Cognitive impairment in obstructive sleep apnea

Obstructive sleep apnea and quality of life in elderly patients with a pacemaker

Objective:

To evaluate quality of life in elderly patients with obstructive sleep apnea (OSA) who have a pacemaker.

Methods:

This was a cross-sectional study involving elderly patients (≥ 60 years of age) with a pacemaker. The dependent variable was quality of life, as evaluated with the Medical Outcomes Study 36-item Short-Form Health Survey (SF-36). Sociodemographic and clinical parameters, including anxiety and depression (Hospital Anxiety and Depression Scale score), as well as the presence of OSA (defined as an apnea-hypopnea index ≥ 15 events/h), were analyzed as independent variables. Patients with cognitive/neurological deficits or decompensated heart failure were excluded.

Results:

We evaluated 72 patients, 17 (23.6%) of whom presented OSA. Of those 17 patients, 9 (52.9%) were male. The mean age was 72.3 ± 9.3 years. A diagnosis of OSA was not associated with gender (p = 0.132), age (p = 0.294), or body mass index (p = 0.790). There were no differences between the patients with OSA and those without, in terms of the SF-36 domain scores. Fourteen patients (19.4%) presented moderate or severe anxiety. Of those 14 patients, only 3 (21.4%) had OSA (p = 0.89 vs. no OSA). Twelve patients (16.6%) had moderate or severe depression. Of those 12 patients, only 2 (16.6%) had OSA (p = 0.73 vs. no OSA).

Conclusions:

In elderly patients with a pacemaker, OSA was not found to be associated with quality of life or with symptoms of anxiety or depression.

Hypoglossal nerve stimulation in three adults with down syndrome and severe obstructive sleep apnea

We present three adults with Down syndrome and obstructive sleep apnea (OSA) treated with hypoglossal nerve stimulation. The average age of these three males was 37.3 years. All patients had severe OSA on polysomnography. Postimplantation titration sleep studies exhibited residual OSA according to average total apnea-hypopnea index (AHI), but there were significant reductions (86%-100%) in the titrated AHI at the ideal device setting. Morbidity of the surgery was low, and there was excellent device adherence, with an average of 57.3 hours/week. All patients reported subjective improvements in symptoms, and one patient experienced improved blood sugar control. Laryngoscope, 129:E402-E406, 2019.

The role of NF-κB-mediated JNK pathway in cognitive impairment in a rat model of sleep apnea

Background

The aim of this study is to determine the role of nuclear factor kappa B (NF-κB)-mediated c-Jun N-terminal kinase (JNK) pathway in cognitive impairment induced by chronic intermittent hypoxia (CIH).

Methods

Ninety-six male Sprague-Dawley rats were randomly divided into 8 groups: sham group, sustained hypoxia (SH) group, CIH group, CIH + melatonin group, CIH + vitamin E group, CIH + DMSO group, CIH + BAY 11-7082 group and CIH + normal saline (NS) group. Rats were exposed to normoxia, CIH (21% O₂ for 60 s and 10% O₂ for 60 s, cyclically repeated for 10 h/day) or SH (10% O₂ for 10 h/day) for 14 days. Afterwards, Morris water maze test was conducted, and serum and hippocampus tissues were subjected to molecular biological and biochemical analyses.

Results

Compared with the Sham and SH group, oxidative stress was induced by CIH in rat hippocampus with the high level of malondialdehyde (MDA) and 8-iso-PGF2α and the low level of superoxide dismutase (SOD) and glutathione (GSH). Activated NF-κB and its downstream products including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) were highly expressed in CIH rats. These changes were attenuated by pretreatment of the rats with melatonin and vitamin E. CIH also resulted in hippocampus neuron apoptosis with increased caspase 3 level, dUIP nick end labeling (TUNEL)-positive neurons number and cognitive impairment verified by prolonged latency and shortened time in the target quadrant in Morris water maze test. JNK and its downstream transcriptional factors including c-Jun, activating transcription factor 2 (ATF2), and JunD were all significantly phosphorylated in CIH rats. However, pretreatment of NF-κB inhibitor BAY 11-7082 inhibited the activation of NF-κB under CIH condition and also significantly reduced the phosphorylation of JNK as well as c-Jun, ATF2, and JunD. Moreover, hippocampus neuron apoptosis and cognitive impairment were significantly improved with the pretreatment of BAY 11-7082 in rats subjected to CIH.

Conclusions

These findings suggest that NF-κB-mediated JNK pathway is at least partially implicated in CIH-induced hippocampus neuron apoptosis and cognitive impairment. Inhibition of NF-κB activation provided a therapeutic potential for cognitive impairment in sleep apnea (SA).

Sleep Disturbance in Mild Cognitive Impairment and Association With Cognitive Functioning. A Case-Control Study

Objectives: The aims of the current study are to (1) report the frequency of specific sleep disturbance symptoms in Mild Cognitive Impairment (MCI) and cognitive healthy older persons; (2) examine whether overall poor sleep and specific sleep disturbance symptoms are more common in persons with MCI compared to cognitive healthy older controls and; (3) examine the association between sleep disturbances and performance in general and specific cognitive domains in persons with MCI and separately in cognitive healthy older persons.

Methods: Data were collected at the Fondazione Ospedale San Camillo Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Venice, Italy as part of the European VPH-DARE@IT project. We included 69 persons with MCI (mean age 75.7; SD = 7.7) and 72 sex-matched cognitively healthy controls (mean age 71.8; SD = 7.0). Participants underwent extensive neuropsychological assessment and evaluation of subjective sleep performance with the Sleep Continuity in Alzheimer’s Disease Scale(SCADS).

Results: A fifth of MCI patients (21.7%, n = 15) had poor sleep compared to 15.3% (n = 11) of cognitively healthy controls. MCI patients had a 3.2 higher odds of having poor sleep compared to cognitively healthy controls after adjustment for age, education, sex, and general cognitive functioning (Odds Ratio (OR) = 3.2; 95% Confidence Interval (CI) = 1.1–9.2). Persons who reported waking up twice or more during the night had higher odds of being MCI compared to those who never wake or wake only once (OR = 2.6; 95% CI = 1.1–6.1). In MCI patients, poor sleep was associated with better general cognitive functioning and short-term working memory, whereas in cognitive healthy older persons poor sleep was associated with impairment in episodic memory performance and executive functioning.

