[Dr. Freitag's dynamic tracheobronchial prosthesis (or dynamic stent)].
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The use of mechanical ankle exercise devices with continuous passive motion (CPM) of the ankle joint can improve venous reflow in the lower limbs after operations. Duplex ultrasonography allows the observations of blood flow velocity and flow volume during continuous movement of the devices. We tested two different CPM devices for ankle movement in a preclinical study on 10 healthy, uninjured people and saw the following changes in the deep venous system in the common femoral vein: after 5 min of motion the velocity of the venous reflow was increased to 112.5% and the flow volume passing the femoral vein to 123% of the initial mean values. After 15 min of motion the devices led to an increase of the venous reflow velocity to 125% and of flow volume to 143% of the baseline values in the femoral vein. These positive effects were still evident even 15 min after the devices have been turned off.
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The rising standards in dental treatment and the increased expectation s of patients to receive exceptional service are challenging dentists and axuiliaries to constantly look for ways to improve their practice. This article suggests that team involvement is a key ingredient to practice success. It discusses how to establish goals for the practice that can be monitored and setting new standards in patient care. Methods to provide exceptional service and increase patient satisfaction.
Following a brief overview of length scales and system size in computer simulation, it is demonstrated that a simulation sized lipid bilayer (typically a 50 x 50 A2 patch) is in the regime where stretching dominates undulation, while the reverse holds for a flaccid macroscopic membrane. Then it is estimated that current system sizes of membrane simulations must be increased by at least a factor of 10 before thermodynamic limits are approached for quantities such as surface tension.
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For the last thirty years, progress in the field of physics, known as "Chaos theory"--or more precisely: non-linear dynamical systems theory--has increased our understanding of complex systems dynamics. This framework's formalism is general enough to be applied in other domains, such as biology or psychology, where complex systems are the rule rather than the exception. Our goal is to show here that this framework can become a valuable tool in scientific fields such as neuroscience and psychiatry where objects possess natural time dependency (i.e. dynamical properties) and non-linear characteristics. The application of non-linear dynamics concepts on these topics is more precise than a loose metaphor and can throw a new light on mental functioning and dysfunctioning. A class of neural networks (recurrent neural networks) constitutes an example of the implementation of the dynamical system concept and provides models of cognitive processes (15). The state of activity of the network is represented in its state space and the time evolution of this state is a trajectory in this space. After a period of time those networks settle on an equilibrium (a kind of attractor). The strength of connections between neurons define the number and relations between those attractors. The attractors of the network are usually interpreted as "mental representations". When an initial condition is imposed to the network, the evolution towards an attractor is considered as a model of information processing (27). This information processing is not defined in a symbolic manner but is a result of the interaction between distributed elements. Several properties of dynamical models can be used to define a way where the symbolic properties emerge from physical and dynamical properties (28) and thus they can be candidates for the definition of the emergence of mental properties on the basis of neuronal dynamics (42). Nevertheless, mental properties can also be considered as the result of an underlying dynamics without explicit mention of the neuronal one (47). In that case, dynamical tools can be used to elucidate the Freudian psychodynamics (34, 35). Recurrent neuronal networks have been used to propose interpretation of several mental dysfunctions (12). For example in the case of schizophrenia, it has been proposed that troubles in the cortical pruning during development (13) may cause a decrease in neural network storage ability and lead to the creation of spurious attractors. Those attractors do not correspond to stored memories and attract a large amount of initial conditions: they were thus associated to reality distorsion observed in schizophrenia (14). Nevertheless, the behavior of these models are too simple