Subjective sleepiness is a sensitive indicator of insufficient sleep and impaired waking function

Abstract

SUMMARYThe main consequence of insufficient sleep is sleepiness. While measures of sleep latency, continuous encephalographical/electro-oculographical (EEG/EOG) recording and performance tests are useful indicators of sleepiness in the laboratory and clinic, they are not easily implemented in large, real-life field studies. Subjective ratings of sleepiness, which are easily applied and unobtrusive, are an alternative, but whether they measure sleepiness sensitively, reliably and validly remains uncertain. This review brings together research relevant to these issues. It is focused on the Karolinska Sleepiness Scale (KSS), which is a nine-point Likert-type scale. The diurnal pattern of sleepiness is U-shaped, with high KSS values in the morning and late evening, and with great stability across years. KSS values increase sensitively during acute total and repeated partial sleep deprivation and night work, including night driving. The effect sizes range between 1.5 and 3. The relation to driving performance or EEG/EOG indicators of sleepiness is highly significant, strongly curvilinear and consistent across individuals. High (>6) KSS values are associated particularly with impaired driving performance and sleep intrusions in the EEG. KSS values are also increased in many clinical conditions such as sleep apnea, depression and burnout. The context has a strong influence on KSS ratings. Thus, physical activity, social interaction and light exposure will reduce KSS values by 1-2 units. In contrast, time-on-task in a monotonous context will increase KSS values by 1-2 units. In summary, subjective ratings of sleepiness as described here is as sensitive and valid an indicator of sleepiness as objective measures, and particularly suitable for field studies.

The severity of driver fatigue in terms of line crossing: a pilot study comparing day- and night time driving in simulator

“…KSS 9 correspond to Bvery sleepy, great effort to keep alert fighting sleep^and has been proven to be correlated to performance impariments in different settings [25].…”

“…During each driving session the subjects self-reported their sleepiness level on the 9-grade Karolinska Sleepiness Scale (KSS) every five minutes [24]. The KSS scale has been proven to be a sensitive indicator and is well validated [25].…”

Subjective sleep disturbances and quality of life in chronic tetraplegia

“…This is within the range of normal 'middle of the day' values from several studies investigating sleepiness in daytime workers, and detailed in a recent review of the KSS (Table 3). 14 The influence of sleep, demographics and injury severity on quality of life (AQoL utility) Univariate analysis identified BNSQ total, BNSQ Q2b, age, years since injury and injury severity as significantly associated with mean health utility values. None of these variables were collinear.…”

DSPS-4: a Brief Measure of Perceived Daytime Sleepiness

“…Indeed, as revealed in a principal components analysis, the SSS is not a unidimensional scale of sleepiness (MacLean, Fekken, Saskin, & Knowles, 1992). Since the objective and laboratorial tests of sleepiness are not feasible in most of clinical practice, the use of subjective measures appears to be a suitable alternative (Åkerstedt, Anund, Axelsson, & Kecklund, 2014). Besides, Ohayon (2012) posits that "surprisingly, almost no epidemiological studies have questioned the participants about the impact of excessive sleepiness on their daytime functioning" (p.422).…”