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PubMed2005

The marrow cell continuum: stochastic determinism.

Traditional models of hematopoiesis have been hierarchical in nature. Over the past 10 years, we have developed data indicating that hematopoiesis is regulated in a continuum with deterministic and stochastic components. We have shown that the most primitive stem cells, as represented by lineage negative rhodamine(low) Hoechst(low) murine marrow cells are continuously or intermittently cycling as determined by in vivo BrdU labeling. When marrow stem cells are induced to transit cell cycle by in vitro exposure to cytokines, either IL-3, IL-6, IL-11, and steel factor or thrombopoietin, FLT3 ligand, and steel factor, they progress through cycle in a highly synchronized fashion. We have determined that when the stem cells progress through a cytokine stimulated cell cycle the homing, engraftment, adhesion protein, global gene expression, and hematopoietic differentiation phenotypes all change in a reversible fashion. This has led to the continuum model, in which, with cycle transit, chromatin is continually changing altering open transcription areas and providing a continually changing landscape of transcriptional opportunity. More recently, we have extended the changing differentiation profiles to differentiation into lung cells and found that non-hematopoietic differentiation also shows cycle related reversibly modulation. These observations all together support a continuum model of stem cell regulation in which the phenotype of the marrow stem cells is continually and reversibly changing over time.

Animals↗
PubMed2005

Convergence analysis of a deterministic discrete time system of Oja's PCA learning algorithm.

The convergence of Oja's principal component analysis (PCA) learning algorithms is a difficult topic for direct study and analysis. Traditionally, the convergence of these algorithms is indirectly analyzed via certain deterministic continuous time (DCT) systems. Such a method will require the learning rate to converge to zero, which is not a reasonable requirement to impose in many practical applications. Recently, deterministic discrete time (DDT) systems have been proposed instead to indirectly interpret the dynamics of the learning algorithms. Unlike DCT systems, DDT systems allow learning rates to be constant (which can be a nonzero). This paper will provide some important results relating to the convergence of a DDT system of Oja's PCA learning algorithm. It has the following contributions: 1) A number of invariant sets are obtained, based on which we can show that any trajectory starting from a point in the invariant set will remain in the set forever. Thus, the nondivergence of the trajectories is guaranteed. 2) The convergence of the DDT system is analyzed rigorously. It is proven, in the paper, that almost all trajectories of the system starting from points in an invariant set will converge exponentially to the unit eigenvector associated with the largest eigenvalue of the correlation matrix. In addition, exponential convergence rate are obtained, providing useful guidelines for the selection of fast convergence learning rate. 3) Since the trajectories may diverge, the careful choice of initial vectors is an important issue. This paper suggests to use the domain of unit hyper sphere as initial vectors to guarantee convergence. 4) Simulation results will be furnished to illustrate the theoretical results achieved.

Algorithms↗
PubMed1999

Individual based modeling and parameter estimation for a Lotka-Volterra system.

Stochastic component, inevitable in biological systems, makes problematic the estimation of the model parameters from a single sequence of measurements, despite the complete knowledge of the system. We studied the problem of parameter estimation using individual-based computer simulations of a 'Lotka-Volterra world'. Two kinds (species) of particles--X (preys) and Y (predators)--moved on a sphere according to deterministic rules and at the collision (interaction) of X and Y the particle X was changed to a new particle Y. Birth of preys and death of predators were simulated by addition of X and removal of Y, respectively, according to exponential probability distributions. With this arrangement of the system, the numbers of particles of each kind might be described by the Lotka-Volterra equations. The simulations of the system with low (200-400 particles on average) number of individuals showed unstable oscillations of the population size. In some simulation runs one of the species became extinct. Nevertheless, the oscillations had some generic properties (e.g. mean, in one simulation run, oscillation period, mean ratio of the amplitudes of the consecutive maxima of X and Y numbers, etc.) characteristic for the solutions of the Lotka-Volterra equations. This observation made it possible to estimate the four parameters of the Lotka-Volterra model with high accuracy and good precision. The estimation was performed using the integral form of the Lotka-Volterra equations and two parameter linear regression for each oscillation cycle separately. We conclude that in spite of the irregular time course of the number of individuals in each population due to stochastic intraspecies component, the generic features of the simulated system evolution can provide enough information for quantitative estimation of the system parameters.

