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Biomedical subjects

T H Monk

Publications and source records attributed to T H Monk.

At least 109 records · Page 6Linked to original sources
PubMedDate not supplied

Circadian patterns of unintended sleep episodes during a constant routine in remitted depressed patients.

Theoretical models of depression have hypothesized phase or amplitude alterations in circadian measures including the sleep-wake rhythm. Whether such abnormalities occur only during the depressed state, or whether they persist into recovery, is less clear. We investigated the circadian pattern of unintended sleep episodes during 36 h of constant wakeful bedrest in two groups: 26 drug-free patients whose depression remitted following psychotherapy treatment, and a contrast group of 17 healthy young adults. The contrast group was not matched for age or gender. Both remitted depressed and contrast groups showed statistically significant linear and quadratic trends in the number of unintended sleep episodes, indicating monotonic and circadian influences across the study interval. We found no significant group differences in the pattern of sleep episodes. The number and timing of sleep episodes did not correlate significantly with core body temperature amplitude or timing or with baseline sleep duration or efficiency. The results do not support the hypothesis of a phase or amplitude change in sleep propensity as a trait abnormality in depression. However, the inclusion of a moderately depressed out-patient cohort, which showed only minor sleep changes and normal temperature profiles even while depressed, may have biased against finding significant differences.

Adult↗
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Daytime sleepiness and performance among healthy 80 and 20 year olds.

This study investigated the relationship of daytime sleepiness and performance on a vigilance test in a sample of 10 healthy men and 13 women in their 80s (mean age 83.0 +/- 3.1 years) and 18 men and 12 women in their 20s (25.0 +/- 3.1). We hypothesized that "successfully" aged healthy individuals would have more daytime sleepiness with differentially greater decrements in performance than a younger comparison group. Daytime sleepiness was measured physiologically by the Multiple Sleep Latency Test (MSLT) and through self-report by the Stanford Sleepiness Scale (SSS). Morning and evening performance was measured with the Mackworth Clock Test of vigilance. The major findings were the absence of correlation between either MSLT or SSS daytime sleepiness with performance measures, no difference in daytime sleepiness between the old and young groups and performance decrements among the healthy elderly on all parameters. Results suggest that the modest decrements in performance among the elderly cannot be attributed to daytime sleepiness.

Adult↗
PubMedDate not supplied

Inducing jet lag in older people: adjusting to a 6-hour phase advance in routine.

A 15-day simulated jet lag experiment was performed in a time isolation laboratory using 15 old women (79-91 years, mean 82.9 years) and 10 old men (71-86 years, mean 80.5 years). After five full days and nights on the subject's habitual routine, the waketime of night 6 was advanced by 6 h, truncating the sleep episode. All subsequent events occurred 6 h earlier than normal. Adjustment to the phase shift was evaluated by the circadian rhythm in rectal temperature (measured every minute), polysomnography of each sleep episode, and daily averages of mood, activation, and performance speed. While the circadian rhythm amplitude reduction consequent upon the phase shift showed a tendency to be longer lived in the old men, both old groups showed fairly rapid adjustment of the timing of their circadian temperature rhythm, comparable (if not better) to that observed earlier in a study of middle aged men. However, sleep disruption (and daytime sleepiness) appeared to be longer lived in the elderly, showing little of the recovery over time observed in younger subjects. Thus, there appeared to be some separation in the elderly of the sleep disruption and circadian rhythm disruption effects of jet lag.

Affect↗
PubMedDate not supplied

Inducing jet lag in an older person: directional asymmetry.

An 85-year-old woman experienced simulated jet-lag in phase advance and phase delay directions, in laboratory simulations (in temporal isolation) involving 6-h changes in routine. Circadian rhythm amplitude and sleep efficiency were less disrupted in the delay than in the advance condition, in contrast to circadian rhythm timing (phase), which appeared to show more rapid adjustment in the advance condition than in the delay condition.

Aged↗
PubMedDate not supplied

Circadian temperature rhythms of older people.