Discussion: Our results confirm previous studies showing that sleep disturbances are common in MCI, and this may be due to an ongoing neurodegenerative process rather than a symptom of cognitive impairment. Future research with objective sleep measurements are needed in MCI as well as interventions to improve sleep with the aim of preventing cognitive decline.

Androgens modulate chronic intermittent hypoxia effects on brain and behavior

Sleep apnea is associated with testosterone dysregulation as well as increased risk of developing neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). A rodent model of the hypoxemic events of sleep apnea, chronic intermittent hypoxia (CIH), has been previously documented to impair cognitive function and elevate oxidative stress in male rats, while simultaneously decreasing testosterone. Therefore, androgens may modulate neuronal function under CIH. To investigate the role of androgens during CIH, male rats were assigned to one of four hormone groups: 1) gonadally intact, 2) gonadectomized (GDX), 3) GDX + testosterone (T) supplemented, or 4) GDX + dihydrotestosterone (DHT) supplemented. Each group was exposed to either normal room air or CIH exposure for one week, followed by memory and motor task assessments. Brain regions associated with AD and PD (entorhinal cortex, dorsal hippocampus, and substantia nigra) were examined for oxidative stress and inflammatory markers, key characteristics of AD and PD. Gonadally intact rats exhibited elevated oxidative stress due to CIH, but no significant memory and motor impairments. GDX increased memory impairments, regardless of CIH exposure. T preserved memory function and prevented detrimental CIH-induced changes. In contrast, DHT was not protective, as evidenced by exacerbated oxidative stress under CIH. Further, CIH induced significant spatial memory impairment in rats administered DHT. These results indicate androgens can have both neuroprotective and detrimental effects under CIH, which may have clinical relevance for men with untreated sleep apnea.

Reversible Dementias

As the worldwide prevalence of dementia increases, there is a greater and more urgent need for all health care providers to understand how to evaluate and manage cognitive impairment. Many people presenting with a dementing illness have one or more reversible underlying conditions that worsen prognosis and, if treated, can improve cognitive function. This article reviews the major potentially reversible dementias, including the basic workup and management of each condition.

A high risk of sleep apnea is associated with less postoperative cognitive dysfunction after intravenous anesthesia: results of an observational pilot study

Background

The obstructive sleep apnea syndrome (OSAS) is characterized by temporary cerebral hypoxia which can cause cognitive dysfunction. On the other hand, hypoxia induced neurocognitive deficits are detectable after general anesthesia.

The objective of this study was to evaluate the impact of a high risk of OSAS on the postoperative cognitive dysfunction after intravenous anesthesia.

Methods

In this single center trial between June 2012 and June 2013 43 patients aged 55 to 80 years with an estimated hospital stay of at least 3 days undergoing surgery were enrolled. Patients were screened for a high risk of OSAS using the STOP-BANG test. The cognitive function was assessed using a neuropsychological test battery, including the DemTect test for cognitive impairment and the RMBT test for memory, the day before surgery and within 36 h after extubation.

Results

Twenty-two of the 43 analyzed patients were identified as patients with a high risk of OSAS. Preoperatively, OSAS patients showed a significant worse performance only for the DemTect (p = 0.0043). However, when comparing pre- and postoperative test results, the OSAS patients did not show a significant loss in any test but significantly improved in RMBT test, whereas the control group showed a significant worse performance in three of eight tests. In five tests, we found a significant difference between the two groups with respect to the change from pre- to postoperative cognitive function.

Conclusion

Patients with a high risk of OSAS showed a less impairment of memory function and work memory performance after intravenous anesthesia. This might be explained by a beneficial effect of intrinsic hypoxic preconditioning in these patients.

Detection of mild cognitive impairment in middle-aged and older adults with obstructive sleep apnoea

Obstructive sleep apnoea increases the risk for mild cognitive impairment and dementia. The present study aimed to characterise the ability of two cognitive screening tests, the Mini-Mental State Examination and the Montreal Cognitive Assessment, to detect mild cognitive impairment in adults aged 55–85 years with and without obstructive sleep apnoea.

We included 42 subjects with mild and 67 subjects with moderate-to-severe obstructive sleep apnoea. We compared them to 22 control subjects. Mild cognitive impairment was diagnosed by a comprehensive neuropsychological assessment. We used receiver operating characteristic curves to assess the ability of the two screening tests to detect mild cognitive impairment.

The two screening tests showed similar discriminative ability in control subjects. However, among the mild and the moderate-to-severe obstructive sleep apnoea groups, the Mini-Mental State Examination was not able to correctly identify subjects with mild cognitive impairment. The Montreal Cognitive Assessment's discriminant ability was acceptable in both sleep apnoea groups and was comparable to what was observed in controls.

The Mini-Mental State Examination should not be used to screen for cognitive impairment in patients with obstructive sleep apnoea. The Montreal Cognitive Assessment could be used in clinical settings. However, clinicians should refer patients for neuropsychological assessment when neurodegenerative processes are suspected.

False memories in obstructive sleep apnoea syndrome: evidence from the divided attention paradigm at encoding or retrieval

Patients with obstructive sleep apnoea syndrome (OSAS) exhibit impaired retrieval of item-specific information, increasing their propensity to generate false recognitions. The present study investigated the effect of OSAS on false recognition, using a divided-attention paradigm to examine whether reducing the availability of attentional resources during encoding or retrieval in healthy participants mimics the effect of OSAS. We tested four groups of participants, using the Deese - Roediger - McDermott paradigm: patients with OSAS and controls, either under full attention or under divided attention at encoding or retrieval. Results showed that divided attention at retrieval, but not at encoding, mimicked the effects of OSAS on memory performance, as controls in this group exhibited a higher level of false recognition than those under full attention, but a similar level of correct recognition. Our results suggest that the greater susceptibility of patients with OSAS to false recognition may be due to a limited availability of attentional resources, which may specifically disrupt retrieval processes.

