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Indicators and predictors of sleepiness
Umeå University, Faculty of Medicine, Public Health and Clinical Medicine.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sleep is a basic need as important as physical fitness and good nutrition. Without enough sleep, we will create a sleep debt and experience sleepiness. Sleepiness can be defined as the inability to stay awake, a condition that has become a health problem in our 24-hour-7-day-a-week society. Estimates suggest that up to one-third of the population suffers from excessive sleepiness. Among other interactions, sleepiness affects our performance, increasing the risk of being involved in accidents. A considerable portion of work related accidents and injuries are related to sleepiness resulting in large costs for the individuals and society. Professional drivers are one example of workers who are at risk of sleepiness related accidents. Up to 40% of heavy truck accidents could be related to sleepiness. A better knowledge about reliable indicators and predictors of sleepiness is important in preventing sleepiness related accidents.

This thesis investigates both objective and subjective indicators of sleepiness, how these relate to each other, and how their pattern changes over time. The indicators investigated were electroencephalography, heart rate variability, simple reaction time, head movement, and subjective ratings of sleepiness (Study I-IV). In Study V, a questionnaire study was conducted with professional drivers in northern Sweden. This study mainly deals with predictors of sleepiness.

When subjects were sleep deprived both objective and subjective ratings indicated a rapid increase in sleepiness during the first hour of the test followed by a levelling off. This change in pattern was evident for all the indicators except heart rate and heart rate variability. On the other hand, HRV was correlated with the increase of EEG parameters during the post-test sleep period. The changes in pattern of the indicators included in the thesis are analysed in the perspective of temporal patterns and relationships. Of the tested indicators, a subjective rating of sleepiness with CR-10 was considered to be the most reliable indicator of sleepiness.

Of the investigated predictors of sleepiness, prior sleep habits were found to be strongly associated to sleepiness and the sleepiness related symptoms while driving. The influences of driving conditions and individual characteristics on sleepiness while driving were lower.

A multidisciplinary approach when investigating and implementing indicators and predictors of sleepiness is important. In addition to their actual relations to the development of sleepiness, factors such as technical and practical limitations, work, and individual and situational needs must be taken into account.

Place, publisher, year, edition, pages
Umeå: Folkhälsa och klinisk medicin , 2006. , 85 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1003
Keyword [en]
Public health, Sleep Scale (KSS), Category-Ratio Scale (CR-10), sleepiness, sleep, driving, indicator, sleep debt, heart rate variability, electroencephalography (EEG), head movements, performance, truck drivers, sleep habits, predictor
Keyword [sv]
National Category
Public Health, Global Health, Social Medicine and Epidemiology
URN: urn:nbn:se:umu:diva-708ISBN: 91-7264-017-0OAI: diva2:144278
Public defence
2006-03-17, Stora föreläsningsalen, Arbetslivsinstitutet, petrus laestadiusvägen, Umeå, 09:00 (English)
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2009-10-30Bibliographically approved
List of papers
1. Electroencephalography and subjective ratings of sleep deprivation.
Open this publication in new window or tab >>Electroencephalography and subjective ratings of sleep deprivation.
Show others...
2005 (English)In: Sleep Medicine, ISSN 1389-9457, E-ISSN 1878-5506, Vol. 6, no 3, 231-240 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND AND PURPOSE: Sleep-related vehicle accidents account for many injuries and fatalities each year on monotonous motorways and roads. To effectively prevent such incidents requires greater knowledge of the mechanisms and development of the effects of sleep deprivation. Ten volunteers participated in a laboratory study aimed to analyze the way changes in wakefulness were described in terms of EEG changes and subjective ratings. PATIENTS AND METHODS: For each subject, the study consisted of four testing sessions that varied in length on different days: one session each of 60, 90, and 120 min when sleep-deprived, and one session of 120 min when rested. Changes in wakefulness were analyzed using electroencephalographic recordings and ratings on two different scales, the Karolinska Sleepiness Scale (KSS) and the Category-Ratio Scale (CR-10). RESULTS: The results indicate quite conclusively that significant changes in the perception of sleepiness occur during the first 60-90 min of sedentary, monotonous work. Beyond this time period, subjective and physiological changes remained constant throughout the rest of the 120-min period. CONCLUSION: In general, the subjective rating scales highly and significantly correlated with theta activity in both tired and rested states and with alpha activity in the rested state. Similar results were seen using both subjective rating scales.

urn:nbn:se:umu:diva-4957 (URN)10.1016/j.sleep.2004.11.012 (DOI)15854853 (PubMedID)
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2015-01-21Bibliographically approved
2. Heart rate variability during sedentary work and sleep in normal and sleep-deprived states
Open this publication in new window or tab >>Heart rate variability during sedentary work and sleep in normal and sleep-deprived states
2005 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, Vol. 25, no 1, 51-57 p.Article in journal (Refereed) Published
Abstract [en]

The possibility of using heart rate variability (HRV) as an indicator of sleepiness was investigated by analysing heart rate (HR) activity and electroencephalography (EEG) recordings from 10 individuals who performed a monotonous attention task for 120 min in both sleep-deprived and rested states. In both conditions, measurements were collected during 60 min of sleep immediately following a 120 min of non-sleep (awake phase). Although HR decreased significantly in both the rested and the sleep-deprived states during the awake phase, HR significantly changed sooner when subjects were sleep-deprived than when they were rested. No significant changes in HRV were found during the awake phase; however, HRV correlated significantly with alpha and theta power densities when rested but not when sleep-deprived. During the sleep phase, the total HRV and very low and low frequency HRV components significantly decreased approximately 40 min after sleeping in the sleep-deprived condition. These HRV components were also significantly and negatively correlated with delta power densities. HRV does not seem to be a viable indicator of sleepiness; however, HRV may be useful for determining sleep stages.