to be directly compared with real physiological data. In fact, equilibrium attractors are hardly met in biological dynamics. More complex behaviors (such as oscillations or chaos) should thus to be taken into account. The study of chaotic behavior have lead to the development of numerical methods devoted to the analysis of complex time series (17). These methods may be used to characterise the dynamical processes at the time-scales of both the cerebral dynamics and the clinical symptoms variations. The application of these methods to physiological signals have shown that complex behaviors are related to healthy states whereas simple dynamics are related to pathology (8). These studies have thus confirmed the notion of "dynamical disease" (20, 21) which denotes pathological conditions characterised by changes in physiological rhythms. Depression has been studied within this framework (25, 32) in order to define possible changes in brain electrical rhythms related to this trouble and its evolution. It has been shown that controls' brain dynamics is more complex than depressive one and that the recovery of a complex brain activity depends on the number of previous episodes. In the case of the symptoms time evolution, several studies have demonstrated that non-linear dynamical process may be involved in the recurrence of symptoms in troubles such as manic-depressive illness (9) or schizophrenia (51). These observations can contribute to more parcimonious interpretation of the time course of these illnesses than usual theories. In the search of a relationship between brain dynamics and mental troubles, it has been shown in three depressed patients an important correlation between the characteristics of brain dynamics and the intensity of depressive mood (49). This preliminary observation is in accordance with the emergence hypothesis according which changes in neuronal dynamics should be related to changes in mental processes. We reviewed here some theoretical and experimental results related to the use of "physical" dynamical theory in the field of psychopathology. It has been argued that these applications go beyond metaphor and that they are empirically founded. Nevertheless, these studies only constitute first steps on the way of a cautious development and definition of a "dynamical paradigm" in psychopathology. The introduction of concepts from dynamics such as complexity and dynamical changes (i.e. bifurcations) permits a new perspective on function and dysfunction of the mind/brain and the time evolution of symptoms. Moreover, it offers a ground for the hypothesis of the emergence of mental properties on the basis of neuronal dynamics (42). Since this theory can help to throw light on classical problems in psychopathology, we consider that a precise examination of both its theoretical and empirical consequences is requested to define its validity on this topic.
We investigate the dynamics of a series of two-prey-one-predator models in which the predator exhibits adaptive diet choice based on the different energy contents and/or handling times of the two prey species. The predator is efficient at exploiting its prey and has a saturating functional response; these two features combine to produce sustained population cycles over a wide range of parameter values. Two types of models of behavioral change are compared. In one class of models ("instantaneous choice"), the probability of acceptance of the poorer prey by the predator instantaneously approximates the optimal choice, given current prey densities. In the second class of models ("dynamic choice"), the probability of acceptance of the poorer prey is a dynamic variable, which begins to change in an adaptive direction when prey densities change but which requires a finite amount of time to approach the new optimal behavior. The two types of models frequently predict qualitatively different population dynamics of the three-species system, with chaotic dynamics and complex cycles being a common outcome only in the dynamic choice models. In dynamic choice models, factors that reduce the rate of behavioral change when the probability of accepting the poorer prey approaches extreme values often produce complex population dynamics. Instantaneous and dynamic models often predict different average population densities and different indirect interactions between prey species. Alternative dynamic models of behavior are analyzed and suggest, first, that instantaneous choice models may be good approximations in some circumstances and, second, that different types of dynamic choice models often lead to significantly different population dynamics. The results suggest possible behavioral mechanisms leading to complex population dynamics and highlight the need for more empirical study of the dynamics of behavioral change.
