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PubMed1995

Spatial heterogeneity, nonlinear dynamics and chaos in infectious diseases.

There is currently considerable interest in the role of nonlinear phenomena in the population dynamics of infectious diseases. Childhood diseases such as measles are particularly well documented dynamically, and have recently been the subject of analyses (of both models and notification data) to establish whether the pattern of epidemics is chaotic. Though the spatial dynamics of measles have also been extensively studied, spatial and nonlinear dynamics have only recently been brought together. The present review concentrates mainly on describing this synthesis. We begin with a general review of the nonlinear dynamics of measles models, in a spatially homogeneous environment. Simple compartmental models (specifically the SEIR model) can behave chaotically, under the influence of strong seasonal 'forcing' of infection rate associated with patterns of schooling. However, adding observed heterogeneities such as age structure can simplify the deterministic dynamics back to limit cycles. By contrast all current strongly seasonally forced stochastic models show large amplitude irregular fluctuations, with many more 'fadeouts' of infection that is observed in real communities of similar size. This indicates that (social and/or geographical) spatial heterogeneity is needed in the models. We review the exploration of this problem with nonlinear spatiotemporal models. The few studies to date indicate that spatial heterogeneity can help to increase the realism of models. However, a review of nonlinear analyses of spatially subdivided measles data show that more refinements of the models (particularly in representing the impact of human demographic changes on infection dynamics) are required. We conclude with a discussion of the implication of these results for the dynamics of infectious diseases in general and, in particular, the possibilities of cross fertilization between human disease epidemiology and the study of plant and animal diseases.

Communicable Diseases↗
PubMed2001

Pervasive influence of large-scale climate in the dynamics of a terrestrial vertebrate community.

BACKGROUND: Large-scale climatic variability has been implicated in the population dynamics of many vertebrates throughout the Northern Hemisphere, but has not been demonstrated to directly influence dynamics at multiple trophic levels of any single system. Using data from Isle Royale, USA, comprising time series on the long-term dynamics at three trophic levels (wolves, moose, and balsam fir), we analyzed the relative contributions of density dependence, inter-specific interactions, and climate to the dynamics of each level of the community. RESULTS: Despite differences in dynamic complexity among the predator, herbivore, and vegetation levels, large-scale climatic variability influenced dynamics directly at all three levels. The strength of the climatic influence on dynamics was, however, strongest at the top and bottom trophic levels, where density dependence was weakest. CONCLUSIONS: Because of the conflicting influences of environmental variability and intrinsic processes on population stability, a direct influence of climate on the dynamics at all three levels suggests that climate change may alter stability of this community. Theoretical considerations suggest that if it does, such alteration is most likely to result from changes in stability at the top or bottom trophic levels, where the influence of climate was strongest.

Abies↗
PubMed2006

The scale transition: scaling up population dynamics with field data.

Applying the recent developments of scale transition theory, we demonstrate a systematic approach to the problem of scaling up local scale interactions to regional scale dynamics with field data. Dynamics on larger spatial scales differ from the predictions of local dynamics alone because of an interaction between nonlinearity in population dynamics at the local scale and spatial variation in density and environmental factors over the regional population. Our systematic approach to scaling up involves the following five steps. First, define a model for dynamics on the local spatial scale. Second, apply scale transition theory to identify key interactions between nonlinearity and spatial variation that translate local dynamics to the regional scale. Third, measure local-scale model parameters to determine nonlinearities at local scales. Fourth, measure spatial variation. Finally, combine nonlinearity and variation measures to obtain the scale transition. Using field data for the dynamics of grazers and periphyton in a freshwater stream, we show that scale transition terms greatly reduce the growth and equilibrium density of the periphyton population at the stream scale compared to rock scale populations, confirming the importance of spatial mechanisms to stream-scale dynamics.

Ecosystem↗
PubMed2005

Solid film versus solution-phase charge-recombination dynamics of exTTF-bridge-C60 dyads.

