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Biomedical subjects

Gregory Belenky

Publications and source records attributed to Gregory Belenky.

14 recordsLinked to original sources
PubMed2005

Daytime sleep and performance following a zolpidem and melatonin cocktail.

STUDY OBJECTIVES: Pharmacologic enhancement of daytime sleep may help sustain optimal cognitive performance. At effective doses, zolpidem induces sleep but also impairs performance. Combining melatonin with low-dose zolpidem may promote daytime sleep without exacerbating performance impairments seen with high-dose zolpidem alone. DESIGN AND METHODS: Following an 8-hour undisturbed nighttime sleep period, 80 subjects (50 men, 30 women) were administered oral zolpidem 0, 5, 10, or 20 mg at 10:00 am (n = 20 per group) and then oral melatonin 0 or 5 mg at 10:30 am (thus, n = 10 per drug combination) in a double-blind randomized fashion. Subjects napped from 10:00 am to 11:30 am, at which time they were awakened and cognitive tests administered (Restricted Reminding, Paired-Associates, and Psychomotor Vigilance). A second nap ensued from 12:45 pm to 4:00 pm, followed immediately by further testing. RESULTS: Melatonin 5 mg plus zolpidem 0 mg enhanced daytime sleep (P < .05) with no memory or performance impairment (P > .05). Zolpidem 20 mg plus melatonin 0 mg also enhanced daytime sleep (albeit nonsignificantly), but memory and vigilance were impaired (P < .05). Melatonin's sleep-promoting effects were not evident until the second nap. CONCLUSIONS: No advantages to administering melatonin plus zolpidem "cocktails" were evident. Unlike zolpidem, melatonin 5 mg alone improved daytime sleep without impairing memory and vigilance. Functional coupling of sleep-inducing and memory-impairing effects may be specific to benzodiazepine-receptor agonists such as zolpidem, suggesting potential advantages to using melatonin in the operational environment. That melatonin's sleep-promoting effects were delayed for several hours presents a practical consideration that may limit melatonin's usefulness when daytime sleep periods cannot be reliably anticipated or planned in advance.

Adolescent↗
PubMed2005

The Walter Reed palm-held psychomotor vigilance test.

This field-portable reaction time test and analysis software run on devices using the Palm operating system. It is designed to emulate a test and commercial device widely used in sleep deprivation, shift work, fatigue, and stimulant drug research but provides additional capabilities. Experimental comparisons with the standard commercial device in a 40-hour total sleep deprivation study show it to be comparably sensitive to selected experimental variables. A Pocket PC-compatible version is under developement.

Adult↗
PubMed2005

Caffeine maintains vigilance and marksmanship in simulated urban operations with sleep deprivation.

PURPOSE: The purpose of this study was to examine the effects of caffeine (CAF) on physical, vigilance, and marksmanship tasks in soldiers during a sustained 55-h field exercise. METHODS: There were 30 soldiers (23.6 +/- 4.5 yr, 81.8 +/- 10.3 kg) who were divided into a placebo (PLAC) and a CAF group. After a period of restricted sleep of 3 h during the first night, a period of sustained wakefulness began that ended at 11:00 of the third day. PLAC or CAF doses of 100 mg, 200 mg, 100 mg, and 200 mg were administered at 21:45, 23:45, 01:45, and 03:45, respectively. At 22:00 of day 2, subjects began two cycles of marksmanship, urban operations vigilance, and psychomotor vigilance (PVT) testing which ended at 06:00 of day 3. RESULTS: CAF maintained marksmanship vigilance at 85% throughout the second night as compared with PLAC, who significantly declined to 61.4 +/- 28.2% overnight. Marksmanship accuracy also decreased significantly in PLAC from 95.1 +/- 8.3% to 83.3 +/- 19.2%, but no change was observed in CAF. Urban operations vigilance decreased for both groups over the night, but the decrease was less for CAF (81.2 +/- 14.4% to 63.4 +/- 24.1%) compared with PLAC (77.6 +/- 19.2% to 44.0 +/- 30.2%). Reaction time and the number of major and minor lapses with the PVT significantly increased in PLAC but were unaffected in CAF. CONCLUSIONS: It was concluded that CAF was an effective strategy to sustain vigilance and psychomotor performance during military operations involving sleep deprivation.

