A review of the biological effects of total sleep deprivation in man

The Effects of Total Sleep Deprivation on Attention Capture Processes in Young and Older Adults: An ERP Study

BACKGROUND

The present study investigated whether sleep deprivation affects attention capture in young and older adults using event-related potentials (ERPs).

METHODS

Eleven young adults (20-30 y) and nine older adults (60-70 y) were tested following both normal sleep (NS) and total sleep deprivation (TSD). ERPs were recorded during an auditory discrimination task consisting of standard and deviant stimuli.

RESULTS

Deviant stimuli elicited the MMN, P3a, and RON ERPs. TSD attenuated the differences in reaction times between standards and deviants in young adults but not older adults. The P3a was attenuated in older adults compared to young adults. Older adults had a larger RON amplitude compared to young adults following NS, but not TSD.

CONCLUSIONS

The reduced P3a and the absence of behavioral performance alteration in the older group suggests that older adults may utilize different neural processing strategies compared to younger adults to compensate for age-related declines in neural resources for attention capture. Sleep loss influenced age-related differences on the RON, suggesting that older adults may have reduced access to compensatory strategies following sleep loss.

Electrodermal Activity Is Sensitive to Sleep Deprivation but Does Not Moderate the Effect of Total Sleep Deprivation on Affect

Emotion is characterized by dimensions of affective valence and arousal, either or both of which may be altered by sleep loss, thereby contributing to impaired regulatory functioning. Controlled laboratory studies of total sleep deprivation (TSD) generally show alterations in physiological arousal and affective state, but the relationship of affect and emotion with physiological arousal during TSD has not been well characterized. Established methods for examining physiological arousal include electrodermal activity (EDA) measures such as non-specific skin conductance responses (NSSCR) and skin conductance level (SCL). These measures are robust physiological markers of sympathetic arousal and have been linked to changes in experienced emotion. To explore the link between physiological arousal and affect during sleep deprivation, we investigated individuals' EDA under TSD and its relationship to self-reported affect. We also investigated the relationship of EDA to two other measures known to be particularly sensitive to the arousal-decreasing effects of TSD, i.e., self-reported sleepiness and performance on a vigilant attention task. Data were drawn from three previously published laboratory experiments where participants were randomly assigned to either well-rested control (WRC) or 38 h of TSD. In this data set, comprising one of the largest samples ever used in an investigation of TSD and EDA (N = 193 with 74 WRC and 119 TSD), we found the expected impairing effects of TSD on self-reported affect and sleepiness and on vigilant attention. Furthermore, we found that NSSCR, but not SCL, were sensitive to TSD, with significant systematic inter-individual differences. Across individuals, the change in frequency of NSSCR during TSD was not predictive of the effect of TSD on affect, sleepiness, or vigilant attention, nor was it related to these outcomes during the rested baseline. Our findings indicate that while physiological arousal, as measured by EDA, may be useful for assessing TSD-related changes in non-specific arousal at the group level, it is not associated with individuals' self-reported affect at rest nor their change in affect during TSD. This suggests that an essential aspect of the relationship between physiological arousal and self-reported affect is not well captured by EDA as measured by NSSCR.

Sleep Deprivation, Immune Suppression and SARS-CoV-2 Infection

Sleep health and its adaptation to individual and environmental factors are crucial to promote physical and mental well-being across animal species. In recent years, increasing evidence has been reported regarding the relationship between sleep and the immune system and how sleep disturbances may perturb the delicate balance with severe repercussions on health outcomes. For instance, experimental sleep deprivation studies in vivo have reported several major detrimental effects on immune health, including induced failure of host defense in rats and increased risk for metabolic syndrome (MetS) and immune suppression in humans. In addition, two novel risk factors for dysregulated metabolic physiology have recently been identified: sleep disruption and circadian misalignment. In light of these recent findings about the interplay between sleep and the immune system, in this review, we focus on the relationship between sleep deprivation and immunity against viruses, with a special interest in SARS-CoV-2 infection.

Human Performance Deterioration Due to Prolonged Wakefulness Can Be Accurately Detected Using Time-Varying Spectral Analysis of Electrodermal Activity

OBJECTIVE

The aim was to determine if indices of the autonomic nervous system (ANS), derived from the electrodermal activity (EDA) and electrocardiogram (ECG), could be used to detect deterioration in human cognitive performance on healthy participants during 24-hour sleep deprivation.

BACKGROUND

The ANS is highly sensitive to sleep deprivation.

METHODS

Twenty-five participants performed a desktop-computer-based version of the psychomotor vigilance task (PVT) every 2 hours. Simultaneously with reaction time (RT) and false starts from PVT, we measured EDA and ECG. We derived heart rate variability (HRV) measures from ECG recordings to assess dynamics of the ANS. Based on RT values, average reaction time (avRT), minor lapses (RT > 500 ms), and major lapses (RT > 1 s) were computed as indices of performance, along with the total number of false starts.

RESULTS

Performance measurement results were consistent with the literature. The skin conductance level, the power spectral index, and the high-frequency components of HRV were not significantly correlated to the indices of performance. The nonspecific skin conductance responses, the time-varying index of EDA (TVSymp), and normalized low-frequency components of HRV were significantly correlated to indices of performance ( p < 0.05). TVSymp exhibited the highest correlation to avRT (-0.92), major lapses (-0.85), and minor lapses (-0.83).

CONCLUSION

We conclude that indices that account for high-frequency dynamics in the EDA, specifically the time-varying approach, constitute a valuable tool for understanding the changes in the autonomic nervous system.

