Ambulatory monitoring of sleep disorders.

BACKGROUND: Behavioural and functional activity monitoring has a long history in sleep research. The term "Actigraphy" refers to methods using computerized wristwatch-size devices (generally placed on the wrist, but also on the ankle or trunk) to record the movement it undergoes. Collected data are displayed on a computer and analyzed for change in rhythm parameters that in turn provide an estimate on wake-sleep parameters (such as total sleep time, percent of time spent asleep, total wake time, percent of time spent awake and the number of awakenings). Actigraphy provides a useful, cost-effective, non-invasive and portable method for assessing specific sleep disorders. The present review is an amalgam of current knowledge with proposed clinical application and for research of actigraph. CONCLUSION: Actigraphy cannot stand alone as a diagnostic tool for all clinical groups. Particularly so with those diagnosed with sleep disorders with significant motility or long catatonic periods of wakefulness during sleep.

Recommendations for the ethical use of pharmacologic fatigue countermeasures in the U.S. military.

Culture and public opinion strongly influence debates on ethics-and what may be ethically acceptable to one nationality may be unacceptable to others. In military operations, some cognitive performance enhancement technologies are more ethically controversial than others. Of the enhancement technologies, use of psychoactive pharmaceuticals to alter behavior in healthy humans possibly presents the most controversial ethical challenge. Discussion of the bioethics of psychoactive enhancement agents is advisable because their military use is increasing while doctrine for their use remains limited. This paper focuses on psychoactive pharmaceuticals to enhance cognitive performance of military members. The topics addressed include: the use of psychoactive pharmaceuticals within a coalition framework; if ethical circumstances do exist for their use, what are these circumstances in clear and operationally useful terms; and guidelines to aid leaders in making ethically acceptable decisions. These questions should be answered: 1) Is use truly informed and voluntary--e.g., is an individual soldier requesting the medication with full understanding of its primary effects and side effects; 2) Is the medication safe for use in this individual, and safe within the context of the operational environment?; 3) Is the use of the medication consistent with its dosage and pharmacological function--i.e., is a sleep-inducing medication being used at appropriate doses, for a specified period, to facilitate sleep; and 4) Have available non-pharmacologic alternatives been fully utilized? This paper addresses a very narrow segment of the larger bioethics discussion: the use of pharmacologic enhancing agents in military members in times of war or national emergency.

Neurocognitive monitors: toward the prevention of cognitive performance decrements and catastrophic failures in the operational environment.

Network-centric doctrine and the proposed C41SR (command, control, communications, computers, intelligence, surveillance and reconnaissance) distributions to the individual warfighter require that the cognitive performance, judgment, and decision making of warfighters must be sustained and effectively managed in the forward operating environment, where various physiological and psychological stressors abound, in order to reduce human errors and catastrophic failures. The U.S. Army Medical Research and Materiel Command (USAMRMC) established the Cognitive Performance, Judgment, and Decision-Making Research Program (CPJDRP) in 2004 to direct research to this issue. A Neurophysiological Measures and Cognition Focus Team (NMFCT) was formed to work with augmented cognition investigators and to specifically address the development of neurophysiological measures as potential monitors of alertness-cognitive state in warfighters. The USAM-RMC approach complemented the Defense Advanced Research Projects Agency (DARPA) Augmented Cognition approach, which focused on the detection of workload-related impaired cognitive state, and subsequent modification of information flow through automation. In this preface, the premise for neurophysiological measures as neurocognitive monitors is explained using an example of a neurophysiological index: the oculomotor measure, saccadic velocity. The progress of the NMFCT on the development of a neurocognitive monitor is described, as well as the recommendations of a 2005 USAMRMC/Telemedicine and Advanced Technology Research Center (TATRC)-sponsored workshop. Awareness of neurocognitive monitoring is discussed, as are future endeavors related to operational testing and fieldability. Four papers are summarized in this Neurophysiological Monitoring and Augmented Cognition section involving technologies to enhance cognitive performance in the operational environment: one on dynamic cortical electroencephalography, two on oculometrics, and one on a spatial orientation enhancement system.

Stress, mental health, and cognition: a brief review of relationships and countermeasures.

