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Biomedical subjects

A Samel

Publications and source records attributed to A Samel.

At least 19 recordsLinked to original sources
PubMed2006

Controlled release by permeability alteration of cationic ammonio methacrylate copolymers using ionic interactions.

A multiparticulate drug delivery system was studied in which the drug release of a model drug theophylline could be modulated by interactions of ammonio methacrylate polymer and anions. The system consisted of a EUDRAGIT NE coated anionic core, layered with drug and further layered with EUDRAGIT RS. The effects of different anions like chloride, succinate, citrate, and acetate as well as the thickness of the polymer layers on the in vitro drug release were studied. It was seen that succinate and acetate anions had permeability enhancing effects and citrate and chloride anions had permeability retarding effects on the polymer. The results indicate that changing these variables would enable us to get a desired release profile and hence the proposed system could be a viable alternative to existing technologies for the development of a controlled drug delivery system.

Acrylic Resins↗
PubMed2001

Hodgkin's lymphoma of T-cell type: clonal association with a CD30+ cutaneous lymphoma.

The derivation of Reed-Sternberg cells in Hodgkin's lymphoma has been a subject of great interest. In most cases, Reed-Sternberg cells seem to be derived from germinal center B cells. In few sporadic cases, a T-cell origin has been shown. This article supports the concept of a T-cell derivation for rare cases of Hodgkin's lymphoma and provides evidence of a novel mechanism of pathogenesis from chronic inflammation in the skin.

Base Sequence↗
PubMed2000

Lymphomatoid papulosis and anaplastic large cell lymphomas of the skin.

It is now generally accepted that primary CD30+ cutaneous lymphomas comprise a clinical and morphologic spectrum in which a clear distinction between lymphomatoid papulosis (LyP) and lymphoma cannot always be made. Management varies from observation in patients who have relatively asymptomatic, spontaneously remitting disease (as in LyP) to multiagent chemotherapy regimens with or without autologous stem cell transplantation in patients whose disease has spread to involve extracutaneous sites other than regional lymph nodes (as in disseminated CD30+ lymphoma). Choosing an appropriate management strategy requires correlation of the patient's clinical history (including symptoms) with physical exam and pathologic findings. The importance of clinicopathologic correlation cannot be overemphasized, because lesions with clinically "benign" behavior may appear "malignant" by pathology, and failure to interpret pathologic findings in accordance with the patient's clinical history and physical exam can result in unnecessary, overly aggressive, and potentially harmful treatments. This review highlights integration of clinical and pathologic features of these primary cutaneous CD30+ lymphoproliferative disorders.

Diagnosis, Differential↗
PubMed1999

Melatonin and jet-lag.

Caused by time shift, a desynchronisation of the body clock from external zeitgebers occurs after transmeridian flight which leads to disturbances of sleep and circadian rhythms. These disturbances are not pathological and diminish within days. To achieve a faster resynchronisation than naturally, the hormone melatonin is often taken by business people and travelers, and--to some extent--by aircrew. The usefulness of the melatonin intake for alleviation of jet-lag is intensively discussed. Most field studies reporting about a favourable influence of melatonin on jet-lag, have been performed using questionnaires; few studies monitoring physiological circadian functions have found a better adjustment under melatonin treatment. However, from laboratory experiments is known that external melatonin is indeed capable to influence the circadian system. With respect to the efficacy of melatonin on better sleep and performance, there is a lack of information from field studies, and laboratory studies do not provide consistent results. Unequivocal estimations of the dosage of melatonin for best efficacy are not yet performed, although a range of different dosages have been tested. Recommendations about dosage, duration of medication and time of intake (which is of major importance for efficacy) do not rely on systematic examinations of the drug. Adverse effects of melatonin on sleepiness and impaired performance directly after intake of the drug are known. From studies is also derived that an inappropriate timing of intake causes sleep disturbances and unfavourable shifts of the circadian system. The administration of melatonin for influencing sleep and circadian rhythms cannot be recommended for aircrew. Flight physicians should refer to adverse and side effects of the hormone melatonin. Before any general recommendations for the use of melatonin can be presented, genuine clinical studies following good clinical practice should be performed.

