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PubMed2006

Cerebrovascular dynamics and vascular endothelial growth factor in acute mountain sickness.

OBJECTIVE: To determine if serum vascular endothelial growth factor (VEGF) and ultrasonic monitoring of vascular dynamics with dynamic vascular analysis at sea level and high altitude correlate with acute mountain sickness symptoms. METHODS: Nine volunteers participated in a staged ascent from sea level to 4300 m undergoing complete transcranial Doppler studies with dynamic vascular analysis. Serum VEGF levels, Lake Louise scores, Spielberger-1 scores, Subjective Exercise Experiences Scale positive scores, and Symptom Checklist-90 surveys were collected after 24 hours at each altitude. RESULTS: Symptom scores, index of pulsatility, and dynamic flow index differentiated the subjects into 2 distinct groups. Symptomatic subjects had increased VEGF levels at sea level but decreased levels at 4300 m. The dynamic flow index increased in symptomatic subjects at 4300 m compared with the asymptomatic subjects. The mean flow velocity increased in both groups and could not be used to differentiate the subjects. CONCLUSIONS: Altered vascular physiology is associated with acute mountain sickness. Increased vascular permeability increases vascular capacitance, with an increase in dynamic flow index to meet these demands. Altered vascular dynamics were associated with high-altitude cerebral edema in 1 subject. Dynamic vascular analysis demonstrated altered vascular pathophysiology associated with acute mountain sickness. Changes in VEGF were meaningful when interpreted with the dynamic vascular analysis findings. These physiological findings may help explain the vascular changes associated with hypocarbic hypoxemia at altitude.

Acute Disease↗
PubMed2004

Single-molecule spectroscopy studies of conformational change dynamics in enzymatic reactions.

Protein conformational dynamics, often associated with static and dynamic inhomogeneities, plays a crucial role in biomolecular functions. It is extremely difficult to characterize such inhomogeneous dynamics in an ensemble-averaged measurement, especially when the protein involves in a multiple-step complex chemical reaction, such as an enzymatic reaction. Single-molecule spectroscopy is a powerful approach to analyze protein conformational dynamics in real time under physiological conditions, providing dynamic perspectives on a molecular-level understanding of protein structure-function mechanisms. In this minireview, we discuss our recent studies on single-molecule enzymatic reaction dynamics and protein conformational dynamics of the T4 lysozyme hydrolyzation reaction of a polysaccharide by a combined approach of single-molecule spectroscopy, molecular dynamics simulation, and theoretical modeling. Detailed characterization of the complex enzymatic reaction dynamics identified the nature of the inhomogeneity and revealed multiple intermediate conformational states associated with the enzyme-substrate complex formation in the multiple-step enzymatic reaction.

Animals↗
PubMed1997

Stromal invasion by carcinoma of the cervix: assessment with dynamic MR imaging.

OBJECTIVE: The purpose of this study was to evaluate dynamic MR imaging in assessing the depth of stromal invasion by carcinoma of the cervix and to compare dynamic MR imaging with T2-weighted and contrast-enhanced T1-weighted MR imaging. SUBJECTS AND METHODS: Forty-one patients with carcinoma that was clinically considered to be confined to the cervix were examined with T2-weighted, dynamic, and contrast-enhanced T1-weighted MR imaging before surgery. We evaluated enhancement patterns of the cervix and tumor and assessed the degree of stromal invasion with MR imaging. The degree of stromal invasion was divided into two groups: superficial disease (no stromal invasion or invasion of < or = 3 mm) and deep invasion (> 3 mm of stromal invasion). Then we compared these MR findings with histologic results for the depth of stromal invasion. RESULTS: With dynamic MR imaging, cervical carcinoma with deep invasion was seen as a focal enhanced area in the early dynamic phase. The cervical epithelium and stroma enhanced less vividly. In distinguishing deep invasion from superficial disease, we found the accuracy of T2-weighted MR images, dynamic MR images, and contrast-enhanced T1-weighted MR images to be 76%, 98%, and 63%, respectively. In particular, the detectability of 3.1-5.0 mm of stromal invasion with dynamic MR images was significantly higher than that with the other techniques: with T2-weighted MR images, we saw 3.1-5.0 mm of stromal invasion in 23% of patients; with dynamic MR images, in 92%; and with contrast-enhanced T1-weighted MR images, in none. Superficial disease was not revealed with any of the three MR techniques. CONCLUSION: We believe that dynamic MR imaging is superior to T2-weighted MR imaging and contrast-enhanced T1-weighted MR imaging when assessing the depth of invasion of cervical carcinoma.

