Biomedical subjects

T H Monk

Publications and source records attributed to T H Monk.

At least 37 records · Page 2Linked to original sources

PubMed1999

Are age differences in sleep due to phase differences in the output of the circadian timing system?

Our aim was to evaluate whether age-related changes in the phase of the output of the circadian timing system (CTS) can explain age differences in habitual bedtime/wake time and in sleep consolidation parameters. Analyses focused on a group of healthy elderly people (older than 70 years) with no sleep problems and with similar subjective sleep quality as a young control group. The 2-week sleep diary data and 24h laboratory temperature recordings were examined for 70 subjects (22 young men [YM], 19 old men [OM], 29 old women [OW]). Polysomnographic (PSG) sleep data recorded during temperature data acquisition were also available for 62 subjects. These analyses made use of our recently developed technique to demask temperature rhythm data. As expected, compared to the young subjects, older subjects showed earlier habitual bedtime and wake time, more disturbed sleep, and a tendency for an earlier minimum of the circadian temperature rhythm. Despite sleep consolidation differences, the groups showed very similar habitual phase-angle differences (interval between the time occurrence of the fitted temperature minimum and habitual wake time). Both elderly and young subjects woke up on average 3 h after the temperature minimum. After controlling for the effects of age group, habitual bedtime and wake time were related to clock time phase of the circadian temperature rhythm, with an earlier phase associated with earlier habitual bedtime and wake time. None of the sleep consolidation parameters were linked to the temperature phase angle. In conclusion, sleep consolidation changes associated with healthy aging do not appear to be related to changes in the phase-angle difference between the output signal from the CTS and sleep.

Adult↗

PubMed1999

Aging and space flight: findings from the University of Pittsburgh.

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.

Adult↗

PubMed1998

A parallelism between human body temperature and performance independent of the endogenous circadian pacemaker.

A battery of performance tests involving manual dexterity, serial search, and verbal reasoning was given about seven times per day to 2 healthy young male subjects (22 and 25 years of age) involved in separate forced desynchrony studies, each involving several months of temporal isolation. In these studies, the period lengths (denoted T) of the imposed day lengths (sleep/wake and light/dark cycles) were 25.8 and 26.0 h for the 2 subjects. For each subject, the endogenous circadian pacemaker (ECP) failed to entrain to a period of T and instead free ran at a period length denoted tau (24.2 and 24.5 h). By educing performance rhythms (and rectal temperature rhythms) separately at tau and at T (after three complete beating cycles for the first subject and two complete beating cycles for the second subject), the hypothesis could be tested as to whether performance and temperature were parallel, both when educed at tau (indicating ECP influence) and when educed at T (indicating sleep/wake cycle influences). The hypothesis was consistently confirmed at tau and mostly confirmed at T. For most variables, when educed at T, both performance speed and body temperature showed an inverted V-shaped function, with a peak about 9 to 12 h after waking.

Adult↗

PubMed1998

Sleep and circadian rhythms in four orbiting astronauts.

This experiment measured the sleep and circadian rhythms of four male astronauts aboard a space shuttle (STS-78) orbiting the Earth for 17 days. The space mission was specially scheduled to minimize disruptions in circadian rhythms and sleep so that the effects of space flight and microgravity per se could be studied. Data were collected in 72-h measurement blocks: one block 7 days before launch, one early within the mission (3 days after launch), one late in the mission (12 days after launch), and one 18 days after landing. Within each measurement block, all sleep was recorded both polysomnographically and by sleep diary. Core body temperature was sampled every 6 mins. Actillumes were worn continuously. All urine samples were collected separately. Performance was assessed by a computerized test battery (3/day) and by end-of-shift questionnaires (1/day); mood and alertness were measured by visual analogue scales (5/day). Circadian rhythms in orbit appeared to be very similar in phase and amplitude to those on the ground, and were appropriately aligned for the required work/rest schedule. There was no change from early flight to late flight. This was also reflected in mood, alertness, and performance scores, which were satisfactory at both in-flight time points. However, in-flight sleep showed a decreased amount of sleep obtained (mean = 6.1 h), and all four astronauts showed a decrease in delta sleep. No further degradation in sleep was seen when early flight was compared to late flight, and no other sleep parameters showed reliable trends.

