Sleep Is Compromised in −12° Head Down Tilt Position

Abstract

Recent studies are elucidating the interrelation between sleep, cranial perfusion, and cerebrospinal fluid (CSF) circulation. Head down tilt (HDT) as a simulation of microgravity reduces cranial perfusion. Therefore, our aim was to assess whether HDT is affecting sleep (clinicaltrials.gov; identifier NCT 02976168). 11 male subjects were recruited for a cross-over designed study. Each subject participated in two campaigns each comprising 3 days and 2 nights. Intervention started on the second campaign day and consisted of maintenance of horizontal position or −12° HDT for 21 h. Ultrasound measurements were performed before, at the beginning and the end of intervention. Polysomnographic measurements were assessed in the second night which was either spent in horizontal posture or at −12° HDT. Endpoints were sleep efficiency, sleep onset latency, number of sleep state changes and arousals, percentages of N3, REM, light sleep stages and subjective sleep parameters. N3 and REM sleep reduced by 25.6 and 19.1 min, respectively ( P = 0.002, g = -0.898; P = 0.035, g = -0.634) during −12° HDT. Light sleep (N1/2) increased by 33.0 min at −12° HDT ( P = 0.002, g = 1.078). On a scale from 1 to 9 subjective sleep quality deteriorated by 1.3 points during −12° HDT ( P = 0.047, g = -0.968). Ultrasonic measurement of the venous system showed a significant increase of the minimum ( P = 0.009, P < 0.001) and maximum ( P = 0.004, P = 0.002) cross-sectional area of the internal jugular vein at −12° HDT. The minimum cross-sectional area of the external jugular vein differed significantly between conditions over time ( P = 0.001) whereas frontal skin tissue thickness was not significantly different between conditions ( P = 0.077, P = 0.811). Data suggests venous congestion at −12° HDT. Since subjects felt comfortable with lying in −12° HDT under our experimental conditions, this posture only moderately deteriorates sleep. Obviously, the human body can almost compensate the several fold effects of gravity in HDT posture like an affected CSF circulation, airway obstruction, unusual patterns of propioception and effects on the cardiovascular system.

External to internal cranial perfusion shifts during simulated weightlessness: Results from a randomized cross-over trial

“…We propose a possible explanation for venous return, the outflow maybe simultaneously increased via the external jugular vein. As previously described, the minimum cross-sectional area of the external jugular vein, the minimum and maximum cross-sectional area of the internal jugular vein were significantly increased at −12° HDT during this study 8 . One possible explanation of these findings is a shifting from the superficial carotid system towards the internal jugular veins (Fig.…”

Long-Term Bed Rest Delays the Circadian Phase of Core Body Temperature

“…We also did not collect any physiological or neurobehavioral data to identify the relevance of the observed phase shifts. Investigation of the acute effects of horizontal bed rest (HBR) and HDBR on sleep revealed a decrease in slow-wave sleep with HDBR ( Komada et al, 2006 ; Boschert et al, 2019 ). Data from long-duration bed rest studies showed that slow-wave sleep and total sleep time decreased after 21 days in HBR and HDBR ( Gkivogkli et al, 2016 ; Morrison et al, 2017 ), suggesting that bed rest per se rather than tilted posture predominantly accounts for sleep disturbances.…”

Neurofluids—Deep inspiration, cilia and preloading of the astrocytic network

“…Sleep deprivation and circadian disturbances are able to induce Aβ and tau accumulation by impairing glymphatic flow (Wu et al., 2019). HDT of −12° under microgravity‐simulating conditions was able to significantly alter sleep quality and brain perfusion in a recent experimental study of physiology during space flight (Boschert, 2019). In another recent MRI study focusing on sleep and the dimension of the perivascular Virchow‐Robin space (VRS) as parts of the glymphatic system (Wardlaw et al., 2020), it could be shown in rats that sleep and VRS dimensions were negatively correlated.…”