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PubMed2005

Trajectories of Marijuana Use During the Transition to Adulthood: The Big Picture Based on National Panel Data.

The purposes of this study were to: a) identify trajectory groups of frequent marijuana use during emerging adulthood, b) distinguish among trajectory groups according to demographic and lifestyle characteristics, and c) examine how the trajectory groups relate to behavioral, attitudinal, and social-emotional correlates over time. National panel data from the Monitoring the Future study were used: 18 cohorts of high school seniors (classes of 1977-94) were followed biennially through age 24. Frequent marijuana use was defined as 3+ occasions of use in past month and/or 20 to 40+ occasions in past year. Based on four waves of complete longitudinal data (N=19,952), six frequent marijuana use trajectory groups were identified: chronic, decreased, increased, fling, rare, and abstain. Categorical analyses revealed trajectory group differences in demographic and lifestyle characteristics at senior year and age 24. The trajectory groups varied significantly in longitudinal patterns of other substance use, problem behaviors, and well-being.

Journal Article↗

PubMed2006

Health related quality of life trajectories and predictors following coronary artery bypass surgery.

BACKGROUND: Many studies have demonstrated that health related quality of life (HRQoL) improves, on average, after coronary artery bypass graft surgery (CABGS). However, this average improvement may not be realized for all patients, and it is possible that there are two or more distinctive groups with different, possibly non-linear, trajectories of change over time. Furthermore, little is known about the predictors that are associated with these possible HRQoL trajectories after CABGS. METHODS: 182 patients listed for elective CABGS at The Royal Melbourne Hospital completed a postal battery of questionnaires which included the Short-Form-36 (SF-36), Profile of Mood States (POMS) and the Everyday Functioning Questionnaire (EFQ). These data were collected on average a month before surgery, and at two months and six months after surgery. Socio-demographic and medical characteristics prior to surgery, as well as surgical and post-surgical complications and symptoms were also assessed. Growth curve and growth mixture modelling were used to identify trajectories of HRQoL. RESULTS: For both the physical component summary scale (PCS) and the mental component summary scale (MCS) of the SF-36, two groups of patients with distinct trajectories of HRQoL following surgery could be identified (improvers and non-improvers). A series of logistic regression analyses identified different predictors of group membership for PCS and MCS trajectories. For the PCS the most significant predictors of non-improver membership were lower scores on POMS vigor-activity and higher New York Heart Association dyspnoea class; for the MCS the most significant predictors of non-improver membership were higher scores on POMS depression-dejection and manual occupation. CONCLUSION: It is incorrect to assume that HRQoL will improve in a linear fashion for all patients following CABGS. Nor was there support for a single response trajectory. It is important to identify characteristics of each patient, and those post-operative symptoms that could be possible targets for intervention to improve HRQoL outcomes.

Activities of Daily Living↗

PubMed2005

ExoMars alternative escape trajectories with Soyuz/Fregat.

The objectives of ExoMars are to inject an orbiter around Mars and to land a rover on the surface to look for possible traces of life. During the first stages of the feasibility analysis, the mass margin of the orbiter was very small for a direct transfer in the Soyuz/Fregat scenario. An analysis of the combined use of lunar swing-bys and the Sun gravity gradient is performed with WESBOT in order to obtain alternative trajectories for injecting higher mass into Mars transfer. WESBOT is a GMV tool to find WSB transfers to the Moon and to design escape trajectories by performing several swing-bys with the Moon and the Earth. The weak stability boundary has been successfully used for lunar transfers (Hiten, SMART-1). For escape trajectories from the Earth, the potential mass gains depend on the escape direction and the departure date to make a series of gravity assists with the help of the Sun gravity gradient to save DeltaV. Several strategies are studied depending on the number and order of swing-bys. The departing conditions (date and orbit) are optimized but the arrival date to Mars is maintained because of mission requirements. For each type of strategy, a systematic search of initial guess trajectories is performed. The initial guess trajectory is made up of patched conics arcs and multiple shooting arcs when necessary. The optimal trajectories for the various scenarios are presented and show different morphologies. An analysis in terms of applicability to the ExoMars mission is included.

