NEW VARIABLES FOR DEFINING SLEEP CONTINUITY

One very synthetic way to represent a night's sleep is by way of a hyp nogram: a graphical representation of the sleep stages as a function o f time. The hypnogram is generally quantified by a series of variables that measure the durations and latencies of the various sleep stages including wake. These variables, however, do not fully account for all the information contained in the hypnogram, in particular information on sleep continuity. A series of variables that measure and localize disruption of this continuity are proposed and their utility validated on three groups of patients presenting sleep disorders. Utility is es tablished if the variable is capable of differentiating between patien ts and healthy controls. Two sets of variables are examined: those tha t use the entire sleep period as unit of measurement, and those that a re measured within each consecutive NREM-REM sleep cycle. The results show that the variables proposed are able to differentiate between gro ups and, therefore, are useful measures reflecting the hypnogram more precisely. They also show that fragmentation of REM sleep does not pre sent a systematic trend across the night, but that fragmentation of NR EM sleep goes up linearly.