Depth of anesthesia index using cumulative power spectrum

Over the last ten years, monitors of depth of anesthesia have progressively been integrated in the clinical practice. Based on the analysis of the electroencephalogram (EEG), these monitors deliver an index that helps the anesthesiologist to determine the state of the patient during the surgery. Although they employ different kind of algorithms, spectral parameters are always taken into account to achieve the final indexes. In this work, a new spectral parameter based on the cumulative power spectrum is proposed. When compared to the Spectral Edge Frequency (SEF), a classic spectral parameter, the Cumulative Power Spectrum Index (CPSI) presents a higher correlation with reference indexes (AAI, BIS and CePROP) and a higher prediction probability of the state of the patient. Furthermore, when compared to the reference indexes, the CPSI shows similar performances in terms of correlation and presents a higher prediction probability than two of them (BIS and CePROP).

Detrended Fluctuation Analysis of EEG as a Measure of Depth of Anesthesia

For several decades, a number of methods have been developed for the noninvasive assessment of the level of consciousness during general anesthesia. In this paper, detrended fluctuation analysis is used to study the scaling behavior of the electroencephalogram as a measure of the level of consciousness. Three indexes are proposed in order to characterize the patient state. Statistical analysis demonstrates that they allow significant discrimination between the awake, sedated and anesthetized states. Two of them present a good correlation with established indexes of depth of anesthesia. The scaling behavior has been found related to the depth of anesthesia and the methodology allows real-time implementation, which enables its application in monitoring devices.

Approximate entropy of the electroencephalogram in healthy awake subjects and absence epilepsy patients

The approximate entropy (ApEn) of signals in the electroencephalogram (EEG) was evaluated in 8 healthy volunteers and in 10 patients with absence epilepsy, both during seizure-free and seizure intervals. We estimated the nonlinearity of each 3-sec EEG segment using surrogate data methods. The mean (+/- SD) ApEn in EEG was 0.83 +/- 0.22 in healthy subjects awake with eyes closed. It was significantly lower during epileptic seizures (0.48 +/- 0.05) than during seizure-free intervals (0.80 +/- 0.13) (P < 0.001). Nonlinearity was clearly detected in EEG signals from epileptic patients during seizures but not during seizure-free intervals or in EEG signals from healthy subjects. The ApEn of EEG signals estimated over consecutive intervals could serve to determine pathological brain activity such as that occurring during absence epilepsy.

Approximate entropy in the electroencephalogram during wake and sleep

Entropy measurement can discriminate among complex systems, including deterministic, stochastic and composite systems. We evaluated the changes of approximate entropy (ApEn) in signals of the electroencephalogram (EEG) during sleep. EEG signals were recorded from eight healthy volunteers during nightly sleep. We estimated the values of ApEn in EEG signals in each sleep stage. The ApEn values for EEG signals (mean +/- SD) were 0.896 +/- 0.264 during eyes-closed waking state, 0.738 +/- 0.089 during Stage I, 0.615 +/- 0.107 during Stage II, 0.487 +/- 0.101 during Stage II, 0.397 +/- 0.078 during Stage IV and 0.789 +/- 0.182 during REM sleep. The ApEn values were found to differ with statistical significance among the six different stages of consciousness (ANOVA, p<0.001). ApEn of EEG was statistically significantly lower during Stage IV and higher during wake and REM sleep. We conclude that ApEn measurement can be useful to estimate sleep stages and the complexity in brain activity.

Approximate entropy of human respiratory movement during eye-closed waking and different sleep stages

STUDY OBJECTIVE

The breath-to-breath variability of respiratory parameters changes with sleep stage. This study investigates any alteration in the approximate entropy (ApEn) of respiratory movement as a gauge of complexity in respiration, by stage of consciousness, in the light of putative brain interactions.

PARTICIPANTS

Eight healthy men, who were between the ages of 23 and 29 years, were investigated.

MEASUREMENTS AND RESULTS

The signals of chest wall movement and EEG were recorded from 10:30 PM to 6:00 AM. After analog-to-digital conversion, the ApEn of respiratory movement (3 min) and EEG (20 s) were computed. Surrogate data were tested for nonlinearity in the original time series. The most impressive reduction in the ApEn of respiratory movement was associated with stage IV sleep, when the ApEn of the EEG was also statistically significantly decreased. A statistically significant linear relation is found between the ApEn of both variables. Surrogate data indicated that respiratory movement had nonlinear properties during all stages of consciousness that were investigated.

