What is the best measure of daytime sleepiness in adults with heart failure

Sleep disordered breathing (SDB) is extremely common in adults with heart failure (HF). In a recent prevalence study, 61% of HF patients had central or obstructive sleep apnea (MacDonald, Fang, Pittman, White, & Malhotra, 2008). Yet, referral for polysomnography is not routine, even in specialty HF settings (Riegel, Moser, Powell, Rector, & Havranek, 2006). Identification and treatment of SDB is imperative because an untreated sleep disorder amplifies the strain on the heart with increased respiratory effort, hypoxia, and sympathetic stimulation (Valdivia-Arenas, Powers, & Khayat, 2009). Persons with SDB are at increased risk for myocardial infarction, stroke, arrhythmia, and probably early mortality (Selim, Won, & Yaggi, 2010). Treatment of SDB may improve ejection fraction and outcomes for patients with systolic HF and decrease pulmonary artery pressures for those with preserved ejection fraction (Oldenburg et al., 2009). In the general population, people with SDB are typically sleepy during the day and a complaint of excessive daytime sleepiness is the symptom that stimulates a referral for testing. Yet, daytime sleepiness is rarely pronounced in HF patients with SDB (Javaheri, et al, 1998; Kaneko et al., 2003; Sin et al., 1999). Therefore, a sensitive, accurate, and easy-to-administer screening method is needed to identify patients who may have SDB in order to more quickly and efficiently address this dangerous comorbidity. The purpose of this study was to test the sensitivity and specificity of three simple screening measures of daytime sleepiness in adults with HF. Daytime sleepiness is defined as difficulty maintaining a desired level of wakefulness (Young, 2004). Individuals with excessive daytime sleepiness experience a feeling of being drowsy with a tendency to actually fall asleep or nap, known as sleep propensity (Laffont et al., 2002). There is general agreement that sleep propensity reflects the interaction of homeostatic mechanisms and circadian rhythm (Achermann, 2004; Achermann & Borbely, 1994). The homeostatic mechanisms regulate sleep intensity, while the circadian clock regulates the timing of sleep. Others have proposed that sleep propensity depends on the relative strength of the sleep and wake drives (Edgar, Dement, & Fuller, 1993). The sleep drive is the mechanism that tells us of the need for sleep while the wake drive reflects chronobiological and environmental factors such as physical activity, which stimulate arousal (Cluydts, De Valck, Verstraeten, & Theys, 2002). In adults with SDB, sleep intensity and continuity are interrupted by repeated episodes when breathing stops or is markedly reduced, which cause nighttime arousals and daytime sleep propensity (Banno & Kryger, 2007). Measures of Sleepiness A variety of measures are available for the assessment of excessive daytime sleepiness. Cluydts et al (2002) divided these measures into behavioral measures, subjective rating scales, and electrophysiological measures. Behavioral measures include performance tests such as the psychomotor vigilance task (PVT). The PVT is a sensitive measure of lapses in attention in response to daytime sleepiness (Dinges et al., 1997). Subjective rating scales reflect acute or global sleepiness. Two examples of subjective rating scales are the Stanford Sleepiness Scale (SSS) and the Epworth Sleepiness Scale (ESS) (Hoddes, Zarcone, Smythe, Phillips, & Dement, 1973). The SSS measures sleepiness at a particular moment while the ESS measures global or typical sleepiness (Johns, 1992). Electrophysiological measures include tests such as polysomnography, pupillometry, and the Multiple Sleep Latency Test. When sensitivity and specificity of the Multiple Sleep Latency Test, the maintenance of wakefulness test, and the ESS were compared, the ESS was the most discriminating test (Johns, 2000). These measures vary greatly in cost, equipment, and training requirements. As the goal of this study was to identify a measure of daytime sleepiness that is sensitive to daytime dysfunction in adults with HF, self-report measures that can be used to screen patients in an office setting were preferentially tested. We assessed the ability of three such measures of daytime sleepiness to identify sufficiently poor sleep quality to cause complaints of daytime dysfunction in adults with HF. The measure tested in addition to the ESS and the SSS was a simple Likert item assessing sleepiness. Poor sleep quality was measured with the daytime dysfunction subscale of the Pittsburgh Sleep Quality Index (Buysse, 1989). A measure of daytime dysfunction due to poor sleep was chosen because others have shown that SDB can cause daytime dysfunction even in those individuals who do not perceive being sleepy (Verstraeten & Cluydts, 2004).