The charge-recombination dynamics of two exTTF-C60 dyads (exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene), observed after photoinduced charge separation, are compared in solution and in the solid state. The dyads differ only in the degree of conjugation of the bridge between the donor (exTTF) and the acceptor (C60) moieties. In solution, photoexcitation of the nonconjugated dyad C60-BN-exTTF (1) (BN = 1,1'-binaphthyl) shows slower charge-recombination dynamics compared with the conjugated dyad C60-TVB-exTTF (2) (TVB = bisthienylvinylenebenzene) (lifetimes of 24 and 0.6 micros, respectively), consistent with the expected stronger electronic coupling in the conjugated dyad. However, in solid films, the dynamics are remarkably different, with dyad 2 showing slower recombination dynamics than 1. For dyad 1, recombination dynamics for the solid films are observed to be tenfold faster than in solution, with this acceleration attributed to enhanced electronic coupling between the geminate radical pair in the solid film. In contrast, for dyad 2, the recombination dynamics in the solid film exhibit a lifetime of 7 micros, tenfold slower than that observed for this dyad in solution. These slow recombination dynamics are assigned to the dissociation of the initially formed geminate radical pair to free carriers. Subsequent trapping of the free carriers at film defects results in the observed slow recombination dynamics. It is thus apparent that consideration of solution-phase recombination data is of only limited value in predicting the solid-film behaviour. These results are discussed with reference to the development of organic solar cells based upon molecular donor-acceptor structures.

Journal Article↗
PubMedDate not supplied

Dynamic MR imaging of recurrent postoperative cervical cancer.

The value of dynamic-contrast enhanced MR imaging using FLASH technique was studied in 13 patients with postoperative recurrent cervical cancer verified histopathology and in 9 patients without recurrence. Dynamic FLASH imaging and conventional spin-echo T1- and T2-weighted sequences were compared in a prospective fashion with regard to accuracy of the diagnosis of recurrent tumor using biopsy results as the gold standard. The contrast between the recurrent tumor and the surrounding pelvic tissues was also analyzed. The accuracy of depicting recurrent tumor or dynamic images (82%) was superior to that of pre- and postcontrast T1-weighted images and T2-weighted images (64%, 68%, and 64%, respectively). The contrast between the recurrent tumor and pelvic fat was greater on precontrast T1-weighted and dynamic images than on T2-weighted and postcontrast T1-weighted images. The dynamic images clearly showed involvement of the surrounding pelvic organs, because enhancement was observed exclusively in the tumor in the early dynamic phase. Accuracy regarding involvement of the urinary bladder or rectal wall on pre- and postcontrast T1-weighted images and T2-weighted images was lower than that on the dynamic images. Dynamic MR imaging has potential for use in the detection and evaluation of the extent of recurrent postoperative cervical cancer.

Adult↗
PubMed1994

Protein simulations using techniques suitable for very large systems: the cell multipole method for nonbond interactions and the Newton-Euler inverse mass operator method for internal coordinate dynamics.

Two new methods developed for molecular dynamics simulations of very large proteins are applied to a series of proteins ranging up to the protein capsid of tomato bushy stunt virus (TBSV). For molecular dynamics of very large proteins and polymers, it is useful to carry out the dynamics using internal coordinates (say, torsions only) rather than Cartesian coordinates. This allows larger time steps, eliminates problems with the classical description of high energy modes, and focuses on the important degrees of freedom. The resulting equation of motion has the form. [formula: see text] where for T is the vector of generalized forces, M(theta) is the moments of inertia tensor, theta is the vector of torsions, and C is a vector containing Coriolis forces and nonbond forces. The problem is that to calculate the acceleration vector theta from M, C, and T requires inverting M(theta), an order N3 calculation. Since the number of degrees of freedom might be 300,000 for a million atom system, solving these equations every time step is impractical, restricting internal coordinate methods to small systems. The new method, Newton-Euler Inverse Mass Operator (NEIMO) dynamics, constructs the torsional accelerations vector theta = M-1 (T-C) directly by an order N process, allowing internal-coordinate dynamics to be solved for super larger (million atom) systems. The first use of the NEIMO method for molecular dynamics of proteins is presented here. A second serious difficulty for large proteins is calculation of the nonbond forces. We report here the first application to proteins of the new Cell Multipole Method (CMM) to evaluate the Coulomb and van der Waals interactions. The costs of CMM scales linearly with the number of particles while retaining an accuracy significantly better than standard nonbond methods (involving cutoffs). Results for NEIMO and CMM are given for simulations of a wide range of peptide and protein systems, including the protein capsid of TBSV with 488,000 atoms. The computational times for NEIMO and CMM are demonstrated to scale linearly with size. With NEIMO the dynamics time steps can be as large as 20 fs (for small peptides), much larger than possible with standard Cartesian coordinate dynamics. For TBSV we considered both the normal form and the high pH form, in which the Ca2+ ions are removed. These calculations lead to a contraction of the protein for both forms (probably because of ignoring the RNA core not observed in the X-ray).

