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PubMed2003

Spatial separation of the traveling and evanescent parts of dipole radiation.

Electric dipole radiation consists of traveling and evanescent plane waves. When radiation is detected in the far field, only the traveling waves will contribute to the intensity distribution, as the evanescent waves decay exponentially. We propose a method to spatially separate the traveling and evanescent waves before detection. It is shown that when the radiation passes through an interface, evanescent waves can be converted into traveling waves and can subsequently be observed in the far field. Let the radiation be observed under angle theta(t) with the normal. Then there exists an angle theta(ac) such that for 0 < or = theta(t) < theta(ac) all intensity originates in traveling waves, whereas for theta(ac) < theta(t) < pi/2 only evanescent waves contribute. It is shown that with this technique and under the appropriate conditions almost all far-field power can be provided by evanescent waves.

Journal Article↗
PubMed1975

The minimization of travel effort as a delineating influence for urban hospital service areas.

Using a study population of 16,080 live births occurring to residents of Baltimore City in 16 hospitals in 1969, this research measured the existing flow of these patients against the flow "expected" in an optimal accessibility model (where each birth would occur at the hospital with the shortest travel time to the residence of the mother). The results of the study indicate that there is a general pattern of distance minimizing in travel for hospital admission with 50 per cent of the births occurring to women who travelled to one of the four closest hospitals of the 16 alternatives. However, a surprisingly large proportion (20 per cent) of the study population exhibited extreme spatial inefficiency by traveling to those four hospitals of the 16 alternatives which were farthest from their residence. A stepwise regression analysis identified five variables which best explained variation in the spatial efficiency of these urban obstetrical patients: low hospital occupancy, high total hospital admissions, average extra travel time potential (a measure of the difficulty of "spatial choices" facing patients depending upon the location of their residence with respect to the alternative hospitals), race, and the importance of the hospital's obstetrical service (a ratio of births to total admissions).

Birth Rate↗
PubMed1994

Measurement of cochlear basilar membrane traveling wave velocity by derived ABR.

Auditory brainstem response (ABR) can be used to measure the basilar membrane traveling wave velocity (TWV). Traveling wave velocity was calculated from the latency difference between wave V of different derived ABR and the cochlear location distance between the appropriate derived band center frequency. The latency of wave V of derived ABR produced by 6 noise-masked ABR using high pass filtered noise and the location of the corresponding cochlear partition (distance from the stapes foot-plate) were measured, and five traveling wave velocities were estimated based on this parameter. Ten subjects with normal hearing, 7 patients with Meniere's disease, and 8 patients with sensorineural hearing loss were used in this study. The traveling wave velocity in the sensorineural hearing loss group was within normal limits at all frequencies, whereas the traveling wave velocity at 8 kHz in the Meniere group greatly exceeded that of the normal and sensorineural hearing loss group.

Acoustic Stimulation↗
PubMed1991

Apparent travelling wave velocity changes in cases of endolymphatic hydrops.

This study attempted to develop a test which would be specific for endolymphatic hydrops. It is based upon the hypothesis that increased pressure in the scala media will alter the stiffness of the basilar membrane and hence increase the speed of the travelling wave. Auditory brainstem-derived responses were used to measure the basilar membrane travelling wave velocity in normals and to take the equivalent measures in Meniere's patients. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group showed that the travelling wave velocities were within normal limits at all frequencies tested, except 5.7 kHz where the travelling wave velocity greatly exceeded that of the normal group. A theoretical possibility that these findings may be the result of damaged and broadened VIIIth nerve tuning curves is discussed but travelling wave measures and psychophysical tuning curve measurements on the Meniere's group, normals and noise-induced hearing loss (NIHL) cases showed that this was not a significant factor. The data indicate that this technique can detect endolymphatic hydrops and a short duration clinical procedure has been devised.

Adolescent↗
PubMed2000

Oxygen and air travel.

In summary, the environmental stresses of commercial air travel and the possibility of altitude-induced adverse events during flight suggest the importance of evaluating prospective air travelers with chronic pulmonary disease for in-flight supplemental oxygen needs. Although gaps exist in current understanding of the risks of air travel and optimal ways of predicting the need for in-flight oxygen, respiratory clinicians can use available techniques to assess travelers' in-flight oxygen needs in many instances. Significant current variation among commercial air carriers in policies regarding providing oxygen, related equipment, and the cost of in-flight oxygen poses challenges to the prospective air traveler and warrants attention.