Obstructive sleep apnea syndrome and olfactory perception: An OERP study

Obstructive Sleep Apnea Syndrome (OSA) is characterized by snoring associated with repeated apnea and/or obstructive hypopnea. The nasal airways of OSA patients, measured via acoustic rhinometry, could be significantly narrower than healthy subjects and this reduced nasal structure can impair olfactory function. The relationship between nasal structure and olfactory function, assessed via behavioral test results, indicates that there is a high prevalence of nasal airflow problems. Based on these assumptions, the purpose of this study was to carry out an assessment of olfactory perception in OSA patients through the Chemosensory Event-Related Potentials (CSERP), investigating the N1 component and the Late Positive Component (LPC). Twelve OSA patients, non-smokers, were recruited in the Pulmonary Rehabilitation Unit, scored with the Epworth Sleepiness Scales, after Polygraphic Recording, Apnea Hypopnea Index and Body Mass Index evaluation. The control group consisted of twelve healthy controls, non-smokers, recruited as volunteers. Subjects, during an EEG recording, performed an oddball olfactory recognition task based on two scents: rose and eucalyptus. Main results highlighted differences in N1 and LPC between OSA and controls. OSA patients presented faster N1 latencies and greater amplitude. The same trend was found in LPC, where OSA showed decreased latency and increased amplitude during rose stimulation, in the right inferior frontal cortex. and faster latencies in left centroparietal cortex OERP results can suggest an impairment in endogenous components. This result could be the consequence of the exogenous perceptual difficulty highlighted in N1 component. The increased arousal could also be related to the respiratory activity involved during the olfactory task.

Electrophysiological and neuropsychological outcomes of severe obstructive sleep apnea: effects of hypoxemia on cognitive performance

Obstructive sleep apnea syndrome (OSAS) is a sleep disorder characterized with upper airway obstructions. Some studies showed cognitive and electrophysiological changes in patients with OSAS; however, contradictory results were also reported. The purpose of the present study was twofold: (1) to investigate cognitive changes in severe OSAS patients by using neuropsychological tests and electrophysiological methods together, (2) to investigate influence of hypoxemia levels on cognition. Fifty-four severe OSAS patients and 34 age-, gender- and education matched healthy subjects were participated. OSAS patients were further divided into two subgroups according to minimum oxygen saturation levels. All participants underwent a detailed neuropsychological test battery. A classical visual oddball task was used to elicit ERP P300 and mean P300 amplitudes were measured from F_z, C_z and P_z electrode sites. OSAS patients showed reduced mean P300 amplitudes up to 43-51% on all electrode sites compared to healthy controls. Subgroup analysis revealed significant differences in neuropsychological test scores between healthy controls and high hypoxemia OSAS group, as well as between low and high hypoxemia groups. Moreover, both low and high hypoxemia OSAS groups had lower P300 amplitudes compared with healthy controls. P300 amplitudes showed a gradual decline in parallel with increasing hypoxemia severity; however, the difference between high and low hypoxemia OSAS groups did not reach significance. Moderate correlations were found between sleep parameters, neuropsychological test scores and P300 amplitudes. These results suggest that electrophysiological measures could be better indicators of cognitive changes than neuropsychological tests in OSAS, particularly in mildly affected patients.

Change in Cognition and Other Non-Motor Symptoms With Obstructive Sleep Apnea Treatment in Parkinson Disease

STUDY OBJECTIVES

Parkinson disease (PD) non-motor symptoms are associated with sleep disorders and impair quality of life. Our objective was to assess the effect of obstructive sleep apnea (OSA) treatment using continuous positive airway pressure (CPAP) on PD non-motor symptoms.

METHODS

In this prospective observational study, 67 patients with idiopathic PD underwent polysomnography. Those with moderate-severe OSA were offered CPAP therapy. Subjects were divided into those without OSA (OSA-), and those with OSA (OSA+). Analyses were conducted for 6 and 12 months' follow-up data. At 6 months, those who had used CPAP at home for at least 1 month were considered CPAP users (OSA+CPAP+), whereas those who did not try it, or declined further treatment following a short trial were considered non-users (OSA+CPAP-). For the 12-month analysis, only those still actively using CPAP at 12 months were included in the OSA+CPAP+ group. Non-motor symptom measurements were: Epworth Sleepiness Scale, Montreal Cognitive Assessment (MoCA), Unified Parkinson's Disease Rating Scale part 1 (UPDRS1), Parkinson's Disease Sleep Scale (PDSS), Fatigue Severity Scale, Apathy Scale, Beck Depression Inventory, and Hospital Anxiety and Depression Scale (HADS).

RESULTS

Sixty-five participants were re-assessed at least once. At 6 months, 30 participants were categorized as OSA+CPAP+, 11 OSA+CPAP-, and 18 OSA-. At 12 months, 21 were categorized as OSA+CPAP+, 21 OSA+CPAP-, and 17 OSA-. The UPDRS1 and PDSS improved from baseline in OSA+CPAP+ at 6 months (-2.7, standard deviation [SD] 4.0, P = .001, and 7.9, SD 19.0, P = .03, respectively) and 12 months (-4.1, SD 5.4, P = .002, and 11.4, SD 24.4, P = .04, respectively), but not in other groups. The MoCA and HADS-A improved in OSA+CPAP+ at 12 months (1.7, SD 3.5, P = .04, and -2.1, SD 3.8, P = .02, respectively). The MoCA improved in those with low baseline MoCA and those with REM sleep behavior disorder. Mean CPAP use in users at 12 months was 3 hours 36 minutes per night.

CONCLUSIONS

CPAP treatment of OSA in PD is associated with improved overall non-motor symptoms, sleep quality, anxiety, and global cognitive function over a 12-month period.

Sex differences in sleep apnea and comorbid neurodegenerative diseases

Sleep apnea is a disorder, which increasingly affects people worldwide. Whether the associated hypoxic events during sleep are central or obstructive in origin, the end result is excessive daytime sleepiness and an increased risk for several comorbidities, such as cardiovascular and neurodegenerative disorders. Sleep apnea is diagnosed more frequently in men than women, suggesting a role of sex hormones in the pathology of the disease. Furthermore, there are sex differences in the development and progression of comorbid diseases associated with sleep apnea. Therefore, treatment of sleep apnea may be clinically relevant for prevention of subsequent sex-specific comorbid disorders. While the impact sleep apnea has on cardiovascular events has been the subject of many research studies, the role of sleep apnea in neurodegeneration is less established. Here we review known risk factors for sleep apnea and the implications of the observed sex differences in this disease. We also summarize the evidence and mechanisms for how sleep apnea may contribute to the onset of neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease.