CONCLUSION

Respiratory movement and EEG signals are more regular during stage IV sleep than during other stages of consciousness. The change in complexity described by the ApEn of respiration depends in part on the ApEn of the EEG, suggesting the involvement of nonlinear dynamic processes in the coordination between brain and lungs.

Heart rate variability in emergency department patients with sepsis

OBJECTIVE

To test the hypothesis that heart rate variability (HRV) can provide an early indication of illness severity among patients presenting to the emergency department (ED) with sepsis.

METHODS

The authors enrolled a convenience sample of 15 ED patients meeting the American College of Chest Physicians/Society of Critical Care Medicine criteria for sepsis. Each patient had continuous Holter monitoring performed in the ED. Acute Physiology and Chronic Health II (APACHE II) and Sequential Organ Failure (SOFA) scores were calculated for the day of presentation. Holter tapes obtained in the ED were analyzed off-line to calculate HRV variables for the 5-minute segment with the least artifact and non-sinus beats. These variables were correlated with APACHE II and SOFA scores.

RESULTS

LFnu (normalized low-frequency power), an assessment of the relative sympathetic contribution to overall HRV, was correlated with increased illness severity as calculated using APACHE II (r = -0.67, r(2) = 0.43) and SOFA (r = -0.80, r(2) = 0.64) scores. LF/HF ratio (low-frequency/high-frequency ratio), a measure of sympathovagal balance, was correlated with the SOFA score [r = -0.54 (95% CI = -0.83 to -0.01), r(2) = 0.29]. All five patients who required critical care monitoring or ventilatory support or who died during the first 5 days of their hospitalization had LFnu values below 0.5 and LF/HF ratios less than 1.0. None of the patients with measurements greater than these threshold values died or required these interventions during the five days following admission.

CONCLUSIONS

A single variable, LFnu, which reflects sympathetic modulation of heart rate, accounted for 40-60% of the variance in illness severity scores among patients presenting to the ED with sepsis. HRV, as reflected in LFnu and the LF/HF ratio and measured with a single brief (5-minute) period of monitoring while in the ED, may provide the emergency physician with a readily available, noninvasive, early marker of illness severity. The threshold effect of LFnu and LF/HF in the prediction of early clinical deterioration was an unexpected finding and should be regarded as hypothesis-generating, pending further study.

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.

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.

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.

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.

Reproductive Strategies and Karyotype of the Burrowing Nematode, Radopholus similis

Karyotype, gametogenesis, and gonad morphology were characterized for 56 Radopholus spp. isolates collected from Africa, Australia, Central America, Cuba, Dominican Republic, Guadeloupe, Puerto Rico, North America (Florida), and Hawaii. Seven of the isolates, all collected from Florida, were citrus-parasitic. The haploid karyotype for all isolates was n = 5, and gonad organization was similar for each. Furthermore, reproduction did not involve parthenogenesis. Initially, spermatids were produced in young adult females and accumulated in the spermatheca prior to differentiation to sperm. At the cessation of spermatogenesis, oogenesis began and continued for the remainder of the nematode's life. Oocytes first entered a mitotic phase, then a transition zone, and remained in pachytene until they reached the proximal end of the ovary. Thus, Radopholus can reproduce as a hermaphrodite when amphigony does not occur. The gonad is actually an ovatestis.

Phylogenetic Analysis of Geographically Diverse Radopholus similis via rDNA Sequence Reveals a Monomorphic Motif

The nucleic acid sequences of rDNA ITS1 and the rDNA D2/D3 expansion segment were compared for 57 burrowing nematode isolates collected from Australia, Cameroon, Central America, Cuba, Dominican Republic, Florida, Guadeloupe, Hawaii, Nigeria, Honduras, Indonesia, Ivory Coast, Puerto Rico, South Africa, and Uganda. Of the 57 isolates, 55 were morphologically similar to Radopholus similis and seven were citrus-parasitic. The nucleic acid sequences for PCR-amplified ITS1 and for the D2/D3 expansion segment of the 28S rDNA gene were each identical for all putative R. similis. Sequence divergence for both the ITS1 and the D2/D3 was concordant with morphological differences that distinguish R. similis from other burrowing nematode species. This result substantiates previous observations that the R. similis genome is highly conserved across geographic regions. Autapomorphies that would delimit phylogenetic lineages of non-citrus-parasitic R. similis from those that parasitize citrus were not observed. The data presented herein support the concept that R. similis is comprised of two pathotypes-one that parasitizes citrus and one that does not.

