Nineteen-hour variation of postural sway, alertness and rectal temperature during sleep deprivation

Effect of sleep deprivation on postural control and dynamic stability in healthy young adults

BACKGROUND

Postural control results from non-linear interactions of multiple neuromusculoskeletal elements and contextual factors. The use of non-linear analyses that consider the temporal evolution of postural adjustments, such as sample entropy, could inform about the changes in postural control due to contextual disturbances such as sleep deprivation.

RESEARCH QUESTION

What are the effects of sleep deprivation on static postural control and dynamic stability in healthy young adults?

METHODS

A quasi-experimental study was performed with 17 healthy young males submitted to 24 h of monitored sleep deprivation. The postural control was measured using sample entropy, area, and total average velocity of the center of pressure on a force platform. The dynamic stability was measured using the Modified Star Excursion Balance Test (SEBTm) composite score for each lower limb. Repeated-measures analysis of variance (baseline × 12 h × 15 h × 18 h × 21 h × 24 h of sleep deprivation) verified the effect of sleep deprivation in the postural control variables. Paired t-test compared the composite score of the SEBTm between baseline and 24 h sleep deprivation.

RESULTS

Sample entropy decreased after 18 h of sleep deprivation (p = 0.032) and 24 h of sleep deprivation (p = 0.001). Despite the significant main effect for the area (p = 0.012) and speed (p = 0.007) of the center of pressure, no pairwise differences were identified in the post hoc analysis. The non-dominant lower limb SEBTm composite score was reduced after 24 h of sleep deprivation (p = 0.033), and no difference was observed in the dominant limb.

SIGNIFICANCE

Sleep deprivation reduced the adaptability in static postural control and dynamic stability of the non-dominant lower limb of healthy young male adults. Sample entropy seemed more sensitive to capture the effects of sleep deprivation than the classical postural control variables.

Time of Day Influence on Postural Balance of Young and Older Men

BACKGROUND

Many physiologic parameters fluctuate on a diurnal basis following the circadian rhythm function. The purpose of the study was to investigate if postural performance is interdependent of time of day and age.

METHODS

19 young (22.63 ± 3.43 y.o.) and 19 older male adults (60.21 ± 3.67 y.o.) performed three balance tests (quiet stance with open and closed eyes and bipedal balance on a Togu ball) at 12:00 AM and at 12:00 PM. Time and frequency domain variables of the center of pressure were analyzed.

RESULTS

At eyes closed test, the younger had significant less distance traveled by the Center of Pressure (CoP) at night compared to day. At open eyes test, the younger had significant less CoP sway in the anterior-posterior (AP) axis at night compared to day. At Togu ball test the older showed increased peak-to-peak amplitude of CoP in both axes compared to younger. They also had lower frequency in the medial-lateral (ML) axis but higher in the AP axis compared to the younger.

CONCLUSION

Younger seem to function better at night. There is also an indication that the older are better at day. The results on unstable surface indicate different control strategies between the two groups.

Electrophysiological Mechanism of Attention of Sleep Deprivation: Evidence From Event-Related Potentials (ERP) Data

INTRODUCTION

The purpose of this study is to investigate the effects of sleep deprivation on individual attentional function and related electrophysiological mechanisms.

METHODS

Twenty healthy men who were deprived of sleep for 24 h were evaluated by selective attention test, persistent attention test, and event-related potentials (ERP) experiment.

RESULTS

After 24 h of sleep deprivation, the subjects' selective attention decreased, mainly manifested as prolonged response time, decreased motion stability, increased rate of neglect error, decreased sustained attention, prolonged latency of P300 at Cz (p=0.001), and decreased amplitude (p=0.000).

CONCLUSION

After 24 h of sleep deprivation, the attentional ability decreased significantly, and behavioral and ERP indicators showed certain changes.

Detrimental effects of sleep deprivation on the regulatory mechanisms of postural balance: a comprehensive review

This review addresses the effects of sleep deprivation on postural balance based on a comprehensive search of articles dealing with this relationship in the electronic databases PubMed, Google Scholar, and ScienceDirect. Evidence suggests that postural balance is sensitive to acute and chronic sleep deprivation for everyone, including young and healthy subjects. Pathologies, aging and the circadian pattern aggravate and/or accentuate the effects of sleep deprivation on postural balance. It turns out that the different systems of information taking, decision making, and motor execution of the postural balance function are negatively affected by sleep deprivation. For example, regarding the information taking system, the sensitivity of visual perception and visuo-spatial performance and the oculomotricity are disrupted and the vestibulo-ocular reflex and the sensory reweighting are altered. Regarding the decision making system, the different brain areas activated for the regulation of postural balance are less active after sleep deprivation and the executive function and perception of verticality are impaired. Regarding the motor execution system, the agonist-antagonist muscle coordination can be modified. However, the different detrimental effects induced for each system of the postural balance function are not yet fully known and deserve further exploration in order to better understand them.

Evaluation of Age Based-Sleep Quality and Fitness in Adolescent Female Handball Players

The present study aimed to examine the differences in sleep hygiene, balance, strength, agility, and maximum aerobic speed (MAS) between two groups of female handball players aged under 14 (U14) and under 17 (U17) years. Seventy-two female handball players participated and were divided into two groups according to age: U14 (n = 36, age: 13.44 ± 0.5 years) and U17 (n = 36, age: 15.95 ± 0.76 years). Sleep hygiene was evaluated using three questionnaires: Sleep quality and sleepiness via the Pittsburgh (PSQI) and Epworth (ESS) questionnaires, and the insomnia questionnaire via the measurement of the insomnia severity index (ISI). Physical fitness was evaluated with the stork balance tests with eyes open (OEB) and closed (CEB), the vertical jump (SJ), horizontal jump (SBJ), and five jump (FJT) tests, the agility (t-test) and the maximum aerobic speed (MAS) tests. No significant differences were shown between U14 and U17 players in all PSQI, ISI, and ESS scores, and balance and strength performances. Meanwhile, the U17 players’ performances were significant better in agility quality (p = 0.003 < 0.01) and MAS (p = 0.05) compared to the U14 players. Biological gender specificity during the maturation phase may inhibit the improvement of balance, and strength performances between the age of 13 and 17 years, while agility and MAS performances are more affected by age alterations.