Chronic intermittent hypoxia induces oxidative stress and inflammation in brain regions associated with early-stage neurodegeneration

Sleep apnea is a common comorbidity of neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Previous studies have shown an association between elevated oxidative stress and inflammation with severe sleep apnea. Elevated oxidative stress and inflammation are also hallmarks of neurodegenerative diseases. We show increased oxidative stress and inflammation in a manner consistent with early stages of neurodegenerative disease in an animal model of mild sleep apnea. Male rats were exposed to 7 days chronic intermittent hypoxia (CIH) for 8 h/day during the light period. Following CIH, plasma was collected and tested for circulating oxidative stress and inflammatory markers associated with proinflammatory M1 or anti-inflammatory M2 profiles. Tissue punches from brain regions associated with different stages of neurodegenerative diseases (early stage: substantia nigra and entorhinal cortex; intermediate: hippocampus; late stage: rostral ventrolateral medulla and solitary tract nucleus) were also assayed for inflammatory markers. A subset of the samples was examined for 8-hydroxydeoxyguanosine (8-OHdG) expression, a marker of oxidative stress-induced DNA damage. Our results showed increased circulating oxidative stress and inflammation. Furthermore, brain regions associated with early-stage (but not late-stage) AD and PD expressed oxidative stress and inflammatory profiles consistent with reported observations in preclinical neurodegenerative disease populations. These results suggest mild CIH induces key features that are characteristic of early-stage neurodegenerative diseases and may be an effective model to investigate mechanisms contributing to oxidative stress and inflammation in those brain regions.

Sleep, Cognitive impairment, and Alzheimer's disease: A Systematic Review and Meta-Analysis

Study Objectives

Mounting evidence implicates disturbed sleep or lack of sleep as one of the risk factors for Alzheimer's disease (AD), but the extent of the risk is uncertain. We conducted a broad systematic review and meta-analysis to quantify the effect of sleep problems/disorders on cognitive impairment and AD.

Methods

Original published literature assessing any association of sleep problems or disorders with cognitive impairment or AD was identified by searching PubMed, Embase, Web of Science, and the Cochrane library. Effect estimates of individual studies were pooled and relative risks (RR) and 95% confidence intervals (CI) were calculated using random effects models. We also estimated the population attributable risk.

Results

Twenty-seven observational studies (n = 69216 participants) that provided 52 RR estimates were included in the meta-analysis. Individuals with sleep problems had a 1.55 (95% CI: 1.25-1.93), 1.65 (95% CI: 1.45-1.86), and 3.78 (95% CI: 2.27-6.30) times higher risk of AD, cognitive impairment, and preclinical AD than individuals without sleep problems, respectively. The overall meta-analysis revealed that individuals with sleep problems had a 1.68 (95% CI: 1.51-1.87) times higher risk for the combined outcome of cognitive impairment and/or AD. Approximately 15% of AD in the population may be attributed to sleep problems.

Conclusion

This meta-analysis confirmed the association between sleep and cognitive impairment or AD and, for the first time, consolidated the evidence to provide an "average" magnitude of effect. As sleep problems are of a growing concern in the population, these findings are of interest for potential prevention of AD.

Omega-3 Index and Obstructive Sleep Apnea: A Cross-Sectional Study

STUDY OBJECTIVES

Erythrocyte levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Omega-3 Index) were previously found to be associated with obstructive sleep apnea (OSA) at very low levels (< 5.0%) in only one epidemiologic study. OSA has comorbidities, such as arterial hypertension, heart failure, or major depression, also associated with a low Omega-3 Index. These comorbidities can be improved by increasing intake of EPA and DHA, and thus the Omega-3 Index, preferably to its target range of 8% to 11%. Symptoms of OSA might improve by increasing the Omega-3 Index, but more research is needed.

METHODS

In our sleep laboratory, 357 participants with OSA were recruited, and data from 315 participants were evaluated. Three categories of OSA (none/ mild, moderate, severe) were defined based on apnea-hypopnea index. Anthropometrics and lifestyle characteristics (smoking, alcohol, fish intake, omega-3 supplementation) were recorded. Erythrocyte fatty acid compositions were assessed with the HS-Omega-3 Index methodology.

RESULTS

The mean Omega-3 Index in all 3 categories of OSA was 5.7%, and no association with OSA was found. There were more male participants with severe OSA (79.7%, P = .042) than females, and participants with severe OSA had a significantly higher body mass index (32.11 ± 6.39 kg/m², P = .009) than participants with mild or moderate OSA. Lifestyle characteristics were not significantly different.

CONCLUSIONS

In contrast to our hypothesis, an Omega-3 Index of 5.7% was not associated with OSA severity. Previously, an Omega-3 Index < 5.0% was associated. Although our results suggest aiming for an Omega-3 Index > 5.7% in an intervention trial with EPA and DHA in OSA, comorbidities of OSA suggest a target range of 8% to 11%.

Neuropsychological Function in Patients With Acute Tetraplegia and Sleep Disordered Breathing

Study objectives

To investigate the relationship between apnea severity and neuropsychological function in patients with acute-onset tetraplegia and sleep disordered breathing.

Methods

Polysomnography and neuropsychological testing were performed on 104 participants (age M = 45.60, SD = 16.38; 10 female) across 11 international sites, 2 months postinjury (M = 60.70 days, SD = 39.48). Neuropsychological tests assessed attention, information processing, executive function, memory, learning, mood, and quality of life.

Results

More severe sleep apnea was associated with poorer attention, information processing, and immediate recall. Deficits did not extend to memory. Higher preinjury intelligence and being younger reduced the associations with sleep disordered breathing; however, these protective factors were insufficient to counter the damage to attention, immediate recall, and information processing associated with sleep disordered breathing.

Conclusions

These data suggest that new spinal cord injury may function as a model of "acute sleep apnea" and that more widespread sleep apnea-related deficits, including memory, may only be seen with longer exposure to apnea. These findings have important implications for functioning and skill acquisition during rehabilitation and, as such, highlight the importance of sleep health following tetraplegia.

Reviewing the relationship between OSA and cognition: Where do we go from here?