Journal Article↗

PubMed2005

Drinking trajectories from adolescence to the mid-forties among alcohol dependent males.

OBJECTIVE: Identifying differing developmental trajectories of alcohol behavior is fundamental in building theories of alcoholism etiology and course. The purpose of this study was to identify differences in developmental pathways of alcoholism from onset of drinking into middle adulthood. METHOD: Alcohol-related behaviors and psychiatric status were assessed in 330 men from the Vietnam Era Twin Registry having a lifetime diagnosis of alcohol dependence (AD). Using a modified version of Skinner's Lifetime Drinking History, distinct drinking phases were identified that differed in terms of quantity, frequency and context of drinking. Person-year data were created to indicate whether AD criteria were or were not met for each year between drinking onset and age 41. RESULTS: Using Latent Growth Mixture Modeling, a four-class model was identified: Severe Chronic Alcoholics; Severe Non-Chronic Alcoholics (SNCA); Late Onset Alcoholics; and Young Adult Alcoholics. Counterparts for three trajectories could be found in the larger alcoholism literature, whereas the fourth type (SNCA) has not been described, notwithstanding its seeming importance and prevalence. CONCLUSIONS: Present findings support the existence of different alcoholism trajectories and provide a more complete understanding of the variability of alcohol dependence over time. Findings build on the larger alcoholism literature identifying alcoholic subgroups and provide important information regarding alcoholism trajectories and associated features. Future studies are needed with regard to better understanding of the psychosocial influences related to the different alcoholism trajectories, as well as characterizing the different trajectories as individuals transition into older age.

Adolescent↗

PubMedDate not supplied

[5 year trajectories for dependence to psychotropics in a cohort of consumers].

UNLABELLED: The terms regular, excessive or intermittent consumption do not characterize type of consumption, the profile of the drug user, or the threshold of drug dependence. OBJECTIVE: To characterize trajectories of consumption over a 5-year period and identify sociodemographic and medical characteristics, and modes of consumption associated with the types of trajectories. METHODS: 286 drug users from the cohort SUVIMAX agreed to take part in our study. SUVIMAX is a controlled randomized primary prevention trial using nutritional doses of a combination of anti-oxidant vitamins and minerals to reduce cardiovascular diseases and cancers. The data came from the questionnaire that examined each psychotropic drug taken between 1994 and 1998, rates of consumption and the beliefs associated with the drug users' modes of consumption and their dependence profiles. RESULTS: A continuous trajectory is defined as uninterrupted consumption during the 5-year follow-up, and an occasional trajectory as an interruption of consumption for at least 1 month. Only 30% of the drug users with a continuous trajectory considered they could do without psychotropic agents. CONCLUSION: The consumption of psychotropic drugs is not in itself harmful, but the duration and regularity of drug intake registered over a 5-year period indicate the drug dependence profile. The trajectory is a relevant and operational tool for better adapting therapeutic follow-up.

Adult↗

PubMed2003

Trajectories of posttraumatic stress disorder following myocardial infarction: a prospective study.

BACKGROUND: This study examines the trajectories of posttraumatic stress disorder (PTSD) following myocardial infarction (MI). More specifically, it has 2 aims: (1) to examine whether the trajectory of PTSD is predicted by level of threat and the nature of initial reactions and (2) to examine the associations between the trajectory of PTSD and anxiety, somatization, health-related quality of life, and hospitalization 7 months following MI. METHOD: 116 MI patients were examined twice. At time 1, within a week of the patient's MI, acute stress disorder (ASD) was assessed and medical measures were obtained from patients' hospital records. At time 2, 7 months later, PTSD, anxiety, physical residuals, and health-related quality of life were assessed. Data were gathered in 1999. RESULTS: Six percent of the respondents had both ASD and PTSD, 10% did not have ASD but did have PTSD, and 12% had ASD but not PTSD. The trajectory of PTSD was associated with severity of anxiety, somatic complaints, and health-related quality of life. In addition, while the severity of MI did not predict the trajectory of PTSD, the perceived severity did. Patients without PTSD but with prior ASD did not differ in their initial reactions from those without ASD. CONCLUSION: These findings provide support for the considerable variability in the trajectory of the development of PTSD and suggest that although ASD is associated with subsequent PTSD, the predictive role of initial reactions is limited.

