Biomedical subjects

D Minors

Publications and source records attributed to D Minors.

At least 37 records · Page 2Linked to original sources

PubMed1996

Dissociation of body-temperature and melatonin secretion circadian rhythms in patients with chronic fatigue syndrome.

Many patients with chronic fatigue syndrome (CFS) display features of hypothalamic dysfunction. We have investigated aspects of circadian rhythmicity, an important hypothalamic function, in 20 CFS patients and in 17 age- and sex-matched healthy control subjects. There were no differences between the two groups in the amplitude, mesor (mean value) or timing of the peak (acrophase) of the circadian rhythm of core temperature, or in the timing of the onset of melatonin secretion. However, the CFS patients showed no significant correlation between the timing of the temperature acrophase and the melatonin onset (P < 0.5), whereas the normal significant correlation was observed in the controls (P < 0.05). Dissociation of circadian rhythms could be due to the sleep deprivation and social disruption, and/or the reduction in physical activity which typically accompany CFS. By analogy with jet-lag and shift-working, circadian dysrhythmia could be an important factor in initiating and perpetuating the cardinal symptoms of CFS, notably tiredness, impaired concentration and intellectual impairment.

Adult↗

PubMed1996

The difference between activity when in bed and out of bed. II. Subjects on 27-hour "days".

Nine healthy subjects have been studied while exposed to the normal alternation of light and dark, but with their sleep and activity pattern adjusted to a 27-h "day" for 17 imposed "days." Rectal temperature showed clearly the competing influences of 27-h and 24-h components, and these were separated by the method of "purification." The method indicated that the endogenous component had a constant amplitude throughout the experiment and remained entrained to solar (24-h) time; by contrast, the exogenous component followed the imposed 27-h "day" and increased rectal temperature in proportion to the amount of subjects' activity. Wrist movement was used to assess activity while in bed (attempting sleep) and out of bed (when naps were forbidden). While these results confirmed adherence of the subjects to the imposed 27-h "days," they also showed that the dichotomy between "out of bed" activity and "in bed" inactivity depended on the phase relationship between endogenous (24h) and exogenous (27h) components. Thus, the dichotomy was highest and was equal to that during control days (with a conventional 24-h life-style) when the two components were in phase and lowest when the solar and imposed day were in antiphase. This was due to changes in activity, both during time spent in bed and out of bed. We confirm that this protocol can produce valuable information about the properties of the circadian system in humans and the value of the process of purification of temperature data. We have established also that the very simple and noninvasive measurement of wrist movement, coupled with its use to calculate dichotomy indices, provides valuable information that both confirms and extends the results obtained from the more conventional (but also more invasive) measurement of rectal temperature.

Bed Rest↗

PubMed1996

The difference between activity when in bed and out of bed. III. Nurses on night work.

Eight nurses have been studied during rest days and three successive night shifts. Measurements of wrist activity have been made and used to assess the extent to which the pattern of daily activity changes between control (rest) days and days involving night work. One analysis considered wrist activity during time spent in bed; this appears to decrease in parallel with the amount of time in bed that is lost during night work but, when this effect is corrected for, there is greater activity during time spent in bed in the daytime compared with control days (when time in bed is during the night). The dichotomy of activity (between lower values during time spent in bed and higher values when out of bed) also decreases if time in bed is during the daytime while on night shifts. These changes in the amount of wrist activity and the dichotomy between activity in and out of bed are related to the changed quality and quantity of sleep that has been measured by self-report questionnaires and the sleep EEG. It is concluded that results from wrist actimetry can provide valuable information regarding the process of adjustment to night work, and that its convenience (to subject and experimenter), coupled with the new analytical approaches described here, make it a viable method for field studies.

Adult↗

PubMed1996

The difference between activity when in bed and out of bed. I. Healthy subjects and selected patients.