Animals↗
PubMed2001

Tissue as a self-organizing system with fractal dynamics.

Cell is a supramolecular dynamic network. Screening of tissue-specific cDNA library and results of Relative RT-PCR indicate that the relationship between genotype, (i.e., dynamic network of genes and their protein regulatory elements) and phenotype is non-bijective, and mendelian inheritance is a special case only. This implies non-linearity, complexity, and quasi-determinism, (i.e., co-existence of deterministic and non-deterministic events) of dynamic cellular network; prerequisite conditions for the existence of fractal structure. Indeed, the box counting method reveals that morphological patterns of the higher order, such as gland-like structures or populations of differentiating cancer cells possess fractal dimension and self-similarity. Since fractal space is not filled out randomly, a variety of morphological patterns of functional states arises. The expansion coefficient characterizes evolution of fractal dynamics. The coefficient indicates what kind of interactions occurs between cells, and how far from the limiting integer dimension of the Euclidean space the expanding population of cells is. We conclude that cellular phenomena occur in the fractal space; aggregation of cells is a supracollective phenomenon (expansion coefficient > 0), and differentiation is a collective one (expansion coefficient < 0). Fractal dimension or self-similarity are lost during tumor progression. The existence of fractal structure in a complex tissue system denotes that dynamic cellular phenomena generate an attractor with the appropriate organization of space-time. And vice versa, this attractor sets up physical limits for cellular phenomena during their interactions with various fields. This relationship can help to understand the emergence of extraterrestial forms of life. Although those forms can be composed of non-carbon molecules, fractal structure appears to be the common feature of all interactive biosystems.

Animals↗
PubMed2002

Computer-aided intrapatient comparison of brain SPECT images: the gray-level normalization issue applied to children with epilepsy.

UNLABELLED: A tool was developed for automated intrapatient comparison of brain SPECT images, with specific emphasis on gray-level normalization. METHODS: Ictal and interictal (99m)Tc-ethyl cysteinate dimer SPECT images were acquired for 6 children with partial epilepsy (age range, 2-10 y). For each patient, 3-dimensional rigid geometric ictal-to-interictal image registration optimizing different classic criteria (correlation coefficient, ratio uniformity) in a multiscale translation-rotation 6-parameter space was first performed. Gray-level normalization was then performed with different methods, using a 1- or 2-parameter linear model. In the 1-parameter case, the scaling factor was equal to the interictal-to-ictal ratio of the maximum, mean, or median values calculated within different reference volumes (whole brain or cerebellum) or obtained by linear regression between ictal and interictal counts in the brain or by maximizing a robust criterion, the number of deterministic sign changes in the subtraction images. In the 2-parameter case, the scaling factor and additive constant were estimated using these last 2 methods. For each patient, registration validity and normalization plausibility were assessed by considering the correlation scatterplot together with the different normalization lines and by comparing interictal and registered normalized ictal images using a twin display (with isocontours) in the 3 orthogonal planes. Three-dimensional volumes of interest could be selected on coupled interictal-subtraction images for further focused numeric comparison. RESULTS: After a satisfactory and stable geometric registration with both criteria, the different normalization methods led to similar subtraction images for 5 of 6 patients, except the maxima ratio, which gave noticeably different results in 2 patients. For the remaining patient, with highly dissimilar ictal-interictal images, the maxima ratio normalization was obviously wrong and the other 1-parameter methods probably better depicted the data than did the 2-parameter methods. CONCLUSION: When comparing intrapatient brain SPECT images, one should be aware of the potential impact of the gray-level normalization method on clinical interpretation. For ictal-interictal images, simple robust scaling should be recommended. In particular, image maximum should generally not be considered a valid reference, and no additive constant is needed in the linear gray-level normalization model.

Brain↗
PubMed1998

Ion channel stochasticity may be critical in determining the reliability and precision of spike timing.