Adult↗
PubMed2005

Caffeine effects on recovery sleep following 27 h total sleep deprivation.

INTRODUCTION: Caffeine is widely used to reverse alertness and performance decrements. However, caffeine's effects on subsequent recovery sleep and post-recovery performance are not well documented and, therefore, were evaluated. METHODS: Six habitually low (LC: < or = 100 mg x d(-1)) and three habitually high (HC: > or = 400 mg x d(-1)) caffeine users completed a randomized crossover design. After 20 h of wakefulness, repeated doses of caffeine gum [0 (placebo) mg, 100 (low dose) mg, or 300 (high dose) mg] were administered at 03:00, 05:00, and 07:00. At 10:00 (27 h sleep deprivation) subjects slept for 8 h, followed by Psychomotor Vigilance Task (PVT) administration at 33 and 65 min post-awakening. RESULTS: Low dose caffeine increased stage 1 minutes only. However, high dose caffeine impaired sleep maintenance (reduced total sleep time/increased wake) and reduced sleep depth (increased stage 1 minutes/percentage and slow-wave sleep (SWS) latency, and reduced SWS minutes during the first third of the sleep period). With high dose caffeine, LC users had less SWS percentage as compared with HC users. The HC users had reduced stage 2 percentage with high dose caffeine as compared with placebo and low dose caffeine. Caffeine dose and habitual caffeine use did not influence post-recovery sleep PVT performance. DISCUSSION: Caffeine exerts mild deleterious dose-response effects on recovery sleep following total sleep deprivation, primarily early in the sleep period, with potential recovery from these effects after sufficient sleep as suggested by lack of post-recovery sleep performance deficits. Habitual caffeine use appears to minimally reduce caffeine effects.

Adolescent↗
PubMed2005

Oculomotor responses during partial and total sleep deprivation.

INTRODUCTION: Oculomotor responses related to the pupil light reflex (PLR) and saccadic velocity may be sensitive to the effects of sleepiness and therefore could be used to evaluate an individual's fitness for duty. METHODS: There were 12 normal subjects who completed an 8-d study. They were allowed 8 h in bed on the first three nights, 4 h in bed on the fourth night, and then were sleep deprived for the following 64 h. Approximately every 3 h, subjects performed a battery of tests which included a 45-s automated oculomotor test and a 40-min PC-based driving simulator task. Sleepiness was evaluated with a self-assessment instrument. Subjects were allowed 10 h of recovery sleep following sleep deprivation. RESULTS: Oculomotor results for nine subjects showed a significant increase in latency to pupil constriction and a significant decrease in saccadic velocity with total, but not partial, sleep deprivation. The most robust changes during sleep deprivation occurred for saccadic velocity. A night of recovery sleep reversed the effects of total sleep deprivation on latency to pupil constriction and saccadic velocity. Subjective sleepiness and off-road accidents were found to significantly increase over the sleep deprivation period. A significant positive correlation between increasing latency to pupil constriction and increasing sleepiness and driving accidents, and a significant negative correlation between decreasing saccadic velocity and increasing sleepiness and driving accidents during sleep deprivation were found. CONCLUSION: These findings suggest that oculomotor functions, particularly saccadic velocity, are feasible for assessing neurophysiological changes associated with and predictive of sleep deprivation-induced operational performance degradation.

Adult↗
PubMed2005

Multiple caffeine doses maintain vigilance during early morning operations.