Obstructive sleep apnoea (OSA) is a disorder of breathing during sleep resulting in temporary reduction in cerebral oxygenation and sleep disruption. A growing body of research reveals a relatively consistent pattern of deficits in cognition, particularly in attention, episodic memory, and executive function, which are partially remediated by treatment. This is where the consensus ends. Despite a number of competing explanations regarding how OSA affects cognition, reliable evidence is hard to find, which may relate to the many, common conditions co-morbid with OSA or to the methodological challenges in this field. This paper reviews the evidence for cognitive impairment in OSA, the proposed models of cognitive harm, the impact of co-morbidities and the many methodological and theoretical challenges of exploring the effect of OSA on cognition. To overcome some of these challenges, we end by proposing a number of future directions for the field, including suggesting some core design elements for future studies.

BDNF Val66Met Polymorphism Interacts with Sleep Consolidation to Predict Ability to Create New Declarative Memories

It is hypothesized that a fundamental function of sleep is to restore an individual's day-to-day ability to learn and to constantly adapt to a changing environment through brain plasticity. Brain-derived neurotrophic factor (BDNF) is among the key regulators that shape brain plasticity. However, advancing age and carrying the BDNF Met allele were both identified as factors that potentially reduce BDNF secretion, brain plasticity, and memory. Here, we investigated the moderating role of BDNF polymorphism on sleep and next-morning learning ability in 107 nondemented individuals who were between 55 and 84 years of age. All subjects were tested with 1 night of in-laboratory polysomnography followed by a cognitive evaluation the next morning. We found that in subjects carrying the BDNF Val66Val polymorphism, consolidated sleep was associated with significantly better performance on hippocampus-dependent episodic memory tasks the next morning (β-values from 0.290 to 0.434, p ≤ 0.01). In subjects carrying at least one copy of the BDNF Met allele, a more consolidated sleep was not associated with better memory performance in most memory tests (β-values from -0.309 to -0.392, p values from 0.06 to 0.15). Strikingly, increased sleep consolidation was associated with poorer performance in learning a short story presented verbally in Met allele carriers (β = -0.585, p = 0.005). This study provides new evidence regarding the interacting roles of consolidated sleep and BDNF polymorphism in the ability to learn and stresses the importance of considering BDNF polymorphism when studying how sleep affects cognition.

SIGNIFICANCE STATEMENT

Individuals with the BDNF Val/Val (valine allele) polymorphism showed better memory performance after a night of consolidated sleep. However, we observed that middle-aged and older individuals who are carriers of the BDNF Met allele displayed no positive association between sleep quality and their ability to learn the next morning. This interaction between sleep and BDNF polymorphism was more salient for hippocampus-dependent tasks than for other cognitive tasks. Our results support the hypothesis that reduced activity-dependent secretion of BDNF impairs the benefits of sleep on synaptic plasticity and next-day memory. Our work advances the field by revealing new evidence of a clear genetic heterogeneity in how sleep consolidation contributes to the ability to learn.

Interaction of obstructive sleep apnoea and cognitive impairment with slow gait speed in middle-aged and older adults

Objective

to investigate whether slow gait speed is associated with cognitive impairment and further whether the association is modified by obstructive sleep apnoea (OSA).

Methods

in total, 2,222 adults aged 49-80 years, free from dementia, stroke and head injury were asked to walk a 4-m course at fast and usual gait speeds. The time taken to walk was measured. All participants completed the Korean Mini-Mental State Examination, which was validated in the Korean language, to assess cognitive function. Additionally, the participants completed a polysomnography test to ascertain OSA (defined as an apnoea-hypopnoea index ≥15). Multivariable linear regression models were utilised to test the associations.

Results

time taken to walk 4 m showed significant inverse associations with cognitive scores (P value = 0.001 at fast gait speed and P = 0.002 at usual gait speed). Furthermore, a significant interaction according to OSA on the association between time to walk and cognitive impairment was found (P value for interaction = 0.003 at fast gait speed and P value for interaction = 0.007 at usual gait speed).

Conclusion

we found that the inverse association between the time taken to walk 4 m and a cognitive score became significantly stronger, if an individual had OSA.

Recognition and treatment of sleep-disordered breathing: an important component of chronic disease management

Sleep-disordered breathing (SDB) is a highly prevalent condition, and is associated with many debilitating chronic diseases. The role of untreated obstructive sleep apnea (OSA) in arterial hypertension has been recognized in international guidelines. Treatment with continuous positive airway pressure (CPAP) is associated with clinically-relevant reductions in blood pressure. In heart failure (HF), SDB is associated with worse prognosis and increased mortality. Major HF guidelines recommend that patients should be treated for sleep apnea to improve their HF status. Severe OSA increases the risk of arrhythmias, including atrial fibrillation, influences risk management in stroke, and is highly prevalent in patients with type 2 diabetes. Effective treatment with CPAP improves the success of antiarrhythmic interventions, improves outcomes in stroke and reduces hyperglycemia in diabetes. Patients with coronary artery disease also have a high prevalence of SDB, which is independently associated with worse outcomes. The role of CPAP for secondary cardiovascular prevention remains to be determined. Data from large, well-conducted clinical trials have shown that noninvasive ventilation, targeted to markedly reduce hypercapnia, significantly improves survival and reduces readmission in stable hypercapnic chronic obstructive pulmonary disease. The association of SDB with chronic diseases contributes to the high healthcare costs incurred by SDB patients. SDB also has an important negative impact on quality of life, which is reversed by CPAP treatment. The high prevalence of SDB, and its association with diseases that cause significant morbidity and mortality, suggest that the diagnosis and management of SDB is an important therapeutic goal. First, adherent CPAP treatment significantly improves the quality of life of all patients with SDB; second, it eliminates the negative impact of untreated SDB on any associated chronic diseases; and third, it significantly reduces the increased costs of all hospital and medical services directly associated with untreated SDB. In short, the recognition and treatment of SDB is vital for the continued health and wellbeing of individual patients with SDB.

Auditory behavior and auditory temporal resolution in children with sleep-disordered breathing

OBJECTIVE

Intermittent hypoxia caused by obstructive sleep apnea syndrome (OSAS) may lead to damage in brain areas associated to auditory processing. The aim of this study was to compare children with OSAS or primary snoring (PS) to children without sleep-disordered breathing with regard to their performance on the Gaps-in-Noise (GIN) test and the Scale of Auditory Behaviors (SAB) questionnaire.

