A normative study of the maintenance of wakefulness test (MWT)

Abstract

The maintenance of wakefulness test (MWT) is a daytime polysomnographic procedure which quantifies wake tendency by measuring the ability to remain awake during soporific circumstances. We present normative data based on 64 healthy subjects (27 males and 37 females) who adhered to uniform MWT procedural conditions including polysomnographic montage, illuminance level, seating position, room temperature, meal timing, and subject instructions. When allowed a maximum trial duration of 40 min, subjects' mean sleep latency to the first epoch of sustained sleep was 35.2 +/- 7.9 min. The lower normal limit, defined as two standard deviations below the mean, was 19.4 min. Calculation of data on the basis of a maximum trial duration of 20 min and sleep latency to the first appearance of brief sleep (a microsleep episode or one epoch of any stage of sleep) yielded a mean sleep latency of 18.1 +/- 3.6 min and a lower normal limit of 10.9 min. Sleep latency scores were significantly higher than those previously reported in patients with disorders of excessive somnolence. Therefore, the MWT appears to be a useful procedure in differentiating groups with normal daytime wake tendency from those with impaired wake tendency and in identifying individuals with pathologic inability to remain awake under soporific circumstances.

Fig. 1

Distribution of sleep onsets prior to trial termination for the SUSMWT40 Protocol.

Fig. 2

Distribution of mean MWT sleep latency scores for various protocols For definitions of protocols, please see text. Abbreviations: IQ, interquartile, i.e. the distance between the 25th and 75th sample percentiles, represented by the box. Therefore, each box encompasses the middle 50% of the distribution. The vertical lines extend each box to a distance of 1.5 interquartile ranges from the box. Black circles encompass scores falling within three interquartile ranges and asterisks denote extreme outliers falling outside this range.