements were taken of the average exposure to noise and the ambient temperature. Complete data including analysis of the ST-segment on the ambulatory ECG were available for 3,747 blue-collar workers. RESULTS: After excluding subjects with a history of heart disease, among men, silent ST-segment depression was found to be most prevalent in those workers exposed to more than 80 dBA compared with those exposed to less than 70 dBA. (RR = 2,4, p = .1 for men and RR = 1.3, p = .37 for women. Silent ST-segment depression was more prevalent at ambient temperatures up to 20 degrees C than over 25 degrees C (RR = 1.4, p = .22 for men and RR = 2.0, p = .005 for women). These trends persisted after controlling for possible confounding variables, such as age, type of work, smoking, and relative weight; however, only the temperature effects in women remained statistically significant. CONCLUSIONS: These findings suggest that silent ST-segment depression on ambulatory monitoring may be a sensitive measure of the cardiovascular response to exposure to physical stressors in the workplace. Exposures to noise and varying ambient temperature appear to have different effects on men and women.

Adult↗