METHODS

Thirty-seven children (6-12 years old) were submitted to sleep anamnesis and in-lab night-long polysomnography. Three groups were organized according to clinical criteria: OSAS group (13 children), PS group (13 children), and control group (11 children). They were submitted to the GIN test and parents answered SAB questionnaire. The Kruskal-Wallis statistical test was used to compare the groups; p < 0.05 was considered statistically significant.

RESULTS

The OSAS group performed significantly worse than PS (p = 0.011) and Control (p = 0.029) groups on gap detection percentage, while PS and Control groups showed no significant differences. The three groups showed similar gap detection thresholds. Regarding SAB questionnaire, PS group had significantly worse scores when compared to Control (p = 0.011), but not to OSAS (p = 0.101) groups. No statistical difference between OSAS and Control groups were found.

CONCLUSION

Children with OSAS showed worse performance on GIN test in comparison to children with PS and children without sleep-disordered breathing. PS negatively affected auditory behavior in children. These findings suggest that sleep-disordered breathing may lead to auditory behavior impairment.

Reduced cognitive function in patients with Parkinson disease and obstructive sleep apnea

OBJECTIVE

To assess the association between obstructive sleep apnea (OSA) and nonmotor symptoms (NMS), including cognitive dysfunction, in patients with Parkinson disease (PD).

METHODS

Patients with idiopathic PD, recruited from a movement disorder clinic, underwent overnight polysomnography. OSA was defined as an apnea-hypopnea index (AHI) ≥15/h. PD severity was assessed using the Hoehn & Yahr (H&Y) scale and the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). NMS were assessed using the Montreal Cognitive Assessment (MoCA), Epworth Sleepiness Scale (ESS), Fatigue Severity Scale, Apathy Scale, Beck Depression Inventory, Hospital Depression and Anxiety Scale, and PD sleep Scale.

RESULTS

Sixty-seven patients (61.2% male), mean age 64.4 (SD 9.9) years and motor MDS-UPDRS 21.9 (12.6) using levodopa equivalent dose (LED) 752.4 (714.6) mg/d, were studied. OSA occurred in 47 patients (61.6%, mean AHI 27.1/h, SD 20.2/h), and NMS in 57 patients (85%). ESS and MoCA were associated with the AHI (ESS β = 0.0670, p = 0.031; MoCA β = -0.0520, p = 0.043, adjusted for age, sex, body mass index, LED, and H&Y). ESS was associated with respiratory arousals (β = 0.1015, p = 0.011) and intermittent hypoxemia (β = 0.1470, p = 0.006). MoCA was negatively associated with respiratory arousals (β = -0.0596, p = 0.049) but not intermittent hypoxemia.

CONCLUSIONS

OSA is associated with sleepiness and cognitive dysfunction in PD, suggesting that OSA may be a reversible contributor to these NMS. Further studies will be required to evaluate whether OSA treatment can improve excessive sleepiness and cognitive dysfunction in PD.

Intake of tryptophan-enriched whey protein acutely enhances recall of positive loaded words in patients with multiple sclerosis

BACKGROUND & AIMS

Multiple sclerosis (MS) has physiological and/or immunological characteristics that diminish serotonin metabolism, a neurotransmitter associated with affective and cognitive functions. The aim was examine the acute and dose-dependent effects of a dietary tryptophan (TRP) enrichment on affective and cognitive functions in MS patients. We hypothesized that increased dietary availability of the amino acid TRP enhances serotonin concentrations and improves neuropsychological functions.

METHODS

In a double-blind, placebo-controlled, crossover study, MS patients with (n = 15) and without (n = 17) depressed mood ingested a whey protein mixture with 4 different amounts of TRP. Mood states, total plasma TRP and plasma TRP/ΣLNAA ratio were measured during each test session and cognitive tasks were conducted three hours after dietary intake.

RESULTS

A fast, transient and dose-dependent increase of total plasma TRP and TRP/ΣLNAA ratio was found. Ratings of negative mood decreased over time, independent of the TRP dose. Relative to whey-only, immediate word recall and delayed recognition improved after ingestion of the lowest added TRP dose and was mainly due to better recollection for positive loaded words. Executive functions were not affected by a difference in TRP availability.

CONCLUSIONS

A moderate addition of TRP to whey protein enhances memory processes without improving the mood state in MS. ccmo-registration number is NL32316.096.10.

Spontaneous improvement in both obstructive sleep apnea and cognitive impairment after stroke

BACKGROUND

Knowledge available about the relationship between obstructive sleep apnea (OSA) and cognitive impairment after stroke is limited. The evolution of OSA and cognitive performance after stroke is not sufficiently described.

METHODS

We prospectively enrolled and examined acute stroke patients without previously diagnosed OSA. The following information was collected: (1) demographics, (2) sleep cardio-respiratory polygraphy (PG) at 72 h, day seven, month three, and month 12 after stroke, (3) post-stroke functional disability tests at entry and at months three and 12, and (4) cognition (attention and orientation, memory, verbal fluency, language, and visual-spatial abilities) using the revised Addenbrooke's Cognitive Examination (ACE-R) at months three and 12.

RESULTS

Of 68 patients completing the study, OSA was diagnosed in 42 (61.8%) patients. The mean apnea/hypopnea index (AHI) at study entry of 21.0 ± 13.7 spontaneously declined to 11.6 ± 11.2 at month 12 in the OSA group (p < 0.0005). The total ACE-R score was significantly reduced at months three (p = 0.005) and 12 (p = 0.004) in the OSA group. Poorer performance on the subtests of memory at months 3 (p = 0.039) and 12 (p = 0.040) and verbal fluency at months 3 (p < 0.005) and 12 (p < 0.005) were observed in the OSA group compared to non-OSA group. Visual-spatial abilities in both the OSA (p = 0.001) and non-OSA (p = 0.046) groups and the total ACE-R score in the OSA (p = 0.005) and non-OSA (p = 0.002) groups improved.

CONCLUSIONS

A high prevalence of OSA and cognitive decline were present in patients after an acute stroke. Spontaneous improvements in both OSA and cognitive impairment were observed.

Increased Mortality in Relation to Insomnia and Obstructive Sleep Apnea in Korean Patients Studied with Nocturnal Polysomnography

STUDY OBJECTIVES

To elucidate the links between the two most prevalent sleep disorders, insomnia and obstructive sleep apnea (OSA), and mortality.