APPLICATION

This can be used to detect the adverse effects of prolonged wakefulness on human performance.

Sleep Deprivation in Young and Healthy Subjects Is More Sensitively Identified by Higher Frequencies of Electrodermal Activity than by Skin Conductance Level Evaluated in the Time Domain

We analyzed multiple measures of the autonomic nervous system (ANS) based on electrodermal activity (EDA) and heart rate variability (HRV) for young healthy subjects undergoing 24-h sleep deprivation. In this study, we have utilized the error awareness test (EAT) every 2 h (13 runs total), to evaluate the deterioration of performance. EAT consists of trials where the subject is presented words representing colors. Subjects are instructed to press a button (“Go” trials) or withhold the response if the word presented and the color of the word mismatch (“Stroop No-Go” trial), or the screen is repeated (“Repeat No-Go” trials). We measured subjects' (N = 10) reaction time to the “Go” trials, and accuracy to the “Stroop No-Go” and “Repeat No-Go” trials. Simultaneously, changes in EDA and HRV indices were evaluated. Furthermore, the relationship between reactiveness and vigilance measures and indices of sympathetic control based on HRV were analyzed. We found the performance improved to a stable level from 6 through 16 h of deprivation, with a subsequently sustained impairment after 18 h. Indices of higher frequencies of EDA related more to vigilance measures, whereas lower frequencies index (skin conductance leve, SCL) measured the reactiveness of the subject. We conclude that indices of EDA, including those of the higher frequencies, termed TVSymp, EDASymp, and NSSCRs, provide information to better understand the effect of sleep deprivation on subjects' autonomic response and performance.

Schizophrenia: the role of sleep and circadian rhythms in regulating dopamine and psychosis

Schizophrenia has long been associated with abnormalities in circadian rhythms and sleep. Up until now, there have been no thorough reviews of the potential mechanisms behind the myriad of circadian and sleep abnormalities observed in schizophrenia and psychosis. We present evidence of sleep playing an important role in psychosis predominantly mediated by dopaminergic pathways. A synthesis of both human and animal experimental work suggests that the interplay between sleep and dopamine is important in the generation and maintenance of psychosis. In particular, both animal and human data point to sleep disruption increasing dopamine release and sensitivity. Furthermore, elevated dopamine levels disrupt sleep and circadian rhythms. The synthesis of knowledge suggests that circadian rhythms, dopamine dysregulation, and psychosis are intricately linked. This suggests that treatment of circadian disturbance may be a useful target in improving the lives and symptoms of patients with schizophrenia.

Degradation of Performance Due to Sleep Deprivation: A Field Test

During a 72 h field test, two groups of elite, “ranger type” soldiers were evaluted five times (during the first 8 h, after 30 h of continuous field duty, after a rest period, after 30 more h of continuous field duty, and after a second rest). One group (7 soldiers) received two rests of 3 h each. The second group (6 soldiers) received two rests of 6 h each. Five military tasks (map reading, decoding messages, vehicle/aircraft recognition, assembly and disassembly of the M-16 rifle, and preparation of an AN/PRC radio for operation) were used. These tasks were considered by the commander to be representative of duties that the soldiers would do and were considered to be completely familiar to the soldiers. In addition, a peg into pegboard task and a subjective evaluation of fatigue questionnaire were given.

There was no significant effect of time or difference between the two groups. The soldiers completed these tasks of short duration (less than 3 min) without decreasing performance—even after extended periods of sleep loss. These performance results occurred even though subjectively the soldiers reported they were tired.

Transcranial magnetic stimulation in sleep fragmentation: a model to better understand sleep disorders

OBJECTIVE

To investigate practice-dependent plasticity and cortical inhibition/excitability in good sleepers after a night of sleep fragmentation (SF), by means of transcranial magnetic stimulation (TMS).

METHODS

In basal condition (BC), after a full night of spontaneous sleep, and in fragmented condition (FC), after a fragmented night of sleep, motor evoked potential (MEP) amplitude, motor threshold (MT), silent period (SP), and intracortical inhibition were assessed. In both conditions subjects performed, also, a bimanual motor task: MEPs were recorded before and after exercise, and after rest. We evaluated the presence of post-exercise facilitation and delayed facilitation. Subjects reported their alertness level (Stanford Sleepiness Scale-SSS).

RESULTS

MT and SSS were significantly increased in SF. Instead, no significant differences for MEP amplitude or SP or intracortical inhibition were found. In both conditions post-exercise facilitation and delayed facilitation were present.

CONCLUSION

SF produces disruption of nocturnal sleep and increases daytime sleepiness. Confirmatory features of this clinical behaviour could be that in FC we observed a significant increase in SSS and in MT. SF was unable to modify cortical inhibition\excitability and\or to influence plasticity-related parameters. These results seem inconsistent with some of TMS alterations observed in sleep deprivation (SD) and restless legs syndrome (RLS). We suggest that SD and SF represent different phenomena that can depend on various networks acting on motor cortex. We speculate that alterations in cortical excitability found in RLS are intrinsically related to the underlying disease itself and are not instead directly associated with the SF present in RLS.

Effect of short-duration sleep deprivation on the vestibulo-ocular reflex system evaluated by ocular vestibular-evoked myogenic potential test

CONCLUSION

The ocular vestibular-evoked myogenic potential (oVEMP) test yields the same information as the rotational test in sleep-deprived subjects as evidenced by increased vestibulo-ocular reflex (VOR) asymmetry. However, the duration of sleep deprivation (12 h) and testing time required for the oVEMP test are shorter than for the rotational test.