The firing reliability and precision of an isopotential membrane patch consisting of a realistically large number of ion channels is investigated using a stochastic Hodgkin-Huxley (HH) model. In sharp contrast to the deterministic HH model, the biophysically inspired stochastic model reproduces qualitatively the different reliability and precision characteristics of spike firing in response to DC and fluctuating current input in neocortical neurons, as reported by Mainen & Sejnowski (1995). For DC inputs, spike timing is highly unreliable; the reliability and precision are significantly increased for fluctuating current input. This behavior is critically determined by the relatively small number of excitable channels that are opened near threshold for spike firing rather than by the total number of channels that exist in the membrane patch. Channel fluctuations, together with the inherent bistability in the HH equations, give rise to three additional experimentally observed phenomena: subthreshold oscillations in the membrane voltage for DC input, "spontaneous" spikes for subthreshold inputs, and "missing" spikes for suprathreshold inputs. We suggest that the noise inherent in the operation of ion channels enables neurons to act as "smart" encoders. Slowly varying, uncorrelated inputs are coded with low reliability and accuracy and, hence, the information about such inputs is encoded almost exclusively by the spike rate. On the other hand, correlated presynaptic activity produces sharp fluctuations in the input to the postsynaptic cell, which are then encoded with high reliability and accuracy. In this case, information about the input exists in the exact timing of the spikes. We conclude that channel stochasticity should be considered in realistic models of neurons.

Action Potentials↗
PubMed1996

Chaos-related deterministic regulation of heart rate variability in time- and frequency domains: effects of autonomic blockade and exercise.

OBJECTIVES: To study non-linear complexity or chaotic behaviour of heart rate in short time series and its dependence on autonomic tone. METHODS: Ten healthy individuals (5 men, mean age 44 years) were investigated at rest, after intravenous injections of propranolol (0.15 mg/kg), followed by atropine (0.03 mg/kg). On another occasion, investigation was made during exercise on a bicycle ergometer at 40% and at 70% of maximal working capacity. Heart rate variability was assessed by: local sensitive dependence on initial conditions as quantitated by the dominant Lyapunov exponent, coefficient of variation of heart rate, power spectral analysis of high- and low-frequency bands and the 1/f-slope of the very-low-frequency band and time domain analysis. RESULTS: The approximate dominant Lyapunov exponent was positive at rest and remained positive during autonomic blockade and during exercise. The exponent decreased significantly with propranolol+atropine and even more so during exercise but did not attain zero. At baseline approximate predictability was lost after about 30 s whereas after autonomic blockade or exercise it was lost after about 60 s. The 1/f-slope remained unaltered around -1. As expected, power in high- and low-frequency bands as well as time domain index decreased significantly with autonomic blockade. The low-frequency band and time domain index were affected by exercise. CONCLUSIONS: Heart rate variability of sinus rhythm in healthy individuals has characteristics suggestive of low-dimensional chaos-like determinism which is modulated but not eliminated by inhibition of autonomic tone or by exercise. The dominant Lyapunov exponent characterises heart rate variability independent or the other investigated measures.

Adult↗
PubMed1999

A deterministic approach to automated stenosis quantification.

We developed a new approach to quantitative coronary angiography (QCA), which overcomes several limitations of available programs, such as dependence on operator input; limited tracking ability; fixed correction of the point spread function (PSF); and different calibration on empty vs. contrast-filled catheters. The program (Intelligent Images QCA, version 1.4) provides absolute reproducibility by deterministic, operator-independent identification of the skeleton and the edges of the coronary tree. The algorithm works as follows: application of a matched filter to emphasize selectively the coronary arteries; adaptive threshold binarization; binary thinning and skeletonization; perpendicular resampling with sub-pixel interpolation; derivative filtering; minimal cost edge detection; and automatic identification and quantification of the stenosis. Operator's interaction is restricted to definition of a region of interest; editing of either skeleton or edges is not allowed. PSF correction is fine-tuned to the actual frequency response of the imaging chain by calibration on a contrast-filled conical lucite phantom. Catheter calibration is carried out by a second derivative-based edge detection much less sensitive to the presence of contrast. In vitro phantom analysis (0. 5 to 5.0 mm) showed accuracy of 0.028-0.031 mm and precision of 0. 054-0.062 mm on nonmagnified images from the angio TV chain and the cine projector, respectively. In vivo evaluation on a series of consecutive diagnostic angiograms yielded correct contour detection of 70/73 stenoses (96%); interobserver intraframe MLD variability 0. 00 mm; correct tracking of catheter edges 100%; interobserver variation coefficient of catheter calibration 3.3%; and mean difference of calibration factor on contrast-filled vs. empty catheters 2.7%. This new approach significantly improves reproducibility with respect to conventional QCA, maintaining high accuracy, precision, and applicability. Cathet. Cardiovasc. Intervent. 48:435-445, 1999.