Aged↗

PubMed1991

[Isometric forces generated by the human wrist: force trajectories with and without a visual target].

The force trajectories of isometric wrist flexor efforts and corresponding EMG activity of forearm muscles were studied in healthy subjects. A target effort of 50 N was developed after the sound signal: the target level and force trajectory were displayed on the TV indicator. Force trajectories under conditions of visual control, kinesthetic control (without a visual target) and with random alternation of these regimens were compared. Wrist flexor EMG latencies were approximately equal under visual and kinesthetic control and noticeably longer when these conditions were alternated randomly. Relative error of the target effort reproduction and duration of late components of force trajectories were higher in absence of the visual target. When visual and kinesthetic regimes were alternated randomly the delay between EMG onset and force trajectory initiation increased; its values correlated positively with the duration of the first force derivative increase. Formation of different strategies for force trajectory correction under different experimental conditions is discussed.

Adult↗

PubMedDate not supplied

[A wave nature of the central regulation of the trajectory of the articular angle in man].

It is supposed that muscles of a single joint are controlled by a wave propagation of excitation along a central line-ordered neuronal ensemble. The number of steady active output ensemble neurons increases with wave-front displacement and the neurons discretely contribute to the motor command that is defined in terms of shifts of the so-called invariant muscle force-length characteristics. The terminal position of the wave front is responsible for the final angular limb position, whereas the wave velocity responsible for the peak movement speed. To verify the wave model, human time-angle trajectories of rapid arm movements to different positions in the horizontal plane were analysed. The trajectories fall into groups having the following properties: 1) The initial profiles of the trajectories that belong to one group are identical; 2) the duration of the coincidence of any two grouped trajectories increases with their extent; 3) summation of two or more grouped trajectories with a certain time delay between them again gives a trajectory which belongs to the same group. The data obtained are in good agreement with the wave model.

Biomechanical Phenomena↗

PubMed2003

Centering the projection reconstruction trajectory: reducing gradient delay errors.

The projection reconstruction (PR) trajectory was investigated for the effect of gradient timing delays between the actual and requested start time of each physical gradient. Radial trajectories constructed with delayed gradients miss the center of k-space in an angularly dependent manner, causing effective echo times to vary with projection angle. The gradient timing delays were measured in phantoms, revealing delays on the x, y, and z gradients which differed by as much as 5 micro sec. Using this one-time calibration measurement, the trajectories were corrected for gradient delays by addition of compensatory gradient areas to the prephasers of the logical x and y readout gradients. Effective projection-to-projection echo time variability was reduced to less than 1 micro sec for all imaging orientations. Using corrected trajectories, artifacts were reduced in phantom images and in volunteer studies. This correction should potentiate greater clinical use of the PR trajectory.

Algorithms↗

PubMed2003

Importance of k-space trajectory in echo-planar myocardial tagging at rest and during dobutamine stress.