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.

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.

Aggressiveness and Damage Potential of Central American and Caribbean Populations of Radopholus spp. in Banana

Monoxenic cultures of burrowing nematode populations extracted from banana roots from Belize, Guatemala, Honduras, and Costa Rica were established on carrot discs. Cultures of Radopholus spp. were also obtained from Florida, Puerto Rico, Dominican Republic, and Ivory Coast. The aggressiveness (defined as reproductive fitness and root necrosis) of these populations was evaluated by inoculating banana plants (Musa AAA, cv. Grande Naine) with 200 nematodes/plant. Banana plants produced by tissue culture were grown in 0.4-liter styrofoam cups, containing a 1:1 mix of a coarse and a fine sand, at ca. 27 degrees C and 80% RH. Banana plants were acclimated and allowed to grow for 4 weeks prior to inoculation. Plant height, fresh shoot and root weights, root necrosis, and nematode population densities were determined 8 weeks after inoculation. Burrowing-nematode populations varied in aggressiveness, and their reproductive fitness was generally related to damage reported in the field. Plant height and fresh shoot and root weight did not reflect damage caused by nematodes under our experimental conditions. Necrosis of primary roots was closely related to the reproductive fitness of the nematode populations. Variation in aggressiveness among nematode populations followed a similar trend in the two susceptible hosts tested, Grande Naine and Pisang mas. All nematode populations had a low reproductive factor (Rf </=2.5) in the resistant host except for the Ivory Coast population which had a moderate reproductive factor (Rf </= 5) on Pisang Jari Buaya. This is the first report of a burrowing nematode population parasitizing this important source of resistance to R. similis.

Randomly Amplified Polymorphic DNA Differs with Burrowing Nematode Collection Site, but not with Host Range

The genetic variability of 12 burrowing nematode (Radopholus sp.) isolates from Central America, the Caribbean, and Florida, and one isolate from Ivory Coast were compared with RAPD analysis. A high degree of genetic similarity (>0.82) was determined for isolates from the Western Hemisphere. Genome similarity was greatest among isolates collected within a country. Among isolates collected in Central America and the Caribbean, burrowing nematodes from Belize and Guatemala were genetically more distant. However, the genome of the isolate from Ivory Coast was most dissimilar (>0.30). These results suggest that African and American burrowing-nematode isolates may have had different origins or that they have been geographically isolated for a sufficient amount of time to have accumulated genetic changes detectable by RAPD analysis. No relationship was found between the genomic similarity and extent of reproduction or damage to banana or citrus roots. Morphometric analysis involving eight of the isolates indicated that they were morphologically identical and values for morphometric parameters were well within the range previously published for banana and citrusparasitic burrowing nematodes.

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.

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.

Genome Similarity Implies that Citrus-Parasitic Burrowing Nematodes do not Represent a Unique Species

Burrowing nematodes from Central America, Dominican Republic, Florida, Guadeloupe, Hawaii, and Puerto Rico were characterized for their ability to parasitize citrus, but citrus parasites were found only in Florida. Sequence tag sites originally amplified from a citrus-parasitic burrowing nematode were polymorphic among 37 burrowing nematode isolates and were not correlated with citrus parasitism, nematode isolate collection site, or amplification of a 2.4-kb sequence tag site (DK#1). Results of a RAPD analysis and characterization of the isozymes phosphoglucose isomerase, lactate dehydrogenase, and malate dehydrogenase indicated that the burrowing nematode isolates were highly similar. Citrus parasitism in Florida appears to be associated with limited changes in the burrowing nematode genome. Findings did not substantiate a previous report that R. citrophilus was present in Hawaii. Overall, these data do not support assignment of sibling species status to burrowing nematodes that differ with respect to citrus parasitism.

