Validation of a posturographic approach to monitor sleepiness.

Sleepiness is a major risk factor in traffic- and occupational accidents. While sleepiness is a persistent concern, there is no convenient test to monitor impending levels of sleepiness. We show that force platform posturographic balance testing addresses this need because it estimates time awake (TA) accurately and precisely. Testing the TA is appropriate because TA drives the sleep homeostatic process, a component in sleepiness. With 12 subjects we evaluated the accuracy and precision of repeated estimates of TA. Our extended study design that allows evaluating the accuracy and precision of posturographic TA-estimates is new. First, we tested the subjects' balance every 2 h during 36 h of sustained wakefulness. This comprised the subjects' reference curves (balance as a function of known and increasing TA). Then, we tested the subjects' balance once a day over one week. We also tested the subjects' balance once a week over one month. Finally, to estimate the subjects' TA, we equated the balance scores with the scores in their reference curves. The accuracy of the estimates was 86%, and the precision was 97%. The high accuracy and precision of the estimates obtained with this one-month protocol validates the method of posturographic monitoring of sleepiness. So far, force platform posturographic balance testing has generally been used for clinical purposes, to quantify balance control and musculoskeletal performance. Our main result is that we now validated that balance testing provides accurate and precise estimates of TA, and hence, also provides an approach towards an automated monitor of sleepiness.