Circadian rhythm of postural control, sleepiness and verticality perception in older adults

International audienceAbstract Introduction with ageing, the risk of falling increases. It has been reported that fall frequency may depend on the time of the day, suggesting a possible circadian rhythm of postural control. The objective was to test whether postural control in older adults followed a circadian rhythm. Then, in order to examine the possible functions involved in circadian variations in balance performances, circadian rhythm of sleepiness and vertical perception were also tested. Methods eight participants (70.7 ± 4.7 years) were included. Baseline circadian rhythm profile was assessed through continuous core temperature measurement. Static and dynamic balance, subjective sleepiness and fatigue, and verticality perception were measured at 2:00, 6:00, 10:00, 14:00, 18:00 and 22:00, on separate weeks in a random order. Results temperature followed a circadian rhythm, with lowest temperature occurring at 03:50. Circadian rhythm was detected for the centre of pressure displacement length and velocity, in dynamic condition eyes closed, with lowest performances occurring at 18:33 and 16:59, respectively. Subjective sleepiness and fatigue also followed circadian rhythm with lowest sleepiness occurring at 15:46 and 15:50, for the Karolinska Sleeping Scale and the Visual Analogic Scale of fatigue, respectively. Finally, the vertical perception was not significantly following a circadian rhythm. Conclusion older adults present a circadian rhythm of balance, in particular in more challenging conditions, and the lowest performances occurred in the late afternoon These circadian rhythms could explain some of the falls happening at this time in community-dwelling older adults

Twenty-four-hour variation of vestibular function in young and elderly adults

International audienceAnimal and human studies demonstrate anatomical and functional links between the vestibular nuclei and the circadian timing system. This promotes the hypothesis of a circadian rhythm of vestibular function. The objective of this study was to evaluate the vestibular function through the vestibulo-ocular reflex using a rotatory chair at different times of the day to assess circadian rhythmicity of vestibular function. Two identical studies evaluating temporal variation of the vestibulo-ocular reflex (VOR) were performed, the first in young adults (age: 22.4 ± 1.5 y), and the second in older adults (70.7 ± 4.7 y). The slow phase velocity and time constant of the VOR were evaluated in six separate test sessions, i.e., 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. In both studies, markers of circadian rhythmicity (temperature, fatigue, and sleepiness) displayed expected usual temporal variation. In young adults, the time constant of the VOR showed variation throughout the day (p < .005), being maximum 12:25 h (06:00 h test session) before the acrophase of temperature circadian rhythm. In older adults, the slow phase velocity and time constant also displayed temporal variation (p < .05). Maximum values were recorded at 10:35 h (06:00 h test session) before the acrophase of temperature circadian rhythm. The present study demonstrates that vestibular function is not constant throughout the day. The implication of the temporal variation in vestibular system in equilibrium potentially exposes the elderly, in particular, to differential risk during the 24 h of losing balance and falling

Design of the experimental protocol.

<p>The sleep-wake periods and the three test sessions performed after a reference night (RN), a control night (CN), and an experimental night (EN) are shown.</p

Anaerobic power output values and Fatigue Index (mean ± SEM) obtained during the 60-s Wingate test performed the following morning after 3 different nights.

<p>PP, Peak Power; MP_30s and MP_60s, Mean Power recorded during the first 30 s and the full 60 s of the test, respectively; FI: Fatigue Index; RN, test session after a normal reference night; CN, test session after a total sleep deprivation night; EN, test session after a total sleep deprivation night associated with 7.5 h of simulated driving (<i>n</i> = 20).</p

Kinematic variables: Mean angle and ROM (mean ± SEM) of the hip, knee and ankle angles measured throughout the complete crank cycle during interval 1 (I₁) and interval 2 (I₂) of the Wingate test performed the following morning after 3 different nights.

<p>ROM, range of motion; RN, test session after a normal reference night; CN, test session after a total sleep deprivation night; EN, test session after a total sleep deprivation night associated with 7.5 h of simulated driving (<i>n</i> = 20).</p

Kinetic variables: Angle of peak torque and range in torque variation (mean ± SEM) recorded over a complete crank cycle during interval 1 (I₁) and interval 2 (I₂) of the Wingate test performed the following morning after 3 different nights.

<p>RN, test session after a normal reference night; CN, test session after a total sleep deprivation night; EN, test session after a total sleep deprivation night associated with 7.5 h of simulated driving (<i>n</i> = 20).</p

Follow up of ILCs and KSS scores recorded during the nocturnal simulated driving task.

<p>Data are mean ± SEM (<i>n</i> = 20).</p