Associations Between Amyloid Burden, Hypoxemia, Sleep Architecture, and Cognition in Obstructive Sleep Apnea

Obstructive sleep apnea and memory impairments: Clinical characterization, treatment strategies, and mechanisms

Obstructive sleep apnea (OSA), is associated with dysfunction in the cardiovascular, metabolic and neurological systems. However, the relationship between OSA and memory impairment, intervention effects, and underlying pathways are not well understood. This review summarizes recent advances in the clinical characterization, treatment strategies, and mechanisms of OSA-induced memory impairments. OSA patients may exhibit significant memory declines, including impairments in working memory from visual and verbal sources. The underlying mechanisms behind OSA-related memory impairment are complex and multifactorial with poorly understood aspects that require further investigation. Neuroinflammation, oxidative stress, neuronal damage, synaptic plasticity, and blood-brain barrier dysfunction, as observed under exposures to intermittent hypoxia and sleep fragmentation are likely contributors to learning and memory dysfunction. Continuous positive airway pressure treatment can provide remarkable relief from memory impairment in OSA patients. Other treatments are emerging but need to be rigorously evaluated for cognitive improvement. Clinically, reliable and objective diagnostic tools are necessary for accurate diagnosis and clinical characterization of cognitive impairments in OSA patients. The complex links between gut-brain axis, epigenetic landscape, genetic susceptibility, and OSA-induced memory impairments suggest new directions for research. Characterization of clinical phenotypic clusters can facilitate advances in precision medicine to predict and treat OSA-related memory deficits.

Is β- amyloid a reliable marker for assessing neurocognitive functions in middle-aged OSAS patients??

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is a condition defined by recurrent episodes of airflow cessation or significant reduction during sleep, resulting in fragmented sleep patterns and intermittent hypoxemia. These physiological disturbances are known to contribute to cognitive deficits, including impairments in attention, memory, and overall cognitive function. In parallel, amyloid beta (β-Amyloid, Aβ) has gained prominence as a crucial biomarker in Alzheimer's disease pathogenesis, raising interest in its potential role in the early detection of neurocognitive dysfunction. This study aims to explore the association between plasma Aβ levels, neurocognitive performance, and polysomnographic parameters in middle-aged patients diagnosed with OSAS.

METHODS

This prospective, cross-sectional study was conducted over a four-month period in a sleep disorders clinic. Patients who diagnosed as OSA in polysomnographic evaluation with no pre-existing neurocognitive conditions and possessed at least a primary school education were included. The study participants were evaluated using Montreal Cognitive Assessment (MoCA) test and Epworth Sleepiness Scale (ESS). Morning fasting blood samples were collected to measure plasma total Aβ levels.

RESULTS

A total of 126 individuals (mean age: 54.7 ± 7.5 years; 53 females, 42%) participated in the study. Based on their apnea-hypopnea index (AHI), patients were categorized into two groups: Group 1 (AHI < 15, 23.8% mild OSA) and Group 2 (AHI ≥ 15, moderate-severe OSA, 76.2%). The mean MoCA scores were 25 ± 7 in Group 1 and 24 ± 6 in Group 2. Following multivariable adjustment, reduced sleep duration, lower mean nocturnal oxygen saturation, and prolonged time with SpO2 below 90% (T90%) were significantly correlated with lower MoCA scores. Serum Aβ concentrations were notably elevated in patients with severe OSAS, exhibiting a negative correlation with MoCA scores and slow wave sleep stage. Additionally, serum Aβ levels showed a direct correlation with both AHI and oxygen desaturation index (ODI), while an inverse correlation was found with minimum oxygen saturation.

CONCLUSION

Neurocognitive impairment was common in OSAS patients. Elevated serum Aβ levels were found to be directly associated with OSA severity, and OSA-related hypoxemia was linked to diminished cognitive function.

Sex differences in sleep apnea and Alzheimer's Disease: role of cerebrovascular dysfunction

Obstructive sleep apnea (OSA) significantly impacts cardiovascular health in post-menopausal females. Given that cardiovascular and cerebrovascular diseases are tightly linked, OSA-mediated impacts on cerebrovascular function and Alzheimer's Disease (AD) risk are also likely more manifest in females. This review will: summarize sex differences in cerebrovascular function, review the vascular hypothesis of AD, characterize sex differences in the OSA phenotype and implications for cerebrovascular control, and highlight OSA-mediated AD risk.

Systematic bibliometric and visualized analysis of research hotspots and trends in obstructive sleep apnea neuroimaging

BACKGROUND

Obstructive sleep apnea (OSA) patients exhibit neurological symptoms, driving research in sleep medicine and clinical neurology. Neurologists and radiologists explore detection methods to identify unique neural features associated with OSA in the atypical nervous system. Neuroimaging research in OSA encompasses studying the structural, functional connectivity (FC), and neurometabolic aspects of the brain. Limited resources and OSA's heterogeneity pose challenges to effective neuroimaging research. This study aims to conduct a bibliometric analysis of OSA neuroimaging research to identify key trends and emerging themes.

METHODS

This research utilizes various techniques, including functional MRI, structural MRI, diffusion tensor imaging, magnetic resonance spectroscopy, and electroencephalography, among others. Publications from 1993 to 2023 were retrieved from Web of Science on neuroimaging. Analysis tools included Bibliometric.com, CiteSpace, VOSviewer, and R4.3.2.

RESULTS

A total of 714 papers were published in 47 countries, with 651 articles, 55 reviews, and 8 meeting abstracts. The USA led in publications, with the University of California System contributing most, primarily in "Sleep" journal. The study identified 2916 authors, with Macey PM having the highest publication count. Recent years highlighted burst keywords such as network, classification, sleep staging, FC, and brain activity. Analysis of keyword clusters revealed "electroencephalography" with the longest temporal duration.

CONCLUSIONS

Neuroimaging in OSA research has gained increased attention. Incorporating behavioral sleep medicine insights could enhance understanding of OSA's impact on brain function and behavior. This study aims to assist researchers in identifying potential collaborators, institutions, and key themes, providing a comprehensive perspective on OSA neuroimaging research and related sleep disorders.

Decoupling of global signal and cerebrospinal fluid inflow is associated with cognitive decline in patients with obstructive sleep apnoea

OBJECTIVES

The role of cortical glymphatic dysfunction in the cognitive impairment of the obstructive sleep apnea (OSA) requires further study. To compare the coupling between the resting-state blood-oxygen-level-dependent (BOLD) signals and cerebrospinal fluid (CSF) signals (BOLD-CSF coupling), a proxy for the cortical glymphatic function, across patients with differing severities of OSA and relate them with disease characteristics and treatment.

METHODS

A total of 153 participants (89 OSA patients and 64 matched controls) were prospectively included. OSA patients were classified into three groups (mild, moderate, and severe OSA) according to the apnea-hypopnea index (AHI). All participants underwent neuropsychological assessment and BOLD functional magnetic resonance imaging. BOLD-CSF coupling was assessed at global and regional levels and correlated with the cognitive impairment. Alterations in BOLD-CSF coupling and cognitive performance after treatment were assessed in OSA patients.

RESULT

Severe OSA patients exhibited weaker global and anterior BOLD-CSF coupling than mild OSA patients, moderate OSA patients, and healthy controls (HCs). Furthermore, the weaker global and anterior BOLD-CSF coupling was associated with poor cognitive performance in all OSA patients. Notably, cognitive performance and cortical glymphatic function improved significantly in patients with OSA after treatment.

CONCLUSION

Our findings demonstrated cortical glymphatic dysfunction in severe OSA patients, especially in the anterior region of the brain. Cortical glymphatic dysfunction may underlie the cognitive impairment in OSA patients, both of which would improve in OSA patients after treatment.

Prevalence and Misperception: Exploring the Gap Between Objective and Subjective Assessment of Sleep Apnea in a Population at Increased Risk for Dementia

Background: Aging is a well-established independent risk factor for both cognitive impairment and sleep disorders, including obstructive sleep apnea (OSA), a modifiable yet underrecognized condition. OSA has been implicated in biological mechanisms contributing to Alzheimer's disease, including amyloid-β accumulation, tau phosphorylation, and neuroinflammation. This underscores the need to optimize OSA diagnosis in individuals with an increased risk of dementia. Methods: This cross-sectional observational study enrolled adults aged 60-85 years with a CAIDE dementia risk score ≥6. Subjective sleep was evaluated using validated questionnaires (Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, and the Oviedo Sleep Questionnaire), while objective sleep data were obtained through a single-night peripheral arterial tonometry (PAT)-based wearable device, complemented by a 7-day sleep diary. Participants also completed the STOP-BANG and Berlin questionnaires, with clinically relevant findings communicated to participants. Results: Among 322 participants (48.8% women; mean age 71.4 ± 6.4 years), moderate-to-severe OSA (apnea-hypopnea index [AHI] ≥ 15) was identified in 48.49%, despite the absence of prior diagnoses. Subjective screening tools frequently underestimated OSA severity compared to objective assessments. While no significant sex-based differences were noted, higher AHI values correlated strongly with increased body mass index and elevated dementia risk scores. Conclusions: A marked discrepancy between subjective and objective sleep measurements complicates the accurate diagnosis and management of most sleep disorders, including OSA. Sleep disorders remain significantly underdiagnosed in individuals at increased risk for dementia. Integrating wearable technologies and structured tools such as sleep diaries into routine assessments can enhance diagnostic precision, enabling timely interventions for these modifiable risk factors of dementia.

Exploring the relationship between melanopsin gene variants, sleep, and markers of brain health

INTRODUCTION

Melanopsin is a photopigment with roles in mediating sleep and circadian-related processes, which are often disrupted in Alzheimer's disease (AD). Melanopsin also impacts cognition and synaptogenesis. This study investigated the associations between melanopsin genetic variants, sleep, and markers of brain health.