INTRODUCTION: When used to counteract the effects of sleep deprivation, multiple doses of caffeine are typically ingested across an extended period of time. The goal of this study was to determine the optimal dose of caffeine for sustaining performance during sleep loss with administration of multiple doses. METHODS: There were 48 subjects (28 men, 20 women) who were randomly assigned to 1 of 4 groups (placebo, 50, 100, or 200 mg caffeine). After an overnight 8-h sleep period, subjects were required to remain awake for the ensuing 29 h. Control data were collected until 03:00 (Day 3), followed by three 2-h test blocks. At 03:00, 05:00, and 07:00 subjects chewed two sticks of gum (Stay Alerts chewing gum) containing caffeine or placebo. Six 10-min sessions on a version of the Psychomotor Vigilance Test (PVT) were completed during each 2-h test block. The Stanford Sleepiness Scale (SSS) was administered after each PVT. RESULTS: Lapses on the PVT were categorized as response times greater than 1, 3, or 5 s. Lapses in all categories significantly increased in the placebo group. Caffeine significantly reduced the number of lapses in a dose-related manner; and performance was maintained at baseline levels for the entire sleep loss period with multiple doses of 200 mg caffeine. There was a significant main effect for session on the SSS, the score increasing over time, but no significant differences between groups. DISCUSSION: These results indicate that a bi-hourly administration of 200 mg of caffeine maintains vigilance performance across a single night without sleep.

Aerospace Medicine↗
PubMed2004

Comparative utility of instruments for monitoring sleepiness-related performance decrements in the operational environment.

As both military and commercial operations increasingly become continuous, 24-h-per-day enterprises, the likelihood of operator errors or inefficiencies caused by sleep loss and/or circadian desynchrony also increases. Avoidance of such incidents requires the timely application of appropriate interventions--which, in turn, depend on the ability to measure and monitor the performance capacity of individuals in the operational environment. Several factors determine the potential suitability of candidate measures, including their relative sensitivity, reliability, content validity, intrusiveness and cumbersomeness/fieldability. In the present study, the relative sensitivity (defined as the ratio of effect size to 95% confidence interval) of several measures to the effects of sleep loss was compared in a sleep restriction experiment, in which groups were allowed 3, 5, 7, or 9 h time in bed (TIB) across seven consecutive nights. Of the measures compared, the Psychomotor Vigilance Test was among the most sensitive to sleep restriction, was among the most reliable with no evidence of learning over repeated administrations, and possesses characteristics that make it among the most practical for use in the operational environment.

Adult↗
PubMed2004

Fatigue models for applied research in warfighting.

The U.S. Department of Defense (DOD) has long pursued applied research concerning fatigue in sustained and continuous military operations. In 1996, Hursh developed a simple homeostatic fatigue model and programmed the model into an actigraph to give a continuous indication of performance. Based on this initial work, the Army conducted a study of 1 wk of restricted sleep in 66 subjects with multiple measures of performance, termed the Sleep Dose-Response Study (SDR). This study provided numerical estimation of parameters for the Walter Reed Army Institute of Research Sleep Performance Model (SPM) and elucidated the relationships among several sleep-related performance measures. Concurrently, Hursh extended the original actigraph modeling structure and software expressions for use in other practical applications. The model became known as the Sleep, Activity, Fatigue, and Task Effectiveness (SAFTE) Model, and Hursh has applied it in the construction of a Fatigue Avoidance Scheduling Tool. This software is designed to help optimize the operational management of aviation ground and flight crews, but is not limited to that application. This paper describes the working fatigue model as it is being developed by the DOD laboratories, using the conceptual framework, vernacular, and notation of the SAFTE Model. At specific points where the SPM may differ from SAFTE, this is discussed. Extensions of the SAFTE Model to incorporate dynamic phase adjustment for both transmeridian relocation and shift work are described. The unexpected persistence of performance effects following chronic sleep restriction found in the SDR study necessitated some revisions of the SAFTE Model that are also described. The paper concludes with a discussion of several important modeling issues that remain to be addressed.

Aviation↗
PubMed2004

Modulating the homeostatic process to predict performance during chronic sleep restriction.