Adenocarcinoma↗
PubMed2002

Role and limitation of FMPSPGR dynamic contrast scanning in the follow-up of patients with hepatocellular carcinoma treated by TACE.

AIM: To evaluate the role and limitation of fast multiplanar spoiled gradient-recalled (FMPSPGR) MR dynamic contrast scanning in the follow-up of patients with HCC treated by transarterial chemoembolization (TACE). METHODS: Twenty-two patients with 24 HCC lesions confirmed by biopsy or surgical resection underwent MR imaging in 4-9wks after TACE with a superconducting 1.5 T MR scanner, including SE T(1)WI, T(2)WI and FMPSPGR dynamic contrast scanning. The signal intensities of all lesions on SE T(1)WI,T(2)WI and the enhancement patterns on FMPSPGR dynamic contrast scanning were observed, and the comparison was made between MRI findings and pathological results in all the cases. RESULTS: Of the 24 lesions, the signal intensities were various on SE T(1)WI and T(2)WI. On T(1)WI, 13 lesions appeared as hyperintense, 4 lesions were isointense and the other 7 lesions were hypointensese. Histologically, hyperintense lesions showed on T(1)WI were viable tumor or hemorrhage; isointensities were coagulative necrosis or inflammatory infiltration; hypointensities were tumor, liquified necrosis, coagulative necrosis or inflammatory infiltration. On T(2)WI, 15 lesions appeared as hyperintense, 3 lesions were isointense and the other 6 lesions were hypointensese. Hyperintense lesions showed on T(2)WI were residuals of viable tumor, hemorrhage, liquefied necrosis or inflammatory infiltration; isointense lesions were residuals of viable tumor or inflammatory infiltration; hypointense lesions were coagulative necrosis. On FMPSPGR dynamic contrast scanning, 18 of the 24 lesions enhanced on early-phase dynamic scanning corresponding to residuals of viable tumor and the other 6 lesions had no enhancement at this phase because complete necrosis were seen in the histologic examination. On delayed-phase dynamic scanning, 6 lesions had permanent enhancement appeared as inhomogeneous hyperintensity and both residuals of viable tumor and inflammatory infiltration were found by histologic examination. 18 lesions were hypointense at this phase and 8 of them coexisted with peripheral ring-like enhancement of the lesions resulting from viable tumors or inflammatory infiltration. CONCLUSION: FMPSPGR MR dynamic contrast scanning can reflect the pathologic changes of HCC treated by TACE. Especially, early-phase dynamic scanning can evaluate accurately residuals of viable tumor and necrosis in HCC lesions. FMPSPGR dynamic contrast scanning is useful in the follow-up of patients with HCC treated by TACE combined with SE T(1)WI and T(2)WI, but it is difficult to differentiate peripheral viable tumors from inflammatory infiltration.

Carcinoma, Hepatocellular↗
PubMed2000

[Reproducibility of the qualitative interpretation of dynamic salivary radionuclide scans with excretory stimulation].

OBJECTIVE: To evaluate intraobserver and interobserver agreement in the qualitative interpretation of dynamic salivary radionuclide scans to detect salivary disease, and the agreement between interpretation of dynamic and static image compositions. MATERIAL AND METHODS: Two observers (A, B) interpreted 110 dynamic salivary radionuclide scans with excretory stimulation based on dynamic image composition. Both again interpreted every studies: A based on dynamic image composition and B on static image composition. Kappa statistics were used to determine the degree of intraobserver and interobserver agreement. RESULTS: Considering all the studies, the dynamic composition showed an intraobserver agreement of 0.76 and interobserver agreements of 0.58 and 0.61. In patients with clinical sicca syndrome, agreements were 0.60, 0.52 and 0.62, respectively. For all the cases, the agreements between dynamic and static composition was 0.62 (intraobserver), and 0.42 and 0.43 (interobserver). For patients with clinical sicca syndrome these agreements were 0.63 (intraobserver), and 0.36 and 0.51 (interobserver). CONCLUSION: Intraobserver and interobserver agreement in the qualitative interpretation of dynamic salivary radionuclide scan with excretory stimulation are moderate and notable-moderate overall and in patients with clinical sicca syndrome. These agreements are greater than between dynamic and static image composition.

