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Biomedical subjects

J L Caldwell

Publications and source records attributed to J L Caldwell.

At least 19 recordsLinked to original sources
PubMed2001

Work and sleep hours of U.S. Army aviation personnel working reverse cycle.

A one-page questionnaire was administered to 157 aviation personnel from three Army posts to determine when Army aviation personnel work and sleep while on reverse cycle. This project was undertaken as a first step to developing tailor-made fatigue reduction strategies for shift workers in Army aviation. The results indicated that 97.6% of the surveyed aviation personnel had experience working night shift/reverse cycle at some point in their careers, with 69.4% working the night shift within the past 6 months. Of those who had experience working the night shift, 36.2% reported usually working from early in the afternoon to early in the morning, with 52.2% of personnel returning home by 4:00 a.m.; however, 28.3% arrived home after 8:00 a.m. Almost 62% of the respondents indicated that they did not feel they received adequate daytime sleep some of the time or at all while on reverse cycle/night shift. Research is needed to address the issue of helping aviation personnel sleep during the daylight hours, both for training exercises and for deployment. Once the work/rest schedule for a unit is known, countermeasures such as light therapy or gradual changes in scheduling can be tailored to meet the specific needs of the individual or unit.

Adult↗
PubMed2000

A double-blind, placebo-controlled investigation of the efficacy of modafinil for sustaining the alertness and performance of aviators: a helicopter simulator study.

RATIONALE: In 1998, the FDA approved modafinil for treating excessive daytime sleepiness in narcoleptics, and this has raised questions about the appropriateness of this compound for enhancing alertness in sleep-deprived controls. This study explored the efficacy of modafinil for maintaining the performance of volunteers required to accomplish highly demanding tasks despite sleep loss. OBJECTIVE: The principal objective was to determine whether prophylactic doses of modafinil would attenuate decrements in aviator performance and arousal throughout 2 days and 1 night without sleep. METHODS: Six pilots were exposed to two 40-h periods of continuous wakefulness. In one, three 200-mg doses of modafinil were given and in the other, matching placebos were administered. Helicopter simulator flights, resting EEGs, and Profile of Mood States (POMS) questionnaires were evaluated. RESULTS: Modafinil attenuated sleep deprivation effects on four of six flight maneuvers, reduced slow-wave EEG activity, and lessened self-reported problems with mood and alertness in comparison to placebo. The most noticeable benefits occurred between 0330 and 1130 hours, when the combined impact of sleep loss and the circadian trough was most severe. The most frequently observed drug side effects were vertigo, nausea, and dizziness. These could have been related to: 1) the motion-based testing, 2) the use of a simulator rather than an actual aircraft (i.e., "simulator sickness"), and/or 3) the administration of more than 400 mg modafinil. CONCLUSIONS: Modafinil is a promising countermeasure for sleep loss in normals; however, additional studies aimed at reducing side effects are needed before it should be used in aviators.

Adult↗
PubMed2000

Efficacy of Dexedrine for maintaining aviator performance during 64 hours of sustained wakefulness: a simulator study.

INTRODUCTION: The efficacy of Dexedrine for sustaining aviator performance despite 64 h of extended wakefulness was investigated. This study was conducted to extend the findings of earlier research that had proven the efficacy of Dexedrine during shorter periods (i.e., 40 h) of sleep deprivation. METHODS: Dexedrine (10 mg) or placebo was given at midnight, 0400, and 0800 hours on two deprivation days in each of two 64-h cycles of continuous wakefulness. Test sessions consisting of simulator flights, electroencephalographic evaluations, mood questionnaires, and cognitive tasks were conducted at 0100, 0500, 0900, 1300, and 1700 hours on both deprivation days. Two nights of recovery sleep separated the first and second 64-h sleep-deprivation cycles. RESULTS: Simulator flight performance was maintained by Dexedrine throughout sleep deprivation. The most benefit occurred at 0500 and 0900 hours (around the circadian trough) on the first deprivation day, but continued throughout 1700 hours (after 58 h awake) on the second day. Dexedrine suppressed slow-wave EEG activity which occurred under placebo after 23 h awake and continued to exert this effect throughout 55 h (and sometimes 59 h) of deprivation. The drug sustained self-perceptions of vigor while reducing fatigue and confusion. Recovery sleep was slightly less restful under Dexedrine. CONCLUSIONS: Dexedrine sustained aviator performance and alertness during periods of extended wakefulness, but its use should be well controlled. Although effective, Dexedrine is no replacement for adequate crew rest management or restful sleep.

Adult↗
PubMed2000

The use of melatonin: an information paper.

