Heart rate variability under acute simulated microgravity during daytime waking state and nocturnal sleep: Comparison of horizontal and 6° head-down bed rest

Higher habitual lying time is inversely associated with vagal-related heart rate variability outcomes in younger adults

Heart rate variability (HRV) is a well-established noninvasive marker of autonomic cardiac control. We test whether time spent sitting (negatively) versus lying (positively) influences vagal HRV outcomes. HRV (10 min supine electrocardiogram) and free-living postures (dual-accelerometer configuration, 7 days) were measured in 31 young healthy adults (15♀, age: 23 ± 3 years). Habitual lying (66 ± 61 min/day), but not sitting time (558 ± 109 min/day), total sedentary time (623 ± 132 min/day), nor step counts (10 752 ± 3200 steps/day; all, p > 0.090), was associated with root mean square of successive cardiac interval differences (ρ = -0.409, p = 0.022) and normalized high-frequency HRV (ρ = -0.361, p = 0.046). These findings document a paradoxical negative impact of waking lying time on cardioautonomic function.   Take home message Using a multi-accelerometer configuration, we demonstrated that more habitual waking time lying, but not sitting or total sedentary time, was associated with worse vagally mediated cardiac control.

Challenges to the central nervous system during human spaceflight missions to Mars

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Sleep Is Compromised in -12° Head Down Tilt Position

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.

Physiological and Psychological Effects of Viewing a Kiwifruit (Actinidia deliciosa 'Hayward') Orchard Landscape in Summer in Japan

The physiological and psychological relaxation effects of viewing a kiwifruit (Actinidia deliciosa ‘Hayward’) orchard landscape were investigated. Seventeen Japanese adult females (46.1 ± 8.2 years) viewed a kiwifruit orchard landscape or a building site (control) for 10 min. The heart rate variability and heart rate were determined. The modified semantic differential method and the short-form Profile of Mood States were used to assess the psychological effects. Compared with viewing the building site, viewing the kiwifruit orchard landscape resulted in a significant increase in the parasympathetic activity, a marginally significant decrease in the heart rate, a significant increase in “comfortable”, “relaxed” and “natural” feelings and a significant improvement in mood states.

Keeping the right time in space: importance of circadian clock and sleep for physiology and performance of astronauts

The circadian clock and sleep are essential for human physiology and behavior; deregulation of circadian rhythms impairs health and performance. Circadian clocks and sleep evolved to adapt to Earth's environment, which is characterized by a 24-hour light-dark cycle. Changes in gravity load, lighting and work schedules during spaceflight missions can impact circadian clocks and disrupt sleep, in turn jeopardizing the mood, cognition and performance of orbiting astronauts. In this review, we summarize our understanding of both the influence of the space environment on the circadian timing system and sleep and the impact of these changes on astronaut physiology and performance.

Pharmaco-physio-psychologic effect of Ayurvedic oil-dripping treatment using an essential oil from Lavendula angustifolia

Ayurvedic oil-dripping treatment, Shirodhara, involves the use of medicated herbal sesame oils. In our previous reports, we found that Shirodhara with plain sesame oil induced anxiolysis and an altered state of consciousness (ASC) in healthy subjects. We studied the pharmaco-physio-psychologic effect of Shirodhara with medicated sesame oil including an essential oil from Lavendula angustifolia (lavender) in the present study. Sixteen (16) healthy females (38 +/- 8 years old) were assigned at random to three treatments applied by a robotic oil-dripping system: plain sesame oil (plain Shirodhara), medicated sesame oil with a 0.3 volume % of lavender essential oil (lavender Shirodhara), or the control supine position. Psychophysiologic parameters including the heart rate, skin temperature of the dorsum of hands and feet, as well as anxiety and ASC were monitored, and the rates of change of these items were calculated to assess the psychophysiologic changes brought about by Shirodhara. Lavender Shirodhara showed potent anxiolytic and ASC-inducing or promoting effects, and induced the largest increase in foot skin temperature. The correlation between anxiolysis and ASC, as well as the correlation between these psychologic effects and the elevated foot skin temperature were larger in the lavender Shirodhara than in the other two conditions. It was speculated that the psycho-physiologic effects of lavender Shirodhara would be brought about by three mechanisms: (1) the well-known relaxing action of essential oils from L. angustifolia mediated by olfactory nerves, (2) the pharmacologic action of substances absorbed through the skin or mucosa in the sesame oil or lavender essential oil, and (3) the physiologic effect of sesame oil dripped on the forehead induced by the somato-autonomic reflex through thermosensors or pressure sensors in the skin or hair follicles via the trigeminal cranial nerve. The complicated pharmaco-physio-psychologic action of Ayurvedic oil treatment may provide a useful model for future pharmaco-physio-psychotherapy.

Effects of acute simulated microgravity on nocturnal sleep, daytime vigilance, and psychomotor performance: comparison of horizontal and 6 degrees head-down bed rest

This study examined the effect of acute simulated microgravity on nocturnal sleep, daytime vigilance, and psychomotor performance. Each of 7 volunteers were maintained for 3 days of head-down and horizontal bed rest in a counter-balanced design. Assessment measures were polysomnographic recordings on the first night and performance on psychophysiological tasks on the second day involving subjective and objective vigilance, P300, simple reaction time tasks, and dual performance tasks. No clear difference in sleep structure was observed between the head-down and horizontal conditions, except for a slight decrease in Stage 4 for head-down. Both subjective and objective daytime vigilance, P300, and the simple RT task showed no statistical difference, although tracking performance on the dual task showed deterioration at 10:00 for the head-down condition. These results suggest that nocturnal sleep, daytime vigilance, and psychophysiological functions were not disturbed in head-down sleep conditions, although there was a mild deterioration of higher attentional function in the morning.