Aircraft↗
PubMed1999

Culturing and bioassay testing of Daphnia magna using Elendt M4, Elendt M7, and COMBO media.

A performance-based, tiered approach was used to evaluate survival, growth, and reproduction of Daphnia magna in three selected synthetic media: Elendt M4, Elendt M7, and COMBO. Both Elendt M4 and Elendt M7 are high-hardness media currently recommended for Organization for Economic Cooperation and Development (OECD) testing. COMBO is a softer medium similar in total hardness to natural water found in the environment. Tier I consistent of an acclimation phase; Tier II involved a 21-day evaluation of survival, growth, and reproduction; and Tier III used each medium in a 21-day chronic study using a reference toxicant, 3,4-dichloroaniline (3,4-DCA). The evaluation of the performance of each medium was based on acceptance criteria similar to those used by the U.S. Environmental Protection Agency and the European Commission. Tests were run concurrently at three laboratories to assess interlaboratory variability. Daphnids were acclimated to the media for less than 1 month. Daphnid performance in all media exceeded the European Economic Community (EEC) validity criteria; however, reproductive performance and growth were significantly greater in the Elendt media than in COMBO. 3,4-DCA exerted more toxicity to daphnids in COMBO medium [no-observed-effect concentration (NOEC), <3.1microg/liter] compared with those in the Elendt media (NOEC, </=8.8 microg/liter). Elendt M7 medium provided the most consistent NOECs between laboratories (3. 1-8.8 microg/liter). However, results from two of three laboratories indicated decreases in fecundity over time in all media. The use of synthetic media for long-term culturing and bioassay testing of D. magna is still in question.

Animals↗
PubMed1998

Joint NASA-ESA-DARA Study. Part three: circadian rhythms and activity-rest cycle under different CO2 concentrations.

BACKGROUND: During manned space missions, the actual concentration of carbon dioxide (CO2) is frequently elevated to a degree that may affect human functioning and productivity. Therefore, a ground-based international study was performed that tested various psychological and physiological functions under the condition of two different levels of CO2. Thus, a specific experiment aimed at the influence of enhanced CO2-concentrations on the sleep-wake cycle and the circadian system. METHODS: Four volunteers were subjected to a CO2 concentration of 0.7% and 1.2%, respectively, for 24 consecutive days under each condition. Before they were exposed to these elevated levels, baseline measurements were conducted during 5 d under ambient CO2 concentrations (<0.1%). Circadian parameters were assessed by continuous recording of body temperature and by the determination of excretion rates of cortisol, 6-hydroximelatoninsulfate and catecholamines at 3-h intervals during wake. These measurements were conducted on 3 consecutive days 4 times during the two campaigns. Nondominant wrist activity and subjective fatigue was monitored throughout both study phases. RESULTS: Daily means of activity showed significant differences between the two study conditions (with lower values during the 1.2% condition), but these differences only occurred during day-time, whereas during sleep activity levels remained the same. Diurnal mean and circadian amplitude of the temperature rhythm was also significantly lower during the 1.2% condition. CONCLUSIONS: The lower daily mean and circadian amplitudes of temperature during the higher CO2 level can be explained by lower physical activity that was monitored under this level, i.e., a masking effect. We hesitate to explain the lower activity (and hence temperature) as a response to the changed CO2 concentration. More probably, subjects became so acquainted with the procedures of the study protocol during the second study phase (1.2% CO2) that they did not need similar effort to conduct the tasks as during the first phase. The activity level during sleep which was the same during the two phases may support this conclusions. Thus, we conclude that CO2 levels up to 1.2% do not impair the circadian rhythm of healthy men.