Sequence Tag Site and Host Range Assays Demonstrate that Radapholus similis and R. citraphilus are not Reproductively Isolated

Males of citrus-parasitic Radopholus citrophilus (FL1) were mated with non-citrus-parasitic R. similis (FL5) females. Progeny inherited a 2.4-kb sequence tag site (DK#1) and the ability to reproduce in citrus from the paternal parent (FLl); both traits were absent in the maternal line (FL5). The hybrid progeny produced offspring in roots of citrus seedlings over an 8-month period and therefore were considered reproductively viable. Genomic DNA hybridization studies indicated that one or more copies of DK#1 were present in R. citrophilus FL1. It is not likely that DK#1 represents a citrus parasitism gene because it was amplified from some burrowing nematode isolates that did not parasitize citrus and because DK#1 contains no open reading frames. Inability to reliably test individual nematodes for their ability to parasitize citrus was a constraint to obtaining F2 data required for definitive genetic characterization of citrus parasitism in burrowing nematodes, and alternate approaches will be required. Although the physical relationship of DK#1 and the citrus parasitism locus remains undefined, results of controlled mating studies using these parameters as genetic markers enabled us to identify hybrid F progeny. Therefore, R. similis and R. citrophilus are not sibling species since gene flow between the two does not appear to be restricted via geographic isolation (sympatric in Florida) or by genetics.

Nonlinear noise reduction for electrocardiograms

The electrical activity of the heart usually shows dynamical behavior which is neither periodic nor deterministically chaotic: The interbeat intervals seem to contain a random component. Although long term predictions are thus impossible, good predictions can be made for times smaller than one heart cycle. This fact is used in order to suppress measurement errors by a local geometric projection method which was originally developed for chaotic signals. The result constitutes evidence that techniques of time series analysis based on chaos theory can be useful despite the fact that very few natural phenomena have been actually established to be deterministically chaotic. (c) 1996 American Institute of Physics.

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.

Partial Characterization of Cytosolic Superoxide Dismutase Activity in the Interaction of Meloidogyne incognita with Two Cultivars of Glycine max

The closely related soybean (Glycine max) cultivars Centennial and Pickett 71 were confirmed to be resistant and susceptible, respectively, to the root-knot nematode Meloidogryne incognita. Increases in superoxide dismutase (SOD) activity were detected in roots of both soybean cultivars 48 hours following inoculation. Superoxide dismutase activity increased in roots of the susceptible cultivar overall, but declined after 96 hours in roots of the resistant cultivar. The isoelectric points of SOD isolated from preparasitic and parasitic developmental stages of the nematode appeared to differ. The SOD activity increased dramatically as nematodes matured and enlarged. Plant and nematode SOD were present as ca. 40-kDa cuprozinc dimers. Initial increases in SOD activity in infected tissue appeared to involve nematode regulation of plant gene expression. However, as the nematode enlarged, SOD activity could be detected within the female body only.

Colonization of greenhouse nematode cultures by nematophagous mites and fungi

Unproductive > 7-year-old greenhouse cultures of citrus nematode (Tylenchulus semipenetrans) had a well-developed soil invertebrate fauna that included nematophagous mite species characteristic of Florida citrus groves. Nematophagous mite densities in box cultures were 285 +/- 42 mites/liter, 2.5 to 25 times higher than densities in citrus nematode-infested groves. Vigorous root-knot nematode (Meloidogyne incognita) cultures grown in steam-pasteurized soil had few nematophagous mites until more than 3 months after inoculation. Mite species diversity had a significant (P < 0.0001) positive linear relationship with culture age that explained about one-half the variance in species number. Nematophagous mite densities rose and then fell with culture age. In root-knot cultures > 3-months-old, mite densities often exceeded 1,000 mites/liter. Twelve species of nematophagous fungi also were isolated from greenhouse nematode cultures.

