Sleep continuity measured by survival curve analysis.
OBJECTIVE
To develop and demonstrate the utility of measures of sleep continuity based on survival analysis techniques.


METHODS
Retrospective.


METHODS
University sleep laboratory.


METHODS
Anonymous nocturnal polysomnograms from 10 normal subjects, 10 subjects with mild sleep disordered breathing (SDB) (apnea-hypopnea index [AHI], 15-30/hr), and 10 subjects with moderate/severe SDB (AHI > 30/hr).


METHODS
N/A.


RESULTS
Hypnograms were analyzed to measure the lengths of episodes of contiguous sleep and processed using several common survival analysis techniques. Using separate survival curves for each group to describe the durations of continuous epochs of sleep (sleep run lengths), statistically significant differences were found between all groups (p < .001) as well as between the normal and mild SDB groups (p < .001), suggesting differences in the stability of sleep. Using survival regression techniques applied separately to each subject, statistically significant differences were found among all three groups (p < .001) and, more importantly, between the normal and mild SDB groups (p < .005). Similarly, estimation of sleep continuity based on the pooled sleep run data for each group also showed statistically significant differences (normal vs mild, p < .001; Normal vs moderate/severe, p < .001). In addition, the latter technique showed that changes in the "stability" of sleep could be demonstrated as runs progressed.


CONCLUSIONS
Survival curve analysis of the lengths of runs of contiguous sleep provides a potentially useful method of quantifying sleep continuity. The results suggest that sleep becomes more stable as sleep progresses in normal subjects and those with mild SDB and less stable in subjects with moderate/severe SDB.
Norman
Robert G
RG
Division of Pulmonary & Critical Care Medicine, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA. robert.norman@med.nyu.edu
Scott
Marc A
MA
Ayappa
Indu
I
Walsleben
Joyce A
JA
Rapoport
David M
DM
D000328:Adult; D004562:Electrocardiography; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000453:epidemiology*; D012892:Sleep Deprivation / Q000175:diagnosis / Q000453:epidemiology; D018709:Statistics, Nonparametric; D015996:Survival Rate; D014851:Wakefulness / Q000502:physiology