METHODS

We studied 4,225 subjects who were referred to the Center for Sleep and Chronobiology, Seoul National University Hospital, from January 1994 to December 2008. We divided the subjects into five groups: mild OSA (5 ≤ AHI < 15), moderate OSA (15 ≤ AHI < 30), severe OSA (AHI ≥ 30), insomnia, and a no-sleep-disorder group consisting of subjects without sleep disorders. Standardized mortality ratio (SMR), hazard ratio, and the survival rates of the five groups were calculated and evaluated.

RESULTS

The SMR of all-cause mortality was significantly higher in the severe OSA group than in the general population (1.52, 95% CI 1.23-1.85, p < 0.05). The SMR of cardiovascular mortality increased progressively with the severity of OSA (no-sleep-disorder: 0.09, mild: 0.40, moderate: 0.52, severe: 1.79, p < 0.05). Statistical analyses of the hazard ratios indicated that severe OSA is a risk factor for all-cause mortality (HR 3.50, 95% CI 1.03-11.91, p = 0.045) and cardiovascular mortality (HR 17.16, 95% CI 2.29-128.83, p = 0.006). Cardiovascular mortality was also significantly elevated in the insomnia group (HR 8.11, 95% CI 1.03-63.58, p = 0.046).

CONCLUSIONS

Severe OSA was associated with increased all-cause mortality and cardiovascular mortality compared to the no-sleep-disorder group. Insomnia was associated with increased cardiovascular mortality compared to the no-sleep-disorder group.

Cognitive consequences of sleep deprivation, shiftwork, and heat exposure for underground miners

Sleep deprivation, abnormal sleep patterns arising from working rotating shifts, and exposure to high ambient temperatures contribute to physical and cognitive dysfunction. We examined the effects of these on 19 (41.5 ± 5.1 years) male underground miners. Data were collected for 28 to 30 consecutive days such that the participants experienced their full rotating shift schedule, including days off. Objective measures of sleep quality (actigraphy), attentional capacity (psychomotor vigilance task), core body temperature (visceral pill), executive function (BRIEF-A) and subjective measures of fatigue (Karolinska and Epworth Sleepiness scales) were obtained over the 28-30 day period. Non-parametric analyses (χ(2), Wilcoxen Signed ranks) were used to determine differences between shift types and days off. Z-tests were used to compare sample data to population norms. These revealed that the participants experienced poor quality of sleep relative to age-matched norms irrespective of the shift being worked or if the participant was on a scheduled day off [30-39 year olds: z = -14.62, p < 0.001; 40-49 year olds: z = -4.44, p < 0.001]. Participants when working day shift experienced less sleep prior to beginning work compared to their days off or night shift; however, no differences in total sleep time between when participants worked day or night shifts were observed [χ(2) (2, n = 18) = 13.44, p < 0.01]. When measured subjectively, the only time participants reported excessive sleepiness was after a night shift. Objective measures of attentional capacity showed best performance at the beginning of night shifts in contrast to any other time that the task was completed; however, performance degraded dramatically over the course of the night shift [χ(2) (2, n = 12) = 6.50, p < 0.05]. We show that underground miners reported for work sleep deprived. The cognitive consequences of this poor sleep were most pronounced during night shift when their attentional capacity declined rapidly over the course of the night shift.

Fragmentation of Rapid Eye Movement and Nonrapid Eye Movement Sleep without Total Sleep Loss Impairs Hippocampus-Dependent Fear Memory Consolidation

STUDY OBJECTIVES

Sleep is important for consolidation of hippocampus-dependent memories. It is hypothesized that the temporal sequence of nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep is critical for the weakening of nonadaptive memories and the subsequent transfer of memories temporarily stored in the hippocampus to more permanent memories in the neocortex. A great body of evidence supporting this hypothesis relies on behavioral, pharmacological, neural, and/or genetic manipulations that induce sleep deprivation or stage-specific sleep deprivation.

METHODS

We exploit an experimental model of circadian desynchrony in which intact animals are not deprived of any sleep stage but show fragmentation of REM and NREM sleep within nonfragmented sleep bouts. We test the hypothesis that the shortening of NREM and REM sleep durations post-training will impair memory consolidation irrespective of total sleep duration.

RESULTS

When circadian-desynchronized animals are trained in a hippocampus-dependent contextual fear-conditioning task they show normal short-term memory but impaired long-term memory consolidation. This impairment in memory consolidation is positively associated with the post-training fragmentation of REM and NREM sleep but is not significantly associated with the fragmentation of total sleep or the total amount of delta activity. We also show that the sleep stage fragmentation resulting from circadian desynchrony has no effect on hippocampus-dependent spatial memory and no effect on hippocampus-independent cued fear-conditioning memory.

CONCLUSIONS

Our findings in an intact animal model, in which sleep deprivation is not a confounding factor, support the hypothesis that the stereotypic sequence and duration of sleep stages play a specific role in long-term hippocampus-dependent fear memory consolidation.

Role of Oxidative Stress in the Neurocognitive Dysfunction of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is characterized by chronic nocturnal intermittent hypoxia and sleep fragmentations. Neurocognitive dysfunction, a significant and extraordinary complication of OSAS, influences patients' career, family, and social life and reduces quality of life to some extent. Previous researches revealed that repetitive hypoxia and reoxygenation caused mitochondria and endoplasmic reticulum dysfunction, overactivated NADPH oxidase, xanthine oxidase, and uncoupling nitric oxide synthase, induced an imbalance between prooxidants and antioxidants, and then got rise to a series of oxidative stress (OS) responses, such as protein oxidation, lipid peroxidation, and DNA oxidation along with inflammatory reaction. OS in brain could trigger neuron injury especially in the hippocampus and cerebral cortex regions. Those two regions are fairly susceptible to hypoxia and oxidative stress production which could consequently result in cognitive dysfunction. Apart from continuous positive airway pressure (CPAP), antioxidant may be a promising therapeutic method to improve partially reversible neurocognitive function. Understanding the role that OS played in the cognitive deficits is crucial for future research and therapeutic strategy development. In this paper, recent important literature concerning the relationship between oxidative stress and cognitive impairment in OSAS will be summarized and the results can provide a rewarding overview for future breakthrough in this field.

