ALBERT

Description: We investigated in six men the impact of a 17-day head-down bed rest (HDBR) on the circadian rhythms of the hormones and electrolytes involved in hydroelectrolytic regulation. This HDBR study was designed to mimic an actual spaceflight. Urine samples were collected at each voiding before, during and after HDBR. Urinary excretion of aldosterone, arginine vasopressin (AVP), cyclic guanosine monophosphate (cGMP), cortisol, electrolytes (Na+ and K+) and creatinine were determined. HDBR resulted in a significant reduction of body mass (P 〈 0.01) and of caloric intake [mean (SEM) 2,778 (37) kcal.24 h(-1) to 2,450 (36) kcal.24 h(-1), where 1 kcal.h(-1) = 1.163 J.s(-1); P〈 0.01]. There was a significant increase in diastolic blood pressure [71.8 (0.7) mmHg vs 75.6 (0.91) mmHg], with no significant changes in either systolic blood pressure or heart rate. The nocturnal hormonal decrease of aldosterone was clearly evident only before and after HDBR, but the day/night difference did not appear during HDBR. The rhythm of K+ excretion was unchanged during HDBR, whereas for Na+ excretion, a large decrease was shown during the night as compared to the day. The circadian rhythm of cortisol persisted. These data suggest that exposure to a 17-day HDBR could induce an exaggeration of the amplitude of the Na+ rhythm and abolition of the aldosterone rhythm.

Description: Prolonged periods of head-down bed rest (HDBR) are commonly used to mimic the effects of microgravity. HDBR has been shown to produce, as in space, a cephalad redistribution of circulating blood volume with an increase in central blood volume which induces the early adaptations in blood volume regulating hormones. Changes in atrial natriuretic peptide (ANP), arginine vasopressin (AVP), renin activity and aldosterone have been observed. Many reports describe these endocrine adaptations but few investigations of rhythms are in the literature. We proposed to evaluate the circadian rhythms of the hormones and electrolytes involved in the hydro-electrolytic regulation during a HDBR study which was designed to simulate a 17-day spaceflight (Life and Microgravity Spacelab experiment, LMS, NASA).

Description: Whereas most people require more than 6 h of sleep to feel well rested, there appears to be a group of people who can function well on between 3 and 6 h of sleep. The aims of the present study were to compare 12 naturally short (3-6 h) sleepers (9 males 3 females, mean age 39.6 years, SD age 10.1 years) recruited by a media publicity campaign with age, gender and chronotype matched medium length (7-8.5 h) sleepers on various measures. Measurement instruments included diaries and questionnaires to assess sleep duration and timing, as well as questionnaire assessments of sleep pathology, morningness-eveningness, extroversion, neuroticism, pathological daytime sleepiness, subclinical hypomania, optimism, depressive symptoms, exercise, and work habits. Few measures showed reliable differences between naturally short sleepers and controls except the obvious ones related to sleep duration. There was, however, some evidence for subclinical hypomanic symptoms in naturally short sleepers.

Description: Does one night of sleep deprivation alter processes of supervisory attention in general or only a specific subset of such processes? Twenty college-aged volunteers, half female, performed a choice reaction time task. A cue indicated that compatible (e.g., right button, right-pointing arrow) or incompatible (e.g., left button, right-pointing arrow) responses were to be given to a stimulus that followed 50 or 500 ms later. The paradigm assessed response inhibition, task-shifting skill, and task strategy-processes inherent in supervisory attention. Performance, along with heart rate, was assessed for 12 hr following normal sleep or a night of complete sleep deprivation. Sleep deprivation altered neither preparation for task shifting nor response inhibition. The ability to use preparatory bias to speed performance did decrease with sleep deprivation. Sleep deprivation appears to selectively affect this supervisory attention process, which is perceived as an active effort to cope with a challenging task.

Description: OBJECTIVE: The objectives of this study were (1) to assess the circadian rhythms and sleep of a healthy, 42-year-old male astronaut experiencing microgravity (weightlessness) for nearly 5 months while living aboard Space Station Mir as it orbited Earth and (2) to determine the effects of prolonged space flight on the endogenous circadian pacemaker, as indicated by oral temperature and subjective alertness rhythms, and their ramifications for sleep, alertness, and performance. METHODS: For three 12- to 14-day blocks of time (spread throughout the mission), oral temperatures were taken and subjective alertness was self-rated five times per day. Sleep diaries and performance tests were also completed daily during each block. RESULTS: Examination of the subject's circadian alertness and oral temperature rhythms suggested that the endogenous circadian pacemaker seemed to function quite well up to 90 days in space. Thereafter (on days 110-122), the influence of the endogenous circadian pacemaker on oral temperature and subjective alertness circadian rhythms was considerably weakened, with consequent disruptions in sleep. CONCLUSIONS: Space missions lasting more than 3 months might result in diminished circadian pacemaker influence in astronauts, leading to eventual sleep problems.

Description: This review of the shiftwork area focuses on aspects of safety and productivity. It discusses the situations in which shiftworker performance is critical, the types of problem that can develop and the reasons why shiftworker performance can be impaired. The review ends with a discnssion of the various advantages and disadvantages of several shift rotation systems, and of other possible solutions to the problem.

