Researchers Set out to Study Sleep Fragmen- Tation in an Effort to Increase the Under- Standing of Basic Mechanisms Governing Sleep

RESEARCHERS SET OUT TO STUDY SLEEP FRAGMENTATION IN AN EFFORT TO INCREASE THE UNDERSTANDING OF BASIC MECHANISMS GOVERNING SLEEP STRUCTURE, as well as to explore a model of the type of sleep abnormalities found in patients with sleep disorders, particularly obstructive sleep apnea (OSA). The goal of the study reprinted here1 was to establish an operational definition for the level of sleep disruption required to contribute to subsequent daytime sleepiness. Our original intention had been to conduct a study that induced sleep fragmentation in normal sleepers and then evaluate changes in daytime function. However, it was unclear from the literature at the time how much sleep fragmentation was necessary to cause significant changes in the restorative function of the sleep. The best available examples of sleep fragmentation arose from the study of the sleep of patients with OSA. But in these patients, apneas might cause very transient EEG arousals, longer EEG arousals associated with a change in sleep stage, or even awakenings 16 seconds to several minutes in duration. Therefore, our first project studied the relation of six definitions of events that caused sleep fragmentation to subsequent daytime sleepiness in four groups of subjects. It was determined that even the most subtle level of sleep fragmentation, an increase in EEG frequency lasting at least three seconds, in conjunction with increased EMG amplitude, was correlated with increased daytime sleepiness.1 This definition was similar to the definition of arousals adopted by the ASDA in 1992.2 The primary difference is that the ASDA definition does not require a change in EMG during non-REM sleep; the EEG change alone is sufficient to score an arousal. The goal of the present paper is to review the literature on sleep fragmentation since the publication of our 1984 paper. Research aimed at furthering our understanding of the effects of fragmented sleep in humans can be categorized into two general areas: 1) study of the effects of experimentally induced arousals/ awakenings in normal sleepers using auditory stimulation, or 2) study of the sleep of patients with sleep disorders that cause sleep fragmentation. Another literature that has emerged concerns the effects of sleep fragmentation on cardiovascular physiology; and this will be reviewed briefly. Experimental Sleep Fragmentation in Normal Sleepers