Algorithms↗
PubMed2003

Dissociable neural pathways are involved in the recognition of emotion in static and dynamic facial expressions.

Facial expressions of emotion powerfully influence social behavior. The distributed network of brain regions thought to decode these social signals has been empirically defined using static, usually photographic, displays of such expressions. Facial emotional expressions are however highly dynamic signals that encode the emotion message in facial action patterns. This study sought to determine whether the encoding of facial expressions of emotion by static or dynamic displays is associated with different neural correlates for their decoding. We used positron emission tomography to compare patterns of brain activity in healthy men and women during the explicit judgment of emotion intensity in static and dynamic facial expressions of anger and happiness. Compared to judgments of spatial orientation for moving neutral facial expressions, the judgment of anger in dynamic expressions was associated with increased right-lateralized activity in the medial, superior, middle, and inferior frontal cortex and cerebellum, while judgments of happiness were associated with relative activation of the cuneus, temporal cortex, and the middle, medial, and superior frontal cortex. In contrast, the perception of anger or happiness in static facial expressions activated a motor, prefrontal, and parietal cortical network previously shown to be involved in motor imagery. The direct contrast of dynamic and static expressions indicated differential activation of visual area V5, superior temporal sulcus, periamygdaloid cortex, and cerebellum for dynamic angry expressions and differential activation of area V5, extrastriate cortex, brain stem, and middle temporal cortical activations for dynamic happy expressions. Thus, a distribution of neural activations is related to the analysis of emotion messages in the nearly constant biological motion of the face and differ for angry and happy expressions. Static displays of facial emotional expression may represent noncanonical stimuli that are processed for emotion content by mental strategies and neural events distinct from their more ecologically relevant dynamic counterparts.

Adult↗
PubMed1994

Generality versus specificity: a comparison of dynamic and isometric measures of strength and speed-strength.

Considerable debate exists as to whether the qualities of muscle function exist as general or specific physiological capacities. If there is a generality of muscle function then strong relationships would exist between various measures of function for the same muscle(s), independent of the test contraction, mode or velocity. The purpose of this study was to examine the relationship between isometric and dynamic measures of muscle function to determine the existence of generality or specificity. A group of 22 men, experienced in weight training, were tested for lower and upper body dynamic and isometric measures of strength and speed-strength. The changes in these measures consequent to a resistance training programme were also investigated. The results of this study indicated that whilst isometric and dynamic measures of strength did significantly correlate (r = 0.57-0.61), the relationship was below that required to denote statistical generality. More important, the changes in isometric and dynamic strength consequent to a dynamic heavy resistance training programme were unrelated (r = 0.12-0.15). Thus the mechanisms that contribute to enhanced dynamic strength appeared unrelated to the mechanisms that contribute to enhanced isometric strength. Measures of dynamic and isometric speed-strength were unrelated, as were the changes in these measures resulting from training. The results of this study demonstrated that a generality of muscle function did not exist and that modality specific results were observed. Consequently this study calls into question the validity of isometric tests to monitor dynamically induced training adaptations.

Adult↗
PubMed1998

Preoperative Diagnosis of Breast Diseases by Dynamic MR Mammography:Cut-off Point Establishment for Signal Intensity Ratio.

