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At least 811 records · Page 45Linked to original sources
PubMed2000

Steady-state visual evoked potentials and travelling waves.

OBJECTIVE: The amplitude and phase of the steady-state visual evoked potential (SSVEP) is sensitive to cognition and attention but the underlying mechanism is not well understood. This study examines stimulus evoked changes in the SSVEP phase topography and the putative role of travelling waves. METHODS: Eighteen subjects viewed a central-field checkerboard and full-field flicker stimulus temporally modulated at the peak alpha rhythm frequency. EEG was recorded from 10 midline scalp sites and the bipolar SSVEP obtained from differences between adjacent electrodes. RESULTS: The SSVEP phase comprised either progressive variations consistent with travelling waves or a phase reversal consistent with standing waves. The checkerboard pattern elicited travelling wave patterns in 14 subjects with estimated phase velocities ranging from 7 to 11 m/s after correcting for folded cortex. The flicker stimulus elicited phase reversals in 9 subjects, suggesting standing waves. Six subjects demonstrated a phase topography specific to the stimulus with travelling wave patterns associated with the checkerboard and standing wave patterns associated with the flicker. CONCLUSIONS: These differences suggest the emergence of travelling and standing waves under different spatial configurations of visual input to the cortex and that wave phenomena contribute to the spatiotemporal dynamics of the SSVEP.

Adult↗
PubMed1988

Health and health care among travellers.

Travellers, or Gypsies, constitute a minority group with its own culture and traditions for whom access to health care can pose problems. A study of Traveller women and children showed that the sites where they lived were often lacking in facilities and provided a poor environment in terms of cleanliness and safety. Perinatal mortality was above average, and was especially high on sites with inadequate facilities and among the more mobile families. Immunisation and preventive care of children were both inadequate, especially among the more mobile. There continues to be a need for more, and better, permanent sites for Travellers. Other responses include allowing Traveller families to carry their own medical records, providing mobile clinics for Gypsy sites, and appointing specialist health visitors to ensure that Travellers get the heath care to which they are entitled.

Child↗
PubMed2004

Simultaneous minimization of leaf travel distance and tongue-and-groove effect for segmental intensity-modulated radiation therapy.

This paper introduces a method to simultaneously minimize the leaf travel distance and the tongue-and-groove effect for IMRT leaf sequences to be delivered in segmental mode. The basic idea is to add a large enough number of openings through cutting or splitting existing openings for those leaf pairs with openings fewer than the number of segments so that all leaf pairs have the same number of openings. The cutting positions are optimally determined with a simulated annealing technique called adaptive simulated annealing. The optimization goal is set to minimize the weighted summation of the leaf travel distance and tongue-and-groove effect. Its performance was evaluated with 19 beams from three clinical cases; one brain, one head-and-neck and one prostate case. The results show that it can reduce the leaf travel distance and (or) tongue-and-groove effect; the reduction of the leaf travel distance reaches its maximum of about 50% when minimized alone; the reduction of the tongue-and-groove reaches its maximum of about 70% when minimized alone. The maximum reduction in the leaf travel distance translates to a 1 to 2 min reduction in treatment delivery time per fraction, depending on leaf speed. If the method is implemented clinically, it could result in significant savings in treatment delivery time, and also result in significant reduction in the wear-and-tear of MLC mechanics.

Algorithms↗
PubMed1999

Age-dependent atrophy and microgravity travel: what do they have in common?

Space travel and extending human lifespan are two of the many advances of the twentieth century. However, both of these scientific wonders exact a price for their gains; i.e. deleterious effects on normal physiological processes. For example, both old age and prolonged microgravity travel are associated with atrophy in heart, muscle, and bone. The underlying signal transduction pathways, the control mechanisms for the processes of proliferation, differentiation, and apoptosis, may prove to be similarly altered in both old age and microgravity travel. We suggest that the mechanical events involved in space travel provide a telescopic compression of lifespan changes in these tissues; if so, space travel provides an excellent opportunity to investigate how long-term degeneration occurs on Earth. With the aid of biochip technology for multi-factorial analysis, a platform can be generated to create therapeutic modalities to contain, retard, reduce, or prevent this tissue atrophy, either in space or on Earth.

