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Biomedical subjects

D T Kaplan

Publications and source records attributed to D T Kaplan.

16 recordsLinked to original sources
PubMed2001

Relationship between correlation dimension and indices of linear analysis in both respiratory movement and electroencephalogram.

OBJECTIVE: We investigate the relationships between signals from the electroencephalogram (EEG) and those from respiratory movement using the correlation dimension (D(2)). METHODS: Respiratory movement and EEG were recorded for 7.5h from 7 clinically healthy men. D(2) was calculated by applying an algorithm slightly modified from that proposed by Grassberger and Procaccia (Phys Rev Lett 50 (1983) 346). Non-linearity in respiratory movement and EEG was tested by comparing D(2) for the original data with that for surrogate data. RESULTS: A statistically significant positive correlation between D(2) of the EEG and D(2) of the respiratory movement was observed for the original data, but not for the surrogate data. CONCLUSIONS: A reduced D(2) of the EEG may be associated with an increased regularity of breathing in deep sleep (stage IV). Likewise, the increased D(2) of respiratory movement during rapid eye movement may be associated with increased complexity of the signals. Whether there is a direct coordination between brain and lungs or whether brainstem systems, including that of the cholinergic system, affect both respiration and cortex requires further investigation.

Adult↗
PubMed2000

Adaptive estimation and control method for unstable periodic dynamics in spike trains.

Dynamical control of excitable biological systems is often complicated by the difficult and unreliable task of precontrol identification of unstable periodic orbits (UPO's). Here we show that, for both chaotic and nonchaotic systems, UPO's can be located, and their dynamics characterized, during control. Tracking of system nonstationarities emerges naturally from this approach. Such a method is potentially valuable for the control of spike trains of excitable biological systems, for which precontrol UPO identification is often impractical, and nonstationarities (natural or stimulation induced) are common.

Feedback↗
PubMed2000

Time series and the dynamics of demand pacing.

Motivated by a common practice in cardiology, we analyze the dynamics of a demand paced system where one seeks to create a stable periodic response. By using techniques originally developed for controlling chaotic systems, one can enhance the information contained in time series regarding hidden, unstable periodic orbits. This makes it possible, for example, to track drifts in a system's dynamics.

Electrocardiography↗
PubMed1999

Nonstationarity and 1/f noise characteristics in heart rate.

The power spectrum of human heart rate (HR) measured over 24 h exhibits "power-law" 1/f alpha-type spectral behavior with alpha approximately 1. We investigate possible nonstationarity in time of the exponent alpha using maximum likelihood estimation, which allows relatively short data segments to be used. Examination of 24-h HR records from ambulatory normal and congestive heart failure (CHF) subjects indicates that the power-law structure of HR is nonstationary. In addition, alpha varies with time scale and is different for normal (alpha approximately 1) and CHF (alpha approximately 1.5) subjects. Simulations suggest that a possible mechanism underlying the observed power-law spectrum may be a switching between values of alpha near zero (white noise) and near two (Brownian motion). This mechanism generates power-law forms quantitatively similar to CHF subjects when the switching occurs very rapidly and similar to normal subjects when the switching is less rapid.

Artifacts↗
PubMed1998

Fetal ECG extraction with nonlinear state-space projections.

We describe a method to suppress maternal and noise contaminations in single-lead fetal ECG recordings. A nonlinear state space projection technique originally developed for noise reduction in deterministically chaotic signals is used. The method is successfully applied to recordings with fetal components and noise of comparable amplitude.

Electrocardiography↗
PubMed1996

Molecular polymorphisms associated with host range in the highly conserved genomes of burrowing nematodes, Radopholus spp.

Six polymorphic bands of DNA were amplified from purified Radopholus citrophilus genomic DNA from one strain of each of the sibling species R. citrophilus and R. similis in random amplified polymorphic DNA analyses involving 380 single 10-base primers. Four of these polymorphic DNA fragments were successfully cloned and amplified through subsequent use of primers designed to complement the terminal sequences of the polymorphic DNA. Results of ensuing studies using mini-prepped DNA from 14 burrowing nematode strains collected from Florida, Hawaii, and Central America, characterized for their ability to parasitize citrus, indicated that a 2.4-kb fragment appeared to be associated with citrus parasitism in burrowing nematode populations from Florida. However, a fragment of comparable size was also detected in R. citrophilus from Hawaii and from burrowing nematode populations collected from Belize and Puerto Rico. Overall, findings suggest that the genome organization of the burrowing nematode sibling species R. citrophilus and R. similis is highly conserved. This remarkable genetic similarity should facilitate identification of genetic sequence related to important phenotypes such as citrus parasitism. Detection of R. citrophilus-specific DNA fragments in burrowing nematodes collected from Belize and Puerto Rico suggests that R. citrophilus is resident in some Central American countries.

Animals↗
PubMed1992

Geometrical techniques for analyzing ECG dynamics.

Nonlinear dynamical systems theory motivates a new class of techniques for analyzing signals, based on the idea of converting a signal into a geometrical object--a "trajectory" in a reconstructed "state space." This paper discusses one such technique for detecting and quantifying electrical alternans.