Today's network-centric battlefield environment is highly stressful and cognitively demanding. Many warfighters are feeling overwhelmed and end up being medically evacuated from theater due to mental health problems [i.e., post traumatic stress disorder (PTSD) and depression]. Of a sample of troops evacuated for psychiatric reasons, 21% (106 out of 509) had psychiatric histories prior to deploying to the theater of operations. Most cases were either related to stress (i.e., PTSD, n - 33, 310%) or to depression (n = 72, 66%). Stress disorders and depression predominate among the psychiatric causes for medical evacuation. This review paper discusses stress theories as they pertain to warfighting, the types of stress and stress disorders most prevalent on modern battlefields, the relationships among stress, psychiatric disease, and cognitive performance, and potential methods to decrease some types of stress-related acute and chronic disorders (i.e., virtual-reality stress inoculation training).

Cognitive performance and communications in a network-centric battle laboratory.

Many of the technological advances in the information sciences that make the network-centric battlefield possible will also foster methodologies that enable the study of the warfighter in this environment. Specifically, the tactical events and computer networks in a battle laboratory can be designed with capabilities to facilitate capture and analysis of embedded operational performance metrics. This paper refers to the Air Maneuver Battle Laboratory environment, its command and control components, its synthetic battle environment, and its basic communications structure as an example. This paper also introduces two papers. In the first paper, O'Donnell, Moise, and Schmidt describe their generalized methodology to evaluate personnel during performance of operational tasks. They discuss a cognitive taxonomy, test generator, and synthetic cognitive and motor tests with applicability to military or civilian tasks. Personnel are evaluated with these synthetic tests for those very cognitive skills and capabilities most required to successfully perform the actual operational task of interest. Perhaps the illustrative and innovative measurement methodologies described will encourage others to consider how new approaches can be used to leverage the study of cognitive performance of the future warfighter in a network-centric environment. The second paper by Whitmore discusses how communications and embedded operational performance metrics may be acquired in teams. Whitmore highlights some critical aspects leading to the successful measurement of team performance in realistic console operations; discusses the idea of process and outcome measures; presents two types of team data collection systems; and provides an example of team performance assessment.

Monitoring and predicting cognitive state and performance via physiological correlates of neuronal signals.

Judgment, decision making, and situational awareness are higher-order mental abilities critically important to operational cognitive performance. Higher-order mental abilities rely on intact functioning of multiple brain regions, including the prefrontal, thalamus, and parietal areas. Real-time monitoring of individuals for cognitive performance capacity via an approach based on sampling multiple neurophysiologic signals and integrating those signals with performance prediction models potentially provides a method of supporting warfighters' and commanders' decision making and other operationally relevant mental processes and is consistent with the goals of augmented cognition. Cognitive neurophysiological assessments that directly measure brain function and subsequent cognition include positron emission tomography, functional magnetic resonance imaging, mass spectroscopy, near-infrared spectroscopy, magnetoencephalography, and electroencephalography (EEG); however, most direct measures are not practical to use in operational environments. More practical, albeit indirect measures that are generated by, but removed from the actual neural sources, are movement activity, oculometrics, heart rate, and voice stress signals. The goal of the papers in this section is to describe advances in selected direct and indirect cognitive neurophysiologic monitoring techniques as applied for the ultimate purpose of preventing operational performance failures. These papers present data acquired in a wide variety of environments, including laboratory, simulator, and clinical arenas. The papers discuss cognitive neurophysiologic measures such as digital signal processing wrist-mounted actigraphy; oculometrics including blinks, saccadic eye movements, pupillary movements, the pupil light reflex; and high-frequency EEG. These neurophysiological indices are related to cognitive performance as measured through standard test batteries and simulators with conditions including sleep loss, time on task, and aviation flight-induced fatigue.

Cognition, blinks, eye-movements, and pupillary movements during performance of a running memory task.

