Pupillary fluctuation amplitude before target presentation reflects short-term vigilance level in Psychomotor Vigilance Tasks

Our daily activities require vigilance. Therefore, it is useful to externally monitor and predict our vigilance level using a straightforward method. It is known that the vigilance level is linked to pupillary fluctuations via Locus Coeruleus and Norepinephrine (LC-NE) system. However, previous methods of estimating long-term vigilance require monitoring pupillary fluctuations at rest over a long period. We developed a method of predicting the short-term vigilance level by monitoring pupillary fluctuation for a shorter period consisting of several seconds. The LC activity also fluctuates at a timescale of seconds. Therefore, we hypothesized that the short-term vigilance level could be estimated using pupillary fluctuations in a short period and quantified their amplitude as the Micro-Pupillary Unrest Index (M-PUI). We found an intra-individual trial-by-trial positive correlation between Reaction Time (RT) reflecting the short-term vigilance level and M-PUI in the period immediately before the target onset in a Psychomotor Vigilance Task (PVT). This relationship was most evident when the fluctuation was smoothed by a Hanning window of approximately 50 to 100 ms (including cases of down-sampled data at 100 and 50 Hz), and M-PUI was calculated in the period up to one or two seconds before the target onset. These results suggest that M-PUI can monitor and predict fluctuating levels of vigilance. M-PUI is also useful for examining pupillary fluctuations in a short period for elucidating the psychophysiological mechanisms of short-term vigilance.

Sleepiness of day workers and watchkeepers on board at high seas: a cross-sectional study

ObjectivesTo estimate the prevalence of sleepiness on duty among day workers and watchkeepers on board.DesignCross-sectional survey in a maritime field study.Setting10 shipping companies with container vessels under German management.ParticipantsThe whole crew (75 day workers and 123 watchkeepers) during 18 voyages on 18 different container ships.Outcome measuresSleepiness on duty and efficiency of sleep using pupillometry (in a cross-shift design) and the SenseWear armband activity monitor.ResultsThe watchkeepers showed significantly shorter sleep periods than day workers (5.5 hours vs 5.8 hours). The average efficiency of sleep was 69.6% and significantly lower among watchkeepers (OR 0.48; 95% CI 0.26 to 0.88). 396 pupillometric examinations were carried out and revealed 88 study members (22.2%) with a pupillary unrest index (rPUI) in a range characterised as ‘unfit for duty’ and 110 seafarers (27.8%) categorised as ‘particular attention required’. The average rPUI was similar between day workers and watchkeepers. The Epworth Sleepiness Scale revealed recent daytime sleepiness in 70 seafarers, which was similarly often stated by day workers and watchkeepers. Based on the Stanford Sleepiness Scale (SSS), a measurable cross-shift increase in the SSS value during the examined shift was observed, especially among watchkeepers. The amount of time already spent on the vessel at the time of the present examination was significantly associated with the rPUI (p=0.009).ConclusionSleep periods of both the day workers and the watchkeepers aboard vessels were alarmingly short and sleep efficiency was low. Sleepiness on duty is similarly prevalent among day workers and watchkeepers and seems to depend partly on the cumulative working period on the vessels. Preventive measures need to be taken by the shipping industry to counteract fatigue (eg, by enabling sufficient rest and sleep times).

Autonomic instability, as measured by pupillary unrest, is not associated with multiple sclerosis fatigue severity

Multiple sclerosis (MS) fatigue is one of the most common symptoms in MS, but its pathophysiology is still not understood. Sympathovagal imbalance was suggested as a reason for fatigue in chronic fatigue syndrome. We examined the role of an imbalance in the central autonomic nervous system (ANS) as a cause of MS fatigue in 51 MS patients and a control group of 22 healthy volunteers. Fatigue was assessed with the revised MS Fatigue Severity Scale (FSS) and the Modified Fatigue Impact Scale (MFIS). Depression was evaluated with the Beck Depression Inventory (BDI). Disintegration of the central ANS expressed by pupillary fatigue waves was measured with pupillography and documented in the pupillary unrest index (PUI). All subjects had less than five points on the seven-point Stanford Sleepiness Scale and were therefore not sleepy. MS patients had significant higher mean FSS scores (p =0.001) and mean MFIS scores (p =0.003) than our control group. Mean BDI scores were significant higher (p=0.001) in the MS group, but were in the lowest score range (0 -10 points) in both groups. Surprisingly, we found a statistically significant inverse correlation between PUI values and either FSS scores (p=0.001; r = −0.521) or MFIS scores (p =0.002; r = −0.423) in the MS group, but not in healthy participants. We therefore conclude that autonomic instability, as measured by pupillary unrest, is not associated with MS fatigue severity.