Adult↗
PubMed1997

Aircrew fatigue in long-haul operations.

The studies were conducted on the transmeridian routes Düsseldorf (DUS)-Atlanta (ATL) and Hamburg (HAM)-Los Angeles (LAX), and on the north-south route Frankfurt (FRA)-Mahe (SEZ). Scheduled flight duration was between 8:50 hours (ATL-DUS) and 11:50 hours (HAM-LAX). In total, 25 rotations (50 flights) have been investigated by pre-, in- and post-flight data collection of sleep, taskload, fatigue and stress by electroencephalogram and electrocardiogram measurements and subjective ratings. Inflight ratings of taskload showed low perceived exertion during the Atlantic flights, and were moderate during the north-south transitions. Fatigue ratings increased with progressing flight duration. Towards the end of long U.S.-westcoast flights performed at day-time, and in all night flights, fatigue was elevated compared to the 'baseline' ratings collected during the day-time DUS-ATL flights. Fatigue was rated as being 'critical' by several pilots, particularly during the return flight SEZ-FRA when fatigue was severely pronounced. From the findings it is concluded that duty schedules, as performed on the route HAM-LAX (because of long duty hours), and particularly on the route FRA-SEZ (because of consecutive night work), may place excessive demands on mental and physiological capacity. With respect to legal aspects, the results are significant and should promote further deliberations for advanced schemes of flight duty time limitations and rest requirements.

Accidents, Aviation↗
PubMed1997

Bright light: a countermeasure for jet lag?

After time-zone flights, the environmental time is shifted abruptly. The sleep-wake cycle and the circadian system cannot follow this sudden phase shift. Therefore, some or several days are necessary to achieve complete adjustment to a new time zone. The effects resulting from the displacement between internal and external time are well known as jet lag. In principle, timed bright light is able to enhance the resynchronization process of the circadian system after advance or delay shifts. In this report, the effects of bright light exposure on circadian phases and amplitudes after real or simulated time zone transitions are reviewed from the accessible literature and are critically discussed. It can be concluded that laboratory studies have not been unequivocally successful to support the hypothesis that bright light alleviates jet lag. The sparse number of field studies do not yet allow a clear judgment on the beneficial effect of bright light treatment on jet lag.

Acclimatization↗
PubMed1997

Two-crew operations: stress and fatigue during long-haul night flights.

BACKGROUND: As part of a research program concerning legal aspects of two-pilot operations on long-haul routes, the purpose of the study was to investigate two-crew extended range operations during a flight roster with two consecutive night flights and a short layover. HYPOTHESIS: Present flight time regulations may not be adequate for two-crew minimum operations. METHODS: The study was conducted in cooperation with a German airline company on the route Frankfurt (FRA)-Mahe (SEZ). There were 11 rotations (22 flights) that were investigated by pre-, in- and post-flight data collection each time from the two pilots. Recordings included sleep, taskload, fatigue and stress by measurement of EEG, ECG, motor activity, and subjective ratings. The average actual flight times were 9:15 h (FRA-SEZ) and 9:53 h (SEZ-FRA). All flights took place at night. The layover duration in Mahe was 13:30 h during day-time. RESULTS: During layover, sleep was shortened by 2 h on average compared with 8-h baseline sleep. The two consecutive night duties resulted in a sleep loss of 9.3 h upon return to home base. Inflight ratings of taskload showed moderate grades, but for fatigue ratings an increasing level was observed. Fatigue was more pronounced during the return flight and several pilots scored their fatigue at a critical level. Motor activity, brainwave activity (occurrences of micro-events) and heart rate indicated drowsiness and a low state of vigilance and alertness during both night flights, but these effects were more pronounced during the second flight. CONCLUSIONS: From the findings it is concluded that a duty roster, as conducted in this study, may impose excessive demands on mental and physiological capacity.

Adult↗
PubMed1996

[Stress and fatigue in long distance 2-man cockpit crew].