OBJECTIVE

This study utilized the oVEMP test in sleep-deprived subjects to investigate the effect of short-duration sleep deprivation on the VOR system.

METHODS

Twenty healthy resident physicians underwent oVEMP and cervical VEMP (cVEMP) tests twice in a randomized order; one test battery was performed after a normal sleep, and the other was performed after a night duty at the emergency service, which meant a state of 12 h sleep deprivation.

RESULTS

All 20 subjects had clear oVEMPs regardless of whether testing was performed after a normal sleep or 12 h sleep deprivation condition. Significant differences were not identified between the two sleep conditions in terms of characteristic parameters, i.e. latencies and amplitude of oVEMPs. However, the mean asymmetry ratio after sleep deprivation (20 ± 13%) was significantly larger than that after normal sleep (8 ± 12%). Conversely, the cVEMP parameters did not differ significantly between the two sleep conditions.

Novel mechanistic insights into treadmill exercise based rescue of social defeat-induced anxiety-like behavior and memory impairment in rats

Social defeat (SD) induced stress causes physiological and behavioral deficits in rodents, including depression and anxiety-like behaviors, as well as memory impairment. Anxiolytic and mood elevating effects of physical exercise are also known. However, rescue effect of physical exercise in social defeat-induced anxiety, depression or memory impairment has not been addressed. The role of epigenetic mechanisms that potentially contribute to these rescue or protective effects is also not known. The present study investigated the effect of moderate treadmill exercise on anxiety-like behavior and memory function in rats subjected to SD using a modified version of the resident-intruder model for social stress (defeat). Changes in histone acetylation and histone-modifying enzymes were examined in hippocampus, amygdala and frontal cortex which are considered critical for anxiety, depression and cognition. Sprague Dawley rats were randomly assigned in four groups; control, exercised, social defeat, social defeat and exercise. At the end of the SD or control exposure lasting 30 min daily for 7 days, one group of SD rats was subjected to treadmill exercise for 2 weeks, whereas the other SD group was handled without exercise. Anxiety-like behavior tests and radial arm water maze test suggested that moderate treadmill exercise rescued social defeat induced anxiety-like behavior and memory impairment. Moreover, exercise normalized SD-induced increase in oxidative stress, most likely by adjusting antioxidant response. Our data suggests involvement of epigenetic mechanisms including histone acetylation of H3 and modulation of methyl-CpG-binding in the hippocampus that might contribute to the rescue effects of exercise in SD-induced behavioral deficits in rats.

Neurobiological consequences of sleep deprivation

Although the physiological function of sleep is not completely understood, it is well documented that it contributes significantly to the process of learning and memory. Ample evidence suggests that adequate sleep is essential for fostering connections among neuronal networks for memory consolidation in the hippocampus. Sleep deprivation studies are extremely valuable in understanding why we sleep and what are the consequences of sleep loss. Experimental sleep deprivation in animals allows us to gain insight into the mechanism of sleep at levels not possible to study in human subjects. Many useful approaches have been utilized to evaluate the effect of sleep loss on cognitive function, each with relative advantages and disadvantages. In this review we discuss sleep and the detrimental effects of sleep deprivation mostly in experimental animals. The negative effects of sleep deprivation on various aspects of brain function including learning and memory, synaptic plasticity and the state of cognition-related signaling molecules are discussed.

Oxidative stress, cancer, and sleep deprivation: is there a logical link in this association?

INTRODUCTION

Sleep disorders are associated with various human pathologies and interfere with biological processes essential for health and quality of life. On the other hand, cancer is one of the most common diseases worldwide with an average of 1,500 deaths per day in the USA. Is there a factor common to both sleep disorders and cancer that serves to link these conditions?

DISCUSSION

It is a normal process for cellular metabolism to produce reactive oxidant series (ROS). However, when the production of ROS overcomes the antioxidant capacity of the cell to eliminate these products, the resulting state is called oxidative stress. Oxidative DNA damage may participate in ROS-induced carcinogenesis. Moreover, ROS are also produced in the sleep deprivation process. The aim of this article is to review pathways and mechanisms that may point to oxidative stress as a link between sleep deprivation and cancer.

Exercise prevents sleep deprivation-associated anxiety-like behavior in rats: potential role of oxidative stress mechanisms

Our previous work suggests that pharmacological induction of oxidative stress causes anxiety-like behavior in rats. Interestingly, sleep deprivation is reported to cause oxidative damage in the brain and is also reported to be anxiogenic. Minimal mechanistic insights are available. In this study, using a behavioral and biochemical approach, we investigated involvement of oxidative stress mechanisms in sleep deprivation-induced anxiety-like behavior of rats and the protective role of treadmill exercise in this process. We report that acute sleep deprivation (SD) increases oxidative stress in the cortex, hippocampus and amygdala while prior treadmill exercise prevents this increase. Serum corticosterones also increase with SD but its levels are normalized in exercised sleep-deprived rats. Also, anxiety-like behavior of rats significantly increases with SD while prior treadmill exercise prevents this increase. Protein expression of two enzymes involved in antioxidant defense, glyoxalase (GLO)-1 and glutathione reductase (GSR)-1 increased after 24h SD in the hippocampus, cortex and amygdala while their levels were normalized in exercised sleep-deprived rats. It is plausible that oxidative stress via regulation of GLO1 and GSR1 is involved in sleep deprivation-induced anxiety-like behavior of rats.