PURPOSE: The aim of this study was to compare long-term results for patients born with an anorectal malformation and fecal incontinence treated with a dynamic graciloplasty with those for the total group of patients undergoing dynamic graciloplasty. METHODS: Consecutive patients with fecal incontinence after surgical treatment of anorectal malformation and treated with dynamic graciloplasty were included in this study. Preoperative assessment was performed. Postoperative follow-up consisted of anorectal manometry and registration of defecation frequency, continence scores, and postponement time of defecation. RESULTS: Twenty-eight patients with a median age of 25.5 years were included in the study. The median follow-up was 4 years. A high anorectal malformation was present in 89.3 percent of patients. Conventional graciloplasty had been previously performed in 36 percent. All patients were incontinent for stools. Median frequency of defecation was four times/day. Median postponement time of defecation was 0 minutes. Rectoanal inhibition reflex was present in 17 percent of patients. Median preoperative sensory threshold during balloon distention was 30 ml and median maximum urge threshold was 165 ml. Satisfactory continence was reached in 35 percent of patients, however, 7.1 percent of patients gained this continence score by additional bowel irrigation. Twenty-nine percent of patients were incontinent for loose stool, 36 percent were incontinent for formed stool. Satisfactory continence was achieved in only 18 percent of patients with a high anorectal malformation, compared with 100 percent in patients with a low anorectal malformation. In the total group of patients with dynamic graciloplasty, satisfactory continence was obtained in 76 percent. The sensitivity threshold in patients with a successful dynamic graciloplasty was lower than that in patients with a failing dynamic graciloplasty (45 vs. 24 ml, P = 0,06). When we compare median preoperative rectal sensitivity threshold in our study group with that in the total patient group with dynamic graciloplasty, statistical difference was established (P = 0.008). Postponement time (0 to 20 minutes) and anal squeeze pressure (81 to 120 mmHg) increased significantly after surgery. Patients with an anorectal malformation had significantly lower resting and stimulation pressure than that of the total group of patients, but the difference between resting and stimulation pressure in both groups was not significantly different (P = 0.33). The difference between resting and stimulation pressure was not significantly different between anorectal malformation patients with a failing dynamic graciloplasty and patients with a successful dynamic graciloplasty. Complications were noted in 57 percent of patients. Explantation of the dynamic graciloplasty was necessary in 32 percent of patients, mainly because of infection of the implant. CONCLUSIONS: Results of dynamic graciloplasty for fecal incontinence are reasonable for this specific group of patients with limited treatment options. Despite functional dynamic graciloplasty, the results are worse than those for the total group of patients with dynamic graciloplasty. Rectal sensitivity and type of malformation are prognostic factors for outcome and can be used to select patients for treatment with dynamic graciloplasty, thereby improving treatment outcome.
We study coupled dynamics on networks using symbolic dynamics. The symbolic dynamics is defined by dividing the state space into a small number of regions (typically 2), and considering the relative frequencies of the transitions between those regions. It turns out that the global qualitative properties of the coupled dynamics can be classified into three different phases based on the synchronization of the variables and the homogeneity of the symbolic dynamics. Of particular interest is the homogeneous unsynchronized phase, where the coupled dynamics is in a chaotic unsynchronized state, but exhibits qualitative similar symbolic dynamics at all the nodes in the network. We refer to this dynamical behavior as symbolic synchronization. In this phase, the local symbolic dynamics of any arbitrarily selected node reflects global properties of the coupled dynamics, such as qualitative behavior of the largest Lyapunov exponent and phase synchronization. This phase depends mainly on the network architecture, and only to a smaller extent on the local chaotic dynamical function. We present results for two model dynamics, iterations of the one-dimensional logistic map and the two-dimensional Henon map, as local dynamical function.
The evolution of water dynamics from dilute to very high concentration solutions of a prototypical hydrophobic amino acid with its polar backbone, N-acetyl-leucine-methylamide (NALMA), is studied by quasi-elastic neutron scattering (QENS) and molecular dynamics (MD) simulation for both the completely deuterated and completely hydrogenated leucine monomer. The NALMA-water system and the QENS data together provide a unique study for characterizing the dynamics of different hydration layers near a prototypical hydrophobic side chain and the backbone of which it is attached. We observe several unexpected features in the dynamics of these biological solutions under ambient conditions. The NALMA dynamics shows evidence of de Gennes narrowing, an indication of coherent long timescale structural relaxation dynamics. The translational and rotational water dynamics at the highest solute concentrations are found to be highly suppressed as characterized by long residential time and slow diffusion coefficients. The analysis of the more dilute concentration solutions models the first hydration shell with the 2.0 M spectra. We find that for outer layer hydration dynamics that the translational diffusion dynamics is still suppressed, although the rotational relaxation time and residential time are converged to bulk-water values. Molecular dynamics analysis of the first hydration shell water dynamics shows spatially heterogeneous water dynamics, with fast water motions near the hydrophobic side chain, and much slower water motions near the hydrophilic backbone. We discuss the hydration dynamics results of this model protein system in the context of protein function and protein-protein recognition.