Adult↗

PubMed1997

Inducing lifestyle regularity in recovering bipolar disorder patients: results from the maintenance therapies in bipolar disorder protocol.

On the basis of theories we articulated in earlier papers (Ehlers et al 1988: Arch Gen Psychiatry 45:948-952, 1993: Depression 1:285-293), we have developed an adjunctive psychosocial intervention for patients with bipolar 1 disorder. Central to this intervention is the establishment of regularity in daily routines. In this report, we present data from a controlled investigation comparing this new treatment, interpersonal and social rhythm therapy (IPSRT), with a conventional medication clinic approach. Despite comparable changes in symptomatology over a treatment period lasting up to 52 weeks, subjects assigned to IPSRT (n = 18) show significantly greater stability (p = .047) of daily routines with increasing time in treatment, while subjects assigned to the medication clinic condition (n = 20) show essentially no change in their social routines as measured by Social Rhythm Metric (SRM-Monk et al 1990: J Nerv Ment Dis 178(2):120-126) score. We conclude that IPSRT is capable of influencing lifestyle regularity in patients with bipolar 1 disorder, with the possible benefit of protection against future affective episodes.

Adult↗

PubMed1997

Circadian rhythms in human performance and mood under constant conditions.

UNLABELLED: This study explored the relationship between circadian performance rhythms and rhythms in rectal temperature, plasma cortisol, plasma melatonin, subjective alertness and well-being. Seventeen healthy young adults were studied under 36 h of 'unmasking' conditions (constant wakeful bedrest, temporal isolation, homogenized 'meals') during which rectal temperatures were measured every minute, and plasma cortisol and plasma melatonin measured every 20 min. Hourly subjective ratings of global vigour (alertness) and affect (well-being) were obtained followed by one of two performance batteries. On odd-numbered hours performance (speed and accuracy) of serial search, verbal reasoning and manual dexterity tasks was assessed. On even-numbered hours, performance (% hits, response speed) was measured at a 25-30 min visual vigilance task. Performance of all tasks (except search accuracy) showed a significant time of day variation usually with a nocturnal trough close to the trough in rectal temperature. Performance rhythms appeared not to reliably differ with working memory load. Within subjects, predominantly positive correlations emerged between good performance and higher temperatures and better subjective alertness; predominantly negative correlations between good performance and higher plasma levels of cortisol and melatonin. Temperature and cortisol rhythms correlated with slightly more performance measures (5/7) than did melatonin rhythms (4/7). Global vigour correlated about as well with performance (5/7) as did temperature, and considerably better than global affect (1/7). IN CONCLUSION: (1) between-task heterogeneity in circadian performance rhythms appeared to be absent when the sleep/wake cycle was suspended; (2) temperature (positively), cortisol and melatonin (negatively) appeared equally good as circadian correlates of performance, and (3) subjective alertness correlated with performance rhythms as well as (but not better than) body temperature, suggesting that performance rhythms were not directly mediated by rhythms in subjective alertness.

Adult↗

PubMed1997

The effects on human sleep and circadian rhythms of 17 days of continuous bedrest in the absence of daylight.

As part of a larger bedrest study involving various life science experiments, a study was conducted on the effects of 17 days of continuous bedrest and elimination of daylight on circadian rectal temperature rhythms, mood, alertness, and sleep (objective and diary) in eight healthy middle-aged men. Sleep was timed from 2300 to 0700 hours throughout. Three 72-hour measurement blocks were compared: ambulatory prebedrest, early bedrest (days 5-7), and late bedrest (days 15-17). Temperature rhythms showed reduced amplitude and later phases resulting from the bedrest conditions. This was associated with longer nocturnal sleep onset latencies and poorer subjectively rated sleep but with no reliable changes in any of the other sleep parameters. Daily changes in posture and/or exposure to daylight appear to be important determinants of a properly entrained circadian system.

Adult↗

PubMed1997

Longitudinal changes in diary- and laboratory-based sleep measures in healthy "old old" and "young old" subjects: a three-year follow-up.