Adolescent↗
PubMedDate not supplied

Cervical carcinoma with full-thickness stromal invasion: efficacy of dynamic MR imaging in the assessment of parametrial involvement.

The purpose of this study was to investigate the efficacy of dynamic MR imaging in the assessment of parametrial involvement by cervical carcinoma with full-thickness stromal invasion on thin-section oblique axial T2-weighted images. Dynamic MR images of 24 patients with cervical carcinoma with full-thickness stromal invasion on thin-section oblique axial T2-weighted images were evaluated with pathologic correlation. Dynamic MR imaging was performed using a turboFLASH, 3D-FISP, or 2D-FLASH technique. The imaging planes of dynamic MR imaging were oblique axial planes of the uterine cervix. Dynamic MR imaging was performed twice, once for the early phase (40 to 60 sec after the administration of contrast media) and once for the late phase (5 min). Contrast enhancement of the tumor was divided into six types. Type I, cervical stroma with low signal intensity surrounding a tumor with high signal intensity, was seen in the early phase of dynamic MR imaging; type II-RR, the hyperintense rim was seen from the early phase to the late phase; type II-RO, the hyperintense rim was seen in the early phase only; type II-OR, the hyperintense rim was seen in the late phase only; type II-O, the hyperintense rim was not seen at all; and type III, tumor invasion with high signal intensities was seen beyond the cervical stroma in the early phase of dynamic MR imaging. The numbers for each type of cervical carcinoma on dynamic MR images were as follows: type I, four parametrial sites; type II-RR, 0; type II-RO, 0; type II-OR, 13; type II-O, 14; and type III, one. Three-dimensional diameters (transverse, craniocaudal, and anteroposterior) of the primary tumor were measured using dividers. All parametrial sites of type I and type II-OR showed no parametrial involvement. One parametrial site of type III and three parametrial sites of type II-O showed parametrial involvement, and 11 of type II-O showed no parametrial involvement. None of the patients showed type I-RR or type II-RO. When type I and type II-OR were categorized as criteria of no parametrial involvement and type III and transverse diameters of 3.5 cm or over classified as type II-O were categorized as criteria of parametrial involvement, the rate of diagnostic accuracy was 95.8%. Dynamic MR imaging is considered to be substantially useful in the assessment of parametrial involvement with cervical carcinoma with full-thickness stromal invasion by thin-section oblique axial T2-weighted images.

Adult↗
PubMed2001

[Advanced Dynamic Flow]

There are problems for contrast imaging using LevovistTM contrast agent. In case of Doppler mode, poor resolution and large blooming area are the problems. In case of 2nd harmonic imaging and pulse inversion imaging, tissue harmonic image(THI) becomes the problem because Levovist needs high mechanical index(MI). THI increases under the high MI condition and THI interferes with the contrast image of Levovist. And also bubbles of Levovist are easily collapsed under the high MI condition, so it is hard to visualize the bubbles successively. Dynamic Flow has solved the above problems. Dynamic Flow uses Doppler technique, but Dynamic Flow image has higher resolution and less blooming area than the conventional Doppler image. Dynamic Flow doesn't display THI, so the detectability of bubbles is superior to the other mode as far as Levovist. Dynamic Flow is so sensitive that it can show the bubbles in real time. Advanced Dynamic Flow(ADF) has greatly improved in sensitivity and presentation ability from conventional Dynamic Flow. In the contrast application, ADF image looks very similar to B-mode image thanks to the high resolution and wide dynamic range, in spite of using Doppler technique. Detectability of the bubbles is much better than conventional Dynamic Flow. ADF can detect bubbles in much smaller vessels and has much more penetration, with uniform enhancement from shallow to deep regions. ADF is very suitable for Levovist. ADF can also be used without contrast agents. ADF can show small tiny vessels with high resolution and high frame rate. Directional information can be added by different colors. The sensitivity is close to conventional Color/Power Doppler images.

Journal Article↗
PubMed2004

[Maximum likelihood analysis for mapping dynamic trait QTL in outbred population. I . Methodology].