The use of melatonin has been a topic of debate for the past several years. Patients frequently ask their physicians about its use, and many physicians are at a loss about what to tell them. Aviators who have trouble sleeping may choose to buy melatonin and use it since it is a "natural" substance. However, they may lack proper education about its use and the issues of concern. Flight surgeons can help educate their patients in the use of melatonin. This paper will briefly discuss the role of melatonin in humans, its effects on circadian rhythms, its sleep-inducing properties, its effects on mood and performance, and issues pertaining to safety. Flight surgeons and other physicians cannot "prescribe" melatonin, but they at least can offer information about its effects and what is not known about melatonin at this time to the aviators who may ask questions concerning this product.

Circadian Rhythm↗
PubMed1998

Comparison of the effects of zolpidem-induced prophylactic naps to placebo naps and forced rest periods in prolonged work schedules.

The efficacy of zolpidem-induced prophylactic naps was compared to placebo naps and forced-rest periods for sustaining alertness. Eighteen subjects were exposed to three separate 38-hour periods of continuous wakefulness, each separated by 10 hours of recovery sleep. Three conditions were used: a 2-hour evening nap (at 2100 hours) induced with 10 mg zolpidem tartrate; a 2-hour nap (at 2100 hours) with placebo; and a 2-hour rest break with no sleep. Following the naps or rest period, subjects remained awake for 23 additional hours. A VAS was administered at 1-hour intervals, RTSWs and POMS were administered at 2-hour intervals, and a cognitive task was completed at 4-hour intervals. Results indicated the effectiveness of prophylactic naps for sustaining mood, alertness, and performance throughout the final 23 hours of a 39-hour period of sustained operations. Both napping conditions attenuated the decrements normally associated with total sleep deprivation, but the zolpidem nap was the most effective because subjects obtained the most sleep after zolpidem administration. Postnap grogginess persisted for about 2 hours after either the zolpidem or placebo nap, a fact which, despite the overall benefits from prophylactic naps, could compromise performance under operational conditions if insufficient time for awakening is planned.

Adult↗
PubMed1997

Recovery sleep and performance following sleep deprivation with dextroamphetamine.

Twelve subjects were studied to determine the after-effects of using three 10-mg doses of dextroamphetamine to sustain alertness during sleep deprivation. Sleep architecture during recovery sleep was evaluated by comparing post-deprivation sleep after placebo. Performance and mood recovery were assessed by comparing volunteers who received dextroamphetamine first (during sleep deprivation) to those who received placebo first. Stages 1 and 2 sleep, movement time, REM latency, and sleep latency increased on the night after sleep deprivation with dextroamphetamine vs. placebo. Stage 4 was unaffected. Comparisons to baseline revealed more stage 1 during baseline than during either post-deprivation sleep period and more stage 2 during baseline than during sleep following placebo. Stage 4 sleep was lower during baseline and after dextroamphetamine than after placebo. Sleep onset was slowest on the baseline night. Next-day performance and mood were not different as a function of whether subjects received dextroamphetamine or placebo during deprivation. These data suggest dextroamphetamine alters post-deprivation sleep architecture when used to sustain alertness during acute sleep loss, but next-day performance and subjective mood ratings are not substantially affected. A recovery sleep period of only 8 h appears to be adequate to regain baseline performance levels after short-term sleep deprivation.

Adult↗
PubMed1997

An in-flight investigation of the efficacy of dextroamphetamine for sustaining helicopter pilot performance.

A promising countermeasure for fatigue in sustained aviation operations is stimulant administration. However, well-controlled, aviation-relevant studies of the efficacy of medications such as Dexedrine are virtually nonexistent. In this investigation, flight performance, mood, and alertness were evaluated in 10 UH-60 pilots during sleep deprivation periods under Dexedrine or placebo. Relative to placebo, Dexedrine improved flight performance during straight-and-levels, climbs, descents, right turns, and a left-descending turn, with tendencies toward better performance during the left turns and the instrument landing system approach. Dexedrine markedly reduced subjective feelings of fatigue, confusion, and depression while increasing feelings of vigor. Central nervous system arousal was enhanced by Dexedrine relative to placebo. No significant side effects occurred, although Dexedrine was associated with mild asymptomatic increases in heart rate and BP. Thus, Dexedrine appears effective for the short-term sustainment of aviator performance during sustained operations. However, future work should investigate the efficacy of stimulants for longer-term use (e.g., more than 40 h of continuous wakefulness).

Adult↗
PubMed1995

A survey of selected aviators' perceptions regarding Army crew endurance guidelines.

A 59-item questionnaire was administered to Army helicopter pilots from a variety of Army units to assess crew endurance issues. Analysis of 653 completed questionnaires indicated that respondents felt that the maintenance of aviator proficiency was more important than the fulfillment of only currency requirements in improving flight endurance. Approximately three-quarters of the respondents said that physical training was important to them personally, and 63% said that improved physical fitness reduces flight-related fatigue. With regard to the current crew endurance guide, only 1% of the respondents thought that the guide was exceptional and 65% said that they thought it should be rewritten. Adjustments were suggested for some of the recommended flight time limitations, to include liberalizing the factor associated with night-vision device flight. A majority of respondents indicated that data from either in-flight endurance evaluations or questionnaires administered to personnel in the field should be used to develop a new guide. Most respondents did not feel comfortable delegating responsibility for total crew endurance planning to unit commanders.