Description: For more than a decade, the Sleep and Chronobiology Center (SCC) at the University of Pittsburgh has received funding from the National Institute on Aging (NIA), the National Institute of Mental Health (NIMH) and the National Aeronautics and Space Administration (NASA) in order to study the sleep and circadian rhythms of healthy older people, as well as the sleep and circadian rhythms of astronauts and cosmonauts. We have always been struck by the strong synergism between the two endeavors. What happens to the sleep and circadian rhythms of people removed from the terrestrial time cues of Earth is in many ways similar to what happens to people who are advancing in years. Most obviously, sleep is shorter and sleep depth is reduced, but there are also more subtle similarities between the two situations, both in circadian rhythms and in sleep, and in the adaptive strategies needed to enhance 24h zeitgebers.

Description: STUDY OBJECTIVES: To determine the effects of a 90-minute afternoon nap regimen on nocturnal sleep, circadian rhythms, and evening alertness and performance levels in the healthy elderly. DESIGN AND SETTING: Nine healthy elderly subjects (4m, 5f, age range 74y-87y) each experienced both nap and no-nap conditions in two studies each lasting 17 days (14 at home, 3 in the laboratory). In the nap condition a 90-minute nap was enforced between 13:30 and 15:00 every day, in the no-nap condition daytime napping was prohibited, and activity encouraged in the 13:30-15:00 interval. The order of the two conditions was counterbalanced. PARTICIPANTS: N/A INTERVENTIONS: N/A MEASUREMENTS: Diary measures, pencil and paper alertness tests, and wrist actigraphy were used at home. In the 72 hour laboratory studies, these measures were augmented by polysomnographic sleep recording, continuous rectal temperature measurement, a daily evening single trial of a Multiple Sleep Latency Test (MSLT), and computerized tests of mood, activation and performance efficiency. RESULTS: By the second week in the "at home" study, an average of 58 minutes of sleep was reported per siesta nap; in the laboratory, polysomnography confirmed an average of 57 minutes of sleep per nap. When nap and no-nap conditions were compared, mixed effects on nocturnal sleep were observed. Diary measures indicated no significant difference in nocturnal sleep duration, but a significant increase (of 38 mins.) in 24-hour Total Sleep Time (TST) when nocturnal sleeps and naps were added together (p〈0.025). The laboratory study revealed a decrease of 2.4% in nocturnal sleep efficiency in the nap condition (p〈0.025), a reduction of nocturnal Total Sleep Time (TST) by 48 mins. in the nap condition (p〈0.001) which resulted primarily from significantly earlier waketimes (p〈0.005), but no reliable effects on Wake After Sleep Onset (WASO), delta sleep measures, or percent stages 1 & 2. Unlike the diary study, the laboratory study yielded no overall increase in 24-hour TST consequent upon the siesta nap regimen. The only measure of evening alertness or performance to show an improvement was sleep latency in a single-trial evening MSLT (nap: 15.6 mins., no nap: 11.5 mins., p〈0.005). No significant change in circadian rhythm parameters was observed. CONCLUSIONS: Healthy seniors were able to adopt a napping regimen involving a 90-minute siesta nap each day between 13:30 and 15:00, achieving about one hour of actual sleep per nap. There were some negative consequences for nocturnal sleep in terms of reduced sleep efficiency and earlier waketimes, but also some positive consequences for objective evening performance and (in the diary study) 24-hour sleep totals. Subjective alertness measures and performance measures showed no reliable effects and circadian phase parameters appeared unchanged.

Description: This brief review is concerned with how human performance efficiency changes as a function of time of day. It presents an overview of some of the research paradigms and conceptual models that have been used to investigate circadian performance rhythms. The influence of homeostatic and circadian processes on performance regulation is discussed. The review also briefly presents recent mathematical models of alertness that have been used to predict cognitive performance. Related topics such as interindividual differences and the postlunch dip are presented.

Description: STUDY OBJECTIVES: To determine whether wrist actigraphy is useful as a tool for space-based sleep research. Specifically, to determine whether bedtimes and waketimes can be identified from the actigraphic record, and whether actigraphic measures of sleep in space are related to polysomnographic (PSG) ones. DESIGN AND SETTING: Actigraphy, sleep diary, and Polysomnographic (PSG) measures of sleep were obtained from four subjects in two 72h measurement blocks occurring 2d and 12d into a 17d Space Shuttle mission in orbiting the earth in microgravity. PATIENTS: Four healthy male astronauts aged 38y - 47y. INTERVENTIONS: NA. MEASUREMENTS AND RESULTS: Sleep onset and offset at "night" could be quite clearly identified from the actigraphic record and were better estimated by actigraph than by diary. There was a high correlation between actigraphic and PSG estimates of sleep duration (r = 0.96) and sleep efficiency (r = 0.88), and a similarity in the mean estimates obtained. On a minute-by-minute basis, there was a good correlation between sleep stage and actigraphic movement counts, with a higher level of counts per minute recorded in epochs with lighter PSG sleep stages. There was also a high correlation (r = 0.90) between minutes of stage 0 (wake) occurring between bedtime and wake time, and number of non-zero actigraph epochs during the same interval. CONCLUSIONS: Actigraphy worked well in space both as a way of detecting bedtimes and waketimes, and as an indicant of sleep restlessness.