The activity records of five groups of healthy or ill subjects have been measured for 4-26 days by an accelerometer placed on the nondominant wrist. These data, together with a record of times retiring to/rising from bed, have been used to produce a series of dichotomy indices for comparing the amounts of activity when in bed and out of bed. Reliable differences between individuals were found, with healthy subjects showing a greater degree of dichotomy than one subject with delayed sleep phase syndrome or three subjects with colorectal cancer. The method is convenient for extended data collection and offers the possibility of describing an individual's activity profile in a variety of circumstances.

Adolescent↗

PubMed1996

Circadian rhythm adjustment: difficulties in assessment caused by masking.

Measured circadian rhythms consist of endogenous (clock-driven) and exogenous (lifestyle-driven) components. The exogenous components cause difficulties of interpretation of phase and amplitude information. Such effects can be removed by "constant routines", but these protocols are restricted to the laboratory. By contrast, the process of "purification" of circadian rhythms uses the knowledge of an individual's normal lifestyle to separate a measured rhythm into its two components. This method has been shown to be practicable in a variety of circumstances and to provide a feasible alternative to constant routines.

Biological Clocks↗

PubMed1995

Blood pressure, heart rate, and skin temperature in preterm infants: associations with periventricular haemorrhage.

The mean arterial blood pressure (MABP), heart rate, and skin temperature were monitored every 15 minutes in the first 10 days after birth in 34 preterm infants, gestational age 24 to 33 weeks. Ultrasound brain scans carried out daily showed that a periventricular haemorrhage (PVH) occurred in a subgroup of infants (n = 15) of lower birthweight and gestational age. In infants without PVH the daily median of MABP increased with birthweight and postnatal age; that of heart rate was not affected by postnatal age, body weight, or gestational age; and that of skin temperature showed a slight fall with postnatal age. In infants with PVH, on or before the day of PVH, daily medians of MABP and skin temperature were not significantly different from those of infants without PVH, but the daily median of heart rate tended to be slightly higher. The percentage of positive correlations between the 96 15 minute values per day for heart rate and MABP increased with postnatal age and with birthweight, but did not differ in infants who developed a PVH. The coefficient of variation (CV) of the 96 15 minute values for MABP tended to be higher in infants on the day of PVH, and a similar trend was apparent on the day before. The processes of development of blood pressure, heart rate, and skin temperature are similar in infants with or without PVH but at lower gestational ages altered blood pressure control may cause brain haemorrhage.

Birth Weight↗

PubMed1994

Evaluation of a rapidly rotating shift system for tolerance of nurses to nightwork.

Fifteen female nurses, aged between 21 and 29 years and employed in an intensive care unit, were examined with the aim of evaluating their psychophysical adaptation to one of the most commonly used, rapidly rotating shift systems, the "metropolitan rota" (2-2-2-2), with the length of the shifts modified according to the work load (including night shifts of 10h) and with the start of the morning shift delayed (to 7 a.m.). Subjective evaluations of work load and psycho-physical conditions as well as performance measures (reaction time, search and memory test), blood pressure and heart rate were recorded at the start, middle and end of the work shifts on the last 4 days of the shift cycle, comprising one morning, one afternoon and two consecutive nights. During the shifts, plasma cortisol and urinary excretion rate of 6-sulphatoxymelatonin, adrenaline and noradrenaline were also recorded, as well as oral temperature and activity-sleep logs. The results showed that this rapidly rotating shift system including two consecutive night shifts does not significantly alter the normal circadian rhythms of the body, particularly as concerns performance levels, body temperature and hormone excretion. Moreover, the lengthening of the night shift to 10h can be considered acceptable in terms of work efficiency, provided that work load is reduced and there are sufficient rest pauses available to compensate for tiredness and sleepiness. On the other hand, the shortening of the day shifts to 7h and the delayed start of the morning shift to 7 a.m. appeared convenient in relation to both work load and sleep duration.

Adult↗

PubMed1994

The meaning of good sleep: a longitudinal study of polysomnography and subjective sleep quality.