Algorithms↗
PubMed1983

Environmental standards for ionizing radiation: theoretical basis for dose-response curves.

The types of injury attributable to ionizing radiation are subdivided, for purposes of risk assessment and radiological protection, into two broad categories: stochastic effects and nonstochastic effects. Stochastic effects are viewed as probablistic phenomena, varying in frequency but not severity as a function of the dose, without any threshold; nonstochastic effects are viewed as deterministic phenomena, varying in both frequency and severity as a function of the dose, with clinical thresholds. Included among stochastic effects are heritable effects (mutations and chromosome aberrations) and carcinogenic effects. Both types of effects are envisioned as unicellular phenomena which can result from nonlethal injury of individual cells, without the necessity of damage to other cells. For the induction of mutations and chromosome aberrations in the low-to-intermediate dose range, the dose-response curve with high-linear energy transfer (LET) radiation generally conforms to a linear nonthreshold relationship and varies relatively little with the dose rate. In contrast, the curve with low-LET radiation generally conforms to a linear-quadratic relationship, rising less steeply than the curve with high-LET radiation and increasing in slope with increasing dose and dose rate. The dose-response curve for carcinogenic effects varies widely from one type of neoplasm to another in the intermediate-to-high dose range, in part because of differences in the way large doses of radiation can affect the promotion and progression of different neoplasms. Information about dose-response relations for low-level irradiation is fragmentary but consistent, in general, with the hypothesis that the neoplastic transformation may result from mutation, chromosome aberration or genetic recombination in a single susceptible cell.

Animals↗
PubMed1995

A relational database in neurosurgery.

UNLABELLED: This paper describes teh automatic procedure for a clinical record management in a Neurosurgery ward. The automated record allows the storage, querying and effective management of clinical data. This is useful during the patient stay and also for data processing and analysis aiming at clinical research and statistical studies. The clinical record is problem-oriented. It contains a minimum data set regarding every patient and a data set which is defined by a classification nomenclature (using an inner protocol). The main parts of the clinical record are the following tables: PERSONAL DATA: contains the fields relating to personal and admission data of the patient. The compilation of some fields is compulsory because they serve as input for the automated discharge letter. This table is used as an identifier for patient retrieval. ANAMNESIS: composed of five different tables according to the kind of data. They are: familiar anamnesis, physiological anamnesis, past and next pathology anamnesis, and trauma anamnesis. GENERAL OBJECTIVITY: contains the general physical information of a patient. The field hold default values, which quickens the compilation and assures the recording of normal values. NEUROLOGICAL EXAMINATION: contains information about the neurological status of the patient. Also in this table, ther are default values in the fields. COMA: contains standardized ata and classifications. The multiple choices are automated and driven and belong to homogeneous classes. SURGICAL OPERATIONS: the information recording is made defining the general kind of operation and then defining the peculiar kind of operation. INSTRUMENTAL EXAMINATIONS: some examination results are recorded in a free structure, while other ones (TAC, etc.) follow codified structure. In order to identify a pathology by means of TAC, it is enough to record three values corresponding to three variables. THis classification fully describes a lot of neurosurgical pathologies. DISCHARGE: contains conclusions, therapies, result, and hospital course. Medical language is closer to the natural one and presents some abiguities. In order to solve this problem, a classification nomenclature was used for diagnosis definition. DISCHARGE LETTER: the document given to the patient when he is discharged. It extracts data from the previously described modules and contains standard headings. The information stored int he database is structured (e.g., diagnosis, name, surname, etc.) and access to this data takes place when the user wants to search the database, using particular queries where the identifying data of a patient is put as conditions for the research (SELECT age, name WHERE diagnosis="TRAUMA"). Logical operators and relational algebra of the relational DBMS allows more complex queries ((diagnosis="TRAUMA" AND age="19") OR sex="M"). The queries are deterministic, because data management uses a classification nomenclature. Data retrieval takes place through a matching, and the DBMS answers directly to the queries. The information retrieval speed depends upon the kind of system that is used; in our case retrieval time is low because the accesses to disk are few even for big databases. In medicine, clinical records can have a hierarchical structure and/or a relational one. Nevertheless, the hierarchical model presents a disadvantage: it is not very flexible because it is linked to a pre-defined structure; as a matter of fact, the definition of path is established in the beginning and not during the execution. Thus, a better representation of the system at a logical level requries a relational DBMS which exploits the relationships between entities in a vertical and horizontal way. That is why the developers adopted a mixed strategy which exploits the advantages of both models and which is provided by M Technology with SQL language (M/SQL). For the future, it is important to have at one's disposal multimedia technologies, which integrate different kinds of information (alp