Electrocardiography↗
PubMed1991

Aging and the complexity of cardiovascular dynamics.

Biomedical signals often vary in a complex and irregular manner. Analysis of variability in such signals generally does not address directly their complexity, and so may miss potentially useful information. We analyze the complexity of heart rate and beat-to-beat blood pressure using two methods motivated by nonlinear dynamics (chaos theory). A comparison of a group of healthy elderly subjects with healthy young adults indicates that the complexity of cardiovascular dynamics is reduced with aging. This suggests that complexity of variability may be a useful physiological marker.

Adult↗
PubMed1991

Repolarization inhomogeneities in ventricular myocardium change dynamically with abrupt cycle length shortening.

BACKGROUND: In single heart cells, abrupt changes in stimulation rate elicit complex alterations in repolarization. The effects of rate change on dispersion of repolarization, however, have not been well characterized. METHODS AND RESULTS: To determine the effects of abrupt cycle length (CL) shortening on spatial inhomogeneity of repolarization in a syncytium of ventricular cells, 124 action potentials were simultaneously recorded from Langendorff-perfused guinea pig hearts using high-resolution optical mapping with voltage-sensitive dye. The distribution of ventricular action potential durations (APDs) mapped during each cardiac cycle was used to calculate mean APD and repolarization dispersion index (DI), defined as the variance of the distribution. After abruptly shortening CL from 500 to 300 msec, mean APD declined exponentially in normoxic controls (by 23 +/- 3 msec, p less than 0.0001). This response was characterized by beat-to-beat oscillations of APD that were synchronized at all ventricular sites. After 30 minutes of hypoxia, mean APD decreased from 175.0 +/- 13.3 to 76 +/- 25.7 msec. However, during hypoxia, abrupt CL shortening lowered mean APD by only an additional 6 +/- 6 msec, and APD oscillations were no longer synchronized throughout the ventricle. In controls, beat-to-beat DI decreased significantly (-51.0 +/- 6.8%, p less than 0.01) by the sixth post-CL shortening beat and then recovered (by 15-20 beats). In contrast, DI failed to decrease during hypoxia (+7.1 +/- 23%). Two mechanisms for the transient decline of DI in controls were identified: synchronous APD oscillations and transient diminution of the apical-to-basal ventricular APD gradient. CONCLUSIONS: These data demonstrate that inhomogeneity of ventricular repolarization, as measured by DI, changes dynamically with CL shortening. Furthermore, the hypoxic ventricle does not attenuate DI after abrupt CL shortening and thereby lacks a physiological response expected to diminish vulnerability to arrhythmias.

Action Potentials↗
PubMed1990

Is fibrillation chaos?

Ventricular fibrillation is examined to determine whether it is an instance of deterministic chaos. Surface ECGs from dogs in fibrillation were used to generate a state space representation of fibrillation. Our analysis failed to identify a low-dimensional attractor that could be associated with fibrillation. The results suggest that fibrillation is similar to a nonchaotic random signal. We note, however, that such random-looking but nonchaotic behavior can also be generated by a nonlinear deterministic system.

Animals↗
PubMed1988

Nonlinear dynamics in cardiac conduction.

Electrical conduction in the heart shows many phenomena familiar from nonlinear dynamics. Among these phenomena are multiple basins of attraction, phase locking, and perhaps period-doubling bifurcations and chaos. We describe a simple cellular-automation model of electrical conduction which simulates normal conduction patterns in the heart as well as a wide range of disturbances of heart rhythm. In addition, we review the application of percolation theory to the analysis of the development of complex, self-sustaining conduction patterns.

Animals↗
PubMed1988

On the precision of automated activation time estimation.

We examined how the assignment of local activation times in epicardial and endocardial electrograms is affected by sampling rate, ambient signal-to-noise ratio, and sinx/x waveform interpolation. Algorithms used for the estimation of fiducial point locations included dV/dtmax, and a matched filter detection algorithm. Test signals included epicardial and endocardial electrograms overlying both normal and infarcted regions of dog myocardium. Signal-to-noise levels were adjusted by combining known data sets with white noise "colored" to match the spectral characteristics of experimentally recorded noise. For typical signal-to-noise ratios and sampling rates, the template-matching algorithm provided the greatest precision in reproducibly estimating fiducial point location, and sinx/x interpolation allowed for an additional significant improvement. With few restrictions, combining these two techniques may allow for use of digitization rates below the Nyquist rate without significant loss of precision.

Algorithms↗
PubMed1987

Application of non-linear dynamics to the characterization of cardiac electrical instability.

Beat-to-beat alternation in the morphology of the ECG has been previously observed in hearts susceptible to fibrillation. In addition, fibrillation has been characterized by some as a chaotic state. Period doubling phenomena, such as alternation, and the onset of chaos have been connected by non-linear dynamical systems theory. In this paper, we describe the use of a technique from nonlinear dynamics theory, the construction of a first return nap, to assess the susceptibility to fibrillation threshhold in canine experiments.

Animals↗