Aircraft↗
PubMed2004

An ultrasonic motor driven by the phase-velocity difference between two traveling waves.

This paper presents a new ultrasonic motor in which the rotor rotation speed is locked by the phase-velocity difference between the two traveling waves propagating on the stator and the rotor. First, the unique construction to excite two traveling waves both in the stator and the rotor is described. Then, the operation principle of the present motor is revealed by our careful experiments. Dynamics of the two traveling waves are measured by an in-plane laser Doppler vibrometer under various conditions, as well as the motor performances. Our experiments show that the rotation speed of the motor is equal to the phase-velocity difference between the two traveling waves on the contact surfaces of rotor and stator. It is confirmed that the rotor rotates so as to cancel the phase-velocity difference between the traveling vibrations along the circumferences of the rotor and stator. If the load does not exceed the maximum torque that is determined by the vibration amplitude, the rotation speed is subject only to the phase-velocity difference.

Journal Article↗
PubMed1992

On-lap travel: still a problem in motor vehicles.

National observational studies indicate that infants who are not restrained in child safety seats (CSSs) in motor vehicles are usually riding on the lap of another occupant. This study was undertaken to determine the conditions under which children travel on-lap. The extent to which injuries would be reduced if these children were restrained in CSSs was also examined. Data were taken from a multihospital monitoring system for pediatric occupant injuries and from the coroner's office in a single urban county (1980 through 1989). One hundred ten children younger than 1 year of age evaluated in the monitored emergency departments after involvement in a crash had been traveling on-lap. On-lap travel did not appear to result from overcrowding. Eighty-eight percent were riding in vehicles with five or fewer occupants; 83% were in the front seat; 58% sustained injury; 22% of those evaluated were hospitalized; and 15% sustained intracranial injury. A 30% reduction in overall injury, a 75% reduction in hospitalization, and a 69% reduction in intracranial injury were projected for those riding on-lap, had they been restrained in CSSs. Applying national rates of on-lap travel (16.8%) to National Highway Traffic Safety Administration estimates of the number of infants injured in crashes each year indicates that approximately 2218 of these children would be on the lap of another passenger. Substantial savings in terms of injury and associated costs can be realized if children traveling on-lap were in CSSs. Parent education as well as strict enforcement of CSS laws must be implemented.(ABSTRACT TRUNCATED AT 250 WORDS)

Accidents, Traffic↗
PubMed1997

Risky behavior in women with history of casual travel sex.

OBJECTIVES: To define epidemiologic and psychosocial characteristics in women with a history of casual travel sex abroad. STUDY DESIGN: The participants consisted of 996 women attending for contraceptive advice, of whom 276 admitted that they had experience of casual travel sex. The remaining women served as a comparison group. In structured interviews, questions were asked about educational level, partnerships, reproductive history, contraceptive and drug use, smoking, and psychosocial factors such as wariness, success, and attractiveness. RESULTS: The women with experience of casual travel sex were more often single, had more often experienced broken relationships, were more often smokers, and used alcohol or cannabis at a higher-frequency. Their educational level was higher and a history of induced abortions was more common. CONCLUSIONS: The results of this study indicate that women with experience of casual travel sex not only take sexual risks, but take other risks that might impose danger to their health.

Adult↗
PubMed2006

African tick bite fever: a not-so-uncommon illness in international travelers.

BACKGROUND: African tick bite fever is a rickettsial illness that has recently emerged as a significant disease among international travelers. The vector is the Amblyomma tick, which is endemic to sub-Saharan Africa and parts of the eastern Caribbean. OBSERVATIONS: We describe a middle-aged woman who returned from a mission trip to Zimbabwe with an influenzalike illness and inoculation eschar; she also had a history of travel to a game farm. Biopsy revealed a histopathologic pattern consistent with an infectious pathogenesis. Immunohistochemical staining confirmed the presence of rickettsial organisms. In light of the patient's history, the clinical constellation of signs and symptoms, and the results of ancillary laboratory testing, a diagnosis of African tick bite fever was made. The patient was treated with doxycycline hydrochloride and had an uncomplicated course. CONCLUSIONS: This report further highlights the epidemiological and clinical features of African tick bite fever. With the increase in international travel, it is important to recognize the illness in those who have been to endemic countries and to counsel patients regarding preventive measures for planned travel.