INTRODUCTION: Blinks, saccades, and pupil diameter changes are studied for their application as tools to unobtrusively monitor aspects of performance. METHODS: Subjects performed a running memory task for a 60-min period. To evaluate changes in the relationship of blinks to saccades as a function of time on task, the ratio of blinks occurring with and without saccade was calculated for the second following stimulus termination plus the last 0.2 s of stimulus presentation, and also the second preceding stimulus onset plus the initial 0.2 s of stimulus presentation. Changes in pupil diameter following blinks with and without saccades were measured at the beginning, middle, and late in the experiment. RESULTS: Blink frequency increased during both periods as a function of time on task (p < 0.0001). The ratio of blinks concurrent with saccades during the post-stimulus period increased as a function of time on task (p < 0.0001). Pupil diameter increased following blink termination (p < 0.05), regardless of time on task, blink duration, or the presence of a saccade during the blink. CONCLUSION: Our results suggest that the increase in blinking associated with saccades as a function of time on task, and the pupillary dilation following a blink are associated with aspects of information processing. These results provide a framework for future studies assessing higher-order cognitive function in operational environments based on measurements of blink, pupil, and saccades.

Assessing psychoactive pharmaceuticals and transitioning pharmacological fatigue countermeasures into operational environments.

Herein we summarize a discussion on the topic of how psychopharmaceuticals for potential military operational use may be evaluated based on their effects on performance and safety, and introduce two manuscripts: the first (Caldwell and Caldwell; 1) addressing the operational use of fatigue countermeasures; and the second (Rowland; 3) discussing the potential operational use and limitations of ketamine as a field analgesic. Fatigue countermeasures are usually employed by a relatively small number of military members engaged in sustained or continuous operations when sleep is not an option. Clinical treatments are available at any time as required to treat medical conditions. The issue of importance for the operational community, with regard to both clinical use of psychopharmaceuticals and performance maintenance through fatigue countermeasures, should be whether the medication impairs operationally relevant performance, assuming the disorder for which the medication is prescribed does not in itself prohibit operational duties. Applied research paradigms are generally discussed for assessing and transitioning pharmaceutical compounds from the laboratory to the operational environment. Tier 1 focuses on quantifying the impact of stressors and interventions in healthy members of the general population, while Tier 2 testing would use military or operationally matched volunteers in simulated or actual field environments. The section papers address two areas of operational relevance--the Caldwell and Caldwell paper presents guidelines for the use of fatigue countermeasures, and the Rowland paper discusses the potential effects of ketamine, an agent intended to replace morphine as a battlefield analgesic, on cognition.

Human biovibrations: assessment of human life signs, motor activity, and cognitive performance using wrist-mounted actigraphy.

The application of miniature motion sensors (accelerometers) to study the macro- (gross) and micro- (barely discernible) activities associated with human motion has been termed actigraphy. In countless human sleep studies, actigraphy has mostly been applied to distinguish between when a person is asleep or awake. Use of sleep/wake information has been applied to the development of mathematical models that aim to predict aspects of cognitive performance. However, wrist-mounted actigraphy potentially has many more applications to cognitive and physical assessment beyond sleep/wake discrimination. For example, studies reveal that micro-miniature accelerometric sensors can discriminate heart rate, breathing, and life cessation (death) via actigraphically measured biovibration signals. This paper briefly reviews the development of wrist-mounted actigraphy; presents the data showing wrist-monitored ballistocardioimpulses, respirations, and life-signs signals; discusses the application of sophisticated signal processing for new clinical, operational, and cognitive-assessment-related applications; and concludes with recommendations for further research for demodulating the complex actigram signal.

High-frequency EEG as measure of cognitive function capacity: a preliminary report.