The present study sought to investigate the meaning of subjectively good sleep, using a longitudinal and intraindividual design. Eight subjects slept in an isolation unit according to an irregular schedule of 6 h sleeps and 1 h naps, designed to give normal amounts of time in bed (1/3 of total), but variable sleep quality. Eight sleeps and eight naps were used for longitudinal simple and multiple regression analyses with standard polysomnographical sleep variables as predictors and subjective sleep quality as dependent variables. The results showed that subjective sleep quality (and related variables) was closely related to sleep efficiency, but not sleep stages. At least 87% efficiency was required for ratings of 'rather good' sleep. In addition, sleep quality ratings improved with closeness (of the awakening) to the circadian acrophase (17.00-21.00 hours) of the rectal temperature rhythm. The subjective ease of awakening differed from most other other variables in that it was related to low sleep efficiency. Objective and subjective homologues of sleep length and sleep latency showed high mean intraindividual correlations (r = 0.55 and 0.64, respectively). It was concluded that objective measures of sleep continuity were closely reflected in perceived sleep quality and that sleep quality essentially means sleep continuity.

Journal Article↗

PubMed1994

The subjective meaning of good sleep, an intraindividual approach using the Karolinska Sleep Diary.

The present experiment used an intraindividual design to investigate the meaning and measurement of "good sleep". Each of 16 subjects slept in an isolation unit according to a schedule (15 sleeps) designed to give variable quality of sleep. Self-rated sleep measures (from the Karolinska Sleep Diary) were obtained after each sleep and subjected to intraindividual regression analyses across time. Most subjective sleep measures showed a strong covariation across conditions. Subjective quality of sleep mainly involved variables of sleep continuity, in particular, perceived calmness of sleep and sleep efficiency. "Sleep quality," "calm sleep," "ease of falling asleep," and ability to "sleep throughout" the time allotted strongly covaried and formed an index of sleep quality. Self-rated ease of awakening deviated from the general pattern and was associated with poor sleep quality. So was reported dreaming (related to awakenings). It was concluded that most subjective sleep measures tend to covary across conditions and that "good sleep" is mainly a question of sleep continuity.

Adolescent↗

PubMed1994

Circadian rhythms, jet lag, and chronobiotics: an overview.

This overview considers the origins of jet lag in terms of altered circadian rhythmicity. The properties required of a chronobiotic--an agent to cause phase adjustment of the body clock--are discussed, and an account is given of the major candidates at the present time: light, melatonin, activity, and benzodiazepines. It is concluded that current knowledge indicates that a combination of factors is likely to be most effective.

Animals↗

PubMed1994

Effect of masking on circadian adjustment and interindividual differences on a rapidly rotating shift schedule.

OBJECTIVES: The aim of the present study was to define the effect of masking on the estimation of circadian adjustment of and interindividual differences between nurses on a rapidly rotating shift schedule. METHODS: The phase shift of the circadian rhythm of rectal temperature was studied in 17 subjects. The following three different methods for estimating the circadian phase shift were compared: (i) cosinor analysis, (ii) a method using normative endogenous data in which the masking effects are removed ("purification"), and (iii) a method using normative endogenous data in which the masking effects are not removed. RESULTS: The mean phase delay during the second night shift (compared with the morning shift) was 6.3 h according to the cosinor analyses of the raw data and 6.2 h according to the cross-correlation method of the raw data. When the masking effects were removed ("purification"), the phase shift was only 1.7 h. Diurnal type did not significantly explain the differences between individuals in the amount of phase shift of the raw data but was the only significant factor, explaining 32% of the variation between individuals in the phase shift of the purified data. CONCLUSIONS: Masking effects on body temperature should be taken into account before any definite conclusions can be drawn about the relation between individual factors and the adjustment of the circadian rhythm of body temperature.

Adaptation, Psychological↗

PubMed1993

Regulation of sleep and naps on an irregular schedule.

