Fatigue, sleepiness and disturbed sleep are common complaints for seafarers. This occupational group is often exposed to psychophysical stress as well as night and shift work. Noise from the ship’s operations, vibration from the engine and weather-related ship motion are other significant stress factors that can reduce the quality of sleep on board. Because fatigue, sleepiness and sleep disruption can increase the risk of accidents at sea, an objective survey of these strains is an important component not only of seafarers’ health but also of shipboard safety.
In order to obtain a deeper understanding of the architecture of seafarers’ sleep and possible sleeping disorders, ambulatory polysomnography – the gold standard of sleep diagnostics – was used for the first time on board merchant ships. Objective sleepiness was measured using pupillometry. In addition, interviews and questionnaires were conducted on daytime sleepiness (ESS = Epworth Sleepiness Scale) and sleep quality (PSQI = Pittsburgh Sleep Quality Index).
The polysomnographic measurements showed signal qualities and impediments comparable to those in a sleep laboratory. No conspicuous artefacts were detected that could be attributed to the ship‘s environment. It can therefore be assumed that the quality and feasibility of the polysomnography on board were good.
Comparing the seafarers’ sleep architecture with the normal population provided evidence not only that the total sleep time on board is lower, but also that changes in sleep occur in terms of the macro-architecture (shift of deep sleep phases in favour of light sleep phases) as well as the microarchitecture (increased arousal index).
Besides this, the seamen showed an increased risk profile for obstructive sleep apnoea (OSA). In fact, 73.7% of seafarers were diagnosed with at least mild OSA (AHI ≥5), 15.8% with severe OSA (AHI ≥30) and 16.7% with additional excessive daytime sleepiness (AHI ≥5 + ESS >10). A slightly increased prevalence of OSA is likely among seafarers, even though a comparison with the normal population proved difficult. In any case, further studies may be useful to investigate OSA in seafarers and its effects on daytime sleepiness and general health, especially with regard to cardiovascular disease.
The ESS evaluations showed that 61.1% of the seafarer collective had elevated subjective daytime sleepiness (ESS >5). There was a tendency towards a higher ESS value in day workers, with a median of 9 (3-12) compared to a median ESS value of 6 (3-11) in watchkeepers. Both groups exceeded the threshold of increased normal daytime sleepiness of >5 on average. Day workers even reached an ESS >10 in 28.6% of the cases, which indicates the presence of excessive daytime sleepiness.
The results of pupillometry, displaying the effect of objective sleepiness, were also conspicuous in both collectives. Two watchkeepers (33.3%) and one day worker (33.3%) were unfit for duty according to the results of pupillometry. The fact that 61,1% of the seamen showed increased daytime sleepiness (ESS >5), but only 44.4% had abnormal pupillometry indicates that sleepiness tended to be subjectively overestimated.
In addition, poorer objective sleep quality was found in watchkeepers, even though subjectively measured sleep quality using the PSQI did not differ from that of day workers. In general, seafarers slept conspicuously often in the supine position. This sleeping position also correlated with a longer stay on board. The possible causes and effects of this observation should be investigated more closely in future long-term studies with a larger collective.
In conclusion, the results suggest that, for health and safety reasons, the sleep behaviour of seafarers should be investigated further, and that there is a need for intervention with regard to poor sleep quality and sleepiness on board. The increased supine position in combination with frequent breathing events suggests that avoiding the supine position (e.g. by using a backpack) as a therapeutic approach for OSA should also be considered as a cost-effective and easily implemented preventive option in the seafarer population.