The effect of time-of-day and sleep deprivation on postural control: A systematic review

BACKGROUND

Postural control (PC) can be affected by circadian rhythm and sleep deprivation, whereby it has been reported the result of PC measurement in clinical and experimental situations can be influenced by both factors. It has been suggested sleepiness can result in deficiency in PC, which in turn can lead to occupational accidents and subsequent injuries. This is while no study critically reviews or summarizes findings surrounding this topic in the literature.

RESEARCH QUESTION

Is there any significant effect of sleep deprivation and circadian rhythm on PC variables among healthy individuals?

METHODS

PubMed, Web of Science, Scopus, and Embase were used to detect relevant studies. Only studies that examined the effect of time of day and/or sleep loss on PC among healthy individuals were included in this systematic review.

RESULTS

Forty-nine studies were included based on the inclusion criteria. Both circadian rhythm and sleep loss had a significant effect on PC, whereas there are inconsistent findings for optimal postural control regarding time of day. In terms of sleep deprivation, all investigations indicated that sleep loss deteriorates PC.

SIGNIFICANCE

The current systematic review represents a significant effect of circadian rhythm and sleep deprivation on PC, whereby it is suggested that clinicians and researchers consider these factors when measuring PC since it may affect the result of research and clinical test. Moreover, PC may be worsened through sleeplessness; however, some studies revealed there is no linear relationship between time of wakefulness and deteriorating PC due to the influence of circadian rhythm. Hence, while PC, as an objective tool, can help to detect those who are sleep deprived, which in turn can lead to prevent possible musculoskeletal injuries, further studies are needed to reveal more understanding about the effect of sleep loss and circadian rhythm on PC.

Association Between Sleep Parameters and Postural Control: A Literature Review

Background and Objective The purpose of the review was to explore the association between sleep parameters and postural control.Methods The PubMed, Science Direct, and EBSCO were searched using the keywords ‘sleep’ including either sleep quality, sleep deprivation, poor sleep quality; and ‘postural control’ including either dynamic balance, static balance, postural balance, and balance control. Related studies published till December 2017 were selected.Results Acute sleep deprivation resulted in an impairment in postural control. Chronic sleep deprivation and postural control were also found to be related in a similar way to that of total sleep deprivation, thus affecting postural control negatively. Time of day was found to influence the postural control such that the postural control was better in the morning than in the latter part of the day. A study of the impact of aging on the effects of sleep deprivation on postural control revealed that loss of sleep had a more disturbing effect on postural control in the olderadult group than in younger participants, thus indicating a high risk of fall among the elderly.Conclusions Despite various limitations and methodological differences, this review has identified a negative influence on postural control due to impaired sleep in a wide range of populations, indicating the need for a more focused approach to sleep when assessing and measuring postural control.

Is Balance Control Affected by Sleep Deprivation? A Systematic Review of the Impact of Sleep on the Control of Balance

Background

Sleep is a complex physiological function that should be addressed from different perspectives and consider the circadian rhythm. Sleep deprivation, either acute or chronic, negatively affects several functions, including motor control. Balance control is essential in several daily life activities and balance problems are related to falls.

Research Question

This review focuses on how sleep conditions impact balance control.

Methods

Systematic literature review according to PRISMA guidelines.

Results

The literature provided strong evidence that acute sleep deprivation impairs postural control. Chronic sleep deprivation as well as low sleep quality had similar effects, although there is a lower number of works addressing this issue. Furthermore, time awake worsens postural controls and it can be used to detect sleepiness and fatigue. The sleep deprivation showed a stronger negative effect on postural control when removing the visual information (eyes closed) than when reducing proprioceptive feedback (soft surface). There is scarce literature about the effects of chronotype, circadian patterns and chronic sleep deprivation, a frequent problem, on balance control; however they consistently indicate that there is an relationship between them. Most of the studies only consider one-night (acute) sleep deprivation without monitoring prior sleep conditions and the circadian rhythm phase of the participants. However, a few studies indicated that these factors must be considered.

Significance

These results suggest that the sleep conditions of a subject should be considered for several days prior to balance control tests. Therefore, we propose a revision of current postural measurement protocols to include sleep assessment, such as sleep quality questionnaires or actimetry, and to consider the circadian rhythm of the participants to plan the hour of the tests.

Anthropometric, Psychosocial, Physiological, and Postural Observances During Ramadan in Men With Chronic Obstructive Pulmonary Disease

This study aimed to carry out a Ramadan observance (RO) on anthropometric, psychosocial, physiological, and postural characteristics of patients with chronic obstructive pulmonary disease (COPD). Twenty COPD patients were evaluated. Tests performed 1 week before Ramadan (C), and during the second (R-2) and the fourth weeks of Ramadan (R-4) included standard anthropometry, spirometry, a quality of life questionnaire (VQ11), a 6-minute walking test (6MWT), measurement of maximal voluntary contraction force of the quadriceps (MVC), Timed Get Up and Go (TUG), Berg Balance Scale (BBS), and Unipedal Stance (UST). During R-2, there were significant decreases in forced vital capacity and forced expiratory volumes, 6MWT distance, MVC, BBS, and UST, with significant increases in TUG and significant changes in VQ11. During R-4, there was some recovery, but all variables remained significantly different from initial control data. To conclude, RO adversely affects pulmonary function, exercise performance, postural balance, and quality of life in COPD, with some recovery by the R-4. Although a number of functional consequences remain to be elucidated, functional losses were insufficient to limit daily living in our sample, but further studies are recommended in those with more severe COPD, paying particular attention to postural disturbances and a possible increase in the risk of falls.