Aging↗
PubMed1997

Where and when do we look as we approach and step over an obstacle in the travel path?

Spatio-temporal gaze behaviour patterns were analysed as normal participants wearing a mobile eye tracker approached and stepped over obstacles of varying height in the travel path. We examined the frequency and duration of three types of gaze fixation with respect to the participants' stepping patterns: obstacle fixation (ObsFix); travel fixation (TravFix) (when the gaze is stable and travelling at the speed of whole body) and fixation in the 4-6m region (Fix4-6). During the approach phase to the obstacle, participants fixated on the obstacle for approximately 20% of the travel time. Only Fix4-6 duration was modulated as a function of obstacle height by regulating the frequency and reflected the increased time needed for detection of the small low contrast obstacle in the travel path. Frequency of ObsFix increased significantly as a function of obstacle height and reflected visuo-motor transformation needed for limb elevation control. Participants did not fixate on the obstacle as they were stepping over, but did the planning in the steps before. TravFix duration and frequency was constant while Fix4-6 duration was higher in the step before and step over the obstacle reflecting visual search of the landing area for the lead limb following obstacle avoidance. These results clearly show that obstacle information provided by vision is used in a feed-forward rather than on-line control mode to regulate locomotion. Information about self-motion acquired from optic flow during TravFix can be used to control velocity of locomotion.

Fixation, Ocular↗
PubMed2001

Traveling waves in an optimal velocity model of freeway traffic.

Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137].

Journal Article↗
PubMed1995

Risk of Cholera Among Western and Japanese Travelers.

Background: There has been concern about an increased risk of cholera in travelers to Latin America since the spread of the pandemic to this part of the world. Additionally, before this study the continuous high incidence of imported cholera to Japan had so far not been analyzed. Methods: A retrospective analysis of cases notified in 1991 to national surveillance centers in industrialized countries and to the World Health Organization was carried out. Denominator data were obtained by the World Tourism Organization. Results: The reported rate of imported cholera in European and North American travelers visiting endemic areas remains in the range of 0,2 per 100,000, as was observed 10 years ago. This rate is, however, is manyfold higher in Japanese travelers, with a highest value of 13,0 per 100,000 reported in those returning from Indonesia, usually Bali. No secondary outbreaks were observed in those countries to which cholera was imported. Conclusions: It is assumed that the higher rates in Japanese travelers are mainly due to more intensive surveillance. On Bali and elsewhere, further studies are needed to determine both the role of V. cholerae as a cause of traveler's diarrhea in tourists and to re-evaluate the need for cholera vaccination at specific high-risk destinations.

Journal Article↗
PubMed1997

Efficacy of Lactobacillus GG as a Diarrheal Preventive in Travelers.

Traveler's diarrhea can be a debilitating problem for individuals on international trips. Retrospective and prospective studies have shown the incidence of traveler's diarrhea to range from 15-56%. 1,2A placebo-controlled, double-blinded study in Finnish travelers found that the probiotic Lactobacillus GG decreases the incidence of traveler's diarrhea.3 Lactobacillus GG, initially isolated from healthy humans, is remarkable in its ability to resist acid and bile degradation and to adhere to the intestinal mucosa.4 To assess the efficacy of Lactobacillus GG in preventing diarrhea in American tourists, a study was conducted at the Travel and Immunization Center of the Long Island Jewish Medical Center (LIJMC).

Journal Article↗
PubMed1997

Adult Travelers with HIV Infection.

The number of HIV-infected persons who travel to the developing world is increasing. Pleasure, business, other work, and illness or death in families brings these special travelers to all corners of the world.1,2 Health care providers should ask patients who are seeking advice whether they are HIV-infected or at risk so that these travelers can be adequately protected and prepared. In most instances international travel is feasible, but in some cases itineraries may be modified or additional recommendations may be given to make trips safer and more enjoyable. This paper reviews the health problems that persons with HIV infection may face during international travel, and their prevention.

