W. P. Colquhoun

Phase shift in temperature rhythm ffter transmeridian flight, as related to pre-flight phase angle

SummaryFurther analysis of temperature rhythms obtained in an earlier study of 38 subjects subjected to an 8-h eastward transmeridian flight showed that the extent to which the phase of the rhythm was shifted after the flight was related to the phase angle of the pre-flight rhythm. “Late peakers” shifted more than ”early peakers”, and this difference between the two types was still as large after 12 days in the new time zone as on the first day. Because the phase-shift was an “advance” one, this meant that the pre-flight individual differences in phase-angle were abolished by the flight, and had not re-appeared by the end of the observation period. It is suggested that this may have been due to an increase in the rigidity of the routine in the post-flight stage of the study, and that a similar effect may also occur in a switch from day to shiftwork.

Changes in the temperature rhythm of submariners following a rapidly rotating watchkeeping system for a prolonged period.

SummaryOn-watch readings of oral temperature were obtained at hourly intervals from submariners during two continuously submerged voyages of 48 days duration. The subjects followed a rapidly rotating watchkeeping system of 4-h dutyspells during the entire period. In the majority of cases, the amplitude of the circadian temperature rhythm progressively declined, and this was accompanied by a tendency for the rhythm to disintegrate into shorter periods, associated with the length of the duty spell and the particular pattern of sleep adopted. On one voyage, one subjects rhythm showed a tendency to “free-run”, with a period of 24.6 h. It is concluded that the results give pointers to the kind of effect to be looked for in studies of shift-workers following similarly highly irregular patterns of work.

Heart rate patterns in sedentary shift work: influence of circadian rhythm, meals and personality

SummaryHeart rate was recorded at regular intervals during the course of 8-h sessions of simulated sedentary shift work performed for 12 consecutive days. Separate groups of subjects were assigned to one of three shifts, commencing either at 0400 hours (“morning” shift), 0800 hours (“day” shift) or 2200 hours (“night” shift). A major meal was taken during a break in the middle of each shift. In all groups heart rate fell during the pre-break period, but rose after the break in response to the meal. This pattern remained constant over the 12-day period in the morning and day shift groups, but in the night shift group a progressive rise in the general level of the readings, caused mainly by the adjustment of the circadian rhythm to the altered sleeep/wake cycle, was accompanied by systematic changes in the extent of both the pre-break fall and the post-meal rise. Comparison with the results of a control study of 24-h variation in base heart rate suggested that differential responses to the meal observed in the three shift groups may have been due, at least in part, to differences in their personality make-up. It is concluded that, although systematic patterns of heart rate can be observed in sedentary shift work, both the timing of the shift and the personality of the subject must be taken into account when assessing the changes in physiological state likely to occur during work sessions that include a major break for refreshment.

The effects of continuous exposure to carbon monoxide on auditory vigilance in man.

SummarySix different groups of non-smoking young male subjects were studied separately for 18 consecutive days each in a closed controlled-environment human exposure chamber. Each group was subjected to a 5-day control period in fresh air followed successively by an 8-day period of continuous exposure to 50 ppm, 15 ppm or 0 ppm (control) by volume of carbon monoxide (CO) in air, and a 5-day recovery period in fresh air. The subjects performed a 1-h auditory vigilance task every day at the same time of day in a fixed qualitative, quantitative, and temporal relationship with food intake, consumption of stimulating beverages, physical activity, and sleep. It was concluded that such CO exposure, involving the continuous carriage of carboxyhaemoglobin loads up to 7%, was without significant effect on auditory vigilance.