Postural Control and Sleep Quality in Cognitive Dual Tasking in Healthy Young Adults

Although sleep quality disorders can have a negative effect on postural control, studies about this subject are scarce. The aim of this study is to assess the differences in standing posture performance during dual tasking between healthy young adults with a good and poor sleep quality. Thirty-five healthy participants (23.09 ± 3.97 years) performed a postural task (standing posture single task ((ST)) and a dual task (DT): quiet standing while performing a concurrent cognitive task, while the total excursion of the center of pressure (TOTEX CoP), the displacement anterior–posterior (CoP-AP) and medial–lateral (CoP-ML), the mean total velocity displacement of CoP (MVELO CoP) and ellipse sway area (CEA) were measured with a force plate. After assessing the sleep quality with the Pittsburgh Sleep Quality Index, they were divided into two groups (good ((n = 21)) and poor ((n = 14)) sleep quality) to establish comparisons. This study revealed no significant differences in TOTEX CoP, CoP-ML, CoP-AP, MVELO CoP, and CEA among both sleep quality groups. In conclusion, differences in the sleep quality (good or poor sleep quality) among young adults appear not to be a relevant factor in the CoP variation, but the DT versus ST can compromise postural control performance independently of the sleep quality.

Differences in the Effect of Sleep Deprivation on the Postural Stability among Men and Women

Objective: Sleepiness caused by sleep deprivation may increase the risk of injuries and damages during physical activity. Individual data so far indicate a generally better static postural stability of women regardless of sleeping conditions. The main aim of this study was to assess the impact of sleep deprivation on postural stability according to gender after 24 h of sleep deprivation. Methods: Participants included 83 students (36 men and 47 women). Postural stability was measured with eyes open and closed eyes before and after sleep deprivation. Data from posturographic platform were used to assess postural stability objectively. Results: The type of test determined the size of observed changes in postural stability. The data suggest that women are better able to cope with the effects of sleep deprivation than men. Conclusion: Postural control system is very important in sport and in physically active people. The results show that men are more sensitive to sleep deprivation than women because they had higher COP (center of pressure) values in tests. Less postural stability of the body due to sleep deprivation indicates a higher risk of injury during physical activity.

Saccadic Eye Movements Attenuate Postural Sway but Less in Sleep-Deprived Young Adults

Sleep deprivation affects the performance of postural control and several other aspects related to attentional mechanisms that may alter sensory cue acquisition strategies. This study aimed to examine the possible effects of horizontal saccades and ocular fixation on a target in the performance of postural control in young adults with sleep deprivation. Twenty-six adults formed two groups, tested in two evaluations. In the first evaluation, participants slept normally on the night before. In the second evaluation, 13 participants were sleep deprived (SD) and 13 slept normally (control group [CG]) on the night before. In both evaluations, each participant stood upright as still as possible, in two experimental conditions: fixating the eye on a target and performing saccadic movement toward a target presented in two different locations (0.5 Hz). Each participant performed 3 trials in each condition, lasting 62 s each. Body oscillation was obtained in both anterior-posterior and medial-lateral directions. Results showed that SD participants swayed with a larger magnitude and higher velocity after sleep deprivation in the fixation condition. In the saccadic condition, body sway magnitude and velocity were reduced but were still larger/higher in the SD participants. Sleep deprivation deteriorates the performance of postural control. Saccadic eye movements improve postural control performance even in sleep-deprived participants but are still not sufficient to avoid postural control deterioration due to sleep deprivation.

Day-to-day variations in sleep quality affect standing balance in healthy adults

Acute sleep deprivation is known to affect human balance and posture control. However, the effects of variations in sleep quality and pattern over consecutive days have received less attention. This study investigated the associations between day-to-day variations in sleep quality and standing balance in healthy subjects. Twenty volunteers (12 females and 8 males; age: 28.8 ± 5.7 years, body mass index: 23.4 ± 3.4 kg/m2, resting heart rate: 63.1 ± 8.7 bpm) with no history of sleep disorders or balance impairments participated in the study. Sleep and balance were assessed over two consecutive days. Sleep quality variations were assessed using sleep diary, actigraphy and heart rate variability (HRV) measures. Sleep was monitored at home, using an unobtrusive wearable device. Balance was assessed in a gait lab using foot centre of pressure (COP) displacement during quiet standing. Subjects with a day-to-day deterioration in sleep quantity and quality (i.e., decreased duration and increased fragmentation, increased nocturnal activity and decreased HRV) exhibited significant changes in balance (i.e., larger COP area, amplitude and standard deviation). Conversely, subjects with no significant alterations in sleep quantity and quality showed no significant changes in COP displacements. These results confirmed our hypothesis that changes in sleep quality and pattern over consecutive days may affect balance.

Nintendo Wii Fit-Based Sleepiness Testing is Not Impaired by Contagious Sleepiness

Sleep deprivation may cause accidents, and it has deteriorating effects on health. A measurement of postural steadiness by a portable and affordable Nintendo Wii Fit balance board can be used to quantify a person's alertness. At work, people are under the influence of their environment-often other people-that may affect their alertness. This work investigates whether sleep deprivation among people is "contagious," as quantified by sway measures. We measured 21 volunteers' postural steadiness while alert and sleep deprived. During the measurements, a screen placed in front of the participants showed a footage of either alert or sleep-deprived faces. We found a significant difference between the day time and night time steadiness, but found no effect resulting from watching footage of sleep-deprived people. This finding shows that a posturographic sleepiness tester quantifies physiological sleep deprivation, and is insensitive to the influence of social factors.