Animals↗
PubMed1995

Imported malaria. Clinical presentation and examination of symptomatic travelers.

BACKGROUND: The diagnosis of malaria in nonendemic countries presents a continuing challenge. Increasing physician awareness of the variability in its clinical presentation will improve clinical management and health outcomes. METHODS: Charts of patients in whom malaria was diagnosed at two hospital-based tropical disease centers between September 1, 1980, and December 31, 1991, were reviewed. RESULTS: Of a total of 482 cases, 182 were caused by Plasmodium falciparum and 246 by Plasmodium vivax. Fifty-two patients with P falciparum malaria were hospitalized; 13 were classified as having severe falciparum malaria. Nineteen patients with P vivax malaria required hospitalization. The only death was caused by P vivax. Chemoprophylaxis was used by, or prescribed for, 46% of patients; however, of these, only half were compliant in taking their medication. Eighty-seven percent of patients with falciparum malaria presented within 6 weeks of return from travel to an endemic area. One third of patients with P vivax malaria presented more than 6 months after travel. The average time between onset of symptoms and physician contact was 6.7 days. Diagnosis was often delayed in those who sought care outside the referral center. Almost all patients had a history of fever, but only half were febrile at presentation. Presenting symptoms and signs were non-specific. Fifty percent of patients were thrombocytopenic. Other laboratory abnormalities were mild. CONCLUSIONS: Since the presentation of malaria is vague and nonspecific, the diagnosis should be considered in any appropriately symptomatic patient with a history of travel to a malaria-endemic area, and appropriate testing should be done. Up-to-date information on chemoprophylaxis should be provided to all travelers to malaria-endemic regions.

Adult↗
PubMed1982

Is cholera a problem for US travelers?

Only ten cases of cholera in US travelers have been reported since the current cholera pandemic began in 1961. No important risk factors were apparent from assessing the age, place of acquisition, duration of mode of travel before infection, or history of cholera vaccination of the travelers who acquired cholera. All of the patients received medical treatment and all recovered; there were no secondary cases. Nine of the ten were infected by Vibrio cholerae 01 El Tor, the strain responsible for the current pandemic. Using the number of US citizens returning to the United States by commercial air carrier from Asia, Africa, and Oceania to estimate the population at risk, we found that the chance of acquiring a reported case of cholera is less than one case per 500,000 returning travelers.

Adult↗
PubMed2006

Effect of hypobaric hypoxia, simulating conditions during long-haul air travel, on coagulation, fibrinolysis, platelet function, and endothelial activation.

CONTEXT: The link between long-haul air travel and venous thromboembolism is the subject of continuing debate. It remains unclear whether the reduced cabin pressure and oxygen tension in the airplane cabin create an increased risk compared with seated immobility at ground level. OBJECTIVE: To determine whether hypobaric hypoxia, which may be encountered during air travel, activates hemostasis. DESIGN, SETTING, AND PARTICIPANTS: A single-blind, crossover study, performed in a hypobaric chamber, to assess the effect of an 8-hour seated exposure to hypobaric hypoxia on hemostasis in 73 healthy volunteers, which was conducted in the United Kingdom from September 2003 to November 2005. Participants were screened for factor V Leiden G1691A and prothrombin G20210A mutation and were excluded if they tested positive. Blood was drawn before and after exposure to assess activation of hemostasis. INTERVENTIONS: Individuals were exposed alternately (> or =1 week apart) to hypobaric hypoxia, similar to the conditions of reduced cabin pressure during commercial air travel (equivalent to atmospheric pressure at an altitude of 2438 m), and normobaric normoxia (control condition; equivalent to atmospheric conditions at ground level, circa 70 m above sea level). MAIN OUTCOME MEASURES: Comparative changes in markers of coagulation activation, fibrinolysis, platelet activation, and endothelial cell activation. RESULTS: Changes were observed in some hemostatic markers during the normobaric exposure, attributed to prolonged sitting and circadian variation. However, there were no significant differences between the changes in the hypobaric and the normobaric exposures. For example, the median difference in change between the hypobaric and normobaric exposure was 0 ng/mL for thrombin-antithrombin complex (95% CI, -0.30 to 0.30 ng/mL); -0.02 [corrected] nmol/L for prothrombin fragment 1 + 2 (95% CI, -0.03 to 0.01 nmol/L); 1.38 ng/mL for D-dimer (95% CI, -3.63 to 9.72 ng/mL); and -2.00% for endogenous thrombin potential (95% CI, -4.00% to 1.00%). CONCLUSION: Our findings do not support the hypothesis that hypobaric hypoxia, of the degree that might be encountered during long-haul air travel, is associated with prothrombotic alterations in the hemostatic system in healthy individuals at low risk of venous thromboembolism.