Unexpected reductions in regional cerebral perfusion during prolonged hypoxia

KEY POINTS

Cognitive performance is impaired by hypoxia despite global cerebral oxygen delivery and metabolism being maintained. Using arterial spin labelled (ASL) magnetic resonance imaging, this is the first study to show regional reductions in cerebral blood flow (CBF) in response to decreased oxygen supply (hypoxia) at 2 h that increased in area and became more pronounced at 10 h. Reductions in CBF were seen in brain regions typically associated with the 'default mode' or 'task negative' network. Regional reductions in CBF, and associated vasoconstriction, within the default mode network in hypoxia is supported by increased vasodilatation in these regions to a subsequent hypercapnic (5% CO₂ ) challenge. These results suggest an anatomical mechanism through which hypoxia may cause previously reported deficits in cognitive performance.

ABSTRACT

Hypoxia causes an increase in global cerebral blood flow, which maintains global cerebral oxygen delivery and metabolism. However, neurological deficits are abundant under hypoxic conditions. We investigated regional cerebral microvascular responses to acute (2 h) and prolonged (10 h) poikilocapnic normobaric hypoxia. We found that 2 h of hypoxia caused an expected increase in frontal cortical grey matter perfusion but unexpected perfusion decreases in regions of the brain normally associated with the 'default mode' or 'task negative' network. After 10 h in hypoxia, decreased blood flow to the major nodes of the default mode network became more pronounced and widespread. The use of a hypercapnic challenge (5% CO₂ ) confirmed that these reductions in cerebral blood flow from hypoxia were related to vasoconstriction. Our findings demonstrate steady-state deactivation of the default network under acute hypoxia, which become more pronounced over time. Moreover, these data provide a unique insight into the nuanced localized cerebrovascular response to hypoxia that is not attainable through traditional methods. The observation of reduced perfusion in the posterior cingulate and cuneal cortex, which are regions assumed to play a role in declarative and procedural memory, provides an anatomical mechanism through which hypoxia may cause deficits in working memory.

Impact of Obstructive Sleep Apnea on Neurocognitive Function and Impact of Continuous Positive Air Pressure

There is evidence that obstructive sleep apnea (OSA) can negatively impact attention, memory, learning, executive function, and overall intellectual function in adults and children. Imaging techniques, including MRI, MR diffusion tensor imaging, MR spectroscopy, and fMRI, have provided additional insight into the anatomic and functional underpinnings of OSA-related cognitive impairment. Both animal and human studies have looked to elucidate the separate effects of oxygen desaturation and sleep fragmentation on independent aspects of cognition. Data from animal models point to neuro-inflammation and oxidative stress as driving factors of cognitive impairment.

The Effect of Sleep Disordered Breathing on Olfactory Functions: Analysis by Apnea-Hypopnea Index

Objectives

One hypothesis of obstructive sleep apnea syndrome (OSAS) is that long-standing snoring vibrations and hypoxia of the nerves cause a local neuropathy in the upper airway during sleep. The aim of this study was to investigate olfactory function in subjects comprising snorers and untreated subjects with OSAS, and to correlate data with polysomnographic parameters.

Methods

Sixty-nine patients were evaluated for snoring from January 2010 to December 2013. The mild group (apneahypopnea index [AHI]<15) consisted of 19 subjects, and the moderate-severe group (AHI≥15) consisted of 50 subjects. Exclusion criteria were conductive olfactory dysfunction, previous tonsil or soft palatal surgery, central sleep apnea, and medications that are known to affect peripheral nerves. Nocturnal polysomnography and olfactory function test such as Korean version of Sniffin’s stick test I, II (KVSS I, II) were performed.

Results

There was a significant difference in body mass index, average oxygen saturation (SaO2), lowest SaO2, average snoring duration, and KVSS I, II between the two groups. AHI was related to odor threshold score, and average SaO2 was related to odor discrimination score. But, odor identification score showed no relation with AHI and average SaO2 except for age. Average SaO2 and AHI were closely related to the function of smell.

Conclusion

Hypoxia and low nasal airflow caused by OSAS may have an effect on the olfactory function. On comparison between the two groups, patients with a high AHI, especially those with OSAS, had an olfactory dysfunction. Also, low average oxygen is the main risk factor in determining the olfactory function. In people with OSAS, the possibility of olfactory dysfunction should be considered and an olfactory function test should be performed.

Association of Anterior Cingulate Glutathione with Sleep Apnea in Older Adults At-Risk for Dementia

STUDY OBJECTIVES

Sleep disordered breathing (SDB) is common in older adults and is strongly associated with cognitive decline, with increasing evidence suggesting that it may represent a risk factor for dementia. Given that SDB is characterized by intermittent episodes of hypoxemia during sleep, it is possible that cognitive impairment may relate to cerebral oxidative stress. This study aimed to examine the relationship between nocturnal markers of hypoxemia and proton magnetic resonance spectroscopy ((1)H-MRS) markers of oxidative stress within the anterior cingulate cortex (ACC) of the brain.

METHODS

Twenty-four older adults (mean age = 67.9 y) at-risk for dementia were recruited from our Healthy Brain Ageing Research Clinic. At-risk was defined as participants seeking help for assessment and/or intervention for cognitive decline, including those with subjective and/or objective cognitive complaints. This could occur in the context of prior depression or risk factors (e.g., vascular) for dementia. All participants underwent psychiatric, medical and neuropsychological assessment followed by overnight polysomnography. In addition, participants underwent (1)H-MRS to derive levels of ACC metabolite glutathione (GSH) reported as a ratio to creatine (GSH/Cr).

RESULTS

Increased levels of GSH/Cr were associated with lower oxygen desaturation (r = -0.54, P = 0.007) and more severe apnea-hypopnea index scores during rapid eye movement sleep (r = 0.42, P = 0.050). In addition, ACC GSH/Cr correlated with poorer executive functioning (i.e., response inhibition: r = -0.49, P = 0.015; set shifting: r = -0.43, P = 0.037).

CONCLUSIONS

Markers of nocturnal hypoxemia and SDB are associated with cerebral oxidative stress in older people at-risk for dementia, suggesting a potential mechanism by which SDB may contribute to brain degeneration, cognitive decline, and dementia. Further work focused on utilizing this biomarker for the early identification and treatment of this possible modifiable risk factor in older persons is now warranted.

Gait dyspraxia as a clