Elsevier

Sleep Medicine

Volume 23, July 2016, Pages 99-108
Sleep Medicine

Review Article
A review of neurocognitive function and obstructive sleep apnea with or without daytime sleepiness

https://doi.org/10.1016/j.sleep.2016.02.008Get rights and content

Highlights

  • This review summarizes the relationship between neurocognitive function and excessive daytime sleepiness in OSA.

  • The literatures demonstrated more extensive and complex neurocognitive deficits in OSA patients with daytime sleepiness.

  • It is speculated that daytime sleepiness possibly relates to the domain and extent of cognitive impairments.

Abstract

Excessive daytime sleepiness (EDS) and neurocognitive dysfunction are commonly observed in patients with obstructive sleep apnea (OSA), and these daytime functional deficits can be reversed partly or completely with treatment such as continuous positive airway pressure (CPAP). Although daytime sleepiness is a possible etiology for neurocognitive dysfunction in OSA patients, EDS is not universally present in all patients with OSA. The objective of this review is to summarize the relationship between neurocognitive function and EDS in OSA, as well as the difference in cognitive domains, improvement, and application of CPAP therapy between patients with and without EDS.

Two authors independently searched PubMED/Medline, The Cochrane Library and Scopus through May 27, 2015. Sixty-five articles were included in this review. The literature demonstrated a wide range of neurocognitive deficits in OSA patients with EDS, but no more extensive and complex cognitive domains (eg, executive function) in patients without EDS. However, the current literature had very few studies with large sample sizes and extended follow-up that evaluated the effect of CPAP for OSA in patients with and without sleepiness. CPAP failed to improve cognitive dysfunction in OSA patients without EDS after short-term therapy.

The evidence suggests that daytime sleepiness possibly relates to the domain and extent of cognitive impairments in OSA, and CPAP therapy has little effect on the improvement of cognitive deficits in OSA patients without EDS. We recommend that additional prospective studies be performed to further quantify the relationship between neurocognitive function in OSA patients with and without EDS.

Introduction

Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder characterized by repetitive obstruction of the upper airway, intermittent hypoxemia, and arousal from sleep with resulting sleep fragmentation [1]. Excessive daytime sleepiness (EDS) is a significant public health problem, with an estimated prevalence as high as 18% in the general population [2]. Depression, obesity, old age, and insufficient sleep are the risk factors for EDS [3]. EDS is a common complaint in patients with OSA, with daytime dysfunction, reduced quality of life, and psychological and cognitive deficits [4], [5]. The main neurocognitive impairments with OSA typically lie in three domains: (1) attention and vigilance, (2) learning and memory, and (3) executive function [6].

Sleep fragmentation or the subsequent daytime sleepiness are among the most important etiologies related to the decline of neurocognitive function (NCF) in OSA patients. Continuous positive airway pressure (CPAP) is the most efficacious and widely used medical treatment of OSA, since it improves daytime sleepiness and neurocognitive dysfunction. However, EDS is not universally present in all patients with OSA [7], and we therefore explore the following questions. What are the differences in domains of neurocognitive impairments between OSA patients with or without EDS? Is there a similar effect of therapy on cognitive dysfunction in these two groups of patients? The objective of this review is to search the literature as related to EDS, OSA, and NCF, and to summarize NCF in OSA patients with and without EDS.

Section snippets

Methods

Two authors (JZ and MC) independently searched the international literature through May 27, 2015 for articles evaluating NCF in patients with OSA, with and without EDS. Databases searched included PubMED/Medline, The Cochrane Library, and Scopus. The inclusion criteria: studies evaluating OSA patients with and without EDS (with either objective or subjective testing), who also underwent NCF testing. An example of a search performed in PubMED/Medline is: {[(sleepiness) OR (hypersomn*)] AND

Results

A total of 65 studies were included in this review. The four main study themes for this review included: (1) 16 studies describing the relationship between OSA and daytime sleepiness (see Table 1), (2) 16 studies describing the relationship between NCF and OSA with or without daytime sleepiness (see Table 2), (3) 20 studies describing the effects of CPAP treatment on sleepiness in OSA patients (see Table 3), and (4) 13 studies describing the effects of CPAP treatment on NCF in OSA patients (see

Discussion

EDS is a common symptom which can contribute to neurocognitive impairments in OSA patients. EDS is a potentially dangerous daytime symptom, which can result in the increased risk of traffic accidents and may impose a substantial burden on quality of life. Patients with OSA present with varying degrees of sleepiness and this is often one of the first symptoms that leads them to seek medical evaluation for the problem. However, in clinical practice, some patients may have no significant EDS even

Conclusions

EDS can contribute to neurocognitive deficits as well as hypoxemia in patients with OSA. A more extensive and complex neurocognitive dysfunction has been demonstrated in OSA patients with EDS; therefore, daytime sleepiness has been hypothesized to relate to the domain and extent of cognitive impairments. CPAP therapy can significantly improve the subjective daytime sleepiness and can partly reverse neurocognitive deficits in OSA patients with EDS, but fails to improve cognitive dysfunction in

Conflicts of interest

The authors declare no conflicts of interest.

The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2016.02.008.

. ICMJE Form for Disclosure of Potential Conflicts of Interest form.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No: 81501144, 81530002 and 81328010) and the National Basic Research Program of China (No: 2015CB856406).

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