Journal Article↗
PubMed1987

Effects of subsidising bus travel on the occurrence of road traffic casualties.

Between 1975 and 1 April 1986, public transport by bus in the metropolitan county of South Yorkshire, England, was increasingly subsidised. Trends in road traffic accident casualties between 1974 and 1983 in all the six provincial English metropolitan counties have been compared in order to examine the possible effect of this unique subsidy on the incidence of road traffic accident casualties. During that period the total number of casualties in South Yorkshire did not change significantly compared to the other metropolitan counties. However, the proportion of all casualties in South Yorkshire who were bus occupants did increase relative to other metropolitan counties, indicating either an increase in the amount of bus travel or a decrease in travel by other modes. There was a large increase in bus patronage in South Yorkshire relative to the other metropolitan counties, and the conclusion is that it is the transport policy in South Yorkshire which resulted in an actual increase in distances travelled by bus. Since bus is the safest form of road travel, it is concluded that the public transport subsidy in South Yorkshire has benefited the health of the local population by providing the social amenity of additional travel at the least additional health cost.

Accidents, Traffic↗
PubMed1999

Estimating time and travel costs incurred in clinic based screening: flexible sigmoidoscopy screening for colorectal cancer.

OBJECTIVES: To identify the characteristics of mode of travel to screening clinics; to estimate the time and travel costs incurred in attending; to investigate whether such costs are likely to bias screening compliance. SETTING: Twelve centres in the trial of flexible sigmoidoscopy screening for colorectal cancer, drawn from across Great Britain. METHOD: Analysis of 3525 questionnaires completed by screening subjects while attending clinics. Information supplied included sociodemographic characteristics, modes of travel, expenses, activities foregone owing to attendance, and details of companions. RESULTS: More than 80% of subjects arrived at the clinics by car, and about two thirds were accompanied. On average, the clinic visit involved a 14.4 mile (22.8 km) round trip, requiring 130 minutes. Mean travel costs amounted to 6.10 Pounds per subject. The mean gross direct non-medical and indirect cost per subject amounted to 16.90 Pounds, and the mean overall gross cost per attendance was 22.40 Pounds. Compared with the Great Britain population as a whole, non-manual classes were more strongly represented, and the self employed less strongly represented, among the attendees. CONCLUSIONS: In relation to direct medical costs, the time and travel costs of clinic based screening can be substantial, may influence the overall cost effectiveness of a screening programme, and may deter potential subjects from attending.

Aged↗
PubMed2004

Numerical analysis of the Eckhaus instability in travelling-wave convection in binary mixtures.

The Eckhaus stability boundaries of travelling periodic roll patterns arising in binary fluid convection is analysed using high-resolution numerical methods. We present results corresponding to three different values of the separation ratio used in experiments. Our results show that the subcritical branches of travelling waves bifurcating at the onset of convection suffer sideband instabilities that are restabilised further away in the branch. If this restabilisation is produced after the turning point of the travelling-wave branch, these waves do not become stable in a saddle node bifurcation as would have been the case in a smaller domain. In the regions of instability of the uniform travelling waves we expect to find either transitions between states of different wave number or modulated travelling waves arising in these bifurcations.

Journal Article↗
PubMed2002

Contrast material travel times in patients undergoing peripheral MR angiography.