Effects of sleep deprivation on neural functioning: an integrative review

Sleep deprivation has a broad variety of effects on human performance and neural functioning that manifest themselves at different levels of description. On a macroscopic level, sleep deprivation mainly affects executive functions, especially in novel tasks. Macroscopic and mesoscopic effects of sleep deprivation on brain activity include reduced cortical responsiveness to incoming stimuli, reflecting reduced attention. On a microscopic level, sleep deprivation is associated with increased levels of adenosine, a neuromodulator that has a general inhibitory effect on neural activity. The inhibition of cholinergic nuclei appears particularly relevant, as the associated decrease in cortical acetylcholine seems to cause effects of sleep deprivation on macroscopic brain activity. In general, however, the relationships between the neural effects of sleep deprivation across observation scales are poorly understood and uncovering these relationships should be a primary target in future research.

A qualitative study of the experiences of patients following transfer from intensive care

In nursing literature much attention has been paid to patients' experiences while in intensive care. Extensive literature exists examining the longer-term effects of critical care [Jones C, Humphris GM, Griffiths RD. Psychological morbidity following critical illness - the rationale for care after intensive care. Clinical Intensive Care 1998;9:199-205; Griffiths RD, Jones C. ABC of intensive care. Recovery from intensive care. Br Med J 1999;319:417-429]. There is an apparent scarcity of data examining patients' experiences immediately following discharge to wards. A Husserlian phenomenological approach was utilised to gain some understanding of the experience of patients following transfer from intensive care. Ten patients selected purposively comprised the sample. Interviews were performed on the wards 3-5 days following transfer from intensive care. Data was analysed utilising () [Colaizzi PF. Psychological Research as the phenomenologist views it. In: Valle R, King M, editors. Alternatives for psychology. New York: Oxford University Press; 1978. p. 48-71] procedural approach to phenomenological interpretation and analysis. Three major themes emerged: physical response, psychological response and provision of care. These provide a possible framework for patient assessment. Implications for future practice and study are discussed.

Total sleep deprivation and novelty processing: implications for frontal lobe functioning

OBJECTIVE

Mounting evidence suggests that the frontal lobes are particularly vulnerable to total sleep deprivation (TSD). Detection of novelty involves the frontal lobes. The presentation of rare, novel stimuli elicits an event-related potential (novel P3), which maximizes over anterior regions of the scalp. We hypothesized that TSD would impair novelty detection, resulting in a smaller novel P3 over the frontal region, with a topographic shift toward posterior areas.

METHODS

An auditory novelty oddball task was administered to a TSD group after 36 h of waking and again following recovery sleep, and to a control group after 12 h of waking. EEG was recorded from Fz, Cz and Pz.

RESULTS

A large anterior P3 was elicited in the control group. In the TSD group, this novel P3 was smaller at Fz. A later novel positivity appeared in parietal areas. The novel P3 returned to baseline levels and the late novel P3 was difficult to observe following recovery sleep.

CONCLUSIONS

TSD appears to compromise the usual automatic detection of novelty probably due to frontal deactivation. Participants may compensate by relying on posterior brain mechanisms involving active memory comparison. The late novel P3 component may also reflect a secondary effortful attempt to encode and to categorize novel stimuli.

SIGNIFICANCE

This study suggests that TSD may compromise cognitive functioning in different regions of the brain. The detection of novelty, probably mediated by the frontal lobes, is particularly at risk.

Masking effects of posture and sleep onset on core body temperature have distinct circadian rhythms: results from a 90-min/day protocol

Both recumbency and sleep affect core body temperature (CBT). To characterize their circadian effects and interactions, the authors examined the bedtime temperature drops (TDs) of nine men and eight women (aged 20 to 30) who repeated 90-min sleep-wake cycles over 2.5 days. While awake, subjects were exposed to 50 to 250 lux; while asleep, lights were off. Electroencephalogram-monitored time inbed lasted 30 min during each cycle. Cosinor nonlinear mixed-effects regressions modeled the circadian rhythm of TDs. The circadian maximum of TDs occurred approximately 4 h before the time of circadian CBT minimum, in a model that included the effects of baseline expected CBT, deviations from baseline CBT, time in study, and gender-dependent 24- and 12-h adjustments. Rates of temperature drops were faster during initial periods of lying awake than during periods of initially sleeping. Both rates followed separate circadian rhythms. The circadian maximum of TDs was located near customary nocturnal bedtimes, suggesting its role in fostering sleep during a normal bedtime routine. The apparent deceleration of temperature dropping at sleep onset supports the notion that the sleep onset period has complicated circadian neuroregulatory dynamics. These findings confirm the need for nonlinear models of temperature responses to postural changes and sleep that incorporate circadian variability in these masking effects.

Effects of Total Sleep Deprivation on Cardiovascular Parameters: An Absence of Biologically Significant Findings?

Abstract The present study analyzes the variations of heart rate (HR) and systolic and diastolic blood pressure (SBP and DBP) during 60 h of total sleep deprivation (TSD). All variables were evaluated every 2 h in a resting condition, during the performance of a vigilance task. Thirty healthy volunteers (15 men and 15 women) from 18 to 24 years old participated in the experiment. The analyses of variance (ANOVAS) with repeated measures showed some modifications of HR and SBP mean values mainly marked by circadian oscillations. The circadian oscillations had a smaller amplitude for SBP than for HR. HR showed a slight decrease on the second night of TSD and a slight increase on the third day of TSD. SBP decreased during the first 24 h of TSD and after that maintained its values without significant changes. DBP did not show any significant variations during TSD. In addition, there were no differences in function of gender for the TSD effect on the studied variables. All these statistically significant findings, however, seem to have no biological or clinical relevance. These aspects as well as the possible relationships between our results and activation or stress levels during TSD are discussed.