Lectin Binding to Radopholus citrophilus and R. similis Proteins

Lectin-binding glycoproteins in seven populations of two burrowing nematode sibling species were probed with five different biotinylated lectins on Western blots, and differences were correlated with nematode ability to parasitize citrus and to overcome citrus rootstock resistance. Banding patterns of molecular weight standards were fit best by an exponential decay function, and a predictive equation was used to estimate molecular weights (r(2) = 0.999). A band (131 kDa) that labeled with the lectin Concanavalin A (Con A) occurred in extracts from cuticles and egg shells of populations of Radopholus citrophilus that parasitize citrus. Wheat germ agglutin labeled a band (58 kDa) in aqueous homogenates of populations that reproduce in roots of citrus rootstock normally resistant to burrowing nematodes. The two sibling species R. citrophilus and R. similis were distinguished by a high molecular weight Con A-labeled band (608 kDa) from cuticle and egg shells. Probing blots with the lectin Limulus polyphemus agglutinin indicated that each population contained a band (12-16 kDa) specifically inhibited by the addition of 25 mM neuraminic acid, suggesting that glycoproteins with sialic acid moieties are present in burrowing nematodes.

A bioassay to estimate root penetration by nematodes

An in vitro bioassay with a 96-well microtiter plate was used to study the effect of lectins on burrowing nematode penetration of citrus roots. In each well, one 4-mm root segment, excised from the zone of elongation of rough lemon roots, was buried in 0.88 g dry sand. Addition of a Radopholus citrophilus suspension containing ca. 300 nematodes in 50 mu1 test solution completely moistened the sand in each well. The technique assured uniform treatment concentration throughout the medium. Within 16-24 hours, burrowing nematodes penetrated citrus root pieces, primarily through the cut ends. The lectins (100 mug/ml) Concanavalin A (Con A), soybean agglutinin (SBA), wheat germ agglutinin (WGA), and Lotus tetragonolobus agglutinin (LOT) stimulated an increase in penetration of citrus root segments by Radopholus citrophilus. Concentrations as low as 12.5 mug/ml Con A, LOT, and WGA stimulated burrowing nematode penetration of citrus roots. Heat denaturation of the lectins reversed their effect on penetration; however, incubation of nematodes in lectin (25 mug/ml) with 25 mM competitive sugars did not. The reason for enhanced penetration associated with lectins is unclear.

Dynamics of heart rate

Heart rate oscillates on several different time scales and has long-term variability in the form of 1/f noise. The physiological control of heart rate is briefly reviewed, and several typical patterns of heart rate variability, in health and sickness, are described. Considered briefly are some possible dynamical mechanisms for heart rate variability.

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.

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.

Influence of Lectins on Constricting Ring Formation by Arthrobotrys dactyloides

Incubation of Arthrobotrys dactyloides conidia in the presence of Radopholus citrophilus in lectin solutions with their corresponding sugars did not alter the stimulation of trap formation in solutions containing lectins alone. The lack of inhibition of lectin-stimulated trap formation by sugars or by lectin denaturation and the lack of lectin specificity indicate that the carbohydrate-binding regions of the particular lectins studied are not the stimulatory moieties of these macromolecules.

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.

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.

Antagonists of Plant-parasitic Nematodes in Florida Citrus

In a survey of antagonists of nematodes in 27 citrus groves, each with a history of Tylenchulus semipenetrans infestation, and 17 noncitrus habitats in Florida, approximately 24 species of microbial antagonists capable of attacking vermiform stages of Radopholus citrophilus were recovered. Eleven of these microbes and a species of Pasteuria also were observed attacking vermiform stages of T. semipenetrans. Verticillium chlamydosporium, Paecilomyces lilacinus, P. marquandii, Streptomyces sp., Arthrobotrys oligospora, and Dactylella ellipsospora were found infecting T. semipenetrans egg masses. Two species of nematophagous amoebae, five species of predatory nematodes, and 29 species of nematophagous arthropods also were detected. Nematode-trapping fungi and nematophagous arthropods were common inhabitants of citrus groves with a history of citrus nematode infestation; however, obligate parasites of nematodes were rare.

Improved nematode extraction from carrot disk culture

Radopholus spp. were reared in carrot tissue culture via established procedures, with slight modification. Several plant tissue maceration enzymes and flotation media (salts and sucrose) were evaluated with regard to nematode toxicity and extraction efficiency. Best extraction of viable nematodes and eggs was attained when carrot tissue infested with Radopholus citrophilus or R. similis was macerated with a mixture of 0.50% driselase and 0.50% cellulysin, w/v each, with 2.5 ml of enzyme solution based for each gram of carrot tissue. Maceration slurries containing carrot tissue and nematodes were maintained in open flasks on a rotary shaker (175 rpm) at 26 C for 24 hours. Nematodes and eggs were extracted from resultant culture slurries by flotation with MgSO-7H0 (sp gr 1.1). A protocol is presented to extract large quantities of viable burrowing nematodes and their eggs from carrot disk cultures.