BACKGROUND: In most current sleep/performance models, the homeostatic process is generally conceived as a simple reservoir in which performance capacity increases exponentially during sleep and decays either linearly or exponentially during wakefulness. Models that include this notional homeostatic process have been successful for describing sleep-performance data under conditions of irregular sleep schedules, jet lag, and short periods of total sleep loss. However, recently described data from sleep restriction studies indicate that recovery following chronically restricted sleep is considerably slower than would be predicted by these models. These findings suggest that chronic sleep restriction induces relatively long-term, slow-recovering changes in brain physiology that affect alertness and performance. METHODS: This paper describes, both conceptually and mathematically, a generic modification to sleep/performance models that facilitates the ability to predict the rate at which alertness and performance restoration occurs during recovery sleep following chronic sleep restriction. Weighted nonlinear least-squares methods were used to compare the proposed modulated homeostatic model with recent sleep/performance observations during chronic sleep restriction and recovery. RESULTS: When compared with the classical Walter Reed homeostatic model, this proposed model was found to provide a better description of sleep restriction and recovery observations. The proposed model was also found to be consistent with the data from a recent University of Pennsylvania study. CONCLUSIONS: These two models make significantly different predictions of performance during both the recovery phase and the chronic sleep restriction phase.

Data Interpretation, Statistical↗
PubMed2004

Modafinil vs. caffeine: effects on fatigue during sleep deprivation.

INTRODUCTION: The extent to which modafinil and caffeine reverse fatigue effects (defined as performance decrements with time on task) during total sleep deprivation was investigated. METHODS: There were 50 healthy young adults who remained awake for 54.5 h (06:30 day 1 to 13:00 day 3). A 10-min vigilance test was administered bi-hourly from 08:00 day 1 until 22:00 day 2. At 23:55 day 2 (after 41.5 h awake), double-blind administration of one of five drug doses (placebo; modafinil 100, 200, or 400 mg; or caffeine 600 mg; n = 10 per group) was followed by hourly testing from 00:00 through 12:00 day 3. Response speed (reciprocal of reaction time) across the 10-min task (by 1-min block) was analyzed prior to and after drug administration. RESULTS: A fatigue effect (response speed degradation across the 10-min task) was exacerbated by sleep deprivation and circadian rhythmicity. Prior to the drug, this effect was maximal between 08:00 and 12:00 day 3 (24-28 h sleep deprivation). Modafinil 400 mg attenuated fatigue in a manner comparable to that seen with caffeine 600 mg; these effects were especially salient during the circadian nadir of performance (06:00 through 10:00); modafinil 200 mg also reversed fatigue, but for a shorter duration (3 min) than modafinil 400 mg (8 min) or caffeine 600 mg (6 min). DISCUSSION AND CONCLUSIONS: Time-on-task effects contributed to the performance degradation seen during sleep deprivation; effects which were reversed by caffeine and, at appropriate doses, by modafinil. Because the duration of efficacy for reversing time-on-task effects was shorter at lower drug dosages, the latter must be considered when determining the appropriate dose to use during sustained operations.

Adolescent↗
PubMed2003

Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose-response study.

Daytime performance changes were examined during chronic sleep restriction or augmentation and following subsequent recovery sleep. Sixty-six normal volunteers spent either 3 (n = 18), 5 (n= 16), 7 (n = 16), or 9 h (n = 16) daily time in bed (TIB) for 7 days (restriction/augmentation) followed by 3 days with 8 h daily TIB (recovery). In the 3-h group, speed (mean and fastest 10% of responses) on the psychomotor vigilance task (PVT) declined, and PVT lapses (reaction times greater than 500 ms) increased steadily across the 7 days of sleep restriction. In the 7- and 5-h groups speed initially declined, then appeared to stabilize at a reduced level; lapses were increased only in the 5-h group. In the 9-h group, speed and lapses remained at baseline levels. During recovery, PVT speed in the 7- and 5-h groups (and lapses in the 5-h group) remained at the stable, but reduced levels seen during the last days of the experimental phase, with no evidence of recovery. Speed and lapses in the 3-h group recovered rapidly following the first night of recovery sleep; however, recovery was incomplete with speed and lapses stabilizing at a level comparable with the 7- and 5-h groups. Performance in the 9-h group remained at baseline levels during the recovery phase. These results suggest that the brain adapts to chronic sleep restriction. In mild to moderate sleep restriction this adaptation is sufficient to stabilize performance, although at a reduced level. These adaptive changes are hypothesized to restrict brain operational capacity and to persist for several days after normal sleep duration is restored, delaying recovery.