Pattern analysis of sleep-deprived human EEG

Progress during the past decade in non-linear dynamics and instability theory has provided useful tools for understanding spatio-temporal pattern formation. Procedures which apply principle component analysis (using the Karhunen-Loeve decomposition technique) to the multichannel electroencephalograph (EEG) time series have been developed. This technique shows localized changes of cortical functioning; it identifies increases and decreases of the activity of localized cortical regions over time while the subject performs a simple task or test. It can be used to demonstrate the change in cortical dynamics in response to a continuous challenge. Using 16 EEG electrodes, the technique provides spatio-temporal information not obtained with power spectrum analysis, and includes the weighted information given with omega complexity. As an application, we performed a pattern analysis of sleep-deprived human EEG data in 20 healthy young men. Electroencephalograph recordings were performed on subjects for <2 min, with eyes closed after normal sleep and after 24 h of experimentally-induced sleep deprivation. The significant changes in the eigenvector components indicated the relative changes of local activity in the brain with progressive sleep deprivation. A sleep deprivation effect was observed, which was hemispherically correlated but with opposite directional dynamics. These changes were seen in the temporo-parietal regions bilaterally. The application of the technique showed that the simple test task was performed with a limited unilateral hemispheric involvement at baseline, but needed a much larger cortical participation with decreased frontal activity and increased coherence and bilateral hemispheric involvement. The calculations performed demonstrated that the same weighted changes as those obtained with omega complexity were shown, but the technique had the added advantage of showing the localized directional changes of the principle eigenvector at each studied electrode, pointing out the cortical localized region affected by the sleep deprivation and toward which direction the environmental challenge induced the spatial change. This methodology may allow the evaluation of changes in local dynamics in brain activity in normal and pathological conditions.

Lifestyle, stress and cortisol response: Review II : Lifestyle

To prevent lifestyle related diseases, it is important to modify lifestyle behavior. The control of mental stress level and prevention of mental stress-related diseases have become one of the most important problems in Japan. To check mental stress level objectively during the early stage of stress-related diseases and determine appropriate coping methods, it is necessary to design a useful index for mental stress. Cortisol is a steroid hormone secreted by the adrenal cortex. This is an essential hormone to human survival, and plays a key role in adaptation to stress. In another review, we concluded that cortisol appears to be an adequate index for mental stress.However, lifestyle factors such as alcohol drinking, smoking, lack of exercise etc., are strongly associated with mental stress. Thus, in this review, we focus on the relationship between cortisol and lifestyle.The present findings suggested that lifestyle factors; smoking, alcohol drinking, exercise, sleep and nutrition are strongly associated with cortisol levels, and it may be impossible to determine whether alterations in cortisol levels are due to mental stress.It was suggested that those lifestyle effects on not only mental stress itself but also cortisol levels should be considered, when assessing mental stress by cortisol levels.

Hormonal responses to exercise after partial sleep deprivation and after a hypnotic drug-induced sleep

The aim of this study was to determine the hormonal responses, which are dependent on the sleep wake cycle, to strenuous physical exercise. Exercise was performed after different nocturnal regimens: (i) a baseline night preceded by a habituation night; (ii) two nights of partial sleep deprivation caused by a delayed bedtime or by an early awakening; and (iii) two nights of sleep after administration of either a hypnotic compound (10 mg zolpidem) or a placebo. Eight well-trained male endurance athletes with a maximal oxygen uptake of 63.5 +/- 3.8 ml x kg(-1) x min(-1) (mean value +/- s(x)) were selected on the basis of their sleeping habits and their physical training. Polygraphic recordings of EEG showed that both nights with partial sleep loss led to a decrease (P< 0.01) in stage 2 and rapid eye movement sleep. A delayed bedtime also led to a decrease (P < 0.05) in stage 1 sleep. Zolpidem had no effect on the different stages of sleep. During the afternoon after an experimental night, exercise was performed on a cycle ergometer. After a 10-min warm-up, the participants performed 30 min steady-state cycling at 75% VO(2-max) followed by a progressively increased workload until exhaustion. The recovery period lasted 30 min. Plasma growth hormone, prolactin, cortisol, catecholamine and lactate concentrations were measured at rest, during exercise and after recovery. The concentration of plasma growth hormone and catecholamine were not affected by partial sleep deprivation, whereas that of plasma prolactin was higher (P < 0.05) during the trial after an early awakening. Plasma cortisol was lower (P < 0.05) during recovery after both sleep deprivation conditions. Blood lactate was higher (P < 0.05) during submaximal exercise performed after both a delayed bedtime and an early awakening. Zolpidem-induced sleep did not affect the hormonal and metabolic responses to subsequent exercise. Our results demonstrate only minor alterations in the hormonal responses to exercise after partial sleep deprivation.

Patients' perspective of quality of care in a high-dependency unit

This study was designed to identify and explore the patients' perspective of the concept quality of care within the context of a high-dependency unit (HDU). Data were collected in two phases. In phase one, 55 patients were interviewed to clarify the concept quality of care. In phase two, 77 patients were interviewed to explore this concept in further detail. This study has clarified the patients' concept of quality of care into the principal constructs of the environment, meeting individual needs, staff attitudes and manners, organization of care, communication, staff skills and family and friends. It has been successful in providing patients with a voice to comment upon an aspect of service provision. A well-known concept has been clarified and applied to a high-dependency environment. This has identified the need for future evaluation of HDUs to go beyond traditional physiological measures, to incorporate the service experience itself and the impact it has upon the patients.