Driving, drowsiness, indicator, sleep, sleepiness
urn:nbn:se:umu:diva-14218 (URN)10.1111/j.1475-097X.2004.00589.x (DOI)15659081 (PubMedID)
Available from: 2007-02-27 Created: 2007-02-27 Last updated: 2009-10-30Bibliographically approved
3. Performance on a simple reaction time task while sleep deprived
Open this publication in new window or tab >>Performance on a simple reaction time task while sleep deprived
2006 (English)In: Perceptual and Motor Skills, ISSN 0031-5125, Vol. 102, no 2, 589-599 p.Article in journal (Refereed) Published
Abstract [en]

Divergent results have been reported on the effect of a night's sleep loss on performance of a single monotonous task. The present experiment examined the effect that partial sleep deprivation had on 10 participants' performance on a simple reaction time task requiring low responding for 120 min. compared to performance on the same task when well rested. Participants missed significantly more signals and had slower reaction times when sleep deprived. Reaction times increased with time when participants were both sleep deprived and rested, but the number of misses did not significantly change over time. Reaction time was significantly correlated with subjective ratings of sleepiness and heart rate in both conditions. EEG and heart-rate variability measures did not correlate significantly with reaction time. Misses correlated significantly with subjective ratings and heart rate but only in the rested condition.

urn:nbn:se:umu:diva-4959 (URN)16826680 (PubMedID)
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2009-10-30Bibliographically approved
4. Sleepiness and head movements
Open this publication in new window or tab >>Sleepiness and head movements
2006 (English)In: Industrial Health, ISSN 0019-8366, Vol. 44, no 4, 564-576 p.Article in journal (Refereed) Published
Abstract [en]

Sleepiness in working life is critical and strongly associated to work related accidents. The relationship between sleepiness and head movements is poorly investigated. The pattern of head movements over time was investigated in a laboratory study with ten subjects either sleep-deprived or rested. Head movements were obtained by an inclinometer placed on the subject's forehead, and the recording was continuous. Results show that subjects when sleep-deprived moved their head more and had more extreme head movements compared to when rested. An increase of the velocity and the number of extreme head movements over time were noted when the subjects were sleep-deprived and when rested. The increase of head movements was more linear over time in the rested condition, whereas in sleep-deprived conditions most of the increase appeared during the first hour. No significant differences of between forward-backward movements and left-right movements could be found. When rested, the changes in head movements correlated with ratings of sleepiness, EEG activity, and heart rate variability. Head movements can be a used as an indicator of sleepiness.

urn:nbn:se:umu:diva-4960 (URN)10.2486/indhealth.44.564 (DOI)17085917 (PubMedID)
Available from: 2006-02-24 Created: 2006-02-24Bibliographically approved
5. Symptoms of sleepiness while driving and their relationship to prior sleep, work and individual characteristics.
Open this publication in new window or tab >>Symptoms of sleepiness while driving and their relationship to prior sleep, work and individual characteristics.
2006 (English)In: Transportation Research Part F: Traffic Psychology and Behaviour, ISSN 1369-8478, Vol. 9, no 3, 207-226 p.Article in journal (Refereed) Published
Abstract [en]

In total, 154 lorry and bus drivers participated in a questionnaire study dealing with sleepiness in traffic. The questionnaire included questions about sleep before work, appearance of sleepiness, the type of sleepiness they experienced while driving, and ways to counter sleepiness while driving. Driver sleepiness was analysed with respect to age, type of driving, traffic intensity, experience of work, and sleep before work. About 14% of the drivers reported regular sleepiness while driving, 33% had occasionally fought sleepiness while driving, and 8% had experienced nodding of the head while driving. The majority of the drivers had once been so tired that they had to stop driving. Sleepiness normally occurred between 03.00 and 06.00, at the end of longer trips, and was most frequently appeared in autumn. Poor sleep and poor working hours were considered as the most important causes to sleepiness. Eye tiredness, yawning, difficulties concentrating on the road, and difficulties keeping one’s thoughts together: these were the most frequently reported symptoms of sleepiness. More sleeping hours before work, better working hours, naps during work, listening to the radio, conversations, and lowering the cabin temperature were the most frequently mentioned countermeasures. The appearances of sleepiness while driving was strongly correlated to lower sleep hours and lower sleep quality before work. Age, type of work, or work experience did not interfere with sleepiness in the investigated group in any systematic way.

Sleepiness; Sleep hours; Drivers; Survey
urn:nbn:se:umu:diva-4961 (URN)10.1016/j.trf.2006.01.001 (DOI)
Available from: 2006-02-24 Created: 2006-02-24Bibliographically approved

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