Hybrid fast gradient echo/echo-planar imaging (FGRE-EPI) can be used to increase temporal resolution, enhance tag contrast, and/or decrease scan time for breathhold myocardial tagging. However, off-resonance effects and motion can lead to local phase discontinuities in FGRE-EPI raw data when a conventional interleaved bottom-up k-space trajectory is used. These discontinuities can be particularly problematic for myocardial tagging, where the image energy is not only concentrated near the k-space origin, but is also concentrated in multiple spectral peaks centered throughout k-space. In this study, tag distortion artifacts in FGRE-EPI tagging due to off-resonance and velocity-induced phase discontinuities were characterized at rest and dobutamine stress, and the flyback and gradient moment smoothing (GMS) methods were shown to reduce these artifacts. For the specific parameters used in this study, flyback and GMS resulted in improved image quality at rest and stress, increased myocardium-tag contrast-to-noise ratio (11.4 +/- 2.1 vs. 10.0 +/- 2.9, P < 0.01 at rest; 11.1 +/- 1.8 vs. 8.1 +/- 2.4, P < 0.01 at stress), and reduced full width at half maximum of the tag profile (3.6 vs. 3.8 pixels at rest; 4.0 vs. 5.1 pixels at stress) compared to the conventional trajectory. A limitation of the improved trajectory is a parameter-dependent decrease in data acquisition efficiency. For the specific imaging protocol used, the repetition time of the improved trajectory increased by 36% compared to the conventional trajectory.

Artifacts↗

PubMed2003

Fast 3D imaging using variable-density spiral trajectories with applications to limb perfusion.

Variable-density k-space sampling using a stack-of-spirals trajectory is proposed for ultra fast 3D imaging. Since most of the energy of an image is concentrated near the k-space origin, a variable-density k-space sampling method can be used to reduce the sampling density in the outer portion of k-space. This significantly reduces scan time while introducing only minor aliasing artifacts from the low-energy, high-spatial-frequency components. A stack-of-spirals trajectory allows control over the density variations in both the k(x)-k(y) plane and the k(z) direction while fast k-space coverage is provided by spiral trajectories in the k(x)-k(y) plane. A variable-density stack-of-spirals trajectory consists of variable-density spirals in each k(x)-k(y) plane that are located in varying density in the k(z) direction. Phantom experiments demonstrate that reasonable image quality is preserved with approximately half the scan time. This technique was then applied to first-pass perfusion imaging of the lower extremities which demands very rapid volume coverage. Using a variable-density stack-of-spirals trajectory, 3D images were acquired at a temporal resolution of 2.8 sec over a large volume with a 2.5 x 2.5 x 8 mm(3) spatial resolution. These images were used to resolve the time-course of muscle intensity following contrast injection.

Contrast Media↗

PubMed1997

MRI using piecewise-linear spiral trajectory.

A new generation of high power gradient systems which allow much faster MR imaging as well as shorter echo times has recently become available. Some of these high-speed gradient systems impose limits on the percentage of time during which the gradient can change in amplitude (slewing duty cycle). While this limitation may be immaterial to many 2DFT and echo planar imaging methods, a traditional circular spiral trajectory is difficult to use on these systems because its gradient waveforms change during the entire course of the trajectory so that the slewing duty cycle during the readout period is 100%. We describe a piecewise-linear spiral trajectory which is composed of linear segments and rounded corners. This trajectory reduces the slewing duty cycle while maintaining the desirable imaging properties of circular spirals including interleaving by simple gradient rotation. For one representative example, the slewing duty cycle is reduced to 46%. A conventional gridding method was used for image reconstruction, but a new numerical algorithm to calculate the density compensation factor was required. Use of piecewise-linear spiral trajectories reduces the impact imposed by limited gradient slewing duty cycle.

Image Processing, Computer-Assisted↗

PubMed1997

A method to measure arbitrary k-space trajectories for rapid MR imaging.

A method to measure arbitrary k-space trajectories was developed to compensate for nonideal gradient performance during rapid magnetic resonance (MR) imaging with actively or nonactively shielded gradients at a magnetic field strength of 4.1 T. Accurate MR image reconstruction requires knowledge of the k-trajectory produced by the gradient waveforms during k-space sampling. Even with shielded gradients, residual eddy currents and imperfections in gradient amplifier performance can cause the true k-space trajectory to deviate from the ideal trajectory. The k-space determination was used for spiral gradient-echo imaging fo the human brain. While individual calibrations are needed for new pulse sequences, the method of k-space determination can be used for any sequence of preparation pulses and readout gradient waveforms and should prove useful for other trajectories, including the rastered lines of echo-planar imaging.