The sensitivity of pharmacodynamic tests for the central nervous system effects of drugs on the effects of sleep deprivation

Various methods are used to quantify sedative drug effects, but it is unknown how these surrogate measures relate to clinically relevant sleepiness. This study assessed the sensitivity of different surrogates of sedation to clinically relevant sleepiness induced by sleep deprivation. Nine healthy volunteers completed a balanced three-way cross-over study with 1-week wash-out periods. Adaptive tracking, smooth-pursuit and saccadic eye movements, body sway, digit symbol substitution (DSST), visual analogue scales (VAS) and electroencephalograms (EEG) were evaluated on three occasions: (1) during the day after normal sleep, (2) during wakefulness at night; and (3) during the day after a night of sleep deprivation. VAS of alertness showed a gradual decline at night and a constant average reduction of 38 percent [95% Confidence intervals (CI), 28-47%] during the day after sleep deprivation. Average mood scores diminished by 14 percent (95%, CI 2-24%) during the day after sleep deprivation. Adaptive tracking, saccadic eye movements and body sway tended to deteriorate at night, but overall this was not statistically significant. After a night of sleep deprivation, adaptive tracking decreased by 21 percent (95% CI, 11-30%), saccadic eye movements decreased by 9-10 percent (95% CI, 5-13%/6-15%) and body sway increased by 37 percent (95% CI, 5-79%). In contrast, EEG beta2-amplitudes declined significantly at night by 18 percent (95% CI, 6-29%), without changes during the day after sleep deprivation. Smooth pursuit, DSST and other EEG-amplitudes remained unchanged. These results emphasize that reductions in adaptive tracking, saccadic peak velocity and body sway caused by sedative drugs really reflect sedation. They also provide a level of clinical significance for these surrogates of sedation. EEG parameters and smooth pursuit were unaffected by sleep deprivation, so drug-induced changes in these measures may not reflect sedation in a stricter sense. The motivation and alertness necessary for DSST may overcome mild sedation.

Mood states and sleepiness in college students: influences of age, sex, habitual sleep, and substance use

Survey and laboratory evidence suggests several factors affecting sleep-wake patterns of college students. These factors include social and academic demands, diminution of parental guidance, reduction of total sleep time, delayed bedtime, and increased nap episodes. In this study, we examined the problem of falling asleep in school as a correlate of negative moods in this population (N = 294). A multivariate analysis showed significant main effects of sleepiness on mood states based on the Profile of Mood States. Students who fell asleep in school reported higher negative mood states. Significant interactions were observed among sleepiness and age, sex, race, and duration of sleep. Specifically, younger men reported higher negative moods. No interactions were noted for alcohol and marijuana consumption; however, students who fell asleep in school consumed more alcoholic beverages and smoked more than those who did not. Perhaps falling asleep in school could be used as an index that characterizes students who manifest adaptive or psychological difficulty.

Effects of sleep deprivation and other stressors on the immune and inflammatory responses of influenza-infected mice

Many stressors have well-documented effects on host immune competence. However, two important stressors that have not been extensively characterized in terms of their immune-modulatory properties are sleep deprivation and alterations in light:dark cycles. We therefore evaluated the effects of these stressors on the immune and inflammatory responses of mice inoculated intranasally with influenza virus. In contrast to a previous report, sleep deprivation did not significantly alter viral clearance or antibody titers of either virus-naive or immunized mice. Exposure to constant light also failed to affect these variables. However, repeated overnight restraint, a well-characterized stressor, reduced the pulmonary inflammatory response elicited by influenza virus, as previously reported. The data indicate that sleep deprivation and altered light cycles do not markedly influence selected host defense responses to influenza infection under the conditions tested.

Enhanced tiredness among young impaired male nighttime drivers

This study focuses on the incidence and amount of tiredness among young impaired male nighttime drivers during the hours between midnight and 6 a.m. One hundred and twenty impaired drivers, aged 18-30 years, with an average blood alcohol concentration of 1.54 g/l (range 0.81-2.99 g/l) are compared to 240 sober drivers of similar age stopped by the police in roadside surveys. A questionnaire shows that the increase in median awake period during the six observation hours is gradual and directly proportional to the time of the night for both groups, while the average awake period is significantly longer and that the average previous sleep period is significantly shorter for the impaired drivers. Self-assessment of tiredness shows 30 "rested," 68 "tired," and 22 "very tired" impaired drivers and 123 "rested," 105 "tired," and 12 "very tired" sober control drivers. This difference in level of "tiredness" is also significant. The questionnaire and the results of a simple visual reaction time test show individual differences for the drivers in both groups, but the difference in mean reaction time between the impaired drivers and the sober drivers is significant. Sub-division of the impaired drivers according to their self-assessed level of "tiredness" also shows significant differences in mean reaction time. The findings of the present study support the hypothesis that tiredness is an inherent and common accident risk factor among young male impaired drivers in nighttime traffic.

Overnight human plasma melatonin, cortisol, prolactin, TSH, under conditions of normal sleep, sleep deprivation, and sleep recovery

Early investigations of the effect of sleep deprivation on plasma melatonin reported no major changes. Recently, 36 hrs of sleep deprivation was reported to elevate melatonin levels on the post-sleep deprivation night. Given these contradictions melatonin, cortisol, prolactin, and thyroid stimulating hormone before, during, and, after sleep deprivation were examined in nine healthy young males following one night of sleep deprivation. Hormone levels at hourly intervals, for each night, were statistically analyzed by a repeated measures, two-way factorial ANOVA. ANOVA was also performed for measures of area under the curve (AUC). No significant differences were observed for melatonin levels. Cortisol was significantly higher on the sleep deprivation night presumably reflecting the aroused state accompanying being awake; however, there were several time points on the control night when it was elevated also. Prolactin was higher on the post-sleep deprivation and control nights but did not rise on the deprivation night, indicating a useful nonpolysomnographic index for discriminating overnight sleep and awake states. TSH levels showed a similar rise during the control and sleep deprivation nights, but remained flat on the post-sleep deprivation night. It appears that the pineal is insulated against feedback from changes to the level of arousal accompanying sleep and wakefulness. In comparison, cortisol, prolactin, and TSH levels vary with these states and are, therefore, useful indices of arousal and sleep-wake.