We have demonstrated that the dynamic study for breast lesions by magnetic resonance imaging(MRI)can differentiate benign from malignant lesions objectively.The cases were 57 histopathologically appraised breast lesions, including 20 cases of breast cancer, 28 cases of mastopathy, 8 cases of fibroadenoma and 1 caseof intraductal papillomatosis. We plotted time-signal intensity ratio curves and then determined 95% confidence intervals, plotting the signal intensity ratio for both breast cancer and mastopathy every 30 seconds during dynamic magnetic resonance mammography(MRM)after gadolinium-diethylenetriamine pentaacetic acid(Gd-DTPA)administration, and further established cut-off points to differentiate between them. We then tried of estimate objectively the benign-malignant differentiation to breast lesions by confirming their signal intensity ratio to be more or less than the cut-off points. We advocate this procedure, and call it the " dynamic ratio method. " As a result, we found highly significant differences between breast cancer and mastopathy at 30 and 60 seconds after Gd-DTPA administration(P < 0.0001). We also confirmed that the cut-off point for the dynamic ratio method was equivalent to 1.4 and 1.8 times the precontrast signal intensity value at30 and 60 seconds after administration of Gd-DTPA respectively. By performing this dynamic ratio method preoperatively we can assess objectively not only the malignancy of breast lesions, but also neighboring infiltration, extending intraductal component, and lymph node metastasis. Furthermore, the dynamic ratio method provides detailed information for selecting the appropriate region for breast conserving surgery preoperatively, and can be expected to reduce unnecessary biopsies of benign cases. The dynamic ratio method had a sensitivity of 95.0%, a specificity of 81.1% and a positive predictive value of 73.1%. Also, for detectinginvasive ductal carcinoma, the sensitivity of the dynamic ratio method was 100.0%.

Journal Article↗
PubMed2003

Functional significance of stiffness in adaptation of multijoint arm movements to stable and unstable dynamics.

This study compared the mechanisms of adaptation to stable and unstable dynamics from the perspective of changes in joint mechanics. Subjects were instructed to make point to point movements in force fields generated by a robotic manipulandum which interacted with the arm in either a stable or an unstable manner. After subjects adjusted to the initial disturbing effects of the force fields they were able to produce normal straight movements to the target. In the case of the stable interaction, subjects modified the joint torques in order to appropriately compensate for the force field. No change in joint torque or endpoint force was required or observed in the case of the unstable interaction. After adaptation, the endpoint stiffness of the arm was measured by applying displacements to the hand in eight different directions midway through the movements. This was compared to the stiffness measured similarly during movements in a null force field. After adaptation, the endpoint stiffness under both the stable and unstable dynamics was modified relative to the null field. Adaptation to unstable dynamics was achieved by selective modification of endpoint stiffness in the direction of the instability. To investigate whether the change in endpoint stiffness could be accounted for by change in joint torque or endpoint force, we estimated the change in stiffness on each trial based on the change in joint torque relative to the null field. For stable dynamics the change in endpoint stiffness was accurately predicted. However, for unstable dynamics the change in endpoint stiffness could not be reproduced. In fact, the predicted endpoint stiffness was similar to that in the null force field. Thus, the change in endpoint stiffness seen after adaptation to stable dynamics was directly related to changes in net joint torque necessary to compensate for the dynamics in contrast to adaptation to unstable dynamics, where a selective change in endpoint stiffness occurred without any modification of net joint torque.

Adaptation, Physiological↗
PubMed2005

Association between dynamic exercise therapy and IGF-1 and IGFBP-3 concentrations in the patients with rheumatoid arthritis.

We aimed to evaluate the relationship between short-term dynamic exercise therapy and insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) levels in rheumatoid arthritis (RA) patients. Forty RA patients were assigned into dynamic or range of motion (ROM) exercise groups. Also control group carried out the same dynamic exercise protocol. Morning stiffness, pain (VAS), Health assessment questionnaire (HAQ) and Ritchie articular index (RAI) were evaluated and erythrocyte sedimentation rate, serum C-reactive protein, IGF-1 and IGFBP-3 levels of the participants were recorded. The assessments were determined before, at the 7th and 15th days of treatment. VAS and RAI scores were significantly improved by the dynamic exercises in RA patients. There were increases on IGF-1 in dynamic exercise group, although IGF-1 levels showed a decrease in ROM exercise and control groups. Also no significant changes were observed on IGFBP-3 in three groups. Our results suggest that short-term dynamic exercise therapy increases serum IGF-1 in RA patients. The manipulation of serum IGF-1 levels by dynamic exercise therapy may indicate the beneficial effects of dynamic exercise in RA patients.