Databases, Factual↗
PubMed2000

The coevolution of parasites with host-acquired immunity and the evolution of sex.

Here I present a deterministic model of the coevolution of parasites with the acquired immunity of their hosts, a system in which coevolutionary oscillations can be maintained. These dynamics can confer an advantage to sexual reproduction within the parasite population, but the effect is not strong enough to outweigh the twofold cost of sex. The advantage arises primarily because sexual reproduction impedes the response to fluctuating epistasis and not because it facilitates the response to directional selection-in fact, sexual reproduction often slows the response to directional selection. Where the cost of sexual reproduction is small, a polymorphism can be maintained between the sexuals and the asexuals. A polymorphism is maintained in which the advantage gained due to recombination is balanced by the cost of sex. At much higher costs of sex, a polymorphism between the asexual and sexual populations can still be maintained if the asexuals do not have a full complement of genotypes available to them, because the asexuals only outcompete those sexuals with which they share the same selected alleles. However, over time we might expect the asexuals to amass the full array of genotypes, thus permanently eliminating sexuals from the population. The sexuals may avoid this fate if the parasite population is finite. Although the model presented here describes the coevolution of parasites with the acquired immune responses of their hosts, it can be compared with other host-parasite models that have more traditionally been used to investigate Red Queen theories of the evolution of sex.

Animals↗
PubMed2005

Population structure within lineages of Wheat streak mosaic virus derived from a common founding event exhibits stochastic variation inconsistent with the deterministic quasi-species model.

Structure of Wheat streak mosaic virus (WSMV) populations derived from a common founding event and subjected to serial passage at high multiplicity of infection (MOI) was evaluated. The founding population was generated by limiting dilution inoculation. Lineages of known pedigree were sampled at passage 9 (two populations) and at passage 15, with (three populations) or without mixing (four populations) of lineages at passage 10. Polymorphism within each population was assessed by sequencing 17-21 clones containing a 1371 nt region (WSMV-Sidney 81 nts 8001-9371) encompassing the entire coat protein cistron and flanking regions. Mutation frequency averaged approximately 5.0 x 10(-4)/nt across all populations and ranged from 2.4 to 11.6 x 10(-4)/nt within populations, but did not consistently increase or decrease with the number of passages removed from the founding population. Shared substitutions (19 nonsynonymous, 10 synonymous, and 3 noncoding) occurred at 32 sites among 44 haplotypes. Only four substitutions became fixed (frequency = 100%) within a population and nearly one third (10/32) never achieved a frequency of 10% or greater in any sampled population. Shared substitutions were randomly distributed with respect to genome position, with transitions outnumbering transversions 5.4:1 and a clear bias for A to G and U to C substitutions. Haplotype composition of each population was unique with complexity of each population varying unpredictably, in that the number and frequency of haplotypes within a lineage were not correlated with number of passages removed from the founding population or whether the population was derived from a single or mixed lineage. The simplest explanation is that plant virus lineages, even those propagated at high MOI, are subject to frequent, narrow genetic bottlenecks during systemic movement that result in low effective population size and stochastic changes in population structure upon serial passage.