Effect of sleep deprivation on diurnal variation of vertical perception and postural control

The aim of the study was to test the effect of total sleep deprivation on performance and time-of-day pattern of subjective visual vertical (SVV) and postural control. Nineteen healthy, young participants (4 women and 15 men 21.9 ± 1.2 yr) were engaged in two counterbalanced experimental sessions with or without total sleep deprivation. Oral temperature, Karolinska Sleepiness Scale, and visual analogic scale for fatigue, postural control, and SVV were randomly measured every 4 h, from 0600 to 2200. A linear mixed model was used to capture the effect of time of day and sleep condition as factors. A classical adjusted COSINOR function was then used to modelize this daily variation. After the control night of sleep, SVV as well as oral temperature, sleepiness, and fatigue showed significant time-of-day variation, contrasting with measures of postural control which remained stable across the day. After sleep deprivation, SVV showed no diurnal variation, but its mean deviation value increased by 29%. Postural control capability also decreased after sleep deprivation, with a higher center of pressure surface (+70.4%) and total length (+7.37%) but remained stable throughout the day. These results further confirm the negative effect of sleep loss on postural control capability. Even if a direct relationship cannot be confirmed, the disruption of SVV capacity after sleep deprivation could strongly play a role in postural control capacity changes. Sleep deprivation should be considered as a potent factor involved in balance loss and subsequent fall. NEW & NOTEWORTHY The topic of sleep deprivation and postural control is not understood, with discrepancy among results. This study described that postural control displays a stable level throughout the day and that sleep deprivation, even if it increases postural sway, does not affect this stable diurnal pattern. The modification of the perception of the vertical level after sleep deprivation could strongly play a role in the observed changes in postural control capacity.

Bayesian inference of physiologically meaningful parameters from body sway measurements

The control of the human body sway by the central nervous system, muscles, and conscious brain is of interest since body sway carries information about the physiological status of a person. Several models have been proposed to describe body sway in an upright standing position, however, due to the statistical intractability of the more realistic models, no formal parameter inference has previously been conducted and the expressive power of such models for real human subjects remains unknown. Using the latest advances in Bayesian statistical inference for intractable models, we fitted a nonlinear control model to posturographic measurements, and we showed that it can accurately predict the sway characteristics of both simulated and real subjects. Our method provides a full statistical characterization of the uncertainty related to all model parameters as quantified by posterior probability density functions, which is useful for comparisons across subjects and test settings. The ability to infer intractable control models from sensor data opens new possibilities for monitoring and predicting body status in health applications.

Chronic Low Quality Sleep Impairs Postural Control in Healthy Adults

The lack of sleep, both in quality and quantity, is an increasing problem in modern society, often related to workload and stress. A number of studies have addressed the effects of acute (total) sleep deprivation on postural control. However, up to date, the effects of chronic sleep deficits, either in quantity or quality, have not been analyzed. Thirty healthy adults participated in the study that consisted of registering activity with a wrist actigraph for more than a week before performing a series of postural control tests. Sleep and circadian rhythm variables were correlated and the sum of activity of the least active 5-h period, L5, a rhythm variable, obtained the greater coefficient value with sleep quality variables (wake after sleep onset WASO and efficiency sleep). Cluster analysis was performed to classify subjects into two groups based on L5 (low and high). The balance tests scores used to asses postural control were measured using Biodex Balance System and were compared between the two groups with different sleep quality. The postural tests were divided into dynamic (platform tilt with eyes open, closed and cursor) and static (clinical test of sensory integration). The results showed that during the tests with eyes closed, the group with worse sleep quality had also worse postural control performance. Lack of vision impairs postural balance more deeply in subjects with chronic sleep inefficiency. Chronic poor sleep quality impairs postural control similarly to total sleep deprivation.

Changes in Postural Control during a 48-Hr. Sleep Deprivation Period

Sleep deprivation has detrimental effects on cognitive abilities; however, there has been limited investigation into the effects of sleep deprivation on postural control or influence of time of day on postural control measures. Therefore, we measured postural control on a force plate every 6 hr. in 24 subjects (11 women, 13 men; M age 20 ± 2.1 yr.; M height 1.68 ± 0.29 m; body mass 63.3 ± 28.7 kg) participating in a 48-hr. dance marathon. During the first 24-hr. period, postural control significantly worsened. Rather than a steady decrease in postural control, during the second day of the event a repeating oscillatory trend of fluctuations in postural control was observed for both days of the event. We hypothesize that the repeating oscillation of postural control followed a circadian rhythm pattern, suggesting that sleep deprivation for 48 hr. does not influence measures of postural control in a consistent manner. The apparent influence of time of day on postural control measures warrants consideration of this factor when conducting studies with repeated measures of postural control across different days.

Sleep-disordered breathing and daytime postural stability

OBJECTIVE

Postural stability depends on the coordination of the central nervous system with visual sense, proprioceptive and vestibular information. Sleep deprivation has been shown to affect this function. The objective of our study was to assess the effects of sleep-disordered breathing (SDB) on postural stability.

METHODS

158 subjects referred for suspected SDB had an overnight sleep study and were placed on a posturographic platform in late afternoon. This platform allows measuring the centre of pressure (CoP) oscillations and to calculate: total displacement of CoP in X and Y axes, mean speed of CoP displacement and the length as function of surface (LFS) ratio (length of CoP displacement/surface of CoP trajectory).

