Circadian amplitude and homeostatic buildup rate in postural control

Reduction in fall risk markers following CPAP treatment of obstructive sleep apnoea in people over 65 years

OBJECTIVES

Falls in older people can lead to serious injury and significant societal health and financial burden. Obstructive sleep apnoea (OSA) is associated with impaired gait/balance and may increase fall risk, yet few studies examined whether treating OSA reduces fall risk. This study examined the effect of continuous positive airway pressure (CPAP) on fall risk markers in people over 65yrs diagnosed with OSA.

DESIGN

Single arm intervention study.

SETTING

University and tertiary care CPAP clinic.

PARTICIPANTS

Individuals over 65 years diagnosed with OSA and recommended CPAP.

INTERVENTION

3-6 months CPAP therapy.

MEASUREMENTS

28 participants had a physiological profile assessment (PPA) at baseline and following 3-6 months of CPAP. The PPA examines visual contrast sensitivity, lower limb proprioception, knee extension strength, reaction time and postural sway to generate a fall risk score (FRS). t-tests were used to determine difference between pre- and post-treatment FRS. Regression was used to examine the associations between CPAP use and daytime sleepiness with FRS.

RESULTS

CPAP significantly reduced the FRS ([Mean ± SD] 0.59 ± 1.0 vs 0.04 ± 1.1, p = 0.016), contrast sensitivity and lower limb proprioception (P < 0.05). Increased CPAP use was associated with improvement in FRS in unadjusted analysis (β = -0.213, 95%CI -0.371 to -0.056, p = 0.01). Reduction in Epworth sleepiness score was associated with a reduction in FRS in unadjusted (p = 0.023) and adjusted analysis (adjusted for AHI p = 0.027 or O2Nadir p = 0.015).

CONCLUSIONS

CPAP may reduce fall risk in people over 65yrs, possibly related to better CPAP adherence and reduced daytime sleepiness. Future controlled trials and mechanistic studies are needed to elucidate how CPAP may reduce fall risk.

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.

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.

Does Time of Day influence postural control and gait? A review of the literature

BACKGROUND

Like many physiologic processes, Time of Day may influence postural control and gait. A better understanding of diurnal variations in postural control and gait may help to improve diagnoses, reduce falls, and optimize rehabilitation and training routines. This review summarizes the current literature that addresses these questions.

RESEARCH QUESTION

Does time of day affect postural control and gait?

METHODS

We searched PubMed, Google Scholar, and IEEE using a combination of keyword and MeSH terms. We included papers that studied human subjects and assessed gait or postural control as a function of time of day. We evaluated the quality of the identified papers based on nine assessment criteria and analyzed them considering the topic (postural control or gait), age, and characteristics of the conducted assessments. We then quantitatively synthesized the results across studies using a meta-analytical approach (i.e., Hedges' g model).

RESULTS

Twenty-two papers considered the relationship between time of day and postural control, and eleven considered the relationship between time of day and gait. Six studies found that postural control was best in the morning, four described postural control being best in the afternoon, four described optimal postural control in the evening, and eight reported no time of day effect. Two studies found gait best in the morning, five described gait best in the afternoon, two described optimal gait in the evening, and two reported no time of day effect. The results of the quantitative analysis suggest that both postural control and gait were best in the evening.

SIGNIFICANCE

While there is no clear consensus on whether there is a time of day effect for postural control and gait, the findings of this review provide initial evidence suggesting that a small but statistically significant effect exists in favor of the evening. Standardized testing, including repeated and continuous evaluations, may help provide more definitive information on time of day influences on postural control and gait.

Initiation gait variability is higher in the morning in elderly inpatients

OBJECTIVE

Although elderly inpatients are known to experience decreased physical activity in the morning, falls occur frequently during this time. Gait variability is an evaluation of gait instability and a risk factor for falls. Gait initiation requires complex processes, and it is important to evaluate gait variability not only during steady-state gait but also during gait initiation. However, the effect of the diurnal pattern on variability in gait characteristics is still unknown. The aim of this study was to investigate the effect of the diurnal pattern on initiation and steady-state gait variability in elderly inpatients.

METHOD

Thirty-seven elderly inpatients (28 women; mean age, 79.7 ± 9.5 years) who could walk without support were sampled in this study. The quantitative measure of gait variability was evaluated using the coefficient of variation (CV) based on four consecutive stride durations determined using triaxial accelerometers. Gait characteristics were evaluated during initiation and steady-state gait and defined as initiation CV and steady-state CV, respectively. This measurement was performed at two time points, morning and daytime.