Adult↗
PubMed2006

On the sensitive dependence on initial conditions of the dynamics of networks of spiking neurons.

We have previously formulated an abstract dynamical system for networks of spiking neurons and derived a formal result that identifies the criterion for its dynamics, without inputs, to be "sensitive to initial conditions". Since formal results are applicable only to the extent to which their assumptions are valid, we begin this article by demonstrating that the assumptions are indeed reasonable for a wide range of networks, particularly those that lack overarching structure. A notable aspect of the criterion is the finding that sensitivity does not necessarily arise from randomness of connectivity or of connection strengths, in networks. The criterion guides us to cases that decouple these aspects: we present two instructive examples of networks, one with random connectivity and connection strengths, yet whose dynamics is insensitive, and another with structured connectivity and connection strengths, yet whose dynamics is sensitive. We then argue based on the criterion and the gross electrophysiology of the cortex that the dynamics of cortical networks ought to be almost surely sensitive under conditions typically found there. We supplement this with two examples of networks modeling cortical columns with widely differing qualitative dynamics, yet with both exhibiting sensitive dependence. Next, we use the criterion to construct a network that undergoes bifurcation from sensitive dynamics to insensitive dynamics when the value of a control parameter is varied. Finally, we extend the formal result to networks driven by stationary input spike trains, deriving a superior criterion than previously reported.

Action Potentials↗
PubMed1996

Ultrasonographic assessment of the swelling of the human masseter muscle after static and dynamic activity.

Work-related fatigue, pain and disorders in skeletal muscles have been related to prolonged static and dynamic activity. Such contractions have been shown to impair blood flow and increase muscle thickness and fluid. In the present study the effect of static and dynamic activity was evaluated from changes in masseter thickness as a measure of oedema, simultaneously with assessment of perceived pain/discomfort and cardiovascular responses. As static activity, fourteen young healthy women bit at 15% maximal voluntary contraction on bite-force transducers in the molar regions until exhaustion or 20 min at maximum (median endurance time 7.1 min). For dynamic activity, the same individuals chewed gum unilaterally until exhaustion or 40 min at maximum (all endured 40 min) with a cycle time of 725 ms, an average load of 9.3% of maximal electromyographic activity (maxEMG) and a peak mean voltage of 54.3% of maxEMG. Muscle thickness was measured by ultrasonography at the mid-portion of the ipsilateral masseter. Immediately after exercise, muscle thickness was significantly increased, more after static (14.0%) than dynamic (8.6%), and returned to pre-exercise values after 20-min recovery. Visual analogue scales (VAS) revealed the concomitant occurrence of pain (static 11.9 VAS%; dynamic 5.9 VAS%), and discomfort (static 8.1 VAS%; dynamic 5.9 VAS%), and both sensations decreased to pre-exercise values after 20-min recovery. Systolic blood pressure increased significantly, more during static (12.5%) than dynamic activity (4.3%), whereas heart rate rose significantly only during dynamic exercise (13.3%). Hence, activity was associated with muscular swelling and pain, and, despite the relatively small size of the masticatory muscles, also with general cardiovascular responses.

Adult↗
PubMedDate not supplied

The influence of membrane proteins on lipid dynamics.