The proposition that dynamic optimization provides better estimates of muscle forces during gait than static optimization is examined by comparing a dynamic solution with two static solutions. A 23-degree-of-freedom musculoskeletal model actuated by 54 Hill-type musculotendon units was used to simulate one cycle of normal gait. The dynamic problem was to find the muscle excitations which minimized metabolic energy per unit distance traveled, and which produced a repeatable gait cycle. In the dynamic problem, activation dynamics was described by a first-order differential equation. The joint moments predicted by the dynamic solution were used as input to the static problems. In each static problem, the problem was to find the muscle activations which minimized the sum of muscle activations squared, and which generated the joint moments input from the dynamic solution. In the first static problem, muscles were treated as ideal force generators; in the second, they were constrained by their force-length-velocity properties; and in both, activation dynamics was neglected. In terms of predicted muscle forces and joint contact forces, the dynamic and static solutions were remarkably similar. Also, activation dynamics and the force-length-velocity properties of muscle had little influence on the static solutions. Thus, for normal gait, if one can accurately solve the inverse dynamics problem and if one seeks only to estimate muscle forces, the use of dynamic optimization rather than static optimization is currently not justified. Scenarios in which the use of dynamic optimization is justified are suggested.
PURPOSE: To increase specificity of MR-mammography by using dynamic T2* sequences. METHODS: 23 patients with suspicious lesions of the breast underwent conventional dynamic T1-weighted (T1-dynamic) breast MRI and, subsequently, dynamic T2*-weighted (T2*-dynamic) perfusion studies. To assess the T1-dynamic, signal enhancement during the first minute (E1) was calculated. To evaluate the T2*-dynamic, relative signal intensity loss after administration of contrast medium was determined. RESULTS: After administration of contrast medium, 6 of 13 malignant lesions did not show a signal decrease during the T2*-dynamic. Two of them exhibited an atypical signal enhancement in the T1-dynamic, with E1 < 100%. On the other hand, in 5 of 10 benign tumors a relative signal decrease of between 5-17% occurred during the T2*-dynamic. Four benign lesions showed a strong early signal enhancement during the T1-dynamic (E1 > 100%), which is more typical for malignant lesions. DISCUSSION: The use of dynamic T2* sequences, following dynamic T1-weighted breast MRI and administration of contrast medium, does not sufficiently increase diagnostic sensitivity. Thus, this study does not support the potential advantage of susceptibility MR imaging for a further characterization of breast lesions.
Learning of coordination patterns was investigated theoretically from the point of view of a dynamic theory of biological coordination and with reference to recent experiments on the learning of relative timing patterns. The theory is based on theoretical and experimental work showing that coordinated movement is characterized not only by the actually performed pattern of coordination but by an entire dynamics of coordination. Theoretically, such dynamics are captured as equations of motion of relevant collective variables. Experimentally, signatures of these underlying dynamics can be found in the temporal stability of coordination patterns, which can be assessed through various stability measures as well as through processes of pattern change. We argue that not only intrinsic coordination tendencies, but also specific behavioral requirements, be they perceived, memorized, or intended, must be expressed in terms of such dynamics. The concept of behavioral information captures such requirements as part of the coordination dynamics. We expound two hypotheses on the nature of learning in this framework. First, we assume that at each point during the learning process the system is governed by a well-defined coordination dynamics. This equation of motion evolves with learning so as to acquire an attractor solution near the to-be-learned pattern. Second, we hypothesize that this change of the coordination dynamics, captured by the time course of memorized behavioral information, can itself be ascribed to an additional layer of dynamics, the slower learning dynamics. Testable consequences of these views are discussed in the light of recent experimental findings on the learning of a relative phase in rhythmic movement: (a) Learning affects dynamic properties of performed coordination patterns, in particular, their stability; (b) the change of the coordination dynamics due to learning leads to specific changes of behavior also under conditions other than the learned condition, namely, to systematic deviation toward the learned patterns; (c) learning may lead to instabilities in the coordination behavior if initial and learned performance differ sufficiently; and (d) the dynamic properties of the performed coordination patterns are distinct on the two time scales of learning and of performance.