METHODS

Linear regression analyses examined the relationship of single-nucleotide polymorphisms (SNPs) within the melanopsin gene (OPN4), with cortical amyloid beta (Aβ), cognition, brain volumes, and self-reported sleep traits in cognitively unimpaired older adults. Further analyses assessed whether sleep traits x OPN4 SNP interactions were associated with markers of brain health.

RESULTS

OPN4 SNPs rs2355009 and rs3740334 were associated with attention and processing speed and ventricular volume and language, respectively. Furthermore, rs3740334 and rs1079610 showed significant interactions with sleep traits in association with language.

DISCUSSION

This study shows associations of OPN4 genetic variants with markers of brain health, and suggests that these variants interact with sleep to exacerbate cognitive effects.

Highlights

The relationships between melanopsin gene (OPN4) variants and markers of brain health were examined cross-sectionally in cognitively unimpaired older individuals.Variation within OPN4is associated with differences in cognition and ventricular volume.rs2355009 and rs3740334 show small-moderate associations with differences in attention and processing speed. Further to this, rs2355009 and rs3740334 were associated with ventricular volumes and language performance, respectively.The interactions between rs3740334 and rs1079610 and sleep traits also showed small-moderate associations with differences in language performance.

Analysis of sleep apnea research with a special focus on the use of positron emission tomography as a study tool

The quality of sleep plays a significant role in determining human well-being, and studying sleep and sleep disorders using various methods can aid in the prevention and treatment of diseases. Positron emission tomography (PET) is a noninvasive and highly sensitive medical imaging technique that has been widely adopted in the clinic. This review article provides data on research activity related to sleep and sleep apnea and discusses the use of PET in investigating sleep apnea and other sleep disorders. We conducted a statistical analysis of the number of original research articles published on sleep and sleep apnea between 1965 and 2021 and found that there has been a dramatic increase in publications since 1990. The distribution of contributing countries and regions has also undergone significant changes. Although there is an extensive body of literature on sleep research (256,399 original research articles during 1965-2021), PET has only been used in 54 of these published studies, indicating a largely untapped area of research. Nonetheless, PET is a useful tool for identifying connections between sleep disorders and pathological changes in various diseases, including neurological, metabolic, and cardiovascular disorders, as well as cancer. To facilitate the broader use of PET in sleep apnea research, further studies are needed in both clinical and preclinical settings.

Suboptimal self-reported sleep efficiency and duration are associated with faster accumulation of brain amyloid beta in cognitively unimpaired older adults

INTRODUCTION

This study investigated whether self-reported sleep quality is associated with brain amyloid beta (Aβ) accumulation.

METHODS

Linear mixed effect model analyses were conducted for 189 cognitively unimpaired (CU) older adults (mean ± standard deviation 74.0 ± 6.2; 53.2% female), with baseline self-reported sleep data, and positron emission tomography-determined brain Aβ measured over a minimum of three time points (range 33.3-72.7 months). Analyses included random slopes and intercepts, interaction for apolipoprotein E (APOE) ε4 allele status, and time, adjusting for sex and baseline age.

RESULTS

Sleep duration <6 hours, in APOE ε4 carriers, and sleep efficiency <65%, in the whole sample and APOE ε4 non-carriers, is associated with faster accumulation of brain Aβ.

DISCUSSION

These findings suggest a role for self-reported suboptimal sleep efficiency and duration in the accumulation of Alzheimer's disease (AD) neuropathology in CU individuals. Additionally, poor sleep efficiency represents a potential route via which individuals at lower genetic risk may progress to preclinical AD.

Highlights

In cognitively unimpaired older adults self-report sleep is associated with brain amyloid beta (Aβ) accumulation.Across sleep characteristics, this relationship differs by apolipoprotein E (APOE) genotype.Sleep duration <6 hours is associated with faster brain Aβ accumulation in APOE ε4 carriers.Sleep efficiency < 65% is associated with faster brain Aβ accumulation in APOE ε4 non-carriers.Personalized sleep interventions should be studied for potential to slow Aβ accumulation.

Obstructive Sleep Apnea and Alzheimer's Disease Pathology: Is Sleep Architecture the Missing Key?

Impairments of the sleep architecture due to disrupted sleep in individuals with obstructive sleep apnea (OSA) may result in reduced slow wave sleep (SWS), intermittent hypoxemia, and excessive day time sleepiness- all factors that have been shown to impact Alzheimer's disease (AD) risk. In this commentary, we comment on the work by Cavuoto and colleagues in which they examine the associations between nocturnal hypoxemia or sleep disruptions (during SWS) and amyloid-β burden in individuals with OSA. We review the findings in the context of other similar studies and highlight the strengths and weaknesses of these published studies. We note the importance of examining these relationships longitudinally with a large sample size, including considering sleep health disparities, vascular components, and multiple cognitive domain tests.