Root Tissue Response of Two Related Soybean Cultivars to Infection by Lectin-treated Meloidogyne spp

Treatment of second-stage juveniles (J2) of Meloidogyne incognita race 1 and M. javanica with soybean agglutinin, Concanavalin A, wheat germ agglutinin, Lotus tetragonolobus agglutinin, or Limax flavus agglutinin or the corresponding competitive sugars for each of these lectins did not alter normal root tissue response of soybean cultivars Centennial and Pickett 71 to infection by M. incognita race 1 or M. javanica. Giant cells were frequently induced in Centennial and Pickett 71 roots 5 and 20 days after inoculation of roots with untreated J2 of a population of M. incognita race 3. Treatment of J2 of M. incognita race 3 with the lectins or carbohydrates listed above caused Centennial, but not Pickett 71, root tissue to respond in a hypersensitive manner to infection by M. incognita race 3. Penetration of soybean roots by J2 of Meloidogyne spp. was strongly inhibited in the presence of 0.1 M sialic acid. Treatment of J2 with sialic acid was not lethal to nematodes, and the inhibitory activity of sialic acid was apparently not caused by low pH. These results suggest that carbohydrates may influence plant-nematode interactions.

Influence of mycorrhizal fungus, phosphorus, and burrowing nematode interactions on growth of rough lemon citrus seedlings

Rough lemon seedlings were grown in mycorrhizal-infested or phosphorus-amended soil (25 and 300 mg P/kg) in greenhouse experiments. Plants Were inoculated with the citrus burrowing nematode, Radopholus citrophilus (0, 50, 100, or 200 nematodes per pot). Six months later, mycorrhizal plants and nonmycorrhizal, high-P plants had larger shoot and root weights than did non-mycorrhizal, low-P plants. Burrowing nematode population densities were lower in roots of mycorrhizal or nonmycorrhizal, high-P plants than in roots of nonmycorrhizal, low-P plants; however, differences in plant growth between mycorrhizal and nonmycorrhizal plants were not significant with respect to initial nematode inoculum densities. Phosphorus content in leaf tissue was significantly greater in mycorrhizal and nonmycorrhizal, high-P plants compared with nonmycorrhizal, low-P plants. Nutrient concentrations of K, Mg, and Zn were unaffected by nematode parasitism, whereas P, Ca, Fe, and Mn were less in nematode-infected plants. Enhanced growth associated with root colonization by the mycorrhizal fungus appeared to result from improved P nutrition and not antagonism between the fungus and the nematode.

Characterization of Carbohydrates on the Surface of Second-stage Juveniles of Meloidogyne spp

Fluorescent conjugates of the lectins soybean agglutinin (SBA), Concanavalin A (Con A), wheat germ agglutinin (WGA), Lotus tetragonolobus agglutinin (LOT), and Limulus polyphemus agglutinin (LPA) bound primarily to amphidial openings and amphidial secretions of viable, preinfective second-stage juveniles (J2) of Meloidogyne incognita races 1 and 3 (Mil, Mi3) and M. javanica (Mj). No substantial difference in fluorescent lectin binding was observed among the populations examined. Binding of only LOT and LPA were inhibited in the presence of 0.1 M competitive sugar. Structural differences in amphidial carbohydrate complexes among populations of Mi 1, Mi3, and Mj were revealed by glycohydrolase treatment of preinfective J2 and subsequent labeling with fluorescent lectins. A quantitative microfiltration enzyme-linked lectin assay revealed previously undetected differences in lectin binding to nonglycohydrolase-treated J2. Freinfective J2 of Mj bound the greatest amount of SBA, LOT, and WGA, whereas J2 of Mil bound the most LPA.

