Objective: Mild obstructive sleep apnea (OSA) affects an estimated 7.4 million Americans with another 1.8 million with moderate or severe OSA. Persons suffering from OSA have twice the prevalence of hypertension, three times as much coronary heart disease, and four times as many strokes compared with national disease data. Recently, the criteria for the diagnosis of OSA were recommended as the presence of physiological impairment (an indicator of disease severity, (RDI > 5) as well as excessive daytime sleepiness (EDS). However, the extent that sleepiness is characteristic of this population and the primary method of measuring daytime sleepiness remains unresolved. It is also unclear how many of those fail to manifest either objective or subjective sleepiness. The purpose of this study was to describe the profile of sleepiness in subjects with OSA and to examine the consistency and proportion of subjects that exhibit sleepiness either objectively, subjectively, both or neither.
Design: Secondary analyses of data from a collaborative multisite project that prospectively studied patients with OSA to determine the relationship between use of nasal continuous positive airway pressure (CPAP) therapy, severity of OSA, and daytime functional behavior.
Population: Sleep clinic patients (N=180)
Sample: Only subjects with complete data for the measures of subjective and objective sleepiness were included in these analyses (n=107). Inclusion criteria were ages 20 - 60, clinical judgment of EDS, RDI > /=20, and a candidate for CPAP. Exclusion criteria included any co-existing sleep disorder or co-morbidity that would affect daily functioning. The sample was 92% male, 87% white, mean age=45.9 (SD=8.9), mean BMI=38.7 (SD=8.6), mean RDI=66 (SD=31).
Setting: Five outpatient sleep disorders centers throughout the US and in Canada.
Years: 1996 – 2001
Concepts: Three distinct concepts of daytime sleepiness guided the study. The first was subjective or self-appraised sleepiness measured by the Epworth Sleepiness Scale [ESS] (Johns, 2000). The second was physiologic sleepiness as measured by the objective test, the Multiple Sleep Latency Test [MSLT] (Carskadon, 1994). The third was the ability to sustain attention, an aspect of objective sleepiness, as indicated by responses to the Psychomotor Vigilance Task [PVT] (Dinges, 1992).
Methods: Subjects completed a battery of outcome measures that included the ESS, MSLT, and PVT at baseline and again following 3 mo. of CPAP use. Sleepy subjects were differentiated from non-sleepy subjects for each of those measures based on the following cut-points for sleepiness: ESS >/=11; MSLT < 10; and presence of >/=2 performance lapses/10 min. on the PVT.
Findings: The sample had a mean ESS=14.1 (SD 4.8), mean MSLT sleep latency=7.3 (SD 5.2), and a mean PVT total lapses=4.5 (SD 8.4), indicating the presence of pathological sleepiness. Although the MSLT measured objective sleepiness in 68% of these subjects with OSA, only 57 % also manifested subjective sleepiness by the ESS, 29% had either subjective or objective sleepiness, and 14 % had neither subjective sleepiness by ESS nor objective sleepiness by MSLT. When the PVT was used to measure sustained attention, only 39% of the subjects with EDS on this objective measure. also showed subjective sleepiness by the ESS. Forty percent had discordance having either subjective sleepiness on the ESS or decreased sustained attention on the PVT; and 21% had neither subjective sleepiness nor objective sleepiness as measured by the PVT. Only 29% of the sample exhibiting sleepiness on all three measures while 13% did not measure high scores on any of the tests. There was a low correlation between the ESS and either the MSLT r=0.26, p=0.0009) or the PVT (r=0.19, p=0.04); there was no significant correlation between PVT and the MSLT (r=0.06).
Conclusion: In this sample of subjects with OSA there was considerable discordance between the manifestations of sleepiness by these often-used assessments. The lack of substantial linear association among these sleepiness probes reflects an unknown combination of true between patient differences in the nature of sleepiness consequences resulting from sleep apnea; true variance due to non-apnea related factors; and measurement error.
Implications: As approximately 1 out of 10 patients did not manifest sleepiness, there are issues regarding the utility of sleepiness assessment for use in treatment decisions, who should be prescribed CPAP therapy, and the assessment of CPAP efficacy. Nurses need to be aware that of the possibility that persons with OSA may or may not have subjective or objective symptoms of EDS.
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