Adolescent↗
PubMed2000

Antibiotic treatment for travellers' diarrhoea.

BACKGROUND: Traveller's diarrhoea is a syndrome frequently encountered in persons crossing an international boundary. Diarrhoea can lead to significant discomfort and interference with travel plans. Bacterial pathogens are a frequent cause of this syndrome. Several antibiotics have been tested for efficacy in reducing the duration and severity of the illness. OBJECTIVES: The aims of this review were to assess the effects of antibiotics on traveller's diarrhoea in relation to duration of illness, severity of illness, and adverse effects of medications. SEARCH STRATEGY: The Cochrane Collaboration Trials Register, MEDLINE, and EMBASE were searched. Additional trials were identified by hand searching. Content experts were contacted. SELECTION CRITERIA: All trials in any language in which travellers older than 5 years were randomly allocated to treatment for acute non-bloody diarrhoea with antibiotics and where the causative organism is not known at allocation. DATA COLLECTION AND ANALYSIS: Two reviewers assessed trial quality and extracted data. MAIN RESULTS: Twenty published studies met inclusion and quality criteria for inclusion. Twelve studies were placebo-controlled. A meta-analysis for the primary outcome was not feasible. All of the 10 trials reported a significant reduction in duration of diarrhoea in participants treated with antibiotics compared with placebo. Data from two trials demonstrated a small reduction for antibiotic treated patients in the number of unformed stools passed per each 24 hour period from randomisation up to 72 hours. Data from six trials demonstrated a greater number of participants being cured of diarrhoea by 72 hours (odds ratio [OR] 5. 9, 95% confidence interval [CI] 4.06 to 8.57). Data regarding side effects were available from five trials. There was wide variation in the prevalence of side effects reported in different trials. Persons taking antibiotics experienced more side effects than those taking placebo (OR 2.37, 95% CI 1.5 to 3.75). REVIEWER'S CONCLUSIONS: Antibiotic treatment is associated with shorter duration of diarrhoea but higher incidence of side-effects. Trials generally do not report duration of post-treatment diarrhoea using time-to-event analyses, and should do.

Acute Disease↗
PubMed1984

Malaria prophylaxis in travellers: the current position.

Malaria prevention is a main challenge for physicians, nurses, health officers and tour operators. The attack rate of malaria in travellers is 1-10/10,000 departures, and the case fatality rate of imported malaria is around 0.5/100. Travellers should be informed about the risk they are going to take, how to protect against mosquito bites, about the antimalarials they will have to take and what to do when a malaria breakthrough should occur. The 4-aminoquinolines (chloroquine, amodiaquine) remain the drug of choice for the prevention of Plasmodium vivax and of sensitive P. falciparum infections. The problem is to find an effective and safe drug combination for travellers to areas where P. falciparum is either resistant to chloroquine, to Fansidar (the combination of pyrimethamine plus sulfadoxine) or to both. These travellers will probably best be protected by an individually tailored drug combination, which includes amodiaquine or mefloquine as baseline drugs, and a supplementation with Fansidar, Maloprim (the combination of pyrimethamine with dapsone), paludrine or an antibiotic.

Africa↗
PubMed1989

Results of a double-blind placebo-controlled study using ciprofloxacin for prevention of travelers' diarrhea.