RESULTS

98 men and 60 women were included. Mean age±SD was 45.4±5.5 years old, body mass index (BMI) 27.5±5.6 kg/m(2) and apnoea-hypopnoea index (AHI) 13.6±16.1/h. AHI was <5/h in 64 (41%) subjects, 5-15/h in 43 (27%), 15-30/h in 30 (19%) and >30/h in 21 (13%). In patients with an AHI >5/h versus AHI <5/h, we observed an important increase in LFS (+21%, p<0.001), in XY length (+23%, p<0.001) and in mean speed (+23%, p<0.001). After controlling for age, BMI and sleepiness (Epworth) in multivariate regression models, there was a positive association between all nocturnal breathing parameters (specifically: mean SpO2, AHI, oxygen desaturation index 3% and % time with SpO2 <90%) and the main stability outcomes (all p<0.05).

CONCLUSIONS

SDB severity, especially the mean nocturnal SpO2 level, is associated with impaired daytime postural stability.

Effects of Ramadan Gasting on Postural Balance and Attentional Capacities in Elderly People

OBJECTIVE

To evaluate the effects of Ramadan fasting on postural balance and attentional capacities in older adults.

SETTING

the Neurophysiology department of a University Hospital.

PARTICIPANTS

Fifteen males aged between 65 and 80 years were asked to perform a postural balance protocol and a simple reaction time (SRT) test in four testing phases: one week before Ramadan (BR), during the second (SWR) and the fourth week of Ramadan (FWR) and 3 weeks after Ramadan (AR).

MEASUREMENTS

Postural balance measurements were recorded in the bipedal stance in four different conditions: firm surface/eyes open (EO), firm surface/eyes closed (EC), foam surface/EO and foam surface/EC using a force platform.

RESULTS

Results of the present study demonstrated that center of pressure (CoP) mean velocity (CoPVm), medio-lateral length (CoPLX) and antero-posterior length (CoPLY) were significantly higher during the SWR than BR. Likewise, values of CoPVm and CoPLX increased significantly during the FWR compared to BR. The CoPLX decreased significantly in the FWR compared to the SWR. Values of CoPVm and CoPLX were significantly higher AR in comparison with BR. In addition, SRT values increased significantly during the SWR and the FWR than BR.

CONCLUSION

Ramadan fasting affects postural balance and attentional capacities in the elderly mainly in the SWR and it may, therefore, increase the risk of fall and fall-related injuries. More than three weeks are needed for older adults to recover postural balance impairment due to Ramadan fasting.

The effects of acute treatment with ramelteon, triazolam, and placebo on driving performance, cognitive function, and equilibrium function in healthy volunteers

RATIONALE

Hypnotics are widely used to treat insomnia but adverse effects of different hypnotics, especially benzodiazepine receptor agonists, are getting more attention lately. The effects of novel hypnotics have not been fully examined.

OBJECTIVE

This study aims to assess the effects of two hypnotics, ramelteon and triazolam, on driving performance, cognitive function, and equilibrium function.

METHODS

In this double-blinded, three-way crossover trial, 17 healthy males received acute doses of 8 mg ramelteon, 0.125 mg triazolam, and placebo. The subjects were administered three driving tasks-road-tracking, car-following, and harsh-braking-using a driving simulator and three cognitive tasks-Continuous Performance Test, N-back Test, and Trail-Making Test-at baseline and at 1 and 4 h post-dosing. The Stanford Sleepiness Scale scores and computerized posturography were also assessed.

RESULTS

In the driving simulations, ramelteon and triazolam increased the number of subjects who slid off the road. Triazolam increased the standard deviation of lateral position compared to ramelteon and placebo at 1 h post-dosing. Ramelteon and triazolam significantly increased the time to complete of Trail-Making Test part A and the environmental area in posturography compared to placebo at 1 and 4 h post-dosing. Ramelteon and triazolam significantly increased subjective sleepiness compared to placebo at 1 h post-dosing.

CONCLUSIONS

Ramelteon may affect road-tracking performance, visual attention and/or psychomotor speed measured by Trail-Making Test part A, and body balance in acute dosing. Lower dose of triazolam also impaired performance worse than ramelteon. Physicians should consider risks and benefits when prescribing both drugs, especially in the initial period of administration.

Morning/Evening differences in somatosensory inputs for postural control

The underlying processes responsible for the differences between morning and afternoon measurements of postural control have not yet been clearly identified. This study was conducted to specify the role played by vestibular, visual, and somatosensory inputs in postural balance and their link with the diurnal fluctuations of body temperature and vigilance level. Nineteen healthy male subjects (mean age: 20.5 ± 1.3 years) participated in test sessions at 6:00 a.m. and 6:00 p.m. after a normal night's sleep. Temperature was measured before the subjects completed a sign cancellation test and a postural control evaluation with eyes both open and closed. Our results confirmed that postural control improved throughout the day according to the circadian rhythm of body temperature and sleepiness/vigilance. The path length as a function of surface ratio increased between 6:00 a.m. and 6:00 p.m. This is due to a decrease in the centre-of-pressure surface area, which is associated with an increase in path length. Romberg's index did not change throughout the day; however, the spectral analysis (fast Fourier transform) of the centre-of-pressure excursions (in anteroposterior and mediolateral directions) indicated that diurnal fluctuations in postural control may occur via changes in the different processes responsible for readjustment via muscle contractions.

