Comparison of a frequency-based analysis of electroencephalograms (Z-ratio) and visual scoring on the multiple sleep latency test.

In a sample of multiple sleep latency test naps following nocturnal polysomnograms from a group of 13 patients of varying ages and diagnoses, we compared a computer-derived electroencephalographic (EEG) measure (z-ratio) with standard visual sleep stage scoring. In this clinical population, z-ratio scoring agreed with human scorers approximately 80% of the time when determining sleep versus wake in 30-second epochs. These results show that a single, objectively quantifiable value derived from a single channel of EEG can distinguish between sleep and wakefulness (as defined by Rechtschaffen and Kales) with at least a moderate degree of precision. When refined, the z-ratio method might be of use as the basis for a new sleep scoring system, particularly where an accurate determination of sleep onset is required.

Sleep in normal late pregnancy.

Twelve women in their third trimester of pregnancy and 10 age-matched nonpregnant controls underwent complete polysomnography for one night in the laboratory. Seven of the original women returned for a second study 3-5 months postpartum. During late pregnancy, women showed increased wake after sleep onset (WASO) and a lower sleep efficiency in comparison with the control group. The percentage of rapid eye movement (REM) sleep was significantly decreased and the percentage of stage 1 significantly increased compared to the nonpregnant group. At 3-5 months postpartum, a significant reduction in WASO and increased sleep efficiency were noted. However, only a slight increase was noted in REM sleep during the postpartum period compared to the prepartum period. The most frequent sleep complaints in the pregnant group were restless sleep, low back pain, leg cramps and frightening dreams. In summary, in accordance with their complaints, women in their third trimester demonstrated polysomnographic patterns of sleep maintenance insomnia.