Adaptation, Psychological↗
PubMed2002

The process of awakening: a PET study of regional brain activity patterns mediating the re-establishment of alertness and consciousness.

Awakening from sleep entails rapid re-establishment of consciousness followed by the relatively slow (20-30 min later) re-establishment of alertness--a temporal dissociation that facilitates specification of the physiological underpinnings of each of these facets of the awakening process. H(2)(15)O PET was used to assess changes in regional cerebral blood flow (rCBF) upon awakening from stage 2 sleep. Cerebral blood flow (CBF) was most rapidly re-established in centrencephalic regions (e.g. brainstem and thalamus), suggesting that the reactivation of these regions underlies the re-establishment of conscious awareness. Across the ensuing 15 min of wakefulness, further increases in CBF were evident primarily in anterior cortical regions, suggesting that the dissipation of sleep inertia effects (post-awakening performance and alertness deficits) is effected by reactivation of these regions. Concomitant shifts in correlation patterns of regional brain activity across the post-awakening period [in particular, a waning negative correlation between prefrontal cortex and mesencephalic reticular formation (RF) activity, and a waxing positive correlation between prefrontal cortex and ventromedial caudate nucleus (CAUD) activity] suggest that the post-awakening reversal of sleep inertia effects may be mediated by more than mere reactivation--it may also involve the functional reorganization of brain activity. Conversely, stable post-awakening correlations--such as those found between the anterior cingulate cortex (ACC) and most other brain regions--may denote the pattern of functional connectivity that underlies consciousness itself.

Adult↗
PubMed2001

Maintaining alertness and performance during sleep deprivation: modafinil versus caffeine.

RATIONALE: The performance and alertness effects of modafinil were evaluated to determine whether modafinil should replace caffeine for restoring performance and alertness during total sleep deprivation in otherwise healthy adults. OBJECTIVES: Study objectives were to determine (a) the relative efficacy of three doses of modafinil versus an active control dose of caffeine 600 mg; (b) whether modafinil effects are dose-dependent; and (c) the extent to which both agents maintain performance and alertness during the circadian trough. METHODS: Fifty healthy young adults remained awake for 54.5 h (from 6:30 a.m. day 1 to 1:00 p.m. on day 3) and performance and alertness tests were administered bi-hourly from 8:00 a.m. day 1 until 10:00 p.m. day 2. At 11:55 p.m. on day 2 (after 41.5 h awake), subjects received double blind administration of one of five drug doses: placebo; modafinil 100, 200, or 400 mg; or caffeine 600 mg ( n=10 per group), followed by hourly testing from midnight through 12:00 p.m. on day 3. RESULTS: Performance and alertness were significantly improved by modafinil 200 and 400 mg relative to placebo, and effects were comparable to those obtained with caffeine 600 mg. Although a trend toward better performance at higher modafinil doses suggested a dose-dependent effect, differences between modafinil doses were not significant. Performance enhancing effects were especially salient during the circadian nadir (6:00 a.m. through 10:00 a.m.). Few instances of adverse subjective side effects (nausea, heart pounding) were reported. CONCLUSIONS: Like caffeine, modafinil maintained performance and alertness during the early morning hours, when the combined effects of sleep loss and the circadian trough of performance and alertness trough were manifest. Thus, equivalent performance- and alertness-enhancing effects were obtained with drugs possessing different mechanisms of action. However, modafinil does not appear to offer advantages over caffeine (which is more readily available and less expensive) for improving performance and alertness during sleep loss in otherwise normal, healthy adults.

Administration, Oral↗