For many occupational groups there is an implicit requirement that sleep be taken according to very irregular schedules. The purpose of this study was to investigate the effects of an irregular sleep schedule on sleep and to determine if such effects could be attributed to the timing of sleep. Eight subjects slept in an isolation unit according to an irregular schedule comprising four 8-hour sleep periods, 12 6-hour sleep periods and 12 1-hour naps. The schedule was designed to give normal amounts of time (1/3 of total) in bed. Large variations in mean sleep efficiency (100-46%) were observed, which in individual cases frequently involved a complete absence of sleep. In 6-hour sleep periods the loss was due to an inability to maintain sleep, whereas in naps the loss was due to an inability to initiate sleep. The major causes of reduced sleep were short prior time awake and bedtime close to the circadian acrophase of rectal temperature (i.e. late afternoon). These two components accounted for 46% of the intraindividual variance of total sleep time (TST). TST increased by 9.2 minutes for each hour of prior time awake and by 10 minutes for each hour of deviation from the circadian acrophase of rectal temperature. Prior time awake also exerted a strong influence on slow-wave sleep (SWS), and circadian phase exerted a similar influence on rapid eye movement sleep. We concluded that irregular sleep patterns strongly affect sleep and that circadian and homeostatic influences are clearly discernible despite the irregularity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

Skin temperature and heart rate rhythms in infants of extreme prematurity.

Nine preterm infants of 26 to 29 weeks' gestational age and 792 to 1200 g birth weight spent six to 17 weeks in our neonatal medical unit. Hourly recordings of skin temperature and heart rate were carried out. The first five to 15 weeks were spent in the intensive care ward, in continuous light, due to various medical conditions. After recovery they were moved to a nursery for one to nine weeks, with 12 hourly periods of light and darkness. Four infants developed circadian rhythms in temperature and three in heart rate in light-dark periods, the remainder failing to do so. Some infants take longer than others to develop circadian rhythms but the reasons for this are not clear. It is suggested that earlier exposure to a light-dark environment may synchronize the 'body clock' to a 24 hour period in more preterm infants.

Circadian Rhythm↗

PubMed1991

The development of ultradian and circadian rhythms in premature babies maintained in constant conditions.

Twenty very premature babies, born at 24-29 weeks gestation, have been studied while they were maintained in intensive care with continuous intravenous feeding and constant ambient lighting and temperature. Hourly records of insulated skin temperature and heart rate were made for a continuous period of 6-17 weeks, always starting the recording within 24 h of birth. The development of rhythms within the ultradian, circadian and infradian domains was sought by methods including maximum entropy spectral analysis and autocorrelation. Circadian and ultradian rhythms were present, but not regularly so; rather they appeared and disappeared erratically in successive weeks. As a consequence, the group as a whole did not show an increasing rhythmicity with chronological age. In some cases, babies were later placed in a ward in which the lighting was dimmed at night, and feeding by mouth at regular intervals was instituted. There was some evidence for increases in circadian and ultradian rhythmicity after these changes. These results enable inferences to be drawn as to the origin of fetal rhythms in the third trimester of pregnancy, as well as speculation to be made on the ontogeny of ultradian and circadian rhythms in the neonate.

Age Factors↗

PubMed1988

Sleep and circadian rhythms of temperature and urinary excretion on a 22.8 hr "day".

Two groups of subjects (total N = 6) were studied in an isolation chamber for a period of 3 weeks whilst living on a 22.8 hr "day". Regular samples of urine were taken when the subjects were awake, deep body temperature was recorded continuously and polygraphic EEG recordings were made of alternate sleeps. The excretion in the urine of potassium, sodium, phosphate, calcium and a metabolite of melatonin were estimated. Measurements of the quantity and quality of sleep were made together with assessments of the temperature profiles associated with sleep. In addition, cosinor analysis of circadian rhythmicity in urinary variables and temperature was performed. The 22.8 hr "days" affected variables and subjects differently. These differences were interpreted as indicating that the endogenous component of half the subjects adjusted to the 22.8 hr "days" but that, for the other three, adjustment did not occur. When the behaviour of different variables was considered then some (including urinary potassium and melatonin, sleep length and REM sleep) appeared to possess a larger endogenous component than others (for example, urinary sodium, phosphate and calcium), with rectal temperature behaving in an intermediate manner. In addition, a comparison between different rhythms in any subject enabled inferences to be drawn regarding any links (or lack of them) that might exist between the rhythms. In this respect also, there was a considerable range in the results and no links between any of the rhythms appeared to exist in the group of subjects as a whole. Two further groups (total N = 8) were treated similarly except that the chamber clock ran at the correct rate. In these subjects, circadian rhythms of urinary excretion and deep body temperature (sleep stages and urinary melatonin were not measured) gave no evidence for deterioration. We conclude, therefore, that the results on the 22.8 hr "day" were directly due to the abnormal "day" length rather than to a prolonged stay in the isolation chamber.