We report a longitudinal study of diary- and laboratory-based sleep measures in 50 healthy elderly subjects followed prospectively over a 3-year interval. Our hypothesis was that "old old" subjects (aged 75 to 87; n = 27) would show decline over time in measures of sleep quality, continuity, and depth, whereas "young old" subjects (aged 61 to 74; n = 23) were expected to show stability of outcome measures. Using analysis of variance-based planned contrast procedures, we found that this hypothesis was strongly supported for subjective sleep quality and laboratory measures of sleep latency, sleep efficiency, wakefulness after sleep onset, and slow-wave sleep percent. These changes were accompanied by increased napping in the old old. However, there was no change of habitual time in bed (total time or temporal placement of nighttime sleep), daily social rhythms, or sleep apnea. Change in medical burden scores did not correlate significantly with change in sleep efficiency or other outcome variables in the old old. Intervention designed to slow age-dependent decreases in sleep quality, continuity, and depth is discussed. The current results are representative of healthy elderly; sleep would probably deteriorate earlier and more quickly in elderly with more serious health problems and heavier medication use.

Aged↗

PubMed1997

Speed of mental processing in the middle of the night.

This study aimed to determine whether human mental processing actually slows down during the night hours, separately from the previously documented microsleeps, lapses in attention, and general slowing of motor responses. Eighteen healthy young adults were studied during 36 hours of constant wakeful bedrest. Every 2 hours, they performed a logical reasoning task. Items phrased in the negative voice took reliably longer to respond to than items phrased in the positive voice, indicating the need for more mental processing in those items. By subtracting "negative" from "positive" reaction times at each time of day, we were able to plot a circadian rhythm in the time taken for this extra mental processing to be done separately from microsleeps, psychomotor slowing, and inattention. The extra mental processing took longer at night and on the day following sleep loss than it did during the day before the sleep loss, suggesting that human mental processing slows down during the night under sleep deprivation.

Adult↗

PubMed1997

Sleep and morningness-eveningness in the 'middle' years of life (20-59 y).

The following four issues were assessed in a group of 110 adults between the age of 20 and 59y: (1) the effect of age (regarded as a continuous variable) on polysomnographic sleep characteristics, habitual sleep-diary patterns, and subjective sleep quality; (2) the effects of age on morningness-eveningness; (3) the effects of morningness-eveningness on sleep, after controlling for the effects of age; and (4) the role of morningness-eveningness as a mediator of the age and sleep relationship. Increasing age was related to earlier habitual waketime, earlier bedtime, less time in bed and better mood and alertness at waketime. In the laboratory, increasing age was associated with less time asleep, increased number of awakenings, decreased sleep efficiency, lower percentages of slow-wave sleep (SWS) and rapid eye movement (REM) sleep, higher percentages of Stage 1 and 2, shorter REM latency and reduced REM activity and density. Increasing age was also associated with higher morningness scores. After controlling for the effects of age, morningness was associated with earlier waketime, earlier bedtime, less time in bed, better alertness at waketime, less time spent asleep, more wake in the last 2 h of sleep, decreased REM activity, less stage REM (min and percentage), more Stage 1 (min and percentage) and fewer minutes of Stage 2. For one set of variables (night time in bed, waketime, total sleep time, wake in the last 2 h of sleep and minutes of REM and REM activity), morningness-eveningness accounted for about half of the relationship between age and sleep. For another set of variables (bedtime, alertness at waketime, percentages of REM and Stage 1), morningness-eveningness accounted for the entire relationship between age and sleep. In conclusion, age and morningness were both important predictors of the habitual sleep patterns and polysomnographic sleep characteristics of people in the middle years of life (20-59 y).

Adult↗

PubMed1997

Estimating the endogenous circadian temperature rhythm without keeping people awake.

