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Clinical InvestigationsDaytime Sleepiness, Snoring, and Obstructive Sleep Apnea: The Epworth Sleepiness Scale
Section snippets
SLEEPINESS RECONSIDERED
The word sleepiness did not appear in the index of medical text books in the past. It is a concept that is still not widely used or clearly understood. There is confusion about what different people consider sleepiness to be and this has led some to use a circular argument to define sleepiness as that which is measured by one or other tests of sleepiness.
Some consider sleepiness to be a state involving feelings of tiredness or fatigue and the subjective changes that immediately precede sleep
A FOUR-PROCESS MODEL OF SLEEP AND WAKEFULNESS
A model of sleep and wakefulness must involve at least four processes for it to explain sleepiness. The details and ramifications of such a theory are beyond the scope of this report and will be described elsewhere. However, the essence of this model is that two sleep processes contribute to the total sleep drive and two wake processes contribute to the total wake drive. What I call the primary sleep drive is due to an intrinsic CNS process that varies with a circadian rhythm having a peak at
RATIONALE OF THE ESS
The ESS is a simple questionnaire that asks the subject to rate on a scale of 0 to 3 the chances that, as part of his “usual way of life in recent times,” he would doze in each of eight different situations.4 The situations were chosen on a priori grounds to vary in their soporific nature from highly soporifi c (“lying down to rest in the afternoon when circumstances permit”) to much less soporific (“sitting and talking to someone”).5 The ESS score is the sum of eight item scores and can range
METHODS
All subjects were fee-paying patients, investigated in the Sleep Disorders Unit at Epworth Hospital, a private hospital in Melbourne, Australia. They answered the ESS without assistance at the end of their first interview. They had one night's diagnostic polysomnography with sleep staging by EEG (electrode positions C4-A1), left and right EOG, submental EMG, measurements of nasal and oral airflow, thoracic and abdominal respiratory movements, arterial oxygen saturation measured by a pulse
Analysis of Variance
The results for primary snorers and the three categories of OSAS are summarized in Table 1. There were many more patients with primary snoring or “mild” OSAS than there were with “moderate” or “severe” OSAS. Between these groups there were significant overall differences in the patients' ages, BMI, RDI, minimum SaO2, and ESS scores. However, posthoc Scheffé tests did not reveal significant differences in age between any paired groups. The BMI was significantly lower for primary snorers than for
DISCUSSION
The results provide further evidence that ESS scores give valid measurements of ASP or daytime sleepiness as defined herein. The scores increased linearly with the severity of OSAS and distinguished primary snorers from patients with OSAS, even of mild degree. In the patients with OSAS, it was the frequency of apneas and hypopneas that bore the closest relationship to their ASP as measured by ESS scores. The degree of hypoxemia, measured by the minimum SaO2 overnight, was significantly
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Manuscript received February 5; revision accepted June 2.