Alterations in postural control during the world's most challenging mountain ultra-marathon

We investigated postural control (PC) effects of a mountain ultra-marathon (MUM): a 330-km trail run with 24000 m of positive and negative change in elevation. PC was assessed prior to (PRE), during (MID) and after (POST) the MUM in experienced ultra-marathon runners (n = 18; finish time = 126 ± 16 h) and in a control group (n = 8) with a similar level of sleep deprivation. Subjects were instructed to stand upright on a posturographic platform over a period of 51.2 seconds using a double-leg stance under two test conditions: eyes open (EO) and eyes closed (EC). Traditional measures of postural stability (center of pressure trajectory analysis) and stabilogram-diffusion analysis (SDA) parameters were analysed. For the SDA, a significantly greater short-term effective diffusion was found at POST compared with PRE in the medio-lateral (ML; Dxs) and antero-posterior (AP) directions (Dys) in runners (p<0.05) The critical time interval (Ctx) in the ML direction was significantly higher at MID (p<0.001) and POST (p<0.05) than at PRE in runners. At MID (p<0.001) and POST (p<0.05), there was a significant difference between the two groups. The critical displacement (Cdx) in the ML was significantly higher at MID and at POST (p<0.001) compared with PRE for runners. A significant difference in Cdx was observed between groups in EO at MID (p<0.05) and POST (p<0.005) in the ML direction and in EC at POST in the ML and AP directions (p<0.05). Our findings revealed significant effects of fatigue on PC in runners, including, a significant increase in Ctx (critical time in ML plan) in EO and EC conditions. Thus, runners take longer to stabilise their body at POST than at MID. It is likely that the mountainous characteristics of MUM (unstable ground, primarily uphill/downhill running, and altitude) increase this fatigue, leading to difficulty in maintaining balance.

Diurnal changes in postural control in normal children: Computerized static and dynamic assessments

Mild traumatic brain injury (mTBI) causes postural control deficits and accordingly comparison of aberrant postural control against normal postural control may help diagnose mTBI. However, in the current literature, little is known regarding the normal pattern of postural control in young children. This study was therefore conducted as an effort to fill this knowledge gap. Eight normal school-aged children participated. Posture assessment was conducted before (7–8 a.m. in the morning) and after (4–7 p.m. in the afternoon) school on regular school days using the Balance Master® evaluation system composed of 3 static tests and 2 dynamic balance tests. A significant difference in the weight-bearing squats was detected between morning hours and afternoon hours (P < 0.05). By end of afternoon, the body weight was borne mainly on the left side with the knee fully extended and at various degrees of knee flexion. A significantly better directional control of the lateral rhythmic weight shifts was observed at the end of the afternoon than at morning hours (P < 0.05). In summary, most of our findings are inconsistent with results from previous studies in adults, suggesting age-related differences in posture control in humans. On a regular school day, the capacity of postural control and laterality or medio-lateral balance in children varies between morning and afternoon hours. We suggest that posturographic assessment in children, either in normal (e.g., physical education and sports training) or in abnormal conditions (e.g., mTBI-associated balance disorders), be better performed late in the afternoon.

Circadian amplitude and homeostatic buildup rate in postural control

Postural control during quiet stance is a common everyday physical activity. Sleepiness is increasingly prevalent in our 24-h society. Yet, little research exists that quantitatively links the fluctuations in sleepiness and postural control. This study quantifies the circadian amplitude and homeostatic buildup rate in postural control. With a force plate we assessed postural control in 12 participants (21-38 years) every 2h during 24h of sustained wakefulness. The sway area was 1.39 ± 0.71 mm(2) at the circadian high around noon, and 4.02 ± 0.67 mm(2) at the circadian low around 6 am (a 189% change, p=0.02). The circadian amplitude of the sway area was therefore 2.63 mm(2). The sway area was 1.92 ± 0.64 mm(2) at the start of the 24-h period and 4.42 ± 0.69 mm(2) at the end of the period (a 130% change, p<0.001). The homeostatic buildup rate of sway area was 0.04 h(-1). The circadian- and homeostatic effects on sway variability, sway velocity, sway frequency and fractal dimension were smaller but still significant. This study found that the circadian amplitude and homeostatic buildup rate are quantifiable from posturographic data, and that they have significant impact on postural control. This finding is important because it means that one could apply the framework of the famous two-process model of sleep regulation (published by Borbély in 1982) to explain the previously reported sleepiness-related changes in postural control.

The effect of extended wake on postural control in young adults

The sleep-wake cycle is a major determinant of locomotor activity in humans, and the neural and physiological processes necessary for optimum postural control may be impaired by an extension of the wake period into habitual sleep time. There is growing evidence for such a contribution from sleep-related factors, but great inconsistency in the methods used to assess this contribution, particularly in control for circadian phase position. Postural control was assessed at hourly intervals across 14 h of extended wake in nine young adult participants. Force plate parameters of medio-lateral and anterior-posterior sway, centre of pressure (CoP) trace length, area, and velocity were assessed with eyes open and eyes closed over 3-min periods. A standard measure of psychomotor vigilance was assessed concurrently under constant routine conditions. After controlling for individual differences in circadian phase position, a significant effect of extended wake was found for anterior-posterior sway and for psychomotor vigilance. These data suggest that extended wake may increase the risk of a fall or other consequences of impaired postural control.

Time-of-day influences postural balance in older adults

BACKGROUND

Postural balance assessments are performed in both clinical and basic research settings on a daily basis. During a 24-h time span our physiology and physical performance undergo radical changes as we are influenced by the circadian rhythm. The time-of-day interaction on postural balance is unknown in older adults. The aim of this study was to investigate the time-of-day effect on postural balance in older adults.

METHODS

Center of pressure (CoP) excursion was measured (100 Hz) by force plate analysis in 34 older adults during 30 s of narrow quiet bilateral stance. Measurements were performed around 9a.m., 12.30 p.m. and 4 p.m. on the same day. Postural balance was quantified by velocity-moment, confidence ellipse area, total sway area and total sway length.

RESULTS

An overall significant time-of-day (between 9 a.m. and 4 p.m.) effect was observed for velocity-moment (mm(2)/s) 57 ± 27-65 ± 29 (p = 0.001), confidence ellipse area (mm(2)) 36 ± 16-44 ± 19 (p < 0.001), total sway area (mm(2)) 548 ± 263-627 ± 285 (p = 0.001) and total sway length (mm) 373 ± 120-379 ± 113 (p = 0.037). The variation of postural balance was mostly pronounced from midday (12.30 p.m.) toward the afternoon (4 p.m.) in all sway parameters. Specifically between 12.30 p.m. and 4 p.m. confidence ellipse area increased by 18.5%, total sway area by 17.1%, velocity-moment by 15.8% and total sway length by 4.6%. No differences were observed between 9 a.m. and 12.30 p.m. in any of the sway parameters.