To determine the efficacy, safety and effect on fecal flora of ciprofloxacin in the prevention of travelers' diarrhea, 54 volunteers traveling to Tunisia were randomized in a double-blind manner to receive either 500 mg ciprofloxacin or a placebo once daily for one week. Results of 53 volunteers were available for evaluation of efficacy. One of 25 subjects (4%) receiving ciprofloxacin versus 18 of 28 subjects (64%) in the placebo group experienced travelers' diarrhea (p less than 0.0001). The protection offered by ciprofloxacin was 94%. In one volunteer taking ciprofloxacin, prophylaxis was terminated due to sunburn with blistering. Among 41 subjects reporting sunburn, no statistical difference was observed between the two treatment groups in the percentage of body surface area of sunburn. Quantitative feces cultures revealed a marked decrease in the number of gram-negative organisms in volunteers receiving ciprofloxacin and a significant increase in the number of Escherichia coli in the placebo group. Five weeks after return, the aerobic bacterial flora of both treatment groups showed the pre-travel pattern.

Adult↗
PubMed2002

Neuropsychiatric events during prophylactic use of mefloquine before travelling.

INTRODUCTION: It has been suggested that neuropsychiatric events during use of mefloquine are more common in females than in males and are partly explained by the psychological stress of travelling. Therefore, we investigated neuropsychiatric events in females and males on mefloquine in the 3-week prophylactic period that precedes travelling. Furthermore, we investigated whether first-time users had a higher risk of neuropsychiatric adverse events than subjects with a history of mefloquine use. METHODS: We enrolled all patients who visited a Travel Clinic for mefloquine prophylaxis during the period 1 May 1999 to 7 March 2000. Each patient was followed from baseline (prior to starting mefloquine) up to 3 weeks after the start of mefloquine but before travelling. We asked patients to register any adverse event in a diary and measured the intra-individual change in scores on the Dutch Shortened Profile Of Mood States (POMS) at baseline and at the end of follow-up. RESULTS: The final cohort consisted of 179 subjects with a mean age of 3 years. Females reported adverse events more frequently than males ( P=0.005). Overall, we observed a small but significant increase in the score on the domain fatigue [0.74 points, 95% confidence interval (CI) 0.18, 1.30]. The effect was exclusively present in females and not in males. First-time users of mefloquine increased 2.81 points (95% CI 0.70, 4.92) on the total score of the POMS, and among those, women showed the largest increase of 4.58 points (95% CI 0.74, 8.43). CONCLUSION: The use of mefloquine was associated with neuropsychiatric adverse effects. Females encountered neuropsychiatric effects more frequently than males, which could be confirmed by validated psychological tests. Neuropsychiatric effects were more common in first-time users than in individuals who had used mefloquine before.

Adolescent↗
PubMed2002

[Traveler's thrombosis].

It is pathophysiologically conceivable that prolonged sitting in a tight space (e.g., in airplane or other transport vehicle) may lead to leg vein thrombosis. The association between the incidence of venous thromboembolism and long travel has not been sufficiently documented but seems probable. However, this association is only weak and the incidence of symptomatic thromboembolism much lower than the impression given by the recent publicity. In a healthy person, the risk of suffering a clinically relevant leg vein thrombosis solely because of a flight is extreme low. In persons with risk factors for venous thromboembolism, the flight represents an additional, as yet not quantifiable risk. This risk increases with the duration of the travel. The most important cause of thrombosis during long journeys seems to be venostasis due to relative immobilization. It is not clear whether flight travel represents a higher risk of thrombosis compared to other transport vehicles with comparable duration and immobilization. Until more exact information becomes available, it seems reasonable to recommend simple isometric and isotonic leg exercises during long travel. More aggressive measures must be considered for persons with risk factors for thromboembolism, but these measures should be individualized.

Aircraft↗
PubMed2005

[Travel vaccination recommendations for Central and Eastern European countries based on country-specific risk profiles].

Within the last years, an increasing trend of voyages to Central and Eastern European destinations could be observed. However, Europeans travelling within their own continent do not consider themselves as travellers exposed to possibly travel-associated infections since problem awareness among tourists as well as consulting doctors is rather scanty. The objective of this expert statement is to outline country-specific risk profiles as well as guidelines with regard to relevant travel immunizations for this region. These recommendations are mainly based on risk estimates according to national incidences and prevalences of vaccine-preventable diseases such as hepatitis A, hepatitis B, typhoid fever, meningococcal meningitis, rabies, and tick-borne encephalitis.

Communicable Disease Control↗