BACKGROUND: High-frequency EEG (HFE) as a potential predictor of alertness/drowsiness was first proposed by Kaplan and Loparo. Sampling EEG at 950 Hz, they established an HFE bandwidth of interest ranging from 100-475 Hz. We extend their work by applying discrete Fourier transform (DFT) of HFE signals sampled at 1000 Hz and partitioned into spectral bands along specific frequency ranges for the assessment of sleep-wake state transition, sleep, and active cognitive engagement. METHODS: There were 13 volunteers (6 men, 7 women, 30 +/- 3 yr) who participated in a 40-h sleep-deprivation study, during which time they performed multiple cognitive tasks. EEG, in synchrony with other physiological signals, was collected at a sampling rate of 1000 Hz. EEG and task performance results from two volunteers are discussed in this preliminary analysis of the C3-C4 region data. Spectral components obtained from DFT are delineated into five main frequency bands: low, (LFB, 1-15 Hz); intermediate (IFB, 16-50 Hz); and 3 high frequency bands: HFB1 (51-100 Hz); HFB2 (101-200 Hz); and HFB3 (201-500 Hz) for analysis purposes. RESULTS: LFB in the 1-15 Hz range at 0.40 spectrum proportion indicated declining alertness; LFB above 0.50 signals transition to sleep; and LFB at 0.70 indicates Stage 2/3 sleep. HFB3 in the 201-500 Hz range at 0.25 and above was a marker of cognitive function and/or capacity. CONCLUSIONS: HFE may provide a quantitative measure of cognitive function capacity. LFB may provide a measure for awake, asleep, or awake-sleep transition, and HFB3 an estimate of cognitive task engagement. HFE may be applied for electroencephalographic monitoring of cognitive performance.

Visual perception, psychomotor performance, and complex motor performance during an overnight air refueling simulated flight.

INTRODUCTION: Visual perception task, complex motor flight task, and psychomotor vigilance task performances were evaluated in U.S. Air Force pilots navigating a high-fidelity fixed wing jet simulator over 26.5 h of continuous wakefulness. METHODS: Eight military pilots on flight status performed the primary task of flying a simulated 12.5-h overnight mission in an Air Refueling Part Task Trainer (ARPTT): Response omission to presentation of single- and double-light stimuli displayed in random sequence across the cockpit instrument panel was the metric used to assess choice visual perception task (CVPT) performance. Deviation from an established azimuth heading in the ARPTT during the CVPT was the flight metric used to assess complex motor performance. Speed, lapse, false start, and anticipation were the metrics used to assess psychomotor vigilance task (PVT) performance during crew rest periods. RESULTS: Significant visual perceptual, complex motor, and psychomotor vigilance (speed and lapse) impairments occurred at 19 h awake in the eight-subject group. CVPT response omissions significantly correlated with ARPTT azimuth deviations at r = 0.97, and with PVT speed at r = -0.92 and lapses at r = 0.90. ARPTT azimuth deviations significantly correlated with PVT speed at r = -0.92 and lapses at r = 0.91. CONCLUSIONS: Acute sleep deprivation degrades visual perceptual, complex motor, and simple motor performance. Complex motor impairments strongly correlate with visual perceptual impairments. This research provides support for the use of visual perceptual measures as surrogates of complex motor performance in operational situations where the primary cognitive inputs are through the visual system.

Visual neglect: occurrence and patterns in pilots in a simulated overnight flight.

INTRODUCTION: Visual neglect is the unconscious inability to recognize or acknowledge some visual information in the presence of a structurally intact visual system, and was hypothesized to occur with less than 24 h of continuous wakefulness. Visual perception was evaluated in military pilots during a simulated overnight flight to explore for the possible occurrence of visual neglect. METHODS: There were eight military pilots (male, 31-52 yr of age, mean 37 yr) on flight status who were recruited to perform the primary task of flying a simulated 12.5 h overnight mission after a day of continuous wakefulness and the secondary task of responding to repeated 20 min presentations of single- and double-light stimuli displayed in random sequence at 15 degrees intervals across the cockpit instrument panel. In addition to the visual performance task, simulator shutdowns occurring when the tolerances of the simulator were exceeded were measured and simple reaction time on the psychomotor vigilance task was assessed. Total continuous wakefulness was 26.5 h. RESULTS: Combined performance on the visual perception task showed response omissions increasing at 19 h of continuous wakefulness. Patterns included omissions at all stimulus locations, of primarily peripherally located stimuli, and of one of two simultaneously presented stimuli. Simulator shutdowns began at 21.5 h of continuous wakefulness. Correlation of visual task response omissions with simulator shutdowns was r = 0.95, p < 0.0001. CONCLUSIONS: Significant neglect of visual stimuli occurred in pilots beginning at 19 h of continuous wakefulness in a simulated overnight fixed wing aircraft flight, preceded simulator shutdowns, and correlated at 0.95 with simulator shutdowns.