RESULTS

There was no significant difference between initiation and steady-state gait characteristics in the daytime condition. However, in the morning condition, the initiation CV was higher than the steady-state CV. Furthermore, the initiation CV was higher in the morning than during daytime (p < 0.01).

CONCLUSION

Our study revealed that the variability of initiation gait is higher in the morning. It may be important to assess the risk of falls, including initiation gait, in the morning.

Assessment of postural control after sleep deprivation with a low-cost portable force plate

It is well-known that acute sleep deprivation affects negatively postural control. The analysis of sleep quality during long periods and its impact on motor control and learning performance are crucial aspects of human health. Nevertheless, there is conflicting evidence regarding which postural control variables are more prone to change due to sleep deprivation. Moreover, very few clinicians have at their disposal expensive force plates to measure such variables, so the use of a low-cost portable device could be very interesting. Therefore, we aimed to identify which posture control variables, obtained from a low-cost plate, are more sensitive to sleep deprivation. In order to do so, we have performed a set of experiments with volunteers before and after a night without sleep. Eight participants took part of the study and had their balance measured by a Wii Balance Board before and after one night of sleep deprivation. They were asked to keep a quiet stance on top of the plate with their eyes open and closed, in a balanced design. The main results showed that, regardless the visual information, sleep deprivation has deepest impact on the anterior-posterior center of pressure displacement. Sleep deprivation without visual information had a more pronounced (large effect size) impact on the mean sway in the anterior-posterior direction and its distribution variation. The information that sleep deprivation has a more meaningful impact on anterior-posterior center of pressure excursion may help clinicians and healthcare professionals to better deal with its implications.

Time of day effect on balance performance, functional capacities and risk of fall in women with rheumatoid arthritis

Objective: This study explored the time of day effect of balance performance, functional capacities and risk of fall in three different times in patients with rheumatoid arthritis (RA) and the association between these variations and those of RA symptoms.Methods: A "discontinual" protocol, composed of three test sessions, carried out at 6 am, 2 pm and 10 pm was set up, in order to investigate the time of day effect of balance performance, functional capacities, risk of fall, stiffness, range of motion, swollen and painful joints in women with RA.Results: Time Up and Go Test (TUGT), Functional Reach Test (FRT) and tinetti test scores were significantly higher (p < .01) at 6 am and at 10 pm compared to 2 pm. Stiffness, range of motion, swollen and painful joints values were significantly higher (p < .01) at 6 am and at 10 pm compared to 2 pm. A significant difference was observed on the stiffness, range of motion and swollen joints values between 6 am and 10 pm that were higher at 6 am (p < .05).Using Pearson's coefficient, correlations were found between RA symptom values; and TUGT, FRT and Tinetti test scores.Conclusion: Results showed a time of day effect of balance performance, functional capacities and risk of falls in women with RA. This variation indicates an alteration of performance at 6 am and 10 pm. Fluctuations of stiffness, limited range of motion, swollen and painful joints noted are concomitant to those of balance performance, functional capacities, and risk of fall.Abbreviations: RA: rheumatoid arthritis; H&O questionnaire: Horne and Ostberg questionnaire; PSQI: Pittsburgh sleep quality index; HAQ: health assessment questionnaire; SF-36: the short form-36; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index; TUGT: Time Up and Go Test; FRT: Functional Reach Test.

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.

Prolonged Intermittent Trunk Flexion Increases Trunk Muscles Reflex Gains and Trunk Stiffness

The goal of the present study was to determine the effects of prolonged, intermittent flexion on trunk neuromuscular control. Furthermore, the potential beneficial effects of passive upper body support during flexion were investigated. Twenty one healthy young volunteers participated during two separate visits in which they performed 1 hour of intermittent 60 seconds flexion and 30 seconds rest cycles. Flexion was set at 80% lumbar flexion and was performed with or without upper body support. Before and after intermittent flexion exposure, lumbar range of motion was measured using inertial measurement units and trunk stability was assessed during perturbations applied in the forward direction with a force controlled actuator. Closed-loop system identification was used to determine the trunk translational admittance and reflexes as frequency response functions. The admittance describes the actuator displacement as a function of contact force and to assess reflexes muscle activation was related to actuator displacement. Trunk admittance gain decreased after unsupported flexion, while reflex gain and lumbar range of motion increased after both conditions. Significant interaction effects confirmed a larger increase in lumbar range of motion and reflex gains at most frequencies analysed following unsupported flexion in comparison to supported flexion, probably compensating for decreased passive tissue stiffness. In contrast with some previous studies we found that prolonged intermittent flexion decreased trunk admittance, which implies an increase of the lumped intrinsic and reflexive stiffness. This would compensate for decreased stiffness at the cost of an increase in cumulative low back load. Taking into account the differences between conditions it would be preferable to offer upper body support during activities that require prolonged trunk flexion.