Managing fatigue in operational settings. 1: Physiological considerations and countermeasures

The authors consider three aspects of managing fatigue in the workplace. They provide a brief overview of important scientific findings related to sleep and circadian physiology that establish the psychobiological foundation of fatigue. Their major focus is on the relevance of these findings to operational settings. In addition, they provide examples to describe practical fatigue countermeasures that can be used in operational settings.

A reconceptualization of EEG alpha activity as an index of arousal during sleep: all alpha activity is not equal

Alpha activity occurring during sleep is generally considered to reflect arousal processes and a shift toward wakefulness. This long-standing interpretation is based on physiological and behavioural arousal correlates of alpha activity presumed to have an occipital focus. In addition to the application of this interpretation to sleep/wake state determinations, there have been reports of nonrefreshing or nonrestorative sleep in clinical populations exhibiting dramatic amounts of alpha intrusion during sleep in the absence of awakening. Reports of the presence of alpha activity during sleep in normal subjects without sleep disruption or complaints of daytime sleepiness call into question the interpretation that this activity is associated with arousal. A re-examination of this literature, incorporating the results from recent investigations employing multi-site EEG recordings, electronic processing and source dipole analyses of this activity, suggests the existence of alpha activity which differs in generation site (thalamus), scalp distribution (frontal-central), and behavioural correlates (e.g. enhancement to stimulation during wakefulness, concentration in the first-half of the night during sleep, and absence of sleep disturbance) from occipital alpha activity. Such marked differences in defining characteristics imply different functional correlates for these activities. In this context, it is proposed that this fronto-central alpha activity is associated with sleep-maintaining processes which may be enhanced in response to sleep-disturbing events.

Sleep function(s) and cerebral metabolism

The function(s) of sleep would probably be better understood if the metabolic processes taking place within the central nervous system (CNS) during sleep were known in greater detail. The general pattern of the energy requirements of the brain during sleep is now outlined. Brain energy metabolism dramatically decreases during slow wave sleep (SWS) whereas, during rapid eye movement sleep (REMS), the level of metabolism is similar to that of wakefulness. However, these modifications of the energy metabolism, in good agreement with intracerebral recordings of neuronal firing, do not help in identifying the function(s) of sleep, since they are in line with several theories of sleep function(s) (protection, energy conservation, brain cooling, tissue restitution). On the other hand, several studies of brain basal metabolism suggest an enhanced synthesis of macromolecules such as nucleic acids and proteins in the brain during sleep. However, up to now, these data remain scarce and controversial. As a consequence, the research in the field of the brain metabolism during sleep has now come to a turning point, since the confirmation of sizeable cerebral anabolic processes would provide an outstanding argument in favour of the restorative theory of sleep. In this case, a hypothesis, based on clinical findings and preliminary metabolic data, might be further proposed. The putative biosynthetic processes would not equally benefit all the components of the CNS but would primarily be devoted to the maintenance of an optimal synaptic function.

Somnogenic effects of sleep deprivation and Escherichia coli inoculation in rabbits

To evaluate the impact of sleep deprivation (SD) on microbially induced alterations in sleep, we used gentle handling to deprive rabbits of sleep for 4 h before or after intravenous inoculation with Escherichia coli (EC). Sleep was monitored for the next 20 h. EC inoculation alone increased slow-wave sleep (SWS) time, delta-wave amplitude (DWA) during sleep and SWS bout length during the initial 2-4 h after inoculation. During the following 8-20 h, DWA during SWS was reduced relative to control values. SD alone increased SWS time and SWS bout length for 2 h after the end of the SD period. Rabbits subjected to SD for 4 h prior to EC inoculation demonstrated increases in SWS time, DWA during SWS and SWS bout length 2-4 h postinoculation. At some time points, these effects were greater in magnitude than those induced by either manipulation alone, but they were generally equivalent to the additive effects of the individual treatments. Rabbits subjected to SD after EC inoculation (i.e. during the period in which EC increases sleep) demonstrated increases in SWS time and DWA during SWS for only 2 h after the end of the SD period, suggesting that these animals maintained a sleep deficit as compared to rabbits inoculated with EC alone. SD alone elicited hyperthermia in rabbits, and EC-inoculated rabbits subjected to SD developed fevers greater than those induced by either treatment alone. Other clinical indices were not significantly affected by the combined treatments. These data indicate that the sleep changes that occur subsequent to bacterial inoculation are altered in sleep-deprived rabbits, but that SD does not exacerbate clinical illness in this model.

Sleep, sleep deprivation and infectious disease: studies in animals

Common perceptions that the desire for sleep is increased during mild infectious diseases like colds and 'the flu' have fostered beliefs that sleep promotes recovery from infectious disease and that lack of sleep increases susceptibility to infections. However, until recently, the relationship between infectious disease and vigilance received relatively little systematic study. At present, several model systems provide evidence that infectious disease is accompanied by alterations in sleep. Indeed, increased sleepiness, like fever and anorexia, may be viewed as a facet of the acute phase response to infectious challenge. Recent studies also suggest that sleep, sleep deprivation and infectious disease may be related via mechanisms of the immune system (Fig. 1). Data are now accumulating to address questions such as whether immune processes alter sleep, whether sleep or sleep deprivation influences immune competence, and whether sleep facilitates recovery from infectious disease.