The effects of chronic partial sleep deprivation on cognitive functions of medical residents.

OBJECTIVES: Because of on-call responsibilities, many medical residents are subjected to chronic partial sleep deprivation, a form of sleep restriction whereby individuals have chronic patterns of insufficient sleep. It is unclear whether deterioration in cognitive processing skills due to chronic partial sleep deprivation among medical residents would influence educational exposure or patient safety. METHOD: Twenty-six medical residents were recruited to participate in the study. Participants wore an Actigraph over a period of 5 consecutive days and nights so their sleep pattern could be recorded. Thirteen participants worked on services that forced chronic partial sleep deprivation (<6 hours of sleep per 24h for 5 consecutive days and nights). The other thirteen residents worked on services that permitted regular and adequate sleep patterns. Following the 5-day sleep monitoring period, the participants completed the three following cognitive tasks: (a) the Wisconsin Card Sorting Test (WCST) to assess abstract reasoning and prefrontal cortex performance; (b) the Time Perception Task (TPT) to assess time estimation and time reproduction skills; and (c) the Iowa Gambling Task (IGT) to assess decision-making ability. RESULTS: The results of independent samples t-tests found no significant differences between the group who was chronically sleep deprived and the group who rested adequately (all ps > .05). CONCLUSION: THESE RESULTS MAY HAVE EMERGED FOR SEVERAL POSSIBLE REASONS: (a) chronic partial sleep deprivation may have a lesser impact on prefrontal cortex function than on other cognitive functions; (b) fairly modest chronic sleep restriction may be less harmful than acute and more significant sleep restriction; or (c) our research may have suffered from poor statistical power. Future research is recommended.

Operational implications of varying ambient light levels and time-of-day effects on saccadic velocity and pupillary light reflex.

Changes in maximal saccadic velocity (SV), initial pupil diameter (IPD), constriction latency (CL) and constriction amplitude (CA) determined by the pupillary light reflex have been found to be sensitive indicators of impairment as a result of drugs, sleepiness, and/or fatigue. Ambient illuminance and time of day are controlled when these indices are applied as repeated measures in fitness-for-duty determinations. The application of oculometrics in unrestricted operational environments, where ambient illuminance and time-of-day testing are not constant, requires understanding of, and potential compensation for, the effects of, and interactions among, these multiple uncontrolled variables. SV, IPD, CL, and CA were evaluated in the morning and evening on two consecutive days following adequate nightly sleep under one baseline ambient illuminance and seven test ambient illuminances. Sixteen healthy volunteers (21-38 years, eight females/eight males) participated. Within and across days, SV was unaffected by decreasing ambient light or time-of-day effects. With the increase of ambient light from 670 to 3300 lx, CL decreased by 1%, while IPD and CA decreased by 17% and 20%, respectively. IPD increased with time of day by 1-10% (IPD was smaller in the morning). The results show that SV and CL are essentially resistant to changes in ambient light and time-of-day effects, simplifying their application in uncontrolled operational environments.

Effects of sleep deprivation on lateral visual attention.

Sleep loss temporarily impairs vigilance and sustained attention. Because these cognitive abilities are believed to be mediated predominantly by the right cerebral hemisphere, this article hypothesized that continuous sleep deprivation results in a greater frequency of inattention errors within the left versus right visual fields. Twenty-one participants were assessed several times each day during a 40-h period of sustained wakefulness and following a night of recovery sleep. At each assessment, participants engaged in a continuous serial addition task while simultaneously monitoring a 150 degrees visual field for brief intermittent flashes of light. Overall, omission errors were most common in the leftmost peripheral field for all sessions, and did not show any evidence of a shift in laterality as a function of sleep deprivation. Relative to rested baseline and postrecovery conditions, sleep deprivation resulted in a global increase in omission errors across all visual locations and a general decline in serial addition performance. These findings argue against the hypothesis that sleep deprivation produces lateralized deficits in attention and suggest instead that deficits in visual attention produced by sleep deprivation are global and bilateral in nature.

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.