CONCLUSIONS

This study demonstrates that time-of-day influences postural balance in older adults. These findings have important scientific and clinical relevance, as they imply that time-of-day should be a controlled factor when assessing postural balance in older adults.

Can a simple balance task be used to assess fitness for duty?

Human fatigue, caused by sleep loss, extended wakefulness, and/or circadian misalignment, is a major cause of workplace errors, incidents and accidents. In some industries, employees are required to undertake fitness for duty testing at the start of a shift to identify instances where their fatigue risk is elevated, so that minimisation and/or mitigation strategies can be implemented. Postural balance has been proposed as a fitness for duty test for fatigue, but it is largely untested. Therefore, the purpose of this study was to examine the impact of sleep loss, extended wakefulness and circadian phase on postural balance. Fourteen male participants spent 10 consecutive days in a sleep laboratory, including three adaptation days and eight simulated shiftwork days. To simulate a quickly rotating roster, shiftwork days were scheduled to begin 4h later each day, and consisted of a 23.3-h wake episode and a 4.7-h sleep opportunity. Every 2.5h during wake, balance was measured while standing as still as possible on a force platform with eyes open for one minute, and eyes closed for one minute. Subjective sleepiness was assessed using the Karolinska Sleepiness Scale. Core body temperature, continuously recorded with rectal thermistors, was used to determine circadian phase. For measures of postural balance and subjective sleepiness, data were analysed using three separate repeated measures ANOVA with two within-subjects factors: circadian phase (six phases) and prior wake (nine levels). For subjective sleepiness, there was a significant effect of prior wake and circadian phase. In particular, sleepiness increased as prior wake increased, and was higher during biological night-time than biological daytime. For the eyes open balance task, there was no effect of prior wake or circadian phase. For the eyes closed balance task, there was a significant effect of circadian phase such that balance was poorer during the biological night-time than biological daytime, but there was no effect of prior wake. These results indicate that postural balance may be a viable tool for assessing fatigue associated with time of day, but may not be useful for assessing fatigue associated with extended hours of wake.

Effects of increased homeostatic sleep pressure on postural control and their modulation by attentional resources

OBJECTIVE

This study aimed to determine how increased sleep pressure interferes with postural control according to the availability of attentional resources and visual input.

METHODS

Thirteen healthy young adults performed a psychomotor vigilance task and postural tasks after a night of sleep and after 25 h of sleep deprivation. Primary outcome variables were calculated from the center of pressure (CoP) displacement measured by two force plates in various cognitive load and visual state conditions.

RESULTS

Sleep deprivation increased CoP anterior-posterior range in the no cognitive load condition and decreased CoP mediolateral range and velocity in the high cognitive load conditions. Sleep deprivation effects on the mediolateral range in the eyes open high cognitive load condition were significantly correlated with its effects on the psychomotor vigilance task.

CONCLUSIONS

Sleep deprivation destabilizes postural control when attentional and sensory resources are not challenged. In high cognitive load condition, sleep loss induces a general freezing effect that seems to be modulated by the degree of impairment in psychomotor speed.

SIGNIFICANCE

This study demonstrates that sleep pressure has a destabilizing effect on postural control independently of circadian factors, therefore suggesting that sleep debt may be a significant risk factor for falls.

The influences of time-of-day and sleep deprivation on postural control

The aim of this study was to check the combined and/or dissociated influences of time-of-day and sleep deprivation on postural control. Twenty subjects participated in test sessions which took place at 6:00 am, 10:00 am, 2:00 pm and 6:00 pm either after a normal night's sleep or after a night of total sleep deprivation. Postural control was evaluated by COP surface area, LFS ratio and Romberg's index. The results showed that postural control fluctuates diurnally according to three different periods, pronounced by sleep deprivation: (1) at 6:00 am, there was no modification by sleep deprivation; (2) at 10:00 am and 2:00 pm, an interaction effect was observed for COP surface area and LFS ratio after sleep deprivation. Values of COP surface area were significantly higher (P < 0.01) following the night of sleep deprivation than after the normal night's sleep (139.36 ± 63.82 mm² vs. 221.72 ± 137.13 mm² and 143.78 ± 75.31 mm² vs. 228.65 ± 125.09 mm², respectively); (3) at 6:00 pm, the LFS ratio was higher than during the two other periods (P < 0.001) whereas COP surface area decreased to the level observed at 6:00 am. At this time-of-day, only the LFS ratio was significantly increased (P < 0.05) by the night of sleep deprivation (0.89 ± 0.14 vs. 1.03 ± 0.30). This temporal evolution in postural control does not seem to be related to any deterioration in visual input as Romberg's index (150.09 ± 97.91) was not modified, regardless of the test session.

Principal component analysis detects sleepiness-related changes in balance control

Computerized posturography exploits balance scores that quantify the size, dynamics, or structure of the recorded sway. Since people employ different balance strategies, one single balance score will not detect balance changes in all subjects. Principal component analysis (PCA) can combine balance scores that quantify different features into one new balance score. We tested the score with 20 subjects by measuring their balance every 2 h during 28 h of sustained waking. The new balance score was more sensitive than its components (p<0.001 vs. p≥0.051) to the small sleepiness-related balance decrements that occurred during the short 28-h period. PCA provided a more sensitive balance score that applied to all of the subjects.

