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At least 217 records · Page 12Linked to original sources
PubMed2004

Determination of the length of anteromedial screw trajectory by measuring interforaminal distance in the first sacral vertebra.

STUDY DESIGN: Measurements of the length of pediculocorporeal screw trajectory were performed on bony sacra. Outer interforaminal distances of the first sacral vertebra were measured on bony sacra and anteroposterior sacral radiographs. OBJECTIVES: To demonstrate the correlation of the length of pediculocorporeal screw trajectory of the first sacral vertebra on bony specimens with outer interforaminal distances on their anteroposterior radiographs. SUMMARY OF BACKGROUND DATA: Posterior fixation of the lumbosacral vertebra has been used in the treatment of unstable lumbar spine disorders. To achieve the strongest biomechanical stability and to avoid injury to anterior sacral structures for anteromedial insertion of the posterior transpedicular screw to the first sacral vertebra (S1), it is crucial to determine the optimum screw length for both unicortical and bicortical screw placement. METHODS: Fifty-one dry bony adult sacra were measured and correlated with anteroposterior lumbosacral radiographs. The length of S1 screw trajectory, which was accepted as between inferolateral border of superior articular facet of S1 and sacral promontory, and the outer interforaminal distances of anterior S1 foramens were measured on bony specimens. The outer interforaminal distances of anterior S1 foramens were also measured on anteroposterior sacral radiographs. RESULTS: The outer interforaminal distances were not statistically different from the length of the S1 screw trajectory on bony specimens. Radiographs of the S1 vertebra have also shown that outer interforaminal distances were not statistically different from the length of the S1 screw trajectory. CONCLUSION: In this study, we described an easy and a reliable method to determine the length of anteromedial screw by measuring outer interforaminal distance of S1 vertebra on anteroposterior radiograph of the sacrum.

Adult↗
PubMed2006

Minor depression and physical outcome trajectories in heart failure and pulmonary disease.

We examined conjoint trajectories of depression-physical illness outcomes in elderly inpatients with minor depression and heart failure or pulmonary disease, and identified demographic, psychosocial, physical, and treatment predictors of trajectory. Consecutively admitted patients over age 50 with heart failure and/or chronic pulmonary disease were screened for minor depression using the Structured Clinical Interview for Depression. Follow-up evaluations were performed at 6 and 12 weeks using the Longitudinal Interview Follow-Up Evaluation, Hamilton Depression Scale, and Chronic Heart Failure-Chronic Respiratory Disease Questionnaire. Patients were placed into four depression-physical illness outcome trajectories: (T#1) depression better, illness better; (T#2) depression better, illness same; (T#3) depression same, illness better; and (T#4) depression same, illness same. Bivariate and multivariate predictors were examined. Minor depression was identified in 587 patients. Of these, 487 were evaluated at 6 weeks and 444 at 12 weeks. By 6 weeks, 39.4% of patients improved both on depression and physical illness (T#1), and 27.3% improved on neither (T#4). By 12 weeks, 49.6% had improved on both and 20.5% on neither. Race, admitting hospital, past psychiatric history, family psychiatric history, comorbid physical illnesses, and antidepressant drug treatment independently predicted outcome trajectory. Improvements in depression and physical illness track closely together in elderly inpatients with heart failure or pulmonary disease. Baseline patient characteristics predict which outcome trajectory they are likely to follow after hospital discharge, and may be useful in diagnosis and management.

Aged↗
PubMed2005

Compensatory response 'defends' energy levels but not growth trajectories in brown trout, Salmo trutta L.

Compensatory growth is an organism's reaction to buffer deviations from targeted trajectories. We explored the compensatory patterns of juvenile brown trout under field and laboratory conditions. Divergence of size and condition trajectories was induced by manipulating food levels in the laboratory and then releasing the trout into a river. In the stream, the length trajectories of food-restricted and control fish were parallel, but food-restricted fish exhibited partial compensation for mass and rapid recovery of condition. A laboratory experiment on similar sized fish did not provide evidence for compensatory growth in length or mass. In contrast, data matched the compensatory patterns shown in the stream: length trajectories were parallel and the convergence of mass trajectories ceased as soon as food-restricted fish recovered condition to the level of controls. These results show that (i) brown trout did not compensate for depression in structural growth and (ii) mass recovery was targeted to reinstate condition or energy reserves, but not size at a given age. This does not support the common view that compensatory growth can be a general response to growth depression. Rather, compensation in other salmonids could be related to size thresholds associated with developmental switches at the onset of sexual maturation and migration.

