Sibylle Robens

The cortisol awakening response: a pilot study on the effects of shift work, morningness and sleep duration.

This study concerned the possible influence of experimental shift work, morningness and sleep length on the cortisol awakening response (CAR). Eight morning-oriented (MT) and eight evening-oriented (ET) healthy young men (19-27 years) slept after three consecutive day shifts during the night and after three consecutive night shifts during the day in the laboratory. Salivary cortisol concentrations were ascertained after each sleep period upon awakening and half an hour later, half-hourly during work shifts, and hourly during two 24-h periods, after the three day shift/night sleep sequences and after the three night shift/day sleep sequences. Statistical analyses considered the temporal position of sleep (night, day), the succession of sleep periods, the diurnal type and the polysomnographically verified total sleep time. The CAR was significantly smaller after day than after night sleep and increased significantly with total sleep time in ET. MT had moderately higher cortisol concentrations upon awakening than ET probably because they wake up at a later time of their circadian rhythm. But neither the CARs nor the cortisol concentrations during the following work shifts or during the 24h profiles were different in both diurnal types. The cortisol concentrations during work shifts correlated significantly with the previous post-awakening concentrations in MT but not in ET. Due to the small samples further studies are needed.

Cortisol awakening response: are sampling delays of 15 minutes acceptable?

Cortisol awakening responses (CAR) are often blunted or even extinguished when saliva samplings are delayed. The literature suggests that delays of 10 or 15 min are tolerable. Delays of 15 min were analysed with 510 CARs with the first sample taken within 3 min post-awakening followed by 4 samples taken 15, 30, 45, and 60 min later. Varying delays of up to 30 min were analysed with these and further 148 CARs where sampling began within 30 min post-awakening. Times of awakening and of saliva collection were verified by polysomnography or actimetry and by electronic devices respectively. Simulated sampling delays of 15 min revealed highly significant deviations from correctly taken CARs. No deviations were found for delays of up to 11.5 min suggesting that delays of up to 10 min are acceptable but that delays between 10 and 15 min might become critical.

Shifts of the hormonal rhythms of melatonin and cortisol after a 4 h bright-light pulse in different diurnal types

If applied during corresponding times of the individual melatonin profiles, bright light shifts the circadian phase equally, irrespective of diurnal type. We examined 32 young men: 10 morning types, 11 evening types, and 11 with no predisposition; 16 with high and 16 with low melatonin production. Each completed a 40 h session that included two consecutive nights during which the participants remained, apart from two short breaks during the second day, in bed under an illumination level of 30 lux. A 4 h bright light pulse was applied just after the expected individual melatonin onset the first night to cause a delay of the hormonal profile the second night. Salivary levels of melatonin and cortisol were determined hourly. Melatonin was delayed by 108 min, and cortisol offset and onset by 47 and 110 min, respectively. The cortisol quiescent period (start and end of the quiescent period being defined by the decrease below and the increase above 60% of the average cortisol production between 18:00 and 09:00 h) was prolonged. In contrast to the other subgroups, the delay of melatonin synthesis was about 0.5 h shorter in morning types, and their cortisol quiescent period was shortened. The present study leads to the hypothesis that, despite individually scheduled light exposure, morning types are potentially disadvantaged due to elevated cortisol levels, if persisting, in career night workers.

Experimental studies on the effects of nocturnal noise on cortisol awakening response

Cortisol awakening response (CAR), a considerable increase in cortisol concentrations post-awakening, is considered a reliable indicator of the reactivity of the hypothalamus-pituitary-adrenal axis (HPA). As noise has been shown to activate the HPA-axis, this analysis focuses on CAR as a possible indicator of noise-induced sleep disturbances. This analysis focuses on CAR using two studies. In Study 1, six women and six men (18-26 years) slept for 13 nights each in the laboratory. They were exposed to the noises of three different trains, each with 20, 40 or 80 pass-bys, with equivalent noise levels varying between 44 and 58 dBA, on nine nights. In Study 2, 23 persons slept first for four nights and then four days, in the laboratory; finally 23 persons slept in the reverse order. During six sleep periods, they were randomly exposed to road or rail traffic noises with L Aeq varying between 42 and 56 dBA. To determine the CAR, salivary cortisol concentrations were ascertained in both studies after night sleep immediately after awakening, and 15 and 45 minutes later; in Study 2 also after 30 and 60 minutes later. The time of awakening was determined using the polysomnogram and the participants rated their subjective sleep quality every morning. Subjective sleep quality was rated worse after noisy when compared to quiet nights. CAR was, however, attenuated only after the noisiest nights in a subgroup of Study 2. These persons had just performed a sequence of four consecutive night shifts. They were obviously still in the process of re-adjustment to their usual day-oriented schedule and probably in a state of elevated vulnerability. The study concludes that nocturnal noise exposure affects the CAR only if a person is in a state of at least temporarily elevated vulnerability.

Quantification of Circadian Phase Shifts with the Cross‐Correlation Technique

This paper concerns the applicability of the cross‐correlation technique for the assessment of shifts of the circadian system (e.g., caused by night work). Melatonin and cortisol profiles of 52 healthy young men were ascertained during two 24 h phase assessment procedures. The first was performed after three consecutive day shifts, and the second was performed one week later on 24 men again after three day shifts and on 28 men after three night shifts, where adaptation to night work was accelerated by bright light. The cross‐correlation technique that relies on the processing of all the measured data of a whole profile, as compared to the differences between temporal parameters determined with a conventional method, provided reliable estimates of the phase shifts. Its applicability is restricted to time series with similar profiles assessed at different times and to observation periods of a full diurnal cycle (in the case of substantial shifts) with equally distributed measures, but it is applicable to raw data and available in common statistical packages (e.g., SPSS, SAS, BMDP).

Blink rate during tests of executive performance after nocturnal traffic noise.

This analysis is on the hypothesis that nocturnal traffic noise affects sleep quality whereas performance decrement is avoided by increased effort expressed by a decrease in blink rates (BRs) during a visual task. Twenty-four persons (12 women, 12 men; 19-28 years, 23.56+/-2.49 years) slept during three consecutive weeks in the laboratory while exposed to road, rail, or aircraft noise with weekly permuted changes. Each week consisted of a random sequence of a quiet night (32 dBA) and three nights with equivalent noise levels of 39, 44 and 50 dBA respectively. The polysomnogram was recorded during all nights. Every morning the participants rated their sleep quality and then completed two executive tasks (Go/Nogo-, Switch-task). Neither of the two performance tests was affected by nocturnal noise. Sleep efficiency and subjective sleep quality decreased with increasing noise levels but were not associated with the type of noise. In contrast, BRs were associated with the type of noise, not with noise levels. The results do not support the hypothesis concerning the BR. The possible reasons are discussed. However, the results do not exclude that other physiological parameters such as heart rate or brain potentials measured during the tests might have revealed alterations associated with nocturnal noise exposure.