Adolescent↗

PubMed1985

Some effects of melatonin and the control of its secretion in humans.

Whether or not the pineal gland has a significant physiological role in humans is not known. There has nevertheless been speculation about the potential therapeutic use of melatonin (in view of its hypnotic and possible zeitgeber properties) in conditions such as insomnia and jet lag, and in shift-workers. Our work concerns the effects of melatonin administration in humans and the interactions between melatonin and other circadian variables. Chronic (one month), timed (1700 h), low-dose (2 mg daily) melatonin administration to normal subjects without environmental control consistently increased evening fatigue and slightly modified the 24 h prolactin rhythm without effect on cortisol, growth hormone, luteinizing hormone, thyroxine, testosterone or self-rated mood. In five out of 11 subjects the endogenous melatonin rhythm was advanced by one to three hours. During fractional desynchronization of circadian rhythms by increasing imposed 'day' length (26-29 h, 24 days, 500 lux), 5 mg melatonin per os at lights-out in two subjects resulted in better entrainment of the fatigue rhythm to the zeitgeber than in five out of six control subjects, without major consistent effects on other measured circadian variables. Using a new radioimmunoassay for 6-hydroxymelatonin sulphate (aMT6s), the major melatonin metabolite, we have shown that the urinary aMT6s rhythm is closely correlated to that of melatonin in plasma and is completely suppressed by an acute dose of atenolol (100 mg per os), a peripheral beta-adrenergic antagonist. During fractional desynchronization by increasing imposed 'day' length in one subject and decreasing imposed 'day' length in two subjects, the urinary aMT6s rhythm behaved similarly to that of core temperature. The results suggest that fatigue (or alertness) may be entrained by melatonin, but whether critical performance rhythms can be suitably manipulated remains to be clarified. It is likely that melatonin production is linked to the so-called 'strong' circadian oscillator.

Circadian Rhythm↗

PubMed1976

Timing of single daily meal influences relations among human circadian rhythms in urinary cyclic AMP and hemic glucagon, insulin and iron.

Relations among circadian rhythms in serum iron, glucagon and insulin and urinary cyclic AMP excretion differ drastically when diurnally active, nocturnally resting human adults consume all daily food for one week as breakfast only and for another week as dinner only - a finding of interest to diverse fields, e.g., for optimizing certain kinds of therapy or for a better utilization of calories.

Circadian Rhythm↗

PubMedDate not supplied

Dissecting circadian performance rhythms: implications for shiftwork.

Safety on shift systems will depend, at least in part, on the adjustment of shiftworkers' circadian (c.24h) rhythms in performance capabilities which will in turn depend on their underlying control. In the present study three volunteers lived on a 30h 'day' and performed a range of tasks every 2h (while awake) to allow estimates of the relative magnitude of the endogenous (body clock) and exogenous (masking) components of their rhythms to be made. Performance rhythms were found to differ considerably in this respect with, for example, speed on a 4-choice serial reaction time task appearing to be largely endogenously determined while that on a 5-target Sternberg task was more dependent on exogenous (i.e., 30h) factors. This implies that performance measures may adjust at very different rates to one another to night work, and hence that the optimal form of shift system may vary according to the precise demands of the shiftworker's task.

Adult↗