The quantitative traits whose phenotypic values change with time in life or other quantitative factors, were defined as dynamic traits. Based on the idea about random regression test-day model for estimating breeding values in animal evaluation, a mathematic model was constructed for mapping dynamic trait loci by using Legendre polynomials to model dynamic changes of each genetic effect. The Maximum likelihood analysis implemented via EM algorithm was used to estimate the parameters, including QTL position, fixed genetic regression effects for dynamic trait QTL mapping in outbred population. Compared with the existing method for dynamic trait mapping QTL, the new method presented here not only allowed to sample dynamic trait in disequillibrium way, but also can achieve to map dynamic traits QTL in any resource population by just one step. The further study on dynamic trait mapping QTL was theoretically discussed by incorporating genetic analysis of dynamic trait into general mapping QTL.

Likelihood Functions↗
PubMed2006

[Analysis of short-term results of post total knee arthroplasty using TC-Dynamic posterior stabilized prostheses].

OBJECTIVE: To assess the feasibility, safety, and validity of the TC-Dynamic posterior stabilized prostheses implanted in the total knee arthroplasty (TKA). METHODS: Twelve knees of 10 patients (the TC-Dynamic group) were followed up, who had been implanted with the TC-Dynamic posterior stabilized prostheses from September 2003 to March 2004. Preoperative KSS knee scores were 16.08 +/- 11.58, function scores 13.75 +/- 19.79, and the range of motion (ROM) of the knee 75.00 +/- 26.46 degrees. Meanwhile, 50 knees of 30 patients (the Scorpio group) were followed up, who had undergone TKA with the Scorpio posterior stabilized prostheses. Preoperative KSS knee scores were 19.48 +/- 9.67, function scores 3.16 +/- 19.82, and the ROM of the knee 80.80 +/- 22.82 degrees. The anteroposterior and lateral X-ray films of each knee were examined before and after operation. The statistical Z-test was used to analyze the differences between the 2 groups in the improvement of the KSS knee scores, function scores, and ROM after operation. RESULTS: The average of the 130 days' follow-up revealed that the patients implanted with the TC-Dynamic prostheses had an excellent result. In the TC-Dynamic group, the KSS knee scores were 88.83 +/- 4.04 with improved scores of 72.75 +/- 14.47 compared with those before operation; function scores were 79.17 +/- 5.15 with improved scores of 65.42 +/- 19.47; the ROM of the knee was 107.92 +/- 11.57 degrees with increased degrees of 32.92 +/- 32.22 degrees. Meanwhile, in the Scorpio group, the KSS knee scores were 85.68 +/- 7.36 with improved scores of 66.20 +/- 10.44 compared with those before operation; function scores were 71.40 +/- 12.70 with improved scores of 68.24 +/- 25.35; the ROM of the knee was 109.20 +/- 11.13 degrees with increased degrees of 28.40 +/- 26.41 degrees. There was no significant difference in the improvement of the KSS knee scores, function scores, and ROM after operation between the 2 groups (P > 0.01). All the X-ray films of the knees implanted with both the Scorpio prostheses and the TC-Dynamic prostheses were analyzed. No mal-alignment or lucent line with the prostheses was seen in all these X-ray films. CONCLUSION: The short-term follow-up indicates that the patients implanted with the TC-Dynamic prostheses have an excellent result. The TC-Dynamic prostheses with a scientific and proper design is more suitable for the Chinese. However, the long-term outcome of the patients implanted with the TC-Dynamic prostheses should be observed in a larger number of TKA operations. The basic surgical principles, including excision of both the cruciate ligaments and correction of the bone deformity with the proper balancing of the soft tissues in flexion and extension, are still crucial to successful TKA and to the long-term high survival rate of the knee prostheses.

Adult↗
PubMed1996

[Evaluation of the clinical usefulness of super dynamic 99mTc-HM-PAO SPECT in ischemic cerebrovascular disease--detection of hypo- and hyperperfusion area].