This study was concerned with estimating endogenous temperature rhythms without imposing sleep deprivation. The aim of Experiment 1 was to quantify the masking effect on the circadian temperature rhythm in a group of 18 healthy young subjects (8 women and 10 men, ages 19-29 years). Temperature data collected under a 36-h wakeful bed rest protocol were used as a marker of the endogenous component of the rhythm ("unmasked rhythm"), and temperature data collected under 24 h of a normal nycthemeral routine (immediately before the bed rest protocol) were used as the "masked" rhythm. An algorithm to "demask" the temperature data collected under the nycthemeral condition was then developed, based on the differences observed between the temperature data collected under wakeful bed rest and nycthemeral conditions. The consistency of the demasking technique was tested in Experiment 2, using the same parameters on a group of 19 healthy elderly subjects (8 women and 11 men, ages 78-88 years) who also had experienced both nycthemeral and wakeful bed rest conditions. The demasking technique was evaluated both by comparing nycthemeral, demasked, and unmasked temperature rhythms themselves and by comparing individual estimates of circadian phase and amplitude that had been gleaned from them. In comparison to the unmasked condition, the nycthemeral condition showed lower mean nighttime temperature, earlier mean phase estimates, and higher mean amplitude estimates in both young and elderly subjects. Following application of the demasking procedure to the nycthemeral temperature data, mean demasked temperature curves were closely comparable to mean unmasked temperature curves in both young and elderly subjects. Phase and amplitude estimates derived from the demasked temperature data also were highly comparable to those in the unmasked conditions. Thus, this demasking procedure appears to be a useful tool in estimating the endogenous temperature rhythm and appears to work equally well for young and elderly subjects.

Adult↗

PubMed1997

Differences over the life span in daily life-style regularity.

A diary-based instrument-the Social Rhythm Metric (SRM)-was used to assess the level of stability of daily social and behavioral rhythms in a group of 239 healthy subjects (112 male, 127 female) ranging in age from 20 to 89 years. Each subject completed the instrument for two consecutive weeks, which were averaged to yield one measure (SRM score) of life-style regularity [range 0 (least regular) to 7 (most regular)] and another of activity level index (ALI), corresponding to the number of (diary listed) activities done per week (max. = 119). SRM score increased reliably with age group at an average rate of 0.018 units per year. ALI showed an "inverted U"-shaped function with a maximum at about 50 years. SRM changes appeared not to be related to demographic differences between the age groups, although ALI differences may have been so related. No main effects or interactions were found with gender. Life-style regularity appears to increase over the life span in response to both biological and psychosocial changes and may represent an adaptation to age-related changes in the circadian system's sensitivity to entraining agents. Regular behavioral rhythms may be conducive to continued good health and well-being.

Activities of Daily Living↗

PubMed1997

Generalized covariance-adjusted discriminants: perspective and application.

When discriminant analysis is used in practice for assessing the usefulness of diagnostic markers, the lack of control over covariates motivates the need for their adjustment in the analysis. This necessity for adjustment arises especially when the researcher's aim is classification based on a set of diagnostic markers and is not based on a set of covariates for which there exists known heterogeneity among the subjects with respect to the groups under consideration. The traditional covariance-adjusted approach is restrictive for such applications in that they assume linear covariates and a normal distribution for the the feature vector. Further, there is no available method for variable selection in using such covariance-adjusted models. In this paper, we generalize the traditional covariance-adjusted model to a general normal and logistic model, where these generalized models not only relax the distributional assumptions on the feature vector but also allow for nonlinear covariates. Exact and asymptotic tests are also derived for the problem of variable selection for these new models. The methodology is illustrated with both simulated data and an actual data set from a psychiatric study on using the Social Rhythm Metric for patients with anxiety disorders.

Activities of Daily Living↗

PubMed1996

Social rhythm stability following late-life spousal bereavement: associations with depression and sleep impairment.

The aim of this study was to investigate changes in social rhythm stability and sleep in spousally bereaved subjects (n = 94) and in nonbereaved elderly control subjects (n = 45). Social rhythm stability and activity level were measured with a diary-like instrument, the Social Rhythm Metric (SRM). We observed that spousal bereavement, per se, was not associated with a lower social rhythm stability or activity level except in the presence of a major depressive episode. We also observed an inverse correlation between severity of depression and social rhythm stability, and a positive correlation between depression and both subjective and objective measures of sleep impairment. Higher social rhythm stability was correlated with better sleep in subjects with high activity levels, but not in subjects with low activity levels. Longitudinal data, including pre-bereavement assessment of social rhythm stability, are necessary to ascertain directional effects, i.e., whether loss of spouse occasions disruption of social rhythms or whether such disruption precedes sleep impairment and depression.

Adjustment Disorders↗

PubMed1996

Electroencephalographic sleep profiles during depression. Effects of episode duration and other clinical and psychosocial factors in older adults.