Description of Meloidogyne christiei n. sp. (Nematoda: Meloidogynidae) from Oak with SEM and Host-Range Observations

Meloidogyne christiei n. sp. is described and illustrated from turkey oak (Quercus laevis) in Sanlando Park, Altamonte Springs, Florida. This new nematode species has a distinctive perineal pattern commonly with a high, squarish arch and coarse broken striae which tend to diverge at various angles, especially in and above the anal area. Female labial disc is indented, forming four points or prongs, unlike other species. Eggs are deposited inside the gall in a tubular, coiled manner. Vaginal muscles are exceptionally prominent and dense. SEM observations provided further detail of the perineal pattern and details of the head of females, males, and second-stage juveniles. Galls on the root commonly occur singly, but sometimes in small clusters, and appear as discrete nodules on the side of the root and without adjacent swelling. In general, only one female is found in each gall but occasionally two are present. In greenhouse tests, citrus, tobacco, cotton, pepper, watermelon, peanut, and tomato were not hosts. This nematode occurs throughout central Florida commonly on Q. laevis, the only known host.

Characterization of a New Burrowing Nematode Population, Radopholus citrophilus, from Hawaii

Karyotype, host preference, isozyzme patterns, morphometrics, and mating behavior of two burrowing nematode populations from Hawaii, one infecting Anthurium sp. and the second infecting Musa sp., were compared with Radopholus similis and R. citrophilus populations from Florida. The population from Anthurium sp. had five chromosomes (n = 5), and that from Musa sp. had four (n = 4). Neither of the Hawaiian nematode populations persisted in roots of Citrus limon or C. aurantium. Anthurium clarinerivum and A. hookeri were hosts of the burrowing nematode population from anthurium in Hawaii and of R. citrophilus from Florida, whereas the two anthurium species were poor hosts of the population from Musa sp. in Hawaii and R. similis from Florida. The isozyme pattern of the population isolated from anthurium was identical to that of R. citrophigus, whereas the pattern of the population from banana in Hawaii was identical to that of R. similis. Mating behavior between the burrowing nematode population isolated from Anthurium sp. and a Florida population of R. citrophilus supports their close taxonomic relationship. Mating was observed between the population from Anthurium sp. and the Florida population of R. citrophilus but not between the Hawaiian burrowing nematode population isolated from Musa sp. and a Florida population of R. citrophilus. These findings indicate that a previously unidentified population of R. citrophilus which does not parasitize citrus occurs in Hawaii.

Variation in Radopholus citrophilus Population Densities in the Citrus Rootstock Carrizo Citrange

Seedlings of the hybrid citrus rootstock, Carrizo citrange (Citrus sinensis x Poncirus trifoliata) do not uniformly limit development of the citrus burrowing nematode, Radopholus citrophilus. Variation in nematode population densities in roots of seedlings germinating from the same seed suggests that factors responsible for nematode incompatibility are not functional or are not inherited uniformly among progeny. Seeds which produced a single seedling were more likely to produce plants which suppressed citrus burrowing nematode population increase than were seeds which produced two or three seedlings.

Plant parasitic nematodes associated with leatherleaf fern

Seven species of plant parasitic nematodes were found to be associated with leatherleaf fern (Rumohra adiantiformis) in central Florida. Of these, Pratylenchus penetrans, Tylenchorhynchus claytoni, and Criconemoides curvatum were commonly encountered. Nematode communities generally included two or three species of plant parasitic nematodes, with greatest diversity in nematode species occurring in ferneries shaded by oak trees. Species diversity was not correlated with fernery age. Leatherleaf fern was tolerant of P. penetrans and T. claytoni in microplot tests.

Influence of the Sting Nematode, Belonolaimus longicaudalus, on Young Citrus Trees

The sting nematode, Belonolaimus longicaudatus, was associated with poor growth of citrus in a central Florida nursery. Foliage of trees was sparse and chlorotic. Affected rootstocks included Changsha and Cleopatra mandarin orange; Flying Dragon, Rubidoux, and Jacobsen trifoliate orange; Macrophylla and Milam lemon; Palestine sweet lime; sour orange; and the hybrids - Carrizo, Morton, and Rusk citrange and Swingle citrumelo. Root symptoms included apical swelling, development of swollen terminals containing 3-5 apical meristems and hyperplastic tissue, coarse roots, and a reduction in the number of fibrous roots. Population densities as high as 392 sting nematodes per liter soil were detected, with 80% of the population occurring in the top 30 cm of soil; however, nematodes were detected to 107 cm deep. Although an ectoparasite, the nematode was closely associated with citrus root systems and was transported with bare root nursery stock. Disinfestation was accomplished by hot water treatment (49 C for 5 minutes).