The purpose of this study is to assess the clinical usefulness of super dynamic SPECT of 99mTc-HM-PAO. Six patients with unilateral occlusion of middle cerebral artery (MCA) or internal carotid artery (ICA) in the chronic phase, and 5 patients with subacute cerebral infarction were studied. We used a ring-type SPECT "HEADTOME." Two types of collimator were used: a high sensitivity (HS) collimator for super dynamic scan and a high resolution (HR) collimator for static scan. First, the intravenous constant infusion of 99mTc-HM-PAO (925-1480 MBq) for 1 minute was started. After 30 seconds from the beginning of the injection, we performed the 12 seconds/frame super dynamic SPECT for 2 minutes. Then, the static SPECT for 10 minutes was done. For semiquantitative analyses, differential percentage of regional activity between affected and non-affected hemispheres was calculated in the 6th frame image of super dynamic SPECT and static SPECT image. In all 6 patients with unilateral occlusion of MCA and ICA, super dynamic SPECT images showed the better contrast of low perfusion areas in comparison with the static SPECT images. In 5 patients with subacute cerebral infarction who showed focal hyperactivities on static SPECT, focal hyperactivities (hyperperfusion or hyperemia) were displayed in 3 cases, whereas, focal hypo- or isoactivities (hypo- or isoperfusion) were shown in 2 cases on super dynamic SPECT. However, all patients with subacute cerebral infarction showed hyperfixation on static SPECT as compared with super dynamic SPECT. Although the image quality on super dynamic SPECT is not as high as that on static SPECT, cerebral hemodynamics would be detected with less backdiffusion of 99mTc-HM-PAO from the brain to blood, and with less accumulation of hydrophilic components in subacute infarct region. In conclusion, super dynamic SPECT in early distribution of 99mTc-HM-PAO using dedicated SPECT device might be helpful to detect cerebral perfusion close to true cerebral blood flow distribution.

Aged↗
PubMed1998

Spatial structure, environmental heterogeneity, and population dynamics: analysis of the coupled logistic map.

Spatial extent can have two important consequences for population dynamics: It can generate spatial structure, in which individuals interact more intensely with neighbors than with more distant conspecifics, and it allows for environmental heterogeneity, in which habitat quality varies spatially. Studies of these features are difficult to interpret because the models are complex and sometimes idiosyncratic. Here we analyze one of the simplest possible spatial population models, to understand the mathematical basis for the observed patterns: two patches coupled by dispersal, with dynamics in each patch governed by the logistic map. With suitable choices of parameters, this model can represent spatial structure, environmental heterogeneity, or both in combination. We synthesize previous work and new analyses on this model, with two goals: to provide a comprehensive baseline to aid our understanding of more complex spatial models, and to generate predictions about the effects of spatial structure and environmental heterogeneity on population dynamics. Spatial structure alone can generate positive, negative, or zero spatial correlations between patches when dispersal rates are high, medium, or low relative to the complexity of the local dynamics. It can also lead to quasiperiodicity and hyperchaos, which are not present in the nonspatial model. With density-independent dispersal, spatial structure cannot destabilize equilibria or periodic orbits that would be stable in the absence of space. When densities in the two patches are uncorrelated, the probability that the population in a patch reaches extreme low densities is reduced relative to the same patch in isolation; this "rescue effect" would reduce the probability of metapopulation extinction beyond the simple effect of spreading of risk. Pure environmental heterogeneity always produces positive spatial correlations. The dynamics of the entire population is approximated by a nonspatial model with mean patch characteristics. This approximation worsens as the difference between the patches increases and the dispersal rate decreases: Under extreme conditions, destabilization of equilibria and periodic orbits occurs at mean parameter values lower than those predicted by the mean parameters. Apparent within-patch dynamics are distorted: The local population appears to have the wrong growth parameter and a constant number of immigrants (or emigrants) per generation. Adding environmental heterogeneity to spatial structure increases the occurrence of spatially correlated population dynamics, but the resulting temporal dynamics are more complex than would be predicted by the mean parameter values. The three classes of spatial pattern (positive, negative, and zero correlation), while still mathematically distinct, become increasingly similar phenomenologically.

Animals↗
PubMed2004

On the mechanistic underpinning of discrete-time population models with complex dynamics.

We present a mechanistic underpinning for various discrete-time population models that can produce limit cycles and chaotic dynamics. Specific examples include the discrete-time logistic model and the Hassell model, which for a long time eluded convincing mechanistic interpretations, and also the Ricker- and Beverton-Holt models. We first formulate a continuous-time resource consumption model for the dynamics within a year, and from that we derive a discrete-time model for the between-year dynamics. Without influx of resources from the outside into the system, the resulting between-year dynamics is always overcompensating and hence may produce complex dynamics as well as extinction in finite time. We recover a connection between various standard types of continuous-time models for the resource dynamics within a year on the one hand and various standard types of discrete-time models for the population dynamics between years on the other. The model readily generalizes to several resource and consumer species as well as to more than two trophic levels for the within-year dynamics.