Early axial dynamization and its effect on experimental tibial bone healing was compared with healing under rigid fixation in a time-sequenced manner using dogs. An external fixator that could be rigidly locked or set to allow free axial movement while preventing bending and shear was used. Both tibias were osteotomized and externally fixed, leaving a gap between bone ends of 2 mm. At 1 week, one side was dynamized, whereas the other side was kept rigidly locked as a control. Dogs were euthanized at 1 day and 1, 3, 5, 8, and 11 weeks after dynamization. The outcome measures were static and dynamic load-bearing, periosteal callus development, new bone formation, callus tissue composition, and mechanical strength. Load bearing was higher on the dynamized limbs during standing for the first 5 weeks and during gait for the first 3 weeks after dynamization compared with the controls. Maximum periosteal callus size was reached faster and was distributed more symmetrically on the dynamized side. The periosteal callus area decreased at 12 weeks on the dynamized sides, but there was no significant change in the area on the control sides. Endosteal new bone formation and bone density decreased between 9 and 12 weeks only on the dynamized sides. The dynamized side showed a significantly higher torsional stiffness at 6 weeks than did the controls. There were no significant differences between dynamized and control tibias at other times. Maximum torque also tended to be higher on the dynamized sides at the same time. Early axial dynamization appeared to accelerate callus formation and remodeling and to provide higher mechanical stiffness during early stages of bone healing.
A new dynamic model of left ventricular (LV) pressure-volume relationships in beating heart was developed by mathematically linking chamber pressure-volume dynamics with cardiac muscle force-length dynamics. The dynamic LV model accounted for >80% of the measured variation in pressure caused by small-amplitude volume perturbation in an otherwise isovolumically beating, isolated rat heart. The dynamic LV model produced good fits to pressure responses to volume perturbations, but there existed some systematic features in the residual errors of the fits. The issue was whether these residual errors would be damaging to an application where the dynamic LV model was used with LV pressure and volume measurements to estimate myocardial contractile parameters. Good agreement among myocardial parameters responsible for response magnitude was found between those derived by geometric transformations of parameters of the dynamic LV model estimated in beating heart and those found by direct measurement in constantly activated, isolated muscle fibers. Good agreement was also found among myocardial kinetic parameters estimated in each of the two preparations. Thus the small systematic residual errors from fitting the LV model to the dynamic pressure-volume measurements do not interfere with use of the dynamic LV model to estimate contractile parameters of myocardium. Dynamic contractile behavior of cardiac muscle can now be obtained from a beating heart by judicious application of the dynamic LV model to information-rich pressure and volume signals. This provides for the first time a bridge between the dynamics of cardiac muscle function and the dynamics of heart function and allows a beating heart to be used in studies where the relevance of myofilament contractile behavior to cardiovascular system function may be investigated.