The application of electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) to the study of phospholipid dynamics in membranes is discussed. Using these complementary spectroscopic techniques it is possible to investigate the dynamics of lipids in membranes over a time scale range of from 10(-10) to 1 s. A rather detailed, quantitative description of phospholipid dynamics in pure lipid/water bilayer dispersions has emerged. For example, the correlation time for phosphate group reorientation has been shown to be of the order of 10(-9) s. Chain dynamics can be modelled in terms of three basic types of motion: reorientation about the long axis, fluctuation of the long axis with respect to the bilayer normal, and gauche-trans isomerization about C-C bonds. In the fluid phase, all of these chain motions are in the fast limit on the NMR time scale, but only the gauche-trans isomerization is fast on the EPR time scale. In the gel phase, all of these motions are in the intermediate time scale regime for NMR. While a similarly detailed description of the influence of protein on lipid dynamics has not yet been obtained, these techniques have demonstrated their capability to perform that task. The limited data available suggest that the major effect of protein on lipid dynamics is to increase the relative importance of motions at lower frequency. This is most clearly evident as a slight increase in the correlation time for phosphate group reorientation. The strongest evidence for slower motion of the hydrocarbon chains is from NMR relaxation time and line width measurements. The interpretation of changes in lipid dynamics in terms of protein/lipid interactions will require further studies of protein/lipid phase equilibria as well as molecular dynamics.

Animals↗
PubMed1994

Improved field edge definition in electron arc therapy with dynamic collimation techniques.

PURPOSE: The diffuse shape of the electron beam used for arc therapy requires collimation on the patient's surface to sharply define treatment field edges. The electron beam arcs 10-15 degrees past field edges defined by a custom fitted and manufactured cast which acts as a tertiary collimator. This allows the entire beam profile to be integrated at the field edge. The tertiary collimator is heavy and bulky, requiring two therapists to lift and position the cast. An alternative technique for field edge definition would require the electron arc collimators to dynamically close to zero, while maintaining the projection of the leading edge of the field coincident with the geometric edge of the treatment field. This would allow integration of the entire electron arc profile and maintain a sharply defined treatment edge at the medial and lateral margins of the arc. The present customized cast could be replaced by generic lead strips at only the superior and inferior treatment field borders. This study investigates the dosimetry of dynamically collimated electron arc treatment volumes at field margins and its potential for eliminating the need for tertiary collimation at the arc field margins. METHODS AND MATERIALS: Electron arc isodose distributions were calculated using a pencil beam algorithm for treatment volumes defined by tertiary collimation at the surface of a cylindrical phantom and compared to distributions generated by simulating dynamic collimation to define the same field edges. Phantom measurements were performed using film densitometry to verify computer predictions. RESULTS: Penumbra width is one measure of the sharpness of dose fall off at a treatment field edge. We define it as the distance between the 90% and 20% isodose lines at the field edge measured orthogonal to the incident electron beam. Calculations and phantom film densitometry measurements were performed for electron energies from 6-20 MeV. Dynamic and tertiary collimation both reduce penumbra width by approximately 50% compared to no collimation. There is a small advantage in minimizing penumbra width at low electron energy with tertiary collimation. This shifts to a small advantage with dynamic collimation at high electron energy. CONCLUSION: Dynamic collimation produces a field edge isodose distribution equivalent to tertiary collimation for clinical purposes. These results suggest that tertiary collimation at medial and lateral electron are treatment field margins can be eliminated with dynamic collimation. This should result in greater clinical acceptance of breast electron arc therapy as the capacity for dynamic collimation is added to the next generation of linear accelerators.

Breast Neoplasms↗
PubMed1990

Clinical assessment of ventricular ejection dynamics with and without outflow obstruction.