Tiredness and visual reaction time among young male nighttime drivers: a roadside survey

The study focus on the incidence and importance of tiredness among young male car drivers in nighttime traffic. It took place on a major highway in Copenhagen County, Denmark, and was performed as roadside surveys in the hours between midnight and 6 A.M. The study consisted of a questionnaire with self-assessment of tiredness followed by a simple visual reaction-time test. Two hundred and forty nighttime drivers and 40 early morning drivers joined the study. One hundred and twenty-three nighttime drivers declared themselves as rested, 106 as tired, and 11 as very tired. Thirty-seven early morning drivers declared themselves as rested, while the remaining three declared themselves as tired. The drivers' self-assessed level of tiredness corresponded well with the results of the simple visual reaction-time test, but one self-declared tired driver had to be reclassified as very tired. The visual reaction-time test henceforth showed a mean reaction time of 0.189 seconds for the rested drivers, 0.223 seconds for the tired, and 0.309 seconds for the very tired nighttime drivers (p < .001). Mean reaction time for the early morning drivers was 0.190 seconds corresponding to 0.246 seconds in the equivalent nighttime group (p < .001). The fluctuations in mean reaction time throughout the night for the whole population including the early morning drivers correlated well with the number of tired/very tired drivers (corr. = 0.96). The study shows tiredness as a common affliction among young male nighttime drivers.

Cold thermoregulatory changes induced by sleep deprivation in men

The aim of this study was to evaluate the thermoregulatory changes induced by 27-h of sleep deprivation (SD) in men at rest both in a comfortable ambient temperature and in cold air. A group of 12 male subjects were placed in a comfortable ambient temperature (dry bulb temperature, Tdb = 25 degrees C, relative humidity, rh = 40%-50%, clothing insulation = 1 clo) for 1 h and then they were submitted to a standard cold air test in a climatic chamber for 2 h (Tdb = 1 degree C, rh = 40%-50%, wind speed = 0.8 m.s-1, nude), before and after 27 h of sleep deprivation. Thermoregulatory changes (rectal temperature, Tre; mean skin temperature. Tsk; metabolic heat production M) were monitored continuously. At comfortable ambient temperature, no significant change was observed after SD for Tre, Tsk and M. During the cold test, Tre did not change but Tsk and M were higher after SD (P < 0.05). Increased M (+ 6%, P < 0.05) was related to earlier and higher shivering, with a possible increase in the sensitivity of the thermoregulatory system as shown by the shorter time to onset of continuous shivering (d): 8.66 (SEM 1.33) min versus 28.20 (SEM 1.33) min (P < 0.001) and by a higher Tsk observed at d: 27.60 (SEM 1.40) degrees C versus 21.40 (SEM 0.60) degrees C (P < 0.001). These results were associated with higher cold sensations and shivering following SD. They also suggested that SD modified thermoregulatory responses at a central level especially in a cold environment.

Local sweating responses during recovery sleep after sleep deprivation in humans

Changes in the central control of sweating were investigated in five sleep-deprived subjects (kept awake for 40 h) during their recovery sleep under warm ambient conditions [operative temperature (T(o)) was either 35 or 38 degrees C]. Oesophageal (T(oes)) and mean skin (Tsk) temperatures, chest sweat rate (msw,ch), and concomitant electro-encephalographic data were recorded. Throughout the night at 35 or 38 degrees C T(o), msw,ch changes were measured at a constant local chest skin temperature (Tch) of 35.5 degrees C. The results showed that body temperatures (T(oes) and Tsk) of sleep-deprived subjects were influenced by thermal and hypnogogic conditions. The msw,ch levels correlated positively with T(oes) in the subjects studied during sleep stage 1-2 (light sleep: LS), sleep stage 3-4 (slow wave sleep: SWS) and rapid eye movement (REM) sleep. Contrary to what has been reported in normal sleep, firstly, the T(oes) threshold for sweating onset differed between REM sleep and both LS and SWS, and, secondly, the slopes of the msw,ch versus T(oes) relationships were unchanged between REM and non-REM (i.e. LS or SWS) sleep. The changes observed after sleep deprivation were hypothesized to be due to alterations in the functioning of the central nervous system controller.

Tiredness and visual reaction time among nighttime cab drivers: a roadside survey

The present roadside survey seeks to elucidate the incidence of tiredness among nighttime cab drivers by comparing self-assessed level of tiredness with the results of a simple visual reaction test. Attempts to separate various forms of fatigue from sleepiness are not made, as it appears less important in studies of everyday traffic than in experimental investigations. One-hundred-and-twenty cab drivers of vacant cabs were stopped by the police on a major highway just outside the city of Copenhagen. Eighty drivers declared themselves rested, 38 tired, and 2 very tired. The reaction test showed considerable individual variation, but subdivision of the drivers according to level of tiredness demonstrated a statistically significant and uniform difference throughout the night (p < 0.0001). One self-assessed tired driver was reclassified to the group of very tired based on the questionnaire and reaction test. The investigation indicates that accidents due to "driver asleep" would be expected among the three (2.5%) very tired cab drivers. The questionnaire and visual reaction test turned out to be complementary in the present study and are both useful implements for future roadside surveys of tiredness in nighttime traffic.