SUMMAR Y Although reduced sleep often underlies traffic and occupational accidents, convenient sleepiness testing is lacking. We show that posturographic balance testing addresses this issue, because balance testing predicts hours of wakefulness, which could facilitate sleepiness testing. Here, we equate balance scores from separate trials, blinded to the experimenter, with those recorded as a function of known and increasing time awake (i.e. during sustained wakefulness); we show, that the time awake in separate trials is posturographically measurable: positive predictive value 69%, sensitivity 56%, and specificity 96%. These results encourage further work developing posturographic sleepiness monitoring.

This thesis focuses on the issue of testing sleepiness quantitatively. The issue is relevant to policymakers concerned with traffic-and occupational safety; such testing provides a tool for safety legislation and -surveillance. The findings of this thesis provide guidelines for a posturographic sleepiness tester.Sleepiness ensuing from staying awake merely 17 h impairs our performance as much as the legally proscribed blood alcohol concentration 0.5‰ does. Hence, sleepiness is a major risk factor in transportation and occupational accidents. The lack of convenient, commercial sleepiness tests precludes testing impending sleepiness levels -contrary to simply breath testing for alcohol intoxication. Posturography is a potential sleepiness test, since clinical diurnal balance testing suggests the hypothesis that time awake could be posturographically estimable. Relying on this hypothesis this thesis examines posturographic sleepiness testing for instrumentation purposes.Empirical results from 63 subjects -for whom we tested balance with a force platform during wakefulness for maximum 36 h-show that sustained wakefulness impairs balance. The results show that time awake is posturographically estimable with 88% accuracy and 97% precision -which validates our hypothesis. Results also show that balance scores tested at 13:30 hours serve as a threshold to detect excessive sleepiness. Analytical results show that the test length has a marked effect on estimation accuracy: 18 s tests suffice to identify sleepiness related balance changes, but trades off some of the accuracy achieved with 30 s tests.The procedure to estimate time awake relies on equating the subject's test score to a reference table (comprising balance scores tested during sustained wakefulness, regressed against time awake). Empirical results showed that sustained wakefulness explains 60% of the diurnal balance variations, whereas the time of day explains 40% of the balance variations. The latter fact implies that time awake estimations also must rely on knowing the local times of both test and reference scores. Hypothesis ORIGINAL PUBLICATIONSI. E H ae g g s t r ö m , P Forsman, A Wallin, E Toppila and I Pyykkö. Evaluating S l e e p i n e s s u s i n g F o r c e P l a t f o r m P o s t u r o g r a p h y . I E E E T r a n s B VI. P Forsman, A Tietäväinen, A Wallin, E Toppila, and E Haeggström. Balance control impairment during sustained waking allows posturographic sleepiness testing. J Biomechanics. In press. AUTHOR'S CONTRIBUTIONThe thesis's author designed studies I, III, and IV, performed the measurements in I and III, supervised the measurements in IV, analyzed the results in I-VI, ideated and designed publications II-IV and VI, authored publications II-VI, and co-authored publication I. PUBLICATION SUMMARIESPaper I shows that human balance impairs monotonically with increasing time awake, concurrent with the diurnal balance variation. With 21 subjects we show that the rate of monotone impairment allows separating balance scores recorded at ...

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