BACKGROUND: Limited evidence suggests that polysomnographic alterations may be more prominent early in a depressive episode. Whether the effects of episode duration extend beyond middle age and appear in late-life depression as well has important implications for treatment decisions and for understanding depressive illness across the life span. Furthermore, the impact of episode duration on sleep has not been examined in the context of other factors related to clinical history and psychosocial status. METHODS: Eighty-three persons aged 60 years or older with recurrent depression were studied: 34 had been depressed for 2 to 16 weeks and 49 for longer periods. An age- and gender-matched group of 48 persons with no history of major depression served as controls. Initial univariate analyses examined duration effects on electroencephalographic (EEG) sleep measurements. Multivariate analyses considered the combined effects of episode duration, clinical variables, and psychosocial variables on EEG sleep profile. RESULTS: Episode duration was strongly associated with sleep continuity, architecture, and rapid eye movement: subjects who were earlier in their depressive episodes had their sleep impaired more than those later in their episodes, who, in turn, were more impaired than controls. Moreover, clinical characteristics of subjects' depressive illness, demographic variables, and psychosocial stressors and supports had unique effects on the EEG sleep profile. CONCLUSION: Episode duration appears to be a potent factor to consider when evaluating sleep during depression. The additional contribution of clinical and psychosocial characteristics to the prediction of the EEG sleep profile demonstrates the importance of incorporating these variables into models of the psychobiologic characteristics of depression. The results are relevant to the timing and focus of therapeutic interventions.

Age Factors↗

PubMed1996

Maintaining safety and high performance on shiftwork.

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.

Accident Prevention↗

PubMed1996

Inducing a 6-hour phase advance in the elderly: effects on sleep and temperature rhythms.

The aim of this experiment was to study the effects on sleep and temperature rhythms of a 6-hour (h) phase advance of the sleep/wake cycle in healthy elderly subjects. Twenty-five subjects (77-91 y.o.) lived in a time-isolation apartment on an experimenter-controlled routine for 15 days. The experiment started with five baseline days. The wake time on the 6th night was phase advanced by 6-h and the routine for the remaining nine days was held constant to the new phase position. After the phase shift, temperature circadian rhythms showed rapid phase adjustment leading to a small (1.1 h) phase angle disturbance. Sleep efficiency decreased and showed little evidence of recovery back to baseline following the phase shift. The amount of wakefulness in the first two hours of sleep increased after the phase shift while no effect was found for the amount of wakefulness in the last two hours of sleep. The 6-h phase shift did not change the percentages of REM and SWS. Early night sleep propensity appeared to be very sensitive to a small phase angle disturbance of the circadian oscillator in this healthy elderly sample. The phase angle disturbance induced in this study did not seem to be large enough to have a systematic effect on sleep propensity at the end of the night or on REM sleep parameters, suggesting that these variables are less sensitive to an altered phase relationship with the circadian oscillator than early night sleep propensity. These results indicate that there might be a variable phase tolerance for different sleep parameters in older subjects.

Aged↗

PubMed1996

Subjective alertness rhythms in elderly people.

The aim of this study was to evaluate age-related changes in the circadian rhythm of subjective alertness and to explore the circadian mechanisms underlying such changes. Using a visual analogue scale (VAS) instrument, 25 older men and women (71 y and older; 15 female, 10 male) rated their subjective alertness about 7 times per day during 5 baseline days of temporal isolation during which habitual bedtimes and waketimes were enforced. Comparisons were made with 13 middle-aged men (37-52 y) experiencing the same protocol. Advancing age (particularly in the men) resulted in less rhythmic alertness patterns, as indicated by lower amplitudes and less reliability of fitted 24-h sinusoids. This appeared in spite of the absence of any reliable age-related diminution in circadian temperature rhythm amplitude, thus suggesting the effect was not due to SCN weakness per se, but to weakened transduction of SCN output. In a further experiment, involving 36 h of constant wakeful bedrest, differences in the amplitude of the alertness rhythm were observed between 9 older men (79 y+), 7 older women (79 y+), and 17 young controls (9 males, 8 females, 19-28 y) suggesting that with advancing age (particularly in men) there is less rhythmic input into subjective alertness from the endogenous circadian pacemaker. These results may explain some of the nocturnal insomnia and daytime hypersomnia that afflict many elderly people.

Adult↗