Artifacts↗

PubMed2006

Design and analysis of a practical 3D cones trajectory.

The 3D Cones k-space trajectory has many desirable properties for rapid and ultra-short echo time magnetic resonance imaging. An algorithm is presented that generates the 3D Cones gradient waveforms given a desired field of view and resolution. The algorithm enables a favorable trade-off between increases in readout time and decreases in the total number of required readouts. The resulting trajectory is very signal-to-noise ratio (SNR) efficient and has excellent aliasing properties. A rapid high-resolution ultra-short echo time imaging sequence is used to compare the 3D Cones trajectory to 3D projection reconstruction (3DPR) sampling schemes. For equivalent scan times, the 3D Cones trajectory has better SNR performance and fewer aliasing artifacts as compared to the 3DPR trajectory.

Algorithms↗

PubMed1996

Predictive smooth pursuit of complex two-dimensional trajectories in monkey: component interactions.

Smooth pursuit eye movements were studied in monkeys tracking target spots that moved two-dimensionally. Complex target trajectories were created by applying either two or three sinusoids to horizontal and vertical axes in various combinations. The chance of observing predictable performance was increased by repeated training on each trajectory. Data analyses were based upon repeated presentations of each trajectory within sessions and on successive days. We wished to determine how accurately monkeys could pursue targets moving along these trajectories and to observe interactions among frequency components. At intermediate frequencies, tracking performance was smooth and consistent during repeated presentations with saccadic corrections that were well integrated with smooth pursuit. The mean gain for eight different sum-of-sines trajectories was 0.83 and the mean magnitude (absolute value) of the phase error was 6 degrees. In light of the long delays that have been associated with the processing of visual information, these values indicate that the monkeys were pursuing predictively. Five factors influenced predictive pursuit performance: (1) there was a decline in performance with increasing frequency; (2) horizontal pursuit was better than vertical pursuit; (3) high-frequency components were tracked with higher gains and phase lags, while lower-frequency components were tracked with lower gains and phase leads; (4) the gain of sinusoidal pursuit was always reduced when a second sinusoid was applied to the same axis or, to a lessor extent, when a second sinusoid of higher frequency was applied to the orthogonal axis; (5) the phase of sinusoidal pursuit shifted from a phase lag to a phase lead when combined with a second sinusoid of higher frequency, but was not affected by the addition of a lower-frequency sinusoid. Findings 1 and 2 confirm, in monkeys, results reported for humans, and 3 extends to monkeys and to two-dimensional pursuit results based upon human subjects. All of these findings demonstrate that complex predictive tracking is controlled by a nonlinear and nonhomogeneous system that uses predictive strategies in concert with feedback control to generate good pursuit.

Animals↗

PubMed1995

Adaptive plasticity in the control of locomotor trajectory.

Eight human subjects were exposed to 2 h of walking on the perimeter of a horizontally rotating disc with the body remaining still in space. After adaptation to this experience subjects were blindfolded and asked to walk straight ahead on firm ground. When doing so all subjects generated curved walking trajectories of radii ranging from 65 to 200 inches and angular velocities from 7 to 20 deg/s. Subsequent trials over the next half hour revealed retained, but decreasing, trajectory curvature. Angular velocities associated with these trajectories were well above vestibular sensory threshold, yet all subjects consistently perceived themselves as walking straight ahead. The blindfolded subjects were also asked to propel themselves in a straight line in a wheel chair. Post-adaptation wheel chair trajectories showed no change from those before adaptation. Hence we infer that it was the relation between somatosensory/motor elements of gait and the perception of trunk rotation that had been remodelled during walking on the turning disc. This novel form of adaptive plasticity presumably serves to maintain optimal values of central neural parameters that control the trajectory of locomotion. The findings may have significant implications for the diagnosis and rehabilitation of locomotor and vestibular disorders.