Adult↗
PubMed1995

Sustaining helicopter pilot performance with Dexedrine during periods of sleep deprivation.

BACKGROUND: Around-the-clock operations often are mandated in combat, but while aircraft can function effectively throughout continuous 24-hour periods, aviators often cannot because of sleep loss. An efficacious countermeasure in sustained operations may be the administration of dextroamphetamine (Dexedrine). HYPOTHESIS: Dexedrine will effectively prevent many of the performance problems associated with sleep deprivation in helicopter pilots. METHODS: A placebo-controlled, double blind study was conducted. Six U.S. Army helicopter pilots completed five flights in a UH-60 simulator while their performance was evaluated. Immediately following each flight, data were collected on electroencephalographic (EEG) activity and subjective mood ratings. Testing sessions occurred at 0100, 0500, 0900, 1300, and 1700. One hour prior to each of the first three flights on drug-administration days, the aviators were given 10 mg of Dexedrine or placebo. RESULTS: Dexedrine, in comparison to placebo, improved aviator simulator control on descents, straight-and-levels, standard-rate turns, and a left-descending turn. Performance was facilitated most noticeably at 0500, 0900, and 1700 (after 22, 26, and 34 hours of continuous wakefulness). EEG and mood data showed that alertness was sustained significantly by Dexedrine--there was reduced slow-wave EEG activity and improved rating of vigor and fatigue. No adverse behavioral or physiological effects were observed. CONCLUSIONS: Dexedrine appears to be effective for sustaining helicopter pilot performance during short periods of sleep loss without producing adverse side effects.

Adult↗
PubMed1993

Factors influencing success or failure in the AH-64 course.

A greater percentage of qualified student pilots fail the AH-64 (Apache) transition than any other advanced aircraft transition in the Army. We studied 140 consecutive students presenting for training in an effort to identify factors which might predict success or failure in the AH-64 course. Questionnaires were used to elicit demographic, anxiety level, and motion sickness history information prior to beginning Apache flight training. Motion sickness symptoms (MSS) during the enclosed cockpit, or "bag," phase of training were quantified using pre- and postbag flight symptom questionnaires. Performance measures included grades and flight hours required to pass the course. Only one piece of information obtained prior to flight training was related to performance in the AH-64 course; i.e., students who requested the transition performed measurably better than students who did not. While 7% of pilots described significant MSS on the first day of enclosed cockpit flight, this decreased to 2% by day 5. Severity of symptoms during bag phase was not related to any measure of subsequent performance.

Achievement↗
PubMed1993

The physiological consequences of simulated helicopter flight in NBC protective equipment.

The physiological effects of wearing U.S. Army aviator nuclear-biological-chemical (NBC) individual protective equipment (IPE) were evaluated in the USAARL UH-60 research flight simulator. There were 16 male aviators who flew the simulator in 4 test conditions: standard flight suit and cool cockpit, standard flight suit and hot cockpit, NBC IPE and cool cockpit, NBC IPE and hot cockpit. The cool condition was a WBGT of 17.9 degrees C, the hot 30.6 degrees C. Rectal temperature, mean skin temperature, and heart rate were monitored and showed significant increases for the NBC hot condition compared with the other three. Seven subjects failed to complete the sortie in the NBC hot condition, with a mean survival time of 298 min. All subjects flew for the target 6 h in the other conditions.

Adult↗
PubMed1992

Documentation of activity and rest of a U.S. National Guard attack helicopter battalion.

A. U.S. National Guard attack helicopter battalion was monitored in order to document the activity and rest obtained during the annual training exercises. A total of 39 soldiers wore wrist activity monitors during the 2-week training period. The data from these monitors discriminate activity from rest. Results indicated the following: 1) at some point during the exercises, everyone became sleep deprived; 2) the participants who received the most rest of the group were the enlisted headquarters personnel and the pilots; 3) the soldiers who received the least amount of sleep were the commander of the battalion and the maintenance personnel. Some recommendations are offered for future planning of National Guard training exercises.

Aerospace Medicine↗
PubMed1986

The capacity of normal murine alveolar macrophages to function as antigen-presenting cells for the initiation of primary antibody-forming cell responses to sheep erythrocytes in vitro.