Animals↗
PubMed2001

A bit of sex stabilizes host-parasite dynamics.

To date, only a few studies have focused on the effects of sex on population dynamics. Previous models have typically found that sexual reproduction dampens population fluctuations. Although asexual and sexual reproduction are just the two endpoints along a continuum of varying rates of sex, previous work has ignored the effects of intermediate degrees of sex on population dynamics. Here we study the effects of partial sexual reproduction (i.e. sex occurs only every few generations or with small probability in each generation) on the coupled population dynamics of a Nicholson-Bailey host-parasite model. We show that complex dynamics are simplified for high host population growth rates if the frequency of sex is sufficiently high in both host and parasite: sex decreases fluctuations in population density, and leads to non-chaotic dynamics for population growth rates that would result in chaotic dynamics in the absence of sexual reproduction. However, the simplification does not increase gradually with an increasing frequency of sex but appears abruptly at low-to-intermediate frequencies of sex. For some parameter settings, intermediate frequencies of sexual reproduction can simplify the dynamics more than lower or higher frequencies. Thus, in agreement with earlier results, sexual reproduction typically stabilizes complex population dynamics in our models. Additionally, our results suggest that low-to-intermediate frequencies of sex may often be as (or even more) stabilizing as high frequencies.

Animals↗
PubMed1997

Transients, metastability, and neuronal dynamics.

This paper is about neuronal dynamics and how their special complexity can be understood in terms of nonlinear dynamics. There are many aspects of neuronal interactions and connectivity that engender the complexity of brain dynamics. In this paper we consider (i) the nature of this complexity and (ii) how it depends on connections between neuronal systems (e.g., neuronal populations or cortical areas). The main conclusion is that simulated neural systems show complex behaviors, reminiscent of neuronal dynamics, when these extrinsic connections are sparse. The patterns of activity that obtain, under these conditions, show a rich form of intermittency with the recurrent and self-limiting expression of stereotyped transient-like dynamics. Despite the fact that these dynamics conform to a single (complex) attractor this metastability gives the illusion of a dynamically changing attractor manifold (i.e., a changing surface upon which the dynamics unfold). This metastability is characterized using a measure that is based on the entropy of the time series' spectral density.

Animals↗
PubMed1998

Ontogenetic scaling of foraging rates and the dynamics of a size-structured consumer-resource model.

The ontogenetic scaling of foraging capacity strongly influences the competitive ability of differently sized individuals within a species. We develop a physiologically structured model to investigate the effect of different ontogenetic size scalings of the attack rate on the population dynamics of a consumer-resource system. The resource is assumed to reproduce continuously whereas the consumer only reproduces at discrete time instants. Depending on the ontogenetic size scaling, the model exhibited recruit-driven cycles, stable fixed point dynamics, non-recruit juvenile-driven cycles, quasiperiodic orbits, or chaotic dynamics. The kind of dynamics observed was related to the maintenance resource levels required of differently sized individuals. Stable fixed point dynamics was, besides at the persistence boundary, only observed when the minimum resource levels were similar for newborns and mature individuals. The tendency for large population fluctuations over a wide range of the parameter space was due to the consumer's pulsed reproduction. Background mortality and length of season were major determinants of cycle length. Model dynamics strongly resembled empirically observed dynamics from fish and Daphnia populations with respect to both patterns and mechanisms. The non-recruit juvenile-driven dynamics is suggested to occur in populations with size-dependent interference or preemptive competition like cicada populations.

Animals↗
PubMed1999

Genetic variability in sensitivity to population density affects the dynamics of simple ecological models.