This collection of studies had the aim of exploring whether older (77+ years) men and women have circadian body temperature rhythms different from those of younger adults. A total of 20 older men and 28 older women were compared with either 22 young men or 14 middle-aged men in four protocols; all but the first protocol using a subset of the sample. The four protocols were: 1) 24 h, and 2) 72 h data collections on a normal laboratory routine (sleeping at night); 3) between 36 h and 153 h of field data collection at home; and 4) 36 h of a constant conditions routine (wakeful bedrest under temporal isolation) in the laboratory. There was some evidence for an age-related phase advance in temperature rhythm, especially for the older men on a normal routine, though this was not present in the constant conditions protocol, where 5 of the older subjects showed major delays in the timing of the body temperature trough (10:00 or later). There was no statistically significant evidence from any of the protocols that older subjects generally had lower temperature rhythm amplitudes than younger adults. Only when older men were compared with younger men in 24-h rhythm amplitude by simple t-test did any comparison involving amplitude achieve statistical significance (p < 0.05).

Adult↗
PubMedDate not supplied

Task variables determine which biological clock controls circadian rhythms in human performance.

There are circadian (approximately 24 h) rhythms for a wide range of human physiological and psychological functions including mood and performance efficiency. These rhythms are self-sustaining in conditions of temporal isolation, indicating that internal oscillators (or biological clocks) control them. Recent research has proposed an endogenous two-oscillator model of the human circadian system, with one oscillator indicated by the core body temperature rhythm and a second oscillator responsible for the daily cycle of sleep and wakefulness. The present study was designed to produce a desynchronization in period between the two oscillators, to assess directly the behaviour of the rhythms of different performance tasks. The results, reported here, indicate that a simple manual dexterity task is almost entirely under the control of the temperature rhythm oscillator, whereas a more complex cognitive task demonstrates a periodicity which appears to be influenced by those oscillators controlling temperature and the sleep/wake cycle.

Adult↗
PubMedDate not supplied

Decreased human circadian pacemaker influence after 100 days in space: a case study.

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.

Adult↗
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Shiftworker performance.

Nightwork not only taps into the "low ebb" of certain circadian performance rhythms, it also involves sleep disruption, social and domestic disruption, and the chronic equivalent of jet lag, all of which can radically affect performance and safety. This chapter discusses performance rhythms, their relationship to the circadian system and the sleep/wake cycle, and "on-the-job" shiftworker performance.

Circadian Rhythm↗
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Human growth hormone release is decreased during sleep in temporal isolation (free-running).

Growth hormone (hGH) secretion was measured during sleep in 10 healthy male subjects isolated from all time cues. HGH concentrations following sleep onset were compared between scheduled sleep episodes (entrainment) and self-selected sleep episodes (free-running). Peak sleep-related hGH values were decreased significantly during free-running. The duration of the first slow wave sleep (SWS) episode and the latency to the first REM sleep episode also decreased significantly during free-running. The latencies from sleep onset to SWS and to peak hGH secretion did not differ between entrainment and free-running. These results suggest that sleep-related hGH secretion begins 'on time' during free-running, but is terminated earlier. Thus, while sleep onset facilitates hGH release, the timing of other stages of sleep such as REM may alter the magnitude of sleep-related hGH secretion.

Adult↗
PubMedDate not supplied

A likelihood ratio method for studying the re-entrainment of circadian rhythms.

A simple technique is described that enables the degree of adaptation at different times of day to be studied in organisms that have been subjected to a sudden change in the Zeitgeber (as typically found in shiftwork or after transmeridian flight). The investigator is thus able to place greater emphasis on some readings than on others and to measure the amount of disruption at a particular time of day (e.g. for an important meeting) rather than to merely rely upon an overall daily measure. The method uses the likelihood ratio statistics which also allows a powerful test to be made of the statistical significance of any apparent adaptation. The method is illustrated on some 'jet-lag' data, where it was able to determine differential rates of adaptation according to the time of day at which the subjects were tested.

Adaptation, Physiological↗
PubMedDate not supplied

Circadian rhythms in human performance efficiency under free-running conditions.

A series of four experiments is described in which two men and two women (age range 22-79 years) were allowed to 'free-run' under conditions of isolation from all time cues. The circadian rhythms of performance efficiency were studied for three tasks: serial search, verbal reasoning, and manual dexterity (left and right hand versions). Strong evidence was obtained to suggest that different tasks are under the control of different circadian oscillators. The circadian rhythm in verbal reasoning performance tends to run at a shorter circadian period than that in more simple repetitive tasks, and slight differences in circadian behavior can occur between left- and right-handed dexterity.

Adult↗