Analysis of Variance↗
PubMed2000

Analysis of arm trajectories of everyday tasks for the development of an upper-limb orthosis.

Spatiotemporal arm and body movements of able-bodied subjects performing nine everyday tasks were recorded for the purpose of guiding the development of an upper-limb orthosis. To provide a user the opportunity to carry out these tasks with natural movements, the orthosis should allow replication of the measured trajectories. We outline the orthosis architecture, which supports the user's upper arm and forearm, and analyze the movement data to obtain orthosis design specifications. Trajectories were obtained using six-degree-of-freedom magnetic position sensors affixed to the wrist, elbow, shoulder, trunk and head. Elbow trajectory data were decomposed into ranges along the principle Cartesian axes to provide a generally useful envelope measure. The smallest Cartesian parallel-piped that contained the elbow trajectories for most tasks was approximately 30 cm front/back, 15 cm side/side, and 17 cm up/down. A rough lower bound estimate obtained by asking subjects to repeat the tasks while minimizing elbow movement substantially reduced movement in the up/down and side/side dimensions. Elbow angles were generally in the range 50 degrees-150 degrees, and the angle of the forearm with respect to vertical was 10 degrees-110 degrees. Raw trajectory data may be downloaded from www://asel.udel.edu/robotics/orthosis/range.h tml.

Activities of Daily Living↗
PubMed2004

Understanding complex trajectories in health and social care provision.

Abstract Ensuring collaboration between health and social care providers is a well-established policy concern in most developed countries. Thus far, however, this has proved to be a frustratingly elusive goal. Despite the growing body of empirical work devoted to this issue, social scientific theorising on the management of complex caring trajectories remains under-developed. This paper is an attempt to begin to address this gap in the literature. Drawing on Strauss et al.'s (1985) writings on illness trajectories and Elias's (1978) game model, we offer a framework - centred on the notion of a caring trajectory game - that can assist understanding of the linkages between individual trajectories of care and broader health and social care systems. It is only when we have developed a more theoretically sophisticated understanding of this relationship that we can begin to explain why trajectories of care take the course that they do. The framework arises from our analysis of eight ethnographic case studies of adults undergoing rehabilitation from a first acute stroke. In this paper we illustrate its utility by reference to one specific case: Edward.

Anthropology, Cultural↗
PubMed2005

Psychosocial predictors of smoking trajectories during middle and high school.

AIMS: Little is known about the heterogeneity in and risk factors associated with trajectories of smoking during adolescence. This study aimed to (1) identify smoking trajectories empirically and (2) identify risk factors for trajectory group membership. DESIGN: Latent growth mixture models were used to identify population smoking trajectories, and logistic regression was used to estimate risk factors for group membership. SETTING: The participants were drawn from seven middle schools in a Maryland school district. PARTICIPANTS: Participants consisted of 1320 6th graders who were followed to the 9th grade. MEASUREMENTS: Measurements of smoking risk factors were made in the fall of 6th grade and smoking stage was assessed on five different occasions between the fall of 6th and 9th grades. FINDINGS: Five distinct smoking trajectories were identified. Overall, being female, having friends who smoked, deviance acceptance and outcome expectations were associated with an increased likelihood of being an intender, delayed escalator, early experimenter and early user compared to a never smoker. Additionally, comparisons with never smokers revealed unique identifiers for intenders, early experimenters and early users, but not delayed escalators. CONCLUSIONS: There is much heterogeneity in the manner in which middle-schoolers progress from having no intention of smoking to becoming smokers. Implications for prevention programs are discussed.

Adolescent↗
PubMed1993

Vowel boundaries for steady-state and linear formant trajectories.

Locations of boundaries and slopes of identification functions were tested for /I-epsilon/ vowel continua with steady-state and linearly changing formant trajectories. In experiment 1, the boundaries and slopes for arbitrarily selected trajectory directions were determined for ten normal-hearing and ten hearing-impaired subjects in three listening conditions: Quiet, noise, and reverberation. The boundaries did not depend upon the group of subjects or the listening condition. A boundary shift was found for stimuli with F1 changing in a downward direction relative to boundaries for stimuli with either only F1 or with both F1 and F2 changing in an upward direction. The slope of the identification function for stimuli with F1 changing in a downward direction was shallower than the slopes for stimuli with steady-state formants or stimuli with F1 changing in an upward direction. The slopes obtained from the hearing-impaired subjects were shallower than those of the normal-hearing subjects and were shallower in noise than in either quiet or reverberation. In experiment 2, boundaries and slopes for the trajectory directions found in the natural vowels /I/ and /epsilon/, F1 changing in an upward direction and F2 in a downward direction, were determined for nine normal-hearing subjects in two listening conditions, quiet and reverberation. The boundary for stimuli with both F1 and F2 changing in directions characteristic for natural vowels was shifted relative to the boundary for stimuli with steady-state formants. The directions of the boundary shifts in experiments 1 and 2 indicated a perceptual emphasis on the initial sections of changing F1 and F2. Sound quality of the end-point /I/ and /epsilon/ stimuli depended upon F1 and F2 trajectories. For both vowels, the best quality judgments were found for the stimuli with natural F1 and F2 trajectory directions. The quality judgments were weakly correlated with the slopes of identification functions, with better quality judgments being associated with steeper slopes.