With the advent of multisensor micromanometric/velocimetric catheterization, digital angiography and Doppler and color echocardiography, extensive fluid dynamic quantitation is now possible in cardiology. Such high fidelity instantaneous measurements offer the clinician the prospect of identifying phasic changes in ventricular ejection dynamics that may disclose contraction abnormalities before overt muscle or pump failure is manifested. Accordingly, this review provides a basis for interpreting these measurements and a conceptual framework for understanding ventricular ejection dynamics with and without outflow obstruction. Necessary terminology and fluid dynamic background, including properties of flows generated by large transient forces, Euler and unsteady Bernoulli equations and local and convective acceleration gradients, are reviewed first. Physiologic aspects of ejection dynamics and transvalvular and intraventricular gradients without obstruction are discussed. Maximal outflow acceleration, rather than ejection velocity, coincides with the attainment of the early peak of the nonobstructive pressure gradients. These gradients are characteristically even more asymmetric than are the associated ejection velocity signals. Clinical correlations are introduced, beginning with obstructive transvalvular and subvalvular gradients in aortic stenosis and the phenomenon of recovery of pressure loss in the poststenotic dilation. The large obstructive gradients tend to be distinctively symmetric, as are the ejection waveforms, whose configuration they track more or less closely, depending on the degree of stenosis and relative preponderance of convective effects throughout ejection. Pitfalls in some unwarranted applications of the "simplified Bernoulli equation" are pointed out. Polymorphic gradients of hypertrophic cardiomyopathy, reflecting dynamically dissimilar intraventricular flow regimes in early, mid and late systole, are examined. Enormous late systolic gradients can be associated with progressive shrinkage of flow passage area and sharp increases in linear velocity while volumetric outflow is diminutive. The concept of ventriculoannular disproportion in dilated ventricles is defined and discussed. The implications of ejection fluid dynamics for systolic ventricular and myocardial loading are examined, and the concept of complementarity and competitiveness between intrinsic and extrinsic load components is introduced. Finally, critical research issues are identified and addressed. The primary emphasis is on using the basic principles of fluid dynamics to better understand ejection in the normal or abnormal human left ventricle and aortic root.(ABSTRACT TRUNCATED AT 400 WORDS)

Aortic Valve Stenosis↗
PubMed2004

Enhanced neural activity in response to dynamic facial expressions of emotion: an fMRI study.

Dynamic facial expressions of emotion constitute natural and powerful media of communication between individuals. However, little is known about the neural substrate underlying the processing of dynamic facial expressions of emotion. We depicted the brain areas by using fMRI with 22 right-handed healthy subjects. The facial expressions are dynamically morphed from neutral to fearful or happy expressions. Two types of control stimuli were presented: (i) static facial expressions, which provided sustained fearful or happy expressions, and (ii) dynamic mosaic images, which provided dynamic information with no facial features. Subjects passively viewed these stimuli. The left amygdala was highly activated in response to dynamic facial expressions relative to both control stimuli in the case of fearful expressions, but not in the case of happy expressions. The broad region of the occipital and temporal cortices, especially in the right hemisphere, which included the activation foci of the inferior occipital gyri, middle temporal gyri, and fusiform gyri, showed higher activation during viewing of the dynamic facial expressions than it did during the viewing of either control stimulus, common to both expressions. In the same manner, the right ventral premotor cortex was also activated. These results identify the neural substrate for enhanced emotional, perceptual/cognitive, and motor processing of dynamic facial expressions of emotion.

Adult↗
PubMed2003

A clinical test of dynamic visual acuity for children.

OBJECTIVE: Children with sensorineural hearing impairment (SNHI) and concomitant vestibular hypofunction demonstrate deficits in gaze stability that may affect reading. The objective of this study was to develop a reliable, valid clinical test of dynamic visual acuity (DVA) for children. METHODS: Seventy-six typically developing children, 26 adults and 11 children with sensorineural hearing impairment participated. Visual acuity was tested under three conditions: (1) head stable (static acuity), (2) head tipped forward 30 degrees and passively rotated 30 degrees in the yaw plane at 2 Hz (horizontal dynamic acuity) and (3) head passively moved in the pitch plane 30 degrees at 2 Hz (vertical dynamic acuity, vDVA). The difference, in number of chart lines, between static dynamic acuity was calculated (dynamic acuity score). Based on normative data collected, results were scored as: (1) pass < or =2S.D. from the normative mean and (2) fail > or =2S.D. from normative mean. Children were grouped by age to enable examination of the effect of age on scores. RESULTS: We found excellent test-retest and inter-tester reliability (ICC(2,2)=0.94 and ICC(3,2)=0.84) for the horizontal dynamic acuity (hDVA) test. Sensitivity, specificity, positive and negative predictive values were 100% to identify children with bilateral vestibular hypofunction (BVH). Although a statistical difference was found, the difference was not clinically significant (all achieved DVA scores <2 lines). The vertical dynamic acuity test was not tolerated by most children, precluding its usefulness. CONCLUSIONS: The clinical test of horizontal dynamic acuity is a reliable test for children as young as 3 years. It is simple and inexpensive, and will enable identification of those for whom more extensive testing is warranted.

Adolescent↗