Eight male collegiate weightlifters (age: 21.2 +/- 0.9 years; height: 177.6 +/- 2.3 cm; and body mass: 85.1 +/- 3.3 kg) participated in this study to compare isometric to dynamic force-time dependent variables. Subjects performed the isometric and dynamic mid-thigh clean pulls at 30-120% of their one repetition maximum (1RM) power clean (118.4 +/- 5.5 kg) on a 61 x 121.9-cm AMTI forceplate. Variables such as peak force (PF) and peak rate of force development (PRFD) were calculated and were compared between isometric and dynamic conditions. The relationships between force-time dependent variables and vertical jump performances also were examined. The data indicate that the isometric PF had no significant correlations with the dynamic PF against light loads. On the one hand, there was a general trend toward stronger relationships between the isometric and dynamic PF as the external load increased for dynamic muscle actions. On the other hand, the isometric and dynamic PRFD had no significant correlations regardless of the external load used for dynamic testing. In addition, the isometric PF and dynamic PRFD were shown to be strongly correlated with vertical jump performances, whereas the isometric PRFD and dynamic PF had no significant correlations with vertical jump performances. In conclusion, it appears that the isometric and dynamic measures of force-time curve characteristics represent relatively specific qualities, especially when dynamic testing involves small external loads. Additionally, the results suggest that athletes who possess greater isometric maximum strength and dynamic explosive strength tend to be able to jump higher.
PURPOSE OF THE STUDY: This is a prospective comparative randomised study to compare the immediately postoperative effects of a rigid versus dynamic instrumentation for degenerative spine disease and stenosis on the standing sagittal lumbar spine alignment and to investigate if a dynamic spine system can replace the commonly used rigid systems in order to avoid the above mentioned disadvantages of rigid fixation. MATERIAL & METHODS: 15 randomly selected patients received the rigid instrumentation SCS and an equal number of randomly selected patients the dynamic TWINFLEX device for spinal stenosis associated degenerative lumbar disease. The age of the patients, who received rigid and dynamic instrumentation was 65 +/- 9 years and 62 +/- 10 years respectively. All patients had standing spine radiographs preoperatively and three months postoperatively. The parameters that were measured and compared pre- to postoperatively were: lumbar lordosis (L1-S1), total lumbar lordosis (T12-S1), sacral tilt, distal lordosis (L4-S1), intervertebral angulation, vertebral inclination and disc index. RESULTS: The instrumented levels in the spines that received rigid and dynamic instrumentation were 3.5 +/- 0.53 and 3 +/- 0.7 respectively. The instrumented levels from L3 to L5 were 23, the lumbosacral junction was instrumented in 3 patients of group A and in 4 patients of group B. Lumbar lordosis did not significantly change postoperatively, while total lordosis was significantly (P=0.04) increased in the patients who received the rigid instrumentation, while it was significantly (P=0.012) decreased in the group B. Intervertebral angulation of the non-instrumented level L1-L2 was increased in the group A (P=0.01), while the dynamic instrumentation increased (P=0.02) the intervertebral inclination of the adjacent level L2-L3, immediately above the uppermost instrumented level. Distal lordosis and sacral tilt did not change in any patient in both groups. Both instrumentations did not change the lateral vertebral inclination of L1 to L5 vertebrae. Rigid instrumentation increased the lordotic inclination of L5 (P=0.03) and of S1 (P=0.03). Rigid instrumentation increased (P=0.04) the intervertebral angulation at the uppermost instrumented level L3-L4 The most significant change in vertebral angulation was achieved at the instrumented level L4-L5 by the dynamic (P=0.007) and rigid (0.05). The disc index at the level L2-L3 was increased by both instrumentation [dynamic P=0.007 and rigid (P=0.02)]. The index L3-L4 was increased following dynamic fixation (P=0.0007). The disc index L4-L5 was postoperatively increased by both types of instrumentation (rigid P=0.006, dynamic P=0.02). The disc index L5-S1 did not significantly change postoperatively by either system. CONCLUSION: Both rigid and dynamic instrumentations restored lumbar lordosis, sacral tilt, distal lordosis and increased the foraminal diameter at the level L4-L5 resulting in an indirect decompression of the nerve roots at this level . Both rigid and dynamic instrumentations applied in the lumbosacral spine to treat degenerative disease secured L3 to S1 sagittal spine profile close to preoperative levels, that should theoretically guarantee a pain-free postoperative course. This study supports the belief that the dynamic system can be used with the same indications with the rigid in degenerative lumbar spine because it can offer equally good short-term results regarding sagittal spine alignment while simultaneously it has the previously mentioned advantages (avoidance stress shielding etc).