The precise role of resident alveolar macrophages (AM) in the induction of immune responses to inhaled antigens is not known. In order to gain insight into the immune functions of AM in vivo, the present studies were performed to characterize several immune functional capacities of normal murine AM, to compare these with normal peritoneal macrophages (PM), and to determine the capacity of AM to serve as antigen-presenting cells for the induction of primary antibody-forming cell (AFC) responses to sheep erythrocytes (SRBC) in vitro. We compared the capacities of normal murine AM and of PM to: elaborate interleukin-1 (IL-1), express surface membrane Ia antigen, serve as accessory cells for mitogen-induced blastogenesis, and induce generation of primary AFC responses to SRBC in Mishell-Dutton cultures. We observed that: AM and PM elaborate equivalent IL-1 activity after stimulation with phorbal myristate acetate (PMA); AM "conditioned" with supernatants of concanavilin-A-stimulated spleen cells express surface Ia but do so proportionately less than similarly treated PM; normal AM can serve as accessory cells for mitogen-induced blastogenesis but do so significantly less effectively than do PM; AM substitute poorly for PM with respect to the induction of primary AFC responses to SRBC in standard Mishell-Dutton cultures; however, AM exert potent suppressive activity in these cultures, and this suppression can be reversed by the addition of indomethacin and catalase to cultures, suggesting that both prostaglandins and hydrogen peroxide play suppressive roles; after reversal of suppression in drug-modified Mishell-Dutton cultures, AM can induce primary AFC responses to SRBC but do so less effectively than do similarly treated PM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Immune functions of murine alveolar macrophages: binding of lymphocytes and support of lymphocyte proliferation.

Interactions between alveolar macrophages and lymphocytes may be important in the generation of pulmonary immune responses or in the induction of immunologic lung disease. We compared the relative abilities of normal murine alveolar macrophages and peritoneal macrophages to bind primed lymphocytes and to support antigen-induced lymphocyte proliferation. Alveolar macrophages were obtained by lung lavage and peritoneal macrophages by peritoneal lavage of normal mice. Lymph-node cells were harvested from draining lymph nodes of mice immunized with the peptide antigen (T,G)-A-L. Lymph-node cells were depleted of macrophages by passage through columns of Sephadex G-10 and nylon wool. To study the binding of lymphocytes to macrophages, lymph-node cells were layered over antigen-pulsed alveolar and peritoneal macrophage monolayers and the number of lymphocytes bound to the macrophages counted microscopically after incubation for 1-20 hr. Macrophage support of antigen-induced lymphocyte proliferation was studied by 3H-thymidine uptake of macrophage-depleted primed lymph-node cells cultured in the presence of soluble antigen. Cultures were repleted with graded percentages of alveolar or peritoneal macrophages. The results showed that alveolar macrophages bound significantly fewer lymphocytes than peritoneal macrophages both in a nonspecific and an antigen-specific manner. The difference in lymphocyte-binding affinity between the two macrophage types could not be attributed to factors present in lung lavage fluid. Results of the lymphocyte proliferation studies showed that while alveolar macrophages were able to support lymphocyte proliferation in response to antigen, they did so less effectively than an equal number of peritoneal macrophages. We conclude that alveolar macrophages differ significantly from peritoneal macrophages in their ability to interact with lymphocytes, both with respect to lymphocyte binding and in support of lymphocyte proliferative responses.

Animals↗
PubMed1980

Cytolytic activity of pulmonary and systemic lymphoid cells from C57BL/6 mice following intrapulmonary or intraperitoneal immunization with allogeneic tumor cells.

In order to demonstrate whether specific cytotoxic T cells could be induced in lung parenchyma, C57BL/6 mice were immunized by the intrapulmonary route with allogenetic tumor cells (P815). Ten days after administration of 20 x 10(6) allogeneic cells, peak concentrations of cytotoxic cells were found in lung, tracheobronchial lymph node, and spleen. With reduction in immunizing dose, lytic activity disappeared from spleen and lymph node, but persisted in lung. The cytolytic activity was specific for the immunizing alloantigen, was abolished by antitheta serum, and could not be attributed to macrophages. For comparison, C57BL/6 mice were immunized by the intraperitoneal route with 20 x 10(6) P815 cells. The expected cytolytic activity was found in spleen and lymph nodes: however, unexpectedly high levels of cytolytic activity were also found in pulmonary lymphocytes. This activity was confirmed using a wide range of effector to largest cell ratios in the assay system. Quantitative cytolytic assays demonstrated that the maximum rate of cytolysis by pulmonary lymphocytes obtained from mice immunized intraperitoneally exceeded by 10- to 20-fold the rate of cytolysis by pulmonary lymphocytes obtained from mice receiving intrapulmonary immunization. These data demonstrate that cytolytic T-lymphocytes appear in lung parenchyma after either intrapulmonary or intraperitoneal immunization and that the intraperitoneal route is far more efficient than the intrapulmonary route. This cell-mediated immune mechanism potentially is available for host defense of respiratory tissue.

Animals↗