Chest
Volume 95, Issue 6, June 1989, Pages 1202-1206
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Clinical Investigations
Predictors of Objective Level of Daytime Sleepiness in Patients with Sleep-Related Breathing Disorders

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Excessive daytime sleepiness, the most prevalent symptom associated with the OSAS, is hypothesized to result from either fragmentation of sleep or hypoxemia during sleep. Measures of nocturnal sleep, respiration during sleep, and daytime sleepiness in 466 patients with apnea were collected to evaluate these two hypotheses. The various parameters were submitted to correlation and multiple regression analyses to predict daytime sleepiness as measured by the MSLT. The RAI, which measures the number of arousals from sleep associated with respiratory disturbances (best fragmentation correlation), produced a higher correlation with MSLT scores than did TMES (best hypoxemia correlation); however, the measures were highly intercorrelated, and multiple regression analyses to determine which parameters independently predicted MSLT showed the single best predictor to be the RAI. Additional independent variance in MSLT score was explained by TST and PSG1. Measures of hypoxemia provided little or no independent predictive information. These data support the hypothesis that sleep fragmentation is an important determinant of daytime sleepiness in patients with apnea.

Section snippets

Subjects

The subjects of this report are 466 patients, 415 men and 51 women, (mean age, 52.5 ± 12.2 years), who underwent diagnostic evaluation for sleep apnea at the Henry Ford Hospital Sleep Disorders Center. Each had a complete evaluation, including a nocturnal polysomnogram and a MSLT.

Procedure

For the diagnostic evaluation, patients completed a questionnaire on sleep disorders before their first clinic visit, which detailed the symptoms and history of their sleep complaint. During the clinical interview, the

RESULTS

The demographic characteristics and descriptive measures of the nocturnal sleep and respiratory disturbance of this sample of apneic patients is presented in Tables 1 and 2. The data presented include means, SDs, and CVs. The CV is a measure of the ratio of the mean to the SD which facilitates comparisons of variability among parameters. Variability is desirable in correlation and regression analyses; reduced variability limits the potential size of a correlation. The oximetric parameters

DISCUSSION

These data support the sleep fragmentation hypothesis which states that the daytime sleepiness of patients with OSAS is due to the disruption of sleep by brief electroencephalographic arousals accompanying the cessation of an apnea or hypopnea. These findings do not refute the association of hypoxemia with daytime sleepiness in apneic patients. In fact, the data of this study showed that hypoxemia and daytime sleepiness are correlated; however, these data do indicate that the correlation of

ACKNOWLEDGMENTS

We thank Dr. Meir Kryger for his thoughtful review of an earlier version of this report.

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†Supported by grant R01 NS22758-03.

Manuscript received October 3; revision accepted October 25.

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