Adaptation, Physiological↗

PubMed1987

Trajectory control in targeted force impulses. I. Role of opposing muscles.

The functional role of opposing muscles in the production of isometric force trajectories was studied in six adult subjects producing impulses and steps of elbow flexor force, with different rise times and amplitudes. Rapidly rising forces were invariably associated with an alternating pattern of EMG activity in agonist and antagonist muscles: an agonist burst (AG1) initiated the development of force in the desired direction while a reciprocal burst in the antagonist (ANT-R) led to the deceleration of the force trajectory prior to the peak force. The temporal pattern of agonist and antagonist activation was dependent on force rise time. Force trajectories with long rise times (greater than 200 ms) were entirely controlled by the agonist, and EMG activity closely followed the contours of the rising force trajectory. For rise times of about 120 to 200 ms, agonist activation formed a discrete EMG burst, and force continued to rise during the subsequent silent period. For brief force rise times (less than 120 ms), reciprocal activation of the antagonist muscle occurred at about the time of the peak dF/dt. The integrated magnitude of AG1 was dependent on peak force but was independent of force rise time. AG1 duration varied directly with both peak force and force rise time. The integrated value of ANT-R varied as an inverse function of force rise time and was minimally influenced by peak force. ANT-R was present with the same magnitude and timing in both force impulses and steps when rise times were equal; therefore it did not serve to return force to baseline. Rather it served to truncate the rising force when very brief rise times were required, thus compensating for the low-pass filter properties of the agonist muscle. Subjects were able to voluntarily suppress ANT-R in rapidly accelerated force trajectories, indicating that the linkage between the commands controlling agonist and antagonist is not obligatory; however AG1 was then prolonged. Our findings emphasize that neuronal commands to opposing muscles acting at a joint must be adapted to constraints imposed by the properties of the neuromuscular plant.

Adult↗

PubMed1987

Trajectory control in targeted force impulses. II. Pulse height control.

The present report examines the control strategy adopted by subjects to modulate the amplitude of transient force responses aimed to a target. Previous studies (Freund and Budingen 1978; Ghez and Vicario 1978) suggest that subjects modulate the rate of rise of force while maintaining force rise time at a near-constant value, independent of peak force. Such studies, however, have examined only the most rapid responses where force rise time could have been at a physiological limit. We now examine whether this control policy is dependent on an instruction to produce the fastest possible trajectories, or whether it is freely selected by subjects to maximize accuracy when rise time is unconstrained. We compared responses made by six subjects, under two task conditions: 1. Fast, "make the force impulse as brief as possible"; and 2. Accurate, "be as accurate as possible without regard to rise time". Subjects were trained to produce monotonic flexion force impulses at the elbow to match the amplitudes of visually presented target shifts. Targets of three different were presented in randomized order. Responses made under the Accurate condition were less variable at each target amplitude than those under the Fast condition. Under both conditions, the initial peaks of the first and second time derivatives of force, early measures of trajectory dynamics, were strongly predictive of the peak force achieved and were correlated with the required force (target amplitude). Therefore, response trajectories must have been largely preprogrammed, and, further, the degree to which the initial peak d2F/dt2 predicts the peak force achieved represents a measure of the contribution of a preplanned motor program to trajectory formation. Subjects showed two systematic differences in trajectories between conditions. First, in all subjects force rise time was greater in the Accurate condition than in the Fast condition. Second, while in the Fast condition there was a modest dependence of force rise time on peak force, in the Accurate condition this dependence disappeared. Thus, when subjects were attempting to be as accurate as possible, they more consistently regulated force rise time around a constant value. This pulse height control policy allows responses of different amplitudes to be produced by proportional scaling of a stereotyped waveform. We conclude that a pulse height control policy with regulation of force rise time is a strategy adopted by subjects to simplify accurate control of response amplitude.

Adult↗