Effects of sleep deprivation on human postural control, subjective fatigue assessment and psychomotor performance

This study aimed to investigate the effects of sleep deprivation on postural control, subjective fatigue assessment and psychomotor performance, and to assess the efficiency of an objective posturographic test as an indicator of mental fatigue. Postural sway using static posturography (Romberg's test), subjective fatigue assessment (Stanford Sleepiness Scale) and psychomotor performance (Sternberg dual-task test) were assessed in 12 subjects before and after 24 h of sustained wakefulness. After sustained wakefulness, the Romberg test parameters of circumference area and rectangle area with the eyes-closed, and standard deviation in the anterior-posterior direction with the eyes-open were significantly higher compared with baseline values (before sustained wakefulness). Subjective fatigue assessment scores were also significantly increased, while psychomotor performance was unchanged. Sleep deprivation can arouse a feeling of fatigue and can affect postural stability, hence an objective posturographic test score may be useful as an indicator of mental fatigue.

Quantifying time awake posturographically

Although sleepiness is a major risk factor in traffic and occupational accidents, convenient, quantitative, and commercial sleepiness testing is lacking. The issue is relevant to policymakers concerned with legislation for, and surveillance of, traffic- and occupational safety. This work suggested and examined posturographic sleepiness testing for instrumentation purposes. In 63 subjects--for whom we tested balance with a force platform during sustained waking for maximum 36 h--sustained waking impaired the balance. The sustained waking explained 60% of the diurnal balance variations, whereas the time of day explained 40% of the balance variations. The first finding -that balance depends on the subject's time awake (TA)- allowed to posturographically estimate the subjects' TA with 86% accuracy and 97% precision. Results also show that balance scores tested at 13:30 hours serve as a threshold to detect excessive sleepiness. This work provides guidelines for a posturographic sleepiness tester.

Modeling balance control during sustained waking allows posturographic sleepiness testing

We develop a method to quantify sleepiness. Sleepiness is a major risk factor in traffic and occupational accidents, but lack of convenient tests precludes monitoring impending sleepiness. Posturographic balance testing could address this need because sleepiness increases postural sway. It is, however, unclear how sleepiness influences balance control. Our results, for 12 subjects, show that balance control is more susceptible to increasing time awake (TA) compared to neuromuscular processes. This conclusion is reached since during sustained waking the control process slows down by 3.4% per hour of increased TA. This slowdown accounts for 65% of the variance in diurnal balance. We quantified balance control by modeling the body as an inverted pendulum and by expressing the control as the critical time interval for open-loop control (Deltat(c)) of the center-of-mass movements of this pendulum. To estimate the subjects' TA, we regressed the Deltat(c) scores recorded during sustained waking against increasing TA, and equated separate Deltat(c) test scores with the diurnal Deltat(c) scores. We estimated TA with 68% positive predictive value. The results encourage implementing balance modeling into a device that performs clinical or industrial balance testing because the model-based Deltat(c) score responded to increasing TA.

Effects of proprioceptive vibratory stimulation on body movement at 24 and 36h of sleep deprivation

OBJECTIVE

To investigate whether postural stability and adaptation differed after a normal night of sleep, after 24h (24 SDep) and 36h (36 SDep) of sleep deprivation while subjected to repeated balance perturbations. Also, to determine whether there was any correlation between subjective alertness scores and objective posturographic measurements. Lastly, to investigate the effects of vision on the stability during sleep deprivation.

METHODS

Body movements at five locations were recorded in 18 subjects (mean age 23.8years) using a 3D movement measurement system while subjected with eyes open and closed to vibratory proprioceptive calf stimulation after a normal night of sleep, 24 and 36 SDep.

RESULTS

The clearest sleep deprivation effect was reduced ability to adapt head, shoulder and hip movements, both with eyes open and eyes closed. Additionally, several near falls occurred after being subjected to balance perturbations for 2-3min while sleep deprived. Unexpectedly, postural performance did not continue to deteriorate between 24 and 36h of sleep deprivation, but showed some signs of improvement. Subjective scores of sleepiness correlated poorly with actual changes in postural control performance.

CONCLUSIONS

Sleep deprivation might affect postural stability through reduced adaptation ability and lapses in attention. Subjective alertness might not be an accurate indicator of the physiological effects of sleep deprivation.

SIGNIFICANCE

Sleep deprivation could increase the risk of accidents in attention demanding tasks. There is a need for objective evaluation methods to determine actual performance capacity during sleep deprivation.

Posturographic sleepiness monitoring

Although reduced sleep often underlies traffic and occupational accidents, convenient sleepiness testing is lacking. We show that posturographic balance testing addresses this issue, because balance testing predicts hours of wakefulness, which could facilitate sleepiness testing. Here, we equate balance scores from separate trials, blinded to the experimenter, with those recorded as a function of known and increasing time awake (i.e. during sustained wakefulness); we show, that the time awake in separate trials is posturographically measurable: positive predictive value 69%, sensitivity 56%, and specificity 96%. These results encourage further work developing posturographic sleepiness monitoring.

Daytime Changes in Postural Stability and Repeatability of Posturographic Measurements

OBJECTIVE

Daytime sleepiness correlates with sleep-related accidents, but convenient tests for occupational sleepiness monitoring are scarce. The effect of daytime on balance, on posturographic measurements, and on their repeatability was investigated in 30 healthy volunteers as part of our work to develop such a test.

METHODS

The daytime effect was assessed by measuring balance at 8:30 am, 10:30 am, and 1:30 pm. The repeatability was assessed with morning trials once a week for 1 month. The posturographic test was performed on a static force platform, and the balance was evaluated from a fractal dimension of sway, most common sway amplitude, and time interval for open-loop stance control.

RESULTS

The balance worsened during the day, and it was possible to determine whether the measurement was performed in the morning or in the afternoon. The morning balance remained unchanged during the month-long test.

CONCLUSIONS

Posturographic measurements are repeatable and have a circadian effect, which may be influenced by sleepiness.