The impact of time of day on the gait and balance control of Alzheimer's patients

Alzheimer's patients suffer from circadian dysregulation. The aim of this study was to examine the evolution of balance control and gait at different times of the day (11:00, 14:00, 18:00) in order to identify whether Alzheimer's patients were more likely to fall at certain periods of the day. Spatio-temporal parameters of centre of foot pressure displacements were measured with a force platform and spatio-temporal parameters of walking were evaluated with a gait analysis device. The results highlighted that balance control was worse in the evening and the afternoon than in the morning. Furthermore, the walking speed was faster and support duration, swing duration and cycle duration were shorter in the evening than in the morning and afternoon. The combined analysis of balance control and gait parameters revealed that balance control and walking are concomitantly altered in the evening which increases the fall risk in the evening, in comparison with the morning, for Alzheimer's patients.

Diurnal Fluctuations of Verticality Perception - Lesser Precision Immediately after Waking up in the Morning

Internal estimates of direction of gravity are continuously updated by integrating vestibular, visual and proprioceptive input, and prior experience about upright position. Prolonged static roll-tilt biases perceived direction of gravity by adaptation of peripheral sensors and central structures. We hypothesized that in the morning after sleep, estimates of direction of gravity [assessed by the subjective visual vertical (SVV)] are less precise than in the evening because of adaptation to horizontal body position and lack of prior knowledge about upright position. Using a mobile SVV-measuring device, verticality perception was assessed in seven healthy human subjects on 7 days in the morning immediately after waking up and in the evening while sitting upright. Paired t-tests were applied to analyze diurnal changes in SVV trial-to-trial variability. Average SVV variability in the morning was significantly larger than in the evening (1.9 ± 0.6° vs. 0.9 ± 0.3°, p = 0.002). SVV accuracy was not significantly different (−1.2 ± 0.9° vs. −0.4 ± 0.4°, morning vs. evening, p = 0.058) and was within normal range (±2.3°) in all but one subject. A good night’s sleep has a profound effect on the brain’s ability to estimate direction of gravity. Resulting variability was significantly worse after waking up reaching values more than twice as large as in the evening while there was no significant impact on SVV accuracy. We hypothesize that lacking prior knowledge, adaptation of peripheral sensors, and lower levels of arousal and cerebral metabolism contribute to such impoverished estimates. Our observations have considerable clinical impact as they indicate an increased risk for falls and fall-related injuries in the morning.

Body Sway as a Possible Indicator of Fatigue in Clerical Workers

BACKGROUND

Fatigue has a strong impact on workers' performance and safety, but expedient methods for assessing fatigue on the job are not yet available. Studies discuss posturography as an indicator of fatigue, but further evidence for its use in the workplace is needed. The purpose of the study is to examine whether posturography is a suitable indicator of fatigue in clerical workers.

METHODS

Thirty-six employees (Ø 34.8 years, standard deviation = 12.5) participated in postural tasks (eyes open, eyes closed, arm swinging, and dual task) in the morning and afternoon. Position of their center of pressure (COP) was registered using a Nintendo Wii Balance Board and commercial software. From registered COP time series, we calculated the following parameters: path length (mm), velocity (mm/s), anterior-posterior variance (mm), mediolateral variance (mm), and confidence area (mm(2)). These parameters were reduced to two orthogonal factors in a factor analysis with varimax rotation.

RESULTS

Statistical analysis of the first factor (path length and velocity) showed a significant effect of time of day: COP moved along a shorter path at a lower velocity in the afternoon compared with that in the morning. There also was a significant effect of task, but no significant interaction.

CONCLUSION

Data suggest that postural stability of clerical workers was comparable in the morning and afternoon, but COP movement was greater in the morning. Within the framework of dynamic systems theory, this could indicate that the postural system explored the state space in more detail, and thus was more ready to respond to unexpected perturbations in the morning.