Base Sequence↗
PubMed1997

Circadian rhythmic fractal scaling of heart rate variability in health and coronary artery disease.

BACKGROUND: In clinical cardiology, heart rate variability is a putative index of autonomic cardiovascular function. Signs of reduced vagal activity are not only associated with an enhanced risk of sudden cardiac death, but such impaired heart rate variability became a new predictor of sudden cardiac death and other mortality in patients with a variety of diseased states. HYPOTHESIS: It is postulated (1) that the time structure (chronome) of heart rate variability in clinical health includes a circadian rhythm and deterministic chaos, the latter gauged by the correlation dimensions of RR intervals; and (2) that this chronome is altered in patients with coronary artery disease (CAD). METHODS: From 24-h Holter records of 11 healthy controls and 10 patients with CAD, 500-s sections around 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours were analyzed for smoothed RR intervals sampled at 4 Hz. Correlation integrals were estimated for embedding dimensions from 1 to 20 with a 1.0-s time lag, using an algorithm modified from Grassberger and Procaccia. The Wilcoxon signed-rank test compares circadian end points assessed by cosinor between the CAD patients and age-matched controls. RESULTS: A circadian rhythm characterizes the correlation dimension of healthy subjects peaking during the night (p < 0.005). Patients with CAD have a lowered correlation dimension (p < 0.05) and an altered circadian variation which requires the consideration of an approximately 12-h (circasemidian) component. CONCLUSION: The results demonstrate the sensitivity of circadian rhythms for the detection of disease. A partial 24- to 12-h (circadian-to-circasemidian) frequency multiplication (or partial variance transposition) in CAD of the correlation dimension, apart from being a potential clue to the etiology of the disease, adds a new feature to a chronocardiology combining, with the fractal scaling, an assessment of circadian and circasemidian components as measures of predictable variability to be tested for use in diagnosis, prognosis, and as putative guides to treatment timing.

Adult↗
PubMed2006

Stochastic calcium oscillations.

While the oscillatory release of calcium from intracellular stores is comprised of fundamentally stochastic events, most models of calcium oscillations are deterministic. As a result, the transition to calcium oscillations as parameters, such as IP(3) concentration, are changed is not described correctly. The fundamental difficulty is that whole-cell models of calcium dynamics are based on the assumptions that the calcium concentration is spatially homogeneous, and that there are a sufficiently large number of release sites per unit volume so that the law of large numbers is applicable. For situations where these underlying assumptions are not applicable, a new modelling approach is needed. In this paper, we present a model and its analysis of calcium dynamics that incorporates the fundamental stochasticity of release events. The model is based on the assumptions that release events are rapid, while reactivation is slow. The model presented here is comprised of two parts. In the first, a stochastic version of the fire-diffuse-fire model is studied in order to understand the spark-to-wave transition and the probability of sparks resulting in abortive waves versus whole-cell calcium release. In the second, this information about the spark-to-wave transition is incorporated into a stochastic model (a Chapman-Kolmogorov equation) that tracks the number of activated and inactivated calcium release sites as a function of time. By solving this model numerically, information about the timing of whole-cell calcium release is obtained. The results of this analysis show a transition to oscillations that agrees well with data and with Monte Carlo simulations.

Calcium↗
PubMed1996

[Basis of radiation protection].