Acoustic Stimulation↗
PubMed2000

Curved trajectory prediction using a self-organizing neural network.

Existing neural network models are capable of tracking linear trajectories of moving visual objects. This paper describes an additional neural mechanism, disfacilitation, that enhances the ability of a visual system to track curved trajectories. The added mechanism combines information about an object's trajectory with information about changes in the object's trajectory, to improve the estimates for the object's next probable location. Computational simulations are presented that show how the neural mechanism can learn to track the speed of objects and how the network operates to predict the trajectories of accelerating and decelerating objects.

Acceleration↗
PubMed2003

Stereotypical fingertip trajectories during grasp.

The kinematics of movement of all five digits was analyzed during reach-and-grasp tasks for a variety of objects. Ten healthy subjects performed 20 trials involving the grasp of five objects of distinct size and shape. Joint angles were recorded, and digit trajectories were computed using forward kinematics. For a given subject, fingertip trajectories were consistent across trials. The different-sized objects largely produced movement along different portions of a stereotypical trajectory described by a logarithmic spiral. The spirals fit the actual finger positions with a mean error across all trials of 0.23 +/- 0.25 cm and accounted for over 98% of the variance in finger position. These patterns were consistent independent of initial finger posture. Subjects did not produce straight-line movements, either in Cartesian space or joint space. The direction of the thumb trajectories exhibited a greater dependence on object type than the finger trajectories, but still utilized a small percentage (<5%) of the available workspace. These results suggest that restoration of a small but specific part of the workspace could have significant impact on function following hand impairment.

Adult↗
PubMed1988

The trajectory of human wrist movements.

1. To determine the form of human movement trajectories and the factors that determine this form, normal subjects performed wrist flexion movements against various elastic, viscous, and inertial loads. The subjects were instructed with visual and auditory feedback to make a movement of prescribed amplitude in a present period of time, but were free to choose any trajectory that fulfilled these constraints. 2. The trajectories were examined critically to determine if they corresponded to those which would minimize the root mean square (RMS) value of some kinematic variable or of energy consumption. The data agreed better with the trajectory that minimized the RMS value of jerk (the third derivative of length) than that of acceleration. However, systematic deviations from the minimum jerk predictions were consistently observed whenever movements were made against elastic and viscous loads. 3. Improved agreement could generally be obtained by assuming that the velocity profile varied according to a normal (Gaussian) curve. We conclude that minimization of jerk is not a general principle used by the nervous system in organizing voluntary movements, although movements may approach the predicted form, particularly under inertial loading conditions. 4. The EMG of the agonist muscles consisted of relatively simple waveforms containing ramplike increases and approximately exponential decays. The form of the movements could often be predicted quite well by using the EMG as an input to a linear second-order model of the muscle plus load. Rather than rigorously minimizing a kinematic variable or energy consumption, the nervous system may generate simple waveforms and adjust the parameters of these waveforms by trial and error until a trajectory is achieved that meets the requirements for a given load.

Adult↗
PubMed2000

Afferent roles in hindlimb wipe-reflex trajectories: free-limb kinematics and motor patterns.

