Excessive daytime sleepiness (EDS) is a frequent complaint of patients with obstructive sleep apnea syndrome (OSAS). Although patients may complain mainly of tiredness and fatigue, their sleepiness may lead to significant socioeconomic hardship and to driving and industrial accidents. In a large, unselected population of patients presenting with OSAS, we studied the relationship of specific respiratory variables (particularly respiratory disturbance index [RDI] and several indices of oxygen saturation [Sa02]), age, body mass index (BMI), and sleep disturbances monitored during nocturnal sleep to the results of the multiple sleep latency test (MSLT) administered the following day. This objective test of daytime sleepiness was introduced by the Stanford team in the late 1970s and has subsequently been used in many studies.
The MSLT is based on the simple assumption that sleepy subjects, compared with alert subjects, will fall asleep more quickly during daytime naps. Many factors, including events of the previous night, determine daytime alertness/sleepiness, and the MSLT by itself indicates only sleepiness and not necessarily its cause. Carskadon and Dement2 already have defined the conditions necessary for assessing the relationship between EDS and specific causes. Recently, guidelines on the proper administration of the MSLT also have been published. Based on previous studies, a mean MSLT score below a cutoff point of eight minutes was selected as an indication of sleepiness. Following the Van den Hoed et al findings, we also decided to consider a mean MSLT score of ^5 min as a mean sleep latency associated with subjective reports of severe daytime somnolence.
Criteria for inclusion in the study were (1) a clinical picture of OSAS with report of heavy snoring at night, (2) the absence of clinical signs or symptoms of other disorders of EDS, particularly cataplexy and other symptoms of narcolepsy, and (3) clinical complaints observed with OSAS and an RDI (an apnea/hypopnea index) >10 when tested by nocturnal polysomnography. Before analyzing data from the 50 consecutively seen patients initially monitored, we decided, several months later, to monitor 50 more patients, also consecutively seen, in order to obtain a valid sample. Our total OSAS population, 90 men and ten women, had a mean age of 50.5 ± 10.4 years, median age of 51 years, and range of 19 to 78 years.