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Biomedical subjects

S Folkard

Publications and source records attributed to S Folkard.

17 recordsLinked to original sources
PubMed1992

Sleep on a shortening day/night schedule.

In 2 experiments subjects were exposed for 3.5 weeks to a gradually (0.2 h/day initially) shortening day/night cycle, ending at 22.8 h and 22.0 h, respectively. Shortening of the cycle led to an initial but temporary increase of sleep latency. When the reduction ceased at 22.8 h and this length was maintained, sleep parameters were not further affected and the temperature rhythm in most subjects remained entrained to the 22.8 h period, although some instability occurred towards the end. In the 22.0 h experiment the continued reduction beyond 22.8 h led to disturbed sleep on day 15, at a day length of 22.4 h. Total sleep time, stage 2 and sleep efficiency were then markedly reduced. At this point sleep coincided with the peak of the body temperature rhythm and the amplitude of the latter was extremely small. This was also the point when the body temperature rhythm 'broke out' from the sleep/wake rhythm and showed a large 6 h phase jump (delay). Towards the end of the experiment, when sleep was initiated in the circadian temperature trough, REM propensity was increased. It was concluded that several sleep parameters were affected by the reduction of the day/night cycle although the specific effects depended on the amount of phase advance and on whether desynchronization occurred. Within the range of entrainment, however, most sleep parameters were remarkably unperturbed by the considerable changes of circadian parameters.

Adult↗
PubMed1992

Is there a 'best compromise' shift system?

In his review Wilkinson considers the question 'How fast should the night shift rotate? He concludes quite strongly that with the possible exception of social factors, most of the evidence favours the use of prolonged or permanent night shifts. In this reply I argue that in reaching this conclusion Wilkinson has (i) overestimated the problems associated with rapidly-rotating shift systems; and (ii) underestimated the problems that might be encountered in trying to implement effective permanent night shift systems. The evidence on the various problems reviewed by Wilkinson is reconsidered. Other aspects of shift systems that were ignored by Wilkinson are then also taken into account. It is concluded that the evidence does not allow a general choice to be made between the use of either permanent night shifts or rapidly rotating, delaying, shift system. Rather the choice between them would appear to depend on the relative importance attached to safety and social problems in any given workplace.

Circadian Rhythm↗
PubMed1991

"Demasking" the temperature rhythm after simulated time zone transitions.

Simulated time zone transitions were performed in an isolation unit upon groups of one to four human subjects. In the first series of experiments, the adjustment of the circadian rhythm of body temperature, measured in the presence of sleep and other masking factors, was assessed by cosinor analysis and by cross-correlation methods. These methods modeled the circadian timing system either as a single component or as the sum of two components, those due to exogenous and endogenous influences. The one-component models described a more rapid adjustment of the temperature rhythm to the time zone transition than did the two-component models; we attribute this difference to the masking effects of the exogenous component. In a second series of experiments, we showed that the shift of the endogenous component, as assessed by the two-component models, was not significantly different from that measured during constant routines. The results also showed that, if the zeitgebers were phased in advance of the endogenous component, then advances of the endogenous component were produced only if this mismatch was less than about 10 hr. Mismatches greater than this, and cases where the zeitgebers were delayed with respect to the endogenous component, both produced delays of the endogenous component. We conclude that the two-component cross-correlation methods can be used to estimate shifts of the endogenous component of a circadian rhythm in the presence of masking factors. They are therefore an alternative to constant routines when these latter are impracticable to carry out.

Adaptation, Physiological↗
PubMed1991

Echinococcus multilocularis antigens modify accessory cell function of macrophages.

Peritoneal macrophages and splenic lymphocytes were collected from BALB/c mice, normal or previously infected with Echinococcus multilocularis. In an accessory cell function assay, peritoneal macrophages, in increasing numbers, were added to cultures of splenic lymphocytes. Cultures were stimulated by concanavalin A (Con A) or E. multilocularis culture supernatant (EMSN). Post-infection macrophages, unlike normal macrophages, suppressed Con A- and EMSN-driven lymphocyte transformation. Modification of accessory cells could also be repeatedly induced in vivo by EMSN or a single FPLC fraction of EMSN. Lymphocytes were made more sensitive to accessory cell signals following incubation with EMSN.

Animals↗
PubMed1990

Circadian performance rhythms: some practical and theoretical implications.

Safety and productivity are low at night and this would appear to be because we are a diurnal species. This is reflected not only in our habitual sleep time, but also in our endogenous body clocks that, together with exogenous influences, such as the patterning of meals and activity, result in predictable circadian (24 h) rhythms in our physiological processes. Our performance capabilities also vary over the course of our waking period, with task demands affecting both the precise trend over the day, and the rate at which it adjusts to the changes in sleep timing occasioned by shift work. Studies designed to examine the reasons for this have shown that memory loaded performance may have a quite separate endogenous component to that responsible for more simple performance, suggesting that these two types of performance cannot be causally related. Furthermore, it would appear that the exogenous component of circadian rhythms may also differ across measures, and our attempts to model these endogenous and exogenous components have led us to re-examine the evidence on adjustment to night work. Our findings suggest that shiftworkers merely 'stay up late' on the night shift, rather than adjust to it, and that this is responsible for the reduced safety at night. It would seem that in situations where safety is paramount, the only solution to these problems is the creation of a nocturnal sub-society that not only always works at night but also remains on a nocturnal routine on rest days.

Circadian Rhythm↗
PubMed1976

Comparative study of short-term recovery of mental efficiency after anaesthesia.

Two common general anaesthetic techniques were compared to evaluate the time taken for the patient's mental efficiency to recover sufficiently for him to be escorted home after inguinal herniorrhaphy. Recovery in performance efficiency to at least 60% of the patient's own maximum is suggested as a criterion for discharge, and this needs a stay in hospital of seven to nine hours.

Anesthesia, General↗
PubMed1975

Diurnal variation in logical reasoning.

Subjects performed two tests of logical reasoning at each of six different times of day. In terms of speed, preformance on both tests was found to improve markedly from 08.00 to 14.00 and then to fall off fairly rapidly. Accuracy was found to decrease fairly linearly over the day. The results are interpreted as indicating that the different functions relating performance efficiency to time of day found by previous workers are due to differences in task demands rather than to individual differences. It is suggested that the larger the short-term memory component of a task the earlier in the day performance peaks.

Achievement↗