After an introduction, three selected contributions to the 10th Course on Radiation Protection held at the University Hospital of Basel are presented. The principles of radiation protection and new Swiss legislation are discussed as the basis for radiological protection. Ways are proposed of reducing radiation exposure while optimizing the X-ray picture with a minimum dose to patient and personnel. Radiation effects from low doses. From the beginning, life on this planet has been exposed to ionizing radiation from natural sources. For about one century additional irradiation has reached us from man-made sources as well. In Switzerland the overall annual radiation exposure from ambient and man-made sources amounts to about 4 mSv. The terrestrial and cosmic radiation and natural radionuclids in the body cause about 1.17 mSv (29%). As much as 1.6 mSv (40%) results from exposure to radon and its progenies, primarily inside homes. Medical applications contribute approximately 1 mSv (26%) to the annual radiation exposure and releases from atomic weapons, nuclear facilities and miscellaneous industrial operations yield less than 0.12 mSv (< 5%) to the annual dose. Observations of detrimental radiation effects from intermediate to high doses are challenged by observations of biopositive adaptive responses and hormesis following low dose exposure. The important question, whether cellular adaptive response or hormesis could cause beneficial effects to the human organism that would outweigh the detrimental effects attributed to low radiation doses, remains to be resolved. Whether radiation exerts a detrimental, inhibitory, modifying or even beneficial effect is likely to result from identical molecular lesions but to depend upon their quantity, localization and time scale of initiation, as well as the specific responsiveness of the cellular systems involved. For matters of radiation protection the bionegative radiation effects are classified as deterministic effects or stochastic effects respectively. The various histopathological reactions of tissues and organs following localized tissue irradiation, and the radiation syndromes following total body irradiation, constitute the deterministic effects. There will be a threshold below which deterministic effects do not appear and spontaneous incidences are not known. For low dose risk considerations deterministic effects are of no significance. Genetic effects and carcinogenesis are said to be stochastic effects. Characteristically the probability of stochastic effects increases with dose but the severity of the effects is independent of the dose. The shape of the dose-response relationship at intermediate to high dose levels is linear-quadratic. For exposure to low doses the response becomes linear, as is to be expected for a linear-quadratic function at low dose. No threshold is assumed for stochastic effects. The estimate of probability of fatal cancer by the ICRP is 4 x 10(-2) per Sv for the working population and 5 x 10(-2) per Sv for the total population. Their estimate of probability of serious hereditary disorders within the first two generations is 1 x 10(-2) per Sv. The highest probability coefficient is attributed to mental retardation following exposure in utero. Within the sensitive period at 8-15 weeks of gestation, a risk probability of 40 x 10(-2) per Sv is assumed but a threshold at 0.1 Sv is not excluded. Conclusions drawn from experiments, clinical observations and epidemiological studies following intermediate to high radiation exposures attribute a mutagenic and carcinogenic competence to all radiation doses. Microdosimetric considerations support this assumption. This conclusion cannot be confirmed experimentally nor by epidemiological studies of populations living under different conditions from natural sources of radiation. Nevertheless, a change in the present restrictive radiation protection policy does not yet appear appropriate.

Diagnostic Imaging↗
PubMed2006

Using population viability analysis to predict the effects of climate change on the extinction risk of an endangered limestone endemic shrub, Arizona cliffrose.

The threat of global warming to rare species is a growing concern, yet few studies have predicted its effects on rare populations. Using demographic data gathered in both drought and nondrought years between 1996-2003 in central Arizona upper Sonoran Desert, we modeled population viability for the federally endangered Purshia subintegra (Kearney) Henrickson (Arizona cliffrose). We used deterministic matrix projection models and stochastic models simulating weather conditions during our study, given historical weather variation and under scenarios of increased aridity. Our models suggest that the P. subintegra population in Verde Valley is slowly declining and will be at greater risk of extinction with increased aridity. Across patches at a fine spatial scale, demographic performance was associated with environmental factors. Moist sites (patches with the highest soil moisture, lowest sand content, and most northern aspects) had the highest densities, highest seedling recruitment, and highest risk of extinction over the shortest time span. Extinction risk in moist sites was exacerbated by higher variance in recruitment and mortality. Dry sites had higher cumulative adult survival and lower extinction risk but negative growth rates. Steps necessary for the conservation of the species include introductions at more northern latitudes and in situ manipulations to enhance seedling recruitment and plant survival. We demonstrate that fine spatial-scale modeling is necessary to predict where patches with highest extinction risk or potential refugia for rare species may occur Because current climate projections for the 21st century imply range shifts at rates of 300 to 500 km/century, which are beyond even exceptional examples of shifts in the fossil record of 100-150 km, it is likely that preservation of many rare species will require human intervention and a long-term commitment. Global warming conditions are likely to reduce the carrying capacity of many rare species' habitats.