Common rules on flight-duty times and rest requirements within the European Union are under intense discussion. In the deliberations, results from scientific investigations should be considered. As part of a research programme concerning legal aspects of two-pilot operations on long-haul routes, the purpose of the studies was to investigate two-crew extended range operations during transmeridian and transequatorial flight schedules. The studies were conducted with two German charter airlines on the transmeridian routes Düsseldorf (DUS)-Atlanta (ATL) and Hamburg (HAM)-Los Angeles (LAX), and on the north-south route Frankfurt (FRA)-Mahe (SEZ) including two consecutive night flights with a short layover. In total, 25 rotations (50 flights) have been investigated by pre-, in-, and post-flight data collection from the two pilots being the minimum required crew. Recordings included sleep, taskload, fatigue and stress by measurements of EEG, ECG, motor activity and subjective ratings. During the transmeridian schedules, pilots lost one night of sleep because of the return flights which were conducted at night. The resulting sleep deficit was 8.2 h. During the layover of the SEZ-rotation with a duration of 14 h on average, sleep was shortened by 2 h compared with baseline sleep. The two consecutive night flights resulted in a sleep loss of 9.3 h upon return to home base. Inflight ratings of taskload showed low levels during the atlantic flights, and moderate grades during the north-south transitions. Fatigue ratings exhibited an increasing level with progressing flight duration. Towards the end of long US-westcoast flights performed at day-time, and in all night flights, fatigue was enhanced compared to the "baseline" ratings collected during the DUS-ATL flights. Fatigue was scored at a critical level by several pilots, particularly during the return flight SEZ-FRA when fatigue was severely pronounced. The subjective fatigue ratings were confirmed by the objective measurements of motor activity, brain-wave activity (occurrences of micro-sleep) and heart rate which indicated drowsiness and a low state of vigilance and alertness during all night flights under study. From the findings it is concluded that duty schedules, as conducted on the route HAM-LAX (because of long duty hours), and particularly on the route FRA-SEZ, (because of consecutive night duties) are coming close to the limits of mental and physiological capacity. With respect to legal aspects, the results have significance and should promote further deliberations for advanced schemes of flight duty time limitations and rest requirements.

Adult↗
PubMed1995

Sleepiness of civil airline pilots during two consecutive night flights of extended duration.

Sleepiness of civil airline pilots was studied in a two-crew cockpit during two consecutive night flights of about 10 h duration each. Sleepiness was assessed by EEG recordings and subjective ratings during hourly recurrent short experimental phases. On the second night flight, the alertness component that is related to the preceding sleep showed a modification due to reduced quality and quantity of sleep between flights. The daytime sleep during layover was not sufficient to maintain the same alertness level as observed during the initial flight. This result is in coincidence with investigations in shift workers starting a period of night shifts. It is concluded that improvements such as the introduction of a nap schedule should be considered to alleviate spontaneous sleepiness in the cockpit.

Adult↗
PubMed1995

Jet lag and sleepiness in aircrew.

Jet-lag and day-time sleepiness cannot be avoided in transmeridian operations, because work hours of aircrews interfere with the circadian system through irregular work-rest schedules and rapid time-zone transitions. Although the primary cause of accidents is usually the human factor, jet lag and sleepiness have seldom been officially identified as causes of inadequate functioning in the cockpit. However, research clearly indicates that flights at night and/or across time zones will impair performance and reduce safety. Research on countermeasures have focused on on-board napping, crew augmentation, behavioural strategies against jet-lag, light treatment and melatonin administration. Regrettably, scientific knowledge has been successfully transmitted to only a very few national authorities responsible for work hours of aircrews.

Journal Article↗
PubMed1995

[Therapy of jet lag].

