Neuropsychological changes and treatment compliance in older adults with sleep apnea

Abstract

Introduction: Apnea is a common disorder in older adults and has been shown to affect cognition. Some studies suggest that treatment for apnea improves certain cognitive deficits, but few studies have examined the relationship between compliance and cognitive improvement. We designed a study to answer the following questions about sleep apnea, cognition and treatment in older adults: (1) Which neuropsychological (NP) variables are differentially associated with measures of sleep fragmentation and oxygen desaturation? (2) Does compliant use of CPAP provide a cognitive advantage over noncompliant use? (3) Does NP performance at baseline predict compliance at 3 months? Method: Twelve participants were recruited for the study. All had polysomnographically defined sleep apnea with an RDI of 10 or greater. All were also at least 55 years of age, had no other diagnosable sleep disorder and had no previous treatment for sleep apnea syndrome (SAS). Participants were administered a full NP battery before and 3 months after treatment with CPAP. RDI at baseline was associated with delayed verbal recall, while oxygen desaturation was associated with both delayed recall and constructional abilities. Compliant use of CPAP at 3 months was associated with greater improvements in attention, psychomotor speed, executive functioning and nonverbal delayed recall. Finally, attention measures predicted compliance at 3 months suggesting that those who were least vigilant at baseline were more likely to comply with treatment. Discussion: Results are discussed in terms of the relevance to targeting special populations for compliance interventions, the ways that treatment may specifically affect older adults and the possible dose–response relationship of CPAP.

Introduction

More than 50% of individuals over the age of 65 complain of poor sleep, and it has been suggested that 24–42% of older adults suffer from sleep apnea syndrome (SAS) [1], [2]. SAS is characterized by repeated complete or partial obstructions of the upper airway during sleep (apneas and hypopneas, respectively). The sleep fragmentation and oxygen desaturation associated with SAS may be risk factors for cognitive dysfunction, especially in older adults [3], [4], [5], [6], [7]. Neuropsychologically, SAS has been associated with difficulties in most cognitive domains including memory, attention, vigilance, executive functioning, psychomotor speed, visuospatial abilities and constructional abilities, and cognitive dysfunction may be directly related to severity in middle-aged patients [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. Some studies, however, have failed to relate SAS to cognitive dysfunction, even in older adults. Studies by Phillips et al. [12], [13], [14] suggest no cognitive differences between participants with a Respiratory Disturbance Index (RDI) of five or more and those with less than five events per hour of sleep. The authors of this manuscript, however, focussed solely on mild SAS, with the apneic group averaging only 13.6 episodes per hour of sleep. The only published negative study examining cognitive functioning in older adult apneics at higher RDI levels suffered from a small sample size (five participants with RDI>18), which may have masked underlying effects [15]. Other researchers have found more severe levels of SAS to be related to deficits in attention and psychomotor speed in the elderly [16]. Neuropsychological (NP) research in SAS is typically limited by the choice of cognitive domains studied and the reliability and validity of those tests. Furthermore, conclusions from these studies may be limited by a lack of exploration of treatment effects on cognitive functioning in this population.

At present, the treatment of choice for sleep apnea is nasal continuous positive airway pressure (CPAP). When used properly, CPAP has been shown to diminish sleep fragmentation, increase nocturnal oxygen saturation and improve cognitive functioning [17]. Although there have been many abstracts presented at research conferences, there are few published studies utilizing full NP batteries to examine cognitive changes after CPAP treatment in apneics [18], [19]. One such study examined the effects of only two nights of CPAP use in severe, middle-aged apneics. The authors found that scores on tests of verbal learning correlated with reported levels of alertness after treatment, with participants who reported improvement in alertness after CPAP scoring better on follow-up auditory verbal learning and memory. They also reported that improvements in certain cognitive domains like sustained attention were dependent on the level of oxygen loss (hypoxemia) accompanying the apnea, suggesting that hypoxemic patients were less likely to improve cognitively than nonhypoxemic patients. These results begin to address the effects of treatment and the relative contribution of sleep fragmentation and oxygen deprivation to cognitive dysfunction in apnea. It should be noted, however, that participants were not followed longer to assess and delayed changes in functioning with sustained treatment. The second study examined the effects of 4 weeks of treatment in a randomized, placebo-controlled, crossover trial of CPAP in mild SAS [18]. CPAP treatment was on associated with improvements in two tests of attention, the Paced Auditory Serial Attention Test (PASAT) and Digit Symbol subtest of the Wechsler Adult Intelligence Scale-Revised (WAIS-R). However, it should be noted that patients used CPAP on average only 2.8±2.1 h per night when on active treatment. Improvements at this obviously subthreshold level of treatment are impressive, but the degree to which more complaint treatment would affect cognition remains unclear. Compliance has been addressed in only one study to date. Kribbs et al. [20] found that skipping one night of CPAP markedly impaired cognitive functioning the following day. Yet, after a single night of therapy, select cognitive functions improved, suggesting that the relationship between improve cognitive functioning and apnea after treatment may depend directly on compliance. Compliance must, therefore, play a primary role in any investigation of the cognitive effects of CPAP use, as treatment is often not well tolerated and compliance rates are as low as 28% in some reports [8], [21], [22], [23], [24]. The present study attempts to address this by investigating the association between CPAP compliance and cognitive improvement in older adults with SAS. Three primary questions were addressed: (1) Which NP variables are differentially associated with measures of sleep fragmentation and oxygen desaturation? (2) Does compliant use provide an advantage to improving cognition over noncompliant use? (3) Does NP performance and/or self-reported daytime sleepiness at baseline predict compliance at 3 months?