Arizona↗
PubMedDate not supplied

Chronomes, time structures, for chronobioengineering for "a full life".

Week-long or longer monitoring of blood pressure and heart rate, coupled to time-structure analyses, can help detect disease-risk elevations, as a warning of the need for a preventive prehabilitation. Within the normal range of physiologic variation, computer methods quantify time structures, or chronomes, that can serve as reference values. The major applied purpose for mapping chronomes is the detection of disease-risk syndromes such as blood pressure "overswinging" and heart rate "underswinging." Too much blood pressure variability (circadian hyperamplitude tension; CHAT), is a risk factor for vascular disease. Other risk syndromes are chronome alterations of heart rate variability (CAHRVs), consisting of a loss of "jitter", i.e., a reduced standard deviation of heart rate or of alterations in the spectral element of the heart-rate-variability chronome, such as in the correlation dimension, an endpoint of deterministic chaos. These alterations can again serve for prehabilitation. On the basic side, the spectral element of the heart-rate-variability chronomes extends from focus on the heartbeat's period of about 1 second to periods in heart rate and its standard deviation that are numerical equivalents of about 10.5- and about 21-year cycles of solar activity. A seemingly unnatural physiologic rhythm or pattern (such as one of 81.6 hours) may correspond numerically to a purely physical environmental rhythm. For example, interplanetary magnetic storms, with their cycles as external chronome components, trigger myocardial infarctions, strokes, and traffic accidents. The systematic monitoring of external rhythms along with physiologic ones for the concurrent analysis of rhythms with longer and longer periods could detect alterations anywhere in and between the 1 cycle/sec and the 1 cycle/10.5- or 21-years regions of the spectrum. Chronobiomimetic engineering for discovering both instantaneous and long-term chronorisk alterations can provide warnings of increased risk. If risk-lowering therapy is then instituted automatically, instrumented health care will be extended beyond the pacemaker-cardioverter-defibrillator, which focuses on the frequency of 1 cycle/sec. Instrumentation that automatically detects blood pressure that varies too much and heart rate that varies too little is needed for prompting prophylactic CHAT and CAHRV treatment. A database of reference values that can be used for chronodiagnosis is now accumulating.

Accidents, Traffic↗
PubMed2000

A transform domain SVD filter for suppression of muscle noise artefacts in exercise ECG's.

The proposed filter assumes the noisy electrocardiography (ECG) to be modeled as a signal of deterministic nature, corrupted by additive muscle noise artefact. The muscle noise component is treated to be stationary with known second-order characteristics. Since noise-free ECG is shown to possess a narrow-band structure in discrete cosine transform (DCT) domain and the second-order statistical properties of the additive noise component is preserved due to the orthogonality property of DCT, noise abatement is easily accomplished via subspace decomposition in the transform domain. The subspace decomposition is performed using singular value decomposition (SVD). The order of the transform domain SVD filter required to achieve the desired degree of noise abatement is compared to that of a suboptimal Wiener filter using DCT. Since the Wiener filter assumes both the signal and noise structures to be statistical, with a priori known second-order characteristics, it yields a biased estimate of the ECG beat as compared to the SVD filter for a given value of mean-square error (mse). The filter order required for performing the subspace smoothing is shown to exceed a certain minimal value for which the mse profile of the SVD filter follows the minimum-mean-quare error (mmse) performance warranted by the suboptimal Wiener filter. The effective filter order required for reproducing clinically significant features in the noisy ECG is then set by an upper bound derived by means of a finite precision linear perturbation model. A significant advantage resulting from the application of the proposed SVD filter lies in its ability to perform noise suppression independently on a single lead ECG record with only a limited number of data samples.

Algorithms↗