After transmeridian flights, disturbances of the circadian rhythm and sleep occur due to the desynchronization between the body clock and external zeitgebers. Under normal circumstances, these disturbances are not pathological and disappear within a few days. However, they impair well-being and lead to significant changes in performance and vigilance. These effects are of particular importance for tasks and operations which require enhanced attention and alertness. Some of the acute symptoms of jet-lag can be reduced and shortened by appropriate countermeasures. The application of these therapies is practicable and has been successfully incorporated in clinical measures.

Arousal↗
PubMed1993

Pre-adaptation to shiftwork in space.

Astronauts are often required to work in shift schedules. To test pre-mission adaptation strategies and effects on the circadian system, a study was performed using microgravity simulation by head-down bedrest. Eight male subjects were studied over 4 control days, and 7 days each for pre-mission adaptation, bedrest, and readjustment. The circadian system was assessed by monitoring ECG and temperature, and by collecting urine for determination of hormones and electrolytes. Rhythms did not achieve complete adjustment within the adaptation period when the sleep-wake cycle was shortened by 1 h/day, but resynchronization continued during bedrest. After the bedrest period when the time shift was reversed by a 7-h delay within 2 days, resynchronization was achieved satisfactorily only within 7 days. From the results it is concluded that a sleep-wake cycle advance as used in this study is insufficient to keep the circadian system in pace. Under operational conditions the circadian system of astronauts may become longer and more destabilized than under controlled laboratory conditions.

Adaptation, Physiological↗
PubMed1993

Response of the circadian system to 6 degrees head-down tilt bed rest.

The influence of simulated microgravity and reduced zeitgebers on the circadian system was examined in eight subjects. The 12-d study included a 3-d period for baseline measurements, 7 d of 6 degrees head-down bed rest, and 2 d for recovery. The sleep-wake cycle was kept constant during the study. The state of the circadian system was assessed from continuous measurements of temperature and ECG, and collections of urine at 3-h intervals for the determination of hormone and electrolyte excretions. Results indicate that only minor changes occurred in rhythm acrophases, whereas daily means for several physiological functions and their circadian amplitudes were significantly altered during the bed-rest phase. These studies using head-down tilt confirm previous findings with horizontal bed rest and indicate that rhythm disturbances can occur without change in the sleep-wake cycle. To the degree that bed-rest studies simulate manned spaceflights, results indicate that variations in circadian cycles can occur even during short-term missions and must be taken into account when interpreting subsequently obtained physiological data.

Adult↗
PubMed1991

Influence of melatonin treatment on human circadian rhythmicity before and after a simulated 9-hr time shift.

The hormone melatonin is currently proposed by some investigators to be an efficient means for decreasing the impairing effects of jet lag. Eight healthy male subjects, aged 20 to 32, underwent a 9-hr advance shift in the isolation facility of our institute during two periods each of 15 days' duration. In a double-blind, crossover design, subjects took either melatonin or placebo at 1800 hr local time for 3 days before the time shift and at 1400 hr for 4 days afterwards. The time shift was simulated on days 7 and 8 by shortening the sleep period by 6 hr and the following wake period by 3 hr. Body temperature was recorded every 90 min, and urine was collected at 3-hr intervals all day and night. Melatonin treatment enhanced the resynchronization speed of some, but not all, hormone and electrolyte excretion rates for several days after the time shift. The adaptation speed of the temperature rhythm significantly increased during one postshift day. In addition, the circadian temperature rhythm had a significantly higher amplitude under melatonin treatment than under placebo after the time displacement. For the placebo group, the rhythm of 6-hydroxymelatoninsulfate excretion exhibited an advance shift in five subjects, whereas the other three showed a delay shift, and adjustment did not achieve more than one-half of the expected value within 8 days. A significantly different adjustment could be observed in the melatonin-treated group: Seven subjects underwent an advance shift of the expected 9 hr within an average of 8 days. The results suggest that melatonin treatment can accelerate resynchronization of the melatonin excretion rhythm after eastward time zone transitions. The improvement is not, however, sufficiently great that we can recommend melatonin for the alleviation of jet lag.

Adult↗