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Biomedical subjects

D S Minors

Publications and source records attributed to D S Minors.

At least 37 records · Page 2Linked to original sources
PubMed1990

Removing masking factors from urinary rhythm data in humans.

We have previously developed simple models that enable the exogenous and endogenous components of the circadian rhythm of body temperature to be separated. The present paper extends the method to urinary data. First, we have shown that the basic superiority of the two-component model over the one-component model persists when temperature data are converted into a format that is appropriate for urine sampling (that is, a single overnight sample and two-hourly samples during waking). Second, we provide normative endogenous data for urinary sodium, potassium and urate, data obtained from about 80 constant routines. These data are required for the two-component model. Third, we have compared the rate of adjustment to a simulated eastward time-zone transition of 8 hr in 8 subjects. This showed that the rate of adjustment assessed by the two-component model was significantly less than that assessed by the one-component model and much closer to that assessed in separate experiments (n = 15 subjects) using constant routines. We conclude that the two-component model can be used upon urinary data to give a closer approximation to the shift of the endogenous component, as assessed by constant routines, than can estimates that do not take into account the problem of masking caused by exogenous factors.

Adolescent↗
PubMed1989

Retrospective study of temperature rhythms of intensive care patients.

The hourly rectal temperature record of 15 patients who spent greater than or equal to 8 days in the ICU were analyzed for circadian rhythmicity. Using cosinor analysis, a statistically significant rhythm in a period of 24 h was present on 80% of the patient days studied. The position of the acrophase, or peak, of the rhythm varied markedly both between patients and within patients, with changes of several hours from day to day. There was a tendency for the amplitude of the rhythm to be greater when the patients were unconscious than when they were conscious and in those patients who died compared with those who survived.

Adult↗
PubMed1989

Masking in humans: the problem and some attempts to solve it.

Different types of masking are discussed together with an account of the masking effect that the sleep-wake cycle exerts upon the circadian rhythms of body temperature and urinary excretion. The relative importance to masking of the several components of differences between sleeping and wakefulness are then assessed. Means to deal with the problem of masking fall into two major categories. These attempt to minimise masking effects by protocols such as constant routines or control days, and mathematical models which separate results obtained in the presence of masking influences into endogenous and exogenous components. (The problem of the extent to which masking influences can render the endogenous component of a rhythm an impure reflection of the internal oscillator is considered also.) These different techniques are compared with respect to their usefulness and assumptions. Finally, a brief speculation is given of the usefulness of masking.

Body Temperature↗
PubMed1989

Variation in meals and sleep-activity patterns in aged subjects; its relevance to circadian rhythm studies.

The study was performed upon a sample of aged and non-institutionalized subjects. Information was obtained by questionnaires and diaries on personal factors during a typical week. A random subset was subjected to a more detailed analysis of the composition of their meals. Results showed that increasing age was correlated with: a decreased day-by-day variability in an individual's time of retiring, rising and eating meals; earlier sleep times; increased frequency of daytime naps and nocturnal awakenings; and decreased physical activity. These results occurred both in subjects living alone and in those living with company. Day-by-day differences in the composition of meals tended to decrease with age. When differences between individuals were considered then these tended to increase with age. Some implications of these findings for studies of circadian rhythmicity in aged subjects--in whom the timing of circadian rhythms becomes more erratic and amplitude falls--are discussed.

Aged↗
PubMed1988

Mathematical and statistical analysis of circadian rhythms.

The mathematical and statistical analysis of biological time series is complex and often involves specialised techniques. In this article we review several of these techniques, placing particular emphasis on the usefulness, assumptions and kind of data that they require. Because classical methods of time series analysis often require long spans of data that are not frequently available in biological studies, particularly in clinical circumstances, several alternative techniques are described. Where possible, emphasis is placed upon simple rather than esoteric mathematical descriptions of data. Also covered are problems of interpretation that might arise as a result of the mathematical analysis.

Circadian Rhythm↗
PubMed1988

Effects upon circadian rhythmicity of an alteration to the sleep-wake cycle: problems of assessment resulting from measurement in the presence of sleep and analysis in terms of a single shifted component.

Experiments were performed upon groups of three or four human subjects in an isolation chamber (total n = 14). Subjects lived initially on a conventional lifestyle and then delayed their hours of sleep by 8 hr (so mimicking some aspects of nightwork) for 2 or 5 days. They also performed two constant routines--protocols designed to minimize any effects due to the environment, mealtimes, and activity. Regular samples of urine were taken when subjects were awake, and were analyzed for sodium, potassium, and chloride; rectal temperature was measured and logged at 6-min intervals throughout. Shifts in circadian rhythms produced by the change in sleep time were assessed by cosinor and cross-correlation techniques. The protocol enabled these assessments to be made on days when sleep was allowed and under constant-routine conditions, so that masking and behavioral effects could be investigated also. The results confirmed that adjustment to the change in sleep time was slow and only partial, and that assessments made on days when sleep was allowed overestimated this adjustment. Furthermore, it was concluded that, whereas cosinor and cross-correlation techniques using only one shifting component were equally useful in describing the observed changes, both were inferior to a cross-correlation technique that made use of two shifting components. Some practical and theoretical implications of these results are discussed.

Adolescent↗
PubMed1986

Circadian rhythms and their mechanisms.

Recent work concerning the number, site(s) and means of adjustment to the 24-h day of internal clocks is reviewed. Work on humans is considered wherever possible though much of the work involving ablation and in vitro techniques necessarily involves other species, particularly rodents. It is concluded that, though recent advances have been impressive and present techniques appear likely to continue to produce results and stimulate discussion, more attention should be directed to considering the circadian system as a whole rather than as an assemblage of individual components.

Animals↗
PubMed1986

Irregularity of rest and activity: studies on circadian rhythmicity in man.

1. Rectal temperature, electrolyte excretion and performance were studied in young adults who followed an irregular pattern of work and rest for 9 days in an isolation unit. 2. In the analysis, effects evoked by the pattern of work and rest were separated from the oscillatory component, and rhythms for individual days were examined by the cosinor method. 3. During the schedule, rhythms no longer showed a period of exactly 24 h, and this effect was confirmed by studies using a repeated cycle of irregular work and rest and by studies using constant routines. 4. Temperature and urinary constituents differed in the strength and phase of their rhythms when corrected for evoked effects, as well as in the strength of the evoked effects themselves. 5. There was evidence of deterioration in performance during work periods which exceeded 9 h, but there was no evidence of progressive deterioration in performance over the 9 day schedule.

Activity Cycles↗
PubMed1984

Is there more than one circadian clock in humans? Evidence from fractional desynchronization studies.

Three groups of four healthy volunteers lived in an isolation unit for 24 days. During this time they lived by a clock which, unknown to themselves, ran progressively faster so that, by real time, the 'day' decreased from 24.0 to 22.0 h in length. Throughout this protocol, the subjects lived a regular regimen of sleep, waking and meals based upon their 'local' time clock. They collected regular urine samples that were analysed for a variety of constituents. Rectal temperature was also recorded automatically throughout. The effects of such a protocol upon circadian rhythmicity in these variables were investigated by a variety of techniques including cosinor analysis. The results showed that the temperature rhythm was less able to adjust to a shortening 'day' than were the urinary variables, with the possible exception of potassium; that is, the protocol forced an internal desynchronization to exist between different variables. These results are discussed in terms of both the possibility that more than one internal circadian clock might exist and the direct effect that sleep exerts upon the expression of circadian rhythms.

Adolescent↗