The hindlimb wiping reflex of the frog is an example of a targeted trajectory that is organized at the spinal level. In this paper, we examine this reflex in 45 spinal frogs to test the importance of proprioceptive afferents in trajectory formation at the spinal level. We tested hindlimb to hindlimb wiping, in which the wiping or effector limb and the target limb move together. Loss of afferent feedback from the wiping limb was produced by cutting dorsal roots 7-9. This caused altered initial trajectory direction, increased ankle path curvature, knee-joint velocity reversals, and overshooting misses of the target limb. We established that these kinematic and motor-pattern changes were due mainly to the loss of ipsilateral muscular and joint afferents. Loss of cutaneous afferents alone did not alter the initial trajectory up to target limb contact. However, there were cutaneous effects in later motor-pattern phases after the wiping and target limb had made contact: The knee extension or whisk phase of wiping was often lost. Finally, there was a minor and nonspecific excitatory effect of phasic contralateral feedback in the motor-pattern changes after deafferentation. Specific muscle groups were altered as a result of proprioceptive loss. These muscles also showed configuration-based regulation during wiping. Biceps, semitendinosus, and sartorius (all contributing knee flexor torques) all were regulated in amplitude based on the initial position of the limb. These muscles contributed to an initial electromyographic (EMG) burst in the motor pattern. Rectus internus and semimembranosus (contributing hip extensor torques) were regulated in onset but not in the time of peak EMG or in termination of EMG based on initial position. These two muscles contributed to a second EMG burst in the motor pattern. After deafferentation the initial burst was reduced and more synchronous with the second burst, and the second burst often was broadened in duration. Ankle path curvature and its degree of change after loss of proprioception depended on the degree of joint staggering used by the frog (i.e., the relative phasing between knee and hip motion) and on the degree of motor-pattern change. We examined these variations in 31 frogs. Twenty percent (6/31) of frogs showed largely synchronous joint coordination and little effect of deafferentation on joint coordination, end-point path, or the underlying synchronous motor pattern. Eighty percent of frogs (25/31) showed some degree of staggered joint coordination and also strong effects of loss of afferents. Loss of afferents caused two major joint level changes in these frogs: collapse of joint phasing into synchronous joint motion and increased hip velocity. Fifty percent of frogs (16/31) showed joint-coordination changes of type (1) without type (2). This change was associated with reduction, loss, or collapse of phasing of the sartorius, semitendinosus and biceps (iliofibularis) in the initial EMG burst in the motor pattern. The remaining 30% (9/31) of frogs showed both joint-coordination changes 1 and 2. These changes were associated with both the knee flexor EMG changes seen in the other frogs and with additional increased activity of rectus internus and semimembranosus muscles. Our data show that multiple ipsilateral modalities all play some role in regulating muscle activity patterns in the wiping limb. Our data support a strong role of ipsilateral proprioception in the process of trajectory formation and specifically in the control of limb segment interactions during wiping by way of the regulation and coordination of muscle groups based on initial limb configuration.

Algorithms↗
PubMed1989

Generation of reaching movements: plausibility and implications of the equilibrium trajectory hypothesis.

According to the 'equilibrium trajectory' hypothesis, the generation of multi-joint arm movements by the CNS involves the gradual shifting of the hand equilibrium position between the movement end points. This work presents a model which suggests that reaching movements are explicitly planned in terms of spatially and temporally invariant hand equilibrium trajectories. Implementing the model in computer simulations, and using stiffness parameters which were measured during arm posture, arm trajectories were simulated and compared to measured trajectories. The success of the predicted behavior in capturing the fine kinematic details of measured movements supports the validity of the proposed model for biological trajectory control.

Biomechanical Phenomena↗
PubMed2006

Is the ability to identify deviations in multiple trajectories compromised by amblyopia?

Amblyopia results in a severe loss of positional information and in the ability to accurately enumerate objects (V. Sharma, D. M. Levi, & S. A. Klein, 2000). In this study, we asked whether amblyopia also disrupts the ability to track a near-threshold change in the trajectory of a single target amongst multiple similar potential targets. In the first experiment, we examined the precision for detecting a deviation in the linear motion trajectory of a dot by measuring deviation thresholds as a function of the number of moving trajectories (T). As in normal observers, we found that in both eyes of amblyopes, threshold increases steeply as T increases from 1 to 4. Surprisingly, for T = 1-4, thresholds were essentially identical in both eyes of the amblyopes and were similar to those of normal observers. In a second experiment, we measured the precision for detecting a deviation in the orientation of a static, bilinear "trajectory" by again measuring deviation thresholds (i.e., angle discrimination) as a function of the number of oriented line "trajectories" (T). Relative to the nonamblyopic eye, amblyopes show a marked threshold elevation for a static target when T = 1. However, thresholds increased with T with approximately the same slope as in their preferred eye and in the eyes of the normal controls. We conclude that while amblyopia disrupts static angle discrimination, amblyopic dynamic deviation detection thresholds are normal or very nearly so.

Adult↗
PubMed2004

Finite burn maneuver modeling for a generalized spacecraft trajectory design and optimization system.

The modeling, design, and optimization of finite burn maneuvers for a generalized trajectory design and optimization system is presented. A generalized trajectory design and optimization system is a system that uses a single unified framework that facilitates the modeling and optimization of complex spacecraft trajectories that may operate in complex gravitational force fields, use multiple propulsion systems, and involve multiple spacecraft. The modeling and optimization issues associated with the use of controlled engine burn maneuvers of finite thrust magnitude and duration are presented in the context of designing and optimizing a wide class of finite thrust trajectories. Optimal control theory is used examine the optimization of these maneuvers in arbitrary force fields that are generally position, velocity, mass, and are time dependent. The associated numerical methods used to obtain these solutions involve either, the solution to a system of nonlinear equations, an explicit parameter optimization method, or a hybrid parameter optimization that combines certain aspects of both. The theoretical and numerical methods presented here have been implemented in copernicus, a prototype trajectory design and optimization system under development at the University of Texas at Austin.

Journal Article↗
PubMed2005

New trends in astrodynamics and applications: optimal trajectories for space guidance.

This paper represents recent results on the development of optimal analytic solutions to the variation problem of trajectory optimization and their application in the construction of on-board guidance laws. The importance of employing the analytically integrated trajectories in a mission design is discussed. It is assumed that the spacecraft is equipped with a power-limited propulsion and moving in a central Newtonian field. Satisfaction of the necessary and sufficient conditions for optimality of trajectories is analyzed. All possible thrust arcs and corresponding classes of the analytical solutions are classified based on the propulsion system parameters and performance index of the problem. The solutions are presented in a form convenient for applications in escape, capture, and interorbital transfer problems. Optimal guidance and neighboring optimal guidance problems are considered. It is shown that the analytic solutions can be used as reference trajectories in constructing the guidance algorithms for the maneuver problems mentioned above. An illustrative example of a spiral trajectory that terminates on a given elliptical parking orbit is discussed.

Journal Article↗
PubMed1998

The influence of changes in marital status on developmental trajectories of alcohol use in young adults.

OBJECTIVE: Multiple group latent curve analysis was used to assess the impact of changes in marital status on alcohol use trajectories in young adults and to test if these effects varied across ethnicity and gender. METHOD: Four years of data were obtained from a sample of young adults (N = 4,052; 54% male) drawn from the National Longitudinal Survey of Youth. Alcohol use and marital status were assessed once per year and covariates included age, gender, education and ethnicity. RESULTS: Latent curve models indicated that there was an overall nonlinear negative alcohol use trajectory across the four time points and that becoming married was reliably associated with an added down-turn to this trajectory. Multiple group models indicated that there was an interaction between ethnicity and marital status in the prediction of alcohol growth trajectories, but there was no interaction with gender. CONCLUSIONS: Becoming married for the first time exerted a unique effect on the overall developmental trajectory of alcohol use over time. This effect held for both ethnic groups but was reliably stronger for white compared to black respondents. This interaction may be attributable to lower levels of alcohol use reported by black respondents, or may be related to individual differences in reactivity to social influences by blacks relative to whites.

Adult↗
PubMed2005

What can one learn from two-state single-molecule trajectories?

A time trajectory of an observable that fluctuates between two values (say, on and off), stemming from some unknown multisubstate kinetic scheme, is the output of many single-molecule experiments. Here we show that when all successive waiting times along the trajectory are uncorrelated the on and the off waiting time probability density functions contain all the information. By relating the lack of correlation in the trajectory to the topology of kinetic schemes, we can immediately specify those kinetic schemes that are equally consistent with experiment, and cannot be differentiated by any sophisticated analyses of the trajectory. Correlated trajectories, however, contain additional information about the underlying kinetic scheme, and we consider the strategy that one should use to extract it.

Biophysical Phenomena↗
PubMed2006

Analysis of transient behavior in complex trajectories: application to secretory vesicle dynamics.

Analysis of trajectories of dynamical biological objects, such as breeding ants or cell organelles, is essential to reveal the interactions they develop with their environments. Many previous works used a global characterization based on parameters calculated for entire trajectories. In cases where transient behavior was detected, this usually concerned only a particular type, such as confinement or directed motion. However, these approaches are not appropriate in situations in which the tracked objects may display many different types of transient motion. We have developed a method to exhaustively analyze different kinds of transient behavior that the tracked objects may exhibit. The method discriminates stalled periods, constrained and directed motions from random dynamics by evaluating the diffusion coefficient, the mean-square displacement curvature, and the trajectory asymmetry along individual trajectories. To detect transient motions of various durations, these parameters are calculated along trajectories using a rolling analysis window whose width is variable. The method was applied to the study of secretory vesicle dynamics in the subplasmalemmal region of human carcinoid BON cells. Analysis of transitions between transient motion periods, combined with plausible assumptions about the origin of each motion type, leads to a model of dynamical subplasmalemmal organization.

Cell Line↗