Many 1-dimensional discrete time ecological models contain a sensitivity parameter that does not affect the dynamic complexity of these models. We show that genetic variability in this parameter can have a strong effect on population dynamics. We incorporate ecological dynamics in two different population genetic models with one locus and two alleles. The first is the classical model of a randomly mating population in Hardy-Weinberg equilibrium, and the second is a model of differential selection in males and females. In populations in Hardy-Weinberg equilibrium, variability in the sensitivity parameter can be maintained by overdominance. In this case, the dynamics of the polymorphic population tend to be much simpler than those of monomorphic populations. In the model with different selection in males and females, polymorphisms can be maintained in various ways, e.g., by opposing directional selection in males and females. Polymorphism in the sensitivity parameter tends to simplify population dynamics in the model with different selection in males and females as well. A number of interesting dynamic effects can be observed, e.g., multiple attractors with complicated basins of attraction. Then the final state of the system after a successful invasion by mutant alleles may depend on the mutation rate and on the distribution of mutational steps. In addition, there are situations in which genetic variability destabilizes a stable population dynamic equilibrium in the monomorphic model. There is an analogy between genetic variability and variability imposed by the environment. If differences in sensitivity are caused by the environment, dynamic effects similar to those in the genetic models can be observed. In addition, source-sink structures that are known to occur in spatially structured models can be seen in the genetic model if one of the genotypes is inviable. The results suggest that combining ecological and population genetic models can lead to a number of new insights. More work is needed, e.g., with fertility models, in which fitnesses are not assigned to individuals, but to mating pairs.

Alleles↗
PubMed1997

Population dynamics and the colour of environmental noise.

The effect of red, white and blue environmental noise on discrete-time population dynamics is analyzed. The coloured noise is superimposed on Moran-Ricker and Maynard Smith dynamics, the resulting power spectra are less than examined. Time series dominated by short- and long-term fluctuations are said to be blue and red, respectively. In the stable range of the Moran-Ricker dynamics, environmental noise of any colour will make population dynamics red or blue depending the intrinsic growth rate. Thus, telling apart the colour of the noise from the colour of the population dynamics may not be possible. Population dynamics subjected to red and blue environmental noises show, respectively, more red or blue power spectra than those subjected to white noise. The sensitivity to differences in the noise colours decreases with increasing complexity and ultimately disappears in the chaotic range of the population dynamics. These findings are duplicated with the Maynard Smith model for high growth rates when the strength of density dependence changes. However, for low growth rates the power spectra of the population dynamics with noise are red in stable, periodic and aperiodic ranges irrespective of the noise colour. Since chaotic population fluctuations may show blue spectra in the deterministic case, this implies that blue deterministic chaos may become red under any colour of the noise.

Acoustics↗
PubMed1999

Cardiac interbeat interval dynamics from childhood to senescence : comparison of conventional and new measures based on fractals and chaos theory.

BACKGROUND: New methods of R-R interval variability based on fractal scaling and nonlinear dynamics ("chaos theory") may give new insights into heart rate dynamics. The aims of this study were to (1) systematically characterize and quantify the effects of aging from early childhood to advanced age on 24-hour heart rate dynamics in healthy subjects; (2) compare age-related changes in conventional time- and frequency-domain measures with changes in newly derived measures based on fractal scaling and complexity (chaos) theory; and (3) further test the hypothesis that there is loss of complexity and altered fractal scaling of heart rate dynamics with advanced age. METHODS AND RESULTS: The relationship between age and cardiac interbeat (R-R) interval dynamics from childhood to senescence was studied in 114 healthy subjects (age range, 1 to 82 years) by measurement of the slope, beta, of the power-law regression line (log power-log frequency) of R-R interval variability (10(-4) to 10(-2) Hz), approximate entropy (ApEn), short-term (alpha(1)) and intermediate-term (alpha(2)) fractal scaling exponents obtained by detrended fluctuation analysis, and traditional time- and frequency-domain measures from 24-hour ECG recordings. Compared with young adults (<40 years old, n=29), children (<15 years old, n=27) showed similar complexity (ApEn) and fractal correlation properties (alpha(1), alpha(2), beta) of R-R interval dynamics despite lower spectral and time-domain measures. Progressive loss of complexity (decreased ApEn, r=-0.69, P<0.001) and alterations of long-term fractal-like heart rate behavior (increased alpha(2), r=0.63, decreased beta, r=-0.60, P<0.001 for both) were observed thereafter from middle age (40 to 60 years, n=29) to old age (>60 years, n=29). CONCLUSIONS: Cardiac interbeat interval dynamics change markedly from childhood to old age in healthy subjects. Children show complexity and fractal correlation properties of R-R interval time series comparable to those of young adults, despite lower overall heart rate variability. Healthy aging is associated with R-R interval dynamics showing higher regularity and altered fractal scaling consistent with a loss of complex variability.

Adolescent↗