PURPOSE: To retrospectively review time-resolved two-dimensional projection magnetic resonance (MR) angiographic data to characterize the passage of gadolinium-based contrast material down the leg arteries in patients undergoing peripheral MR angiography. MATERIALS AND METHODS: Data of 87 consecutive standardized peripheral MR angiographic examinations were retrospectively reviewed to determine contrast material arrival times to the common femoral artery (CFA), the popliteal and tibial arteries, and the corresponding veins. Travel times were correlated with clinical data obtained with retrospective chart review and predictive multiparameter models developed with stepwise linear regression. RESULTS: The mean travel time of contrast material to the CFA was 24 seconds +/- 6 (SD), with additional 5 seconds +/- 2 to reach the popliteal artery and 7 seconds +/- 4 to reach the ankle artery. The mean time window of arterial enhancement was 49 seconds +/- 10 in the pelvis, 45 seconds +/- 10 in the thigh, and 35 seconds +/- 14 in the calf. The travel time to CFA was correlated with aortic aneurysm (r = 0.41; P <.001), increasing age (r = 0.31; P =.003), male sex (r = 0.3; P =.005), myocardial infarction (r = 0.26; P =.016), and type 2 diabetes mellitus (r = -0.22; P =.041). Predicted travel time to CFA was 10.6 seconds, plus 0.143 seconds times patient age, plus 4.8 seconds if aneurysm was present, plus 3.8 seconds if male sex, plus 2.8 seconds if history of myocardial infarction. CONCLUSION: Contrast material injected intravenously traveled rapidly down the peripheral arteries at approximately 6 seconds per station, but a long arterial phase time window allowed bolus-chase peripheral MR angiography to function with slower table stepping. Patient-to-patient variations in contrast material kinetics may be anticipated on the basis of age, sex, and clinical parameters.

Adult↗
PubMed2006

P1 and traveling alpha waves: evidence for evoked oscillations.

The hypothesis is tested whether the P1 of the event-related potential (ERP) component behaves like an evoked, traveling alpha wave. This hypothesis is based on different kinds of evidence showing, e.g., that-after undergoing phase reorganization-frequencies in the broad alpha range become synchronized (aligned) in absolute phase and contribute significantly to the generation of the P1. We investigated data from a Stroop task in which subjects had to respond only to the color and ignore the meaning of the presented words. Analyzing topographical phase relationships expressed in terms of traveling speed (with respect to Pz as trailing site) revealed that a systematic posterior to anterior traveling pattern appeared only in the broad time window of the P1-N1 complex and in the extended alpha frequency range. The obtained findings are consistent with the oscillatory ERP model and suggest that the P1 component may be considered a manifestation of an evoked, traveling alpha wave. We assume that the P1 reflects a top-down process in a sense that traveling alpha waves control or "gate" the direction of information processing in the brain.

Adult↗
PubMed2003

Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light.

Jet lag is caused by a misalignment between circadian rhythms and local destination time. As humans typically take longer to re-entrain after a phase advance than a phase delay, eastward travel is often more difficult than westward travel. Previous strategies to reduce jet lag have focused on shaping the perceived light-dark cycle after arrival, in order to facilitate a phase shift in the appropriate direction. Here we tested treatments that travelers could use to phase advance their circadian rhythms prior to eastward flight. Thus, travelers would arrive with their circadian rhythms already partially re-entrained to local time. We determined how far the circadian rhythms phase advanced, and the associated side effects related to sleep and mood. Twenty-eight healthy young subjects participated in 1 of 3 different treatments, which all phase advanced each subject's habitual sleep schedule by 1 h/day for 3 days. The 3 treatments differed in morning light exposure for the 1st 3.5 h after waking on each of the 3 days: continuous bright light (> 3000 lux), intermittent bright light (> 3000 lux, 0.5 h on, 0.5 off, etc.), or ordinary dim indoor light (< 60 lux). A phase assessment in dim light (< 10 lux) was conducted before and after the treatments to determine the endogenous salivary dim light melatonin onset (DLMO). The mean DLMO phase advances in the dim, intermittent, and continuous light groups were 0.6, 1.5, and 2.1 h, respectively. The intermittent and continuous light groups advanced significantly more than the dim light group (p < 0.01) but were not significantly different from each other. The side effects as assessed with actigraphy and logs were small. A 2-h phase advance may seem small compared to a 6- to 9-h time zone change, as occurs with eastward travel from the USA to Europe. However, a small phase advance will not only reduce the degree of re-entrainment required after arrival, but may also increase postflight exposure to phase-advancing light relative to phase-delaying light, thereby reducing the risk of antidromic re-entrainment. More days of preflight treatment could be used to produce even larger phase advances and potentially eliminate jet lag.

Adult↗
PubMed1995

The phenomenon of travelling waves: a review.

As early as 1934 evidence appeared in animals that waves of activity do not always remain stationary but can actually spread over the whole cortex. In the next year some of the earliest studies on the EEG of man showed phase changes of alpha activity that could account for the TW, which later was described when apparatus was built to better view it, especially in the 1950s. The TW has been described mainly as alpha activity that appears to travel both in abnormal and also normal conditions, including the resting state. The phenomenon seems to be enhanced with either external stimuli or endogenous emotional states, which increase phase changes on different brain areas. The travel has been described in all directions from the frontal to the occipital pole, and early work suggests that the posterior-anterior direction may be more often found in abnormal mental states. The speed of travelling over the scalp has varied usually from 1-20 m/sec, but generally has been reported around 5 m/sec. Most investigators have reported that the positive phase is the one which most clearly travels. In exploring the phenomenon of the travelling wave, it is clear that maximal positivity and negativity of the alpha is not always on the occipital regions, as many clinical studies would imply; instead, the fronto-central areas in particular are often the focus of maximal alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Are they really refusing to travel? A qualitative study of prehospital records.

BACKGROUND: Refusal by the patient to travel after calling an emergency ambulance may lead to a preventable waste of scarce resources if it can be shown that an alternative more appropriate response could be employed. A greater understanding is required of the reasons behind 'refusal to travel' (RTT) in order to find appropriate solutions to address this issue. We sought to investigate the reasons why patients refuse to travel following emergency call-out in a rural county. METHODS: Written records made by ambulance crews for patients (n = 397) who were not transported to hospital following an emergency call-out during October 2004 were retrospectively analysed. RESULTS: Twelve main themes emerged for RTT which included non injury or minor injury, falls and recovery after treatment on scene; other themes included alternative supervision, follow-up and treatment arrangements or patients arranging their own transport. Importantly, only 8% of the sample was recorded by ambulance crews as truly refusing to travel against advice. CONCLUSION: A system that facilitates standardised recording of RTT information including social reasons for non-transportation needs to be designed. 'Refused to travel' disclaimers need to reflect instances when crew and patient are satisfied that not going to hospital is the right outcome. These recommendations should be considered within the context of the plans for widening the role of ambulance services.

Journal Article↗
PubMed2006

Active travel to school and cardiovascular fitness in Danish children and adolescents.

PURPOSE: Active travel to school provides an opportunity for daily physical activity. Previous studies have shown that walking and cycling to school are associated with higher physical activity levels. The purpose of this study was to investigate whether the way that children and adolescents travel to school is associated with level of cardiovascular fitness. METHODS: Participants were recruited via a proportional, two-stage cluster sample of schools (N = 25) in the region of Odense, Denmark as part of the European Youth Heart Study (EYHS). Nine hundred nineteen participants (529 children, age 9.7 +/- 0.5 yr; 390 adolescents, age 15.5 +/- 0.4 yr) completed a maximal cycle ergometer test to assess cardiorespiratory fitness (Wmax x kg(-1)). Mode of travel to school was investigated by questionnaire. Physical activity was measured in 531 participants using an accelerometer. Regression analyses with robust standard errors and adjustment for confounders (gender, age, body composition (skinfolds), pubertal status, and physical activity) and the cluster sampling procedure were used to compare fitness levels for different travel modes. Multinomial logistic regression was applied to assess the odds for belonging to quartiles of fitness. RESULTS: Children and adolescents who cycled to school were significantly more fit than those who walked or traveled by motorized transport and were nearly five times as likely (OR 4.8; 95% CI 2.8-8.4) to be in the top quartile of fitness. CONCLUSION: Cycling to school may contribute to higher cardiovascular fitness in young people.

Adolescent↗