Abstract

For a healthy and productive life, good sleep is essential, which has prompted studies on how comfortable sleep can be achieved. Understanding the relationship between thermal environment and physiological responses such as skin and core temperatures, and psychological responses such as thermal and sleep sensations is necessary to identify the most suitable thermal environment for sleep. As an energy-saving and practical method of creating the most appropriate thermal environment for sleep, local heating or cooling is sometimes used, which takes into consideration the differences in local thermal responses. We performed this study to identify the most effective thermal environment for inducing comfortable sleep by identifying the physiological responses during sleep on the basis of sleep experiments conducted under local body heating or cooling conditions. We also used a human thermal model, which can be applied for predicting physiological responses. In the experiments, the feet of the subject were the primary area to be heated or cooled, which was achieved by installing a flexible duct with an outlet placed close to the subjects feet and inlet connected to an air conditioner. Differences in the fluctuation of body temperature and sleep stage depended on the airflow direction from the duct to the feet. When air was blown downward towards the feet, body temperature decreased and the subject was able to sleep well. Measured skin and core temperatures were calculated using an improved 27-node human thermal model that was originally developed for use in subjects who are not in sleep. Although skin temperature fluctuated significantly under local cooling, the results calculated using the proposed model agreed well with the measured results since the changes in heat conductance between the skin surface and surrounding environment as a result of the changes in the posture and feet position were taken into account. This result indicates that posture-associated changes in the heat conductance significantly influence skin temperature.

Abstract

We aimed to investigate whether disruption of the circadian rhythm in rotating shift work (RSW) workers would change anorectal motility and cardiac autonomic function. We also determined whether sleep and psychological status (e.g., anxiety and depression) would affect anorectal motility in RSW workers. Sixteen RSW workers and 11 control individuals were involved in the study. All study participants underwent anorectal manometry and spectral analysis of heart rate variability. All participants completed three questionnaires: the Pittsburgh Sleep Quality Index (PSQI), the State-Trait Anxiety Inventory (STAI) questionnaire, and the Taiwanese Depression Questionnaire (TDQ). The RSW workers had a lower threshold volume for maximal urge (p = 0.006) and greater rectal compliance (p = 0.02), compared to the controls. The RSW workers had a greater PSQI score (p = 0.002) and TDQ score (p = 0.003), compared to the controls. The RSW workers had a significantly increased low-frequency power percentage (LF%), compared to the controls (p = 0.03). The RSW workers had a significant correlation between the resting anal sphincter pressure and high-frequency power percentage (HF%, r = –0.62, p = 0.01), and between the R-R interval and the threshold for maximal urge (r = 0.51, p = 0.04). The PSQI score was significantly correlated with the threshold volume for urge (r = 0.55, p = 0.03) and for compliance (r = 0.51, p = 0.04) in the RSW workers. Rotating shift workers have anorectal dysmotility and cardiac sympathetic hyperactivity. Anorectal dysmotility in RSW workers has a close relationship with cardiac autonomic dysfunction, sleep disturbance, and depression, but not with anxiety.

Abstract

Caffeine is one of the most consumed stimulants in the world, being available in beverages such as coffee, chocolate, tea and energizers. It is a molecule used at the pharmacological level as an analgesic and causes psychostimulant effects related to decreased sleepiness, increased attention, modulation of memory and cognitive performance; In addition, it is recognized for the improvement of sports performance, among others (1).

The relationship between sleep and caffeine has been widely investigated, it has been established that this methylxanthine can prolong sleep latency, generate less total sleep time with decreased deep sleep and a parallel increase in light sleep (2).

Then, a review is presented that addresses the effect of caffeine on the polysomnographic stages of sleep and on the biological interactions that this substance presents in the adenosine receptors to which it joins; In addition, the genetic variations of these receptors will be taken into account, as possible causes of the changes induced by caffeine in sleep.

Abstract

Space agencies such as the National Aeronautics and Space Administration of the United States, the Russian Federal Space Agency, the European Space Agency, the China National Space Administration, the Japan Aerospace Exploration Agency, and Indian Space Research Organization, although differing in their local political agendas, have a common interest in promoting all applied sciences that may facilitate man’s adaptation to life beyond the earth. One of man’s most important adaptations has been the evolutionary development of sleep cycles in response to the 24 hour rotation of the earth. Less well understood has been man’s biological response to gravity. Before humans ventured into space, many questioned whether sleep was possible at all in microgravity environments. It is now known that, in fact, space travelers can sleep once they leave the pull of the earth’s gravity, but that the sleep they do get is not completely refreshing and that the associated sleep disturbances can be elaborate and variable. According to astronauts’ subjective reports, the duration of sleep is shorter than that on earth and there is an increased incidence of disturbed sleep. Objective sleep recordings carried out during various missions including the Skylab missions, space shuttle missions, and Mir missions all support the conclusion that, compared to sleep on earth, the duration in human sleep in space is shorter, averaging about six hours. In the new frontier of space exploration, one of the great practical problems to be solved relates to how man can preserve “normal” sleep in a very abnormal environment. The challenge of managing fatigue and sleep loss during space mission has critical importance for the mental efficiency and safety of the crew and ultimately for the success of the mission itself. Numerous "earthly" examples now show that crew fatigue on ships, trucks, and long-haul jetliners can lead to inadequate performance and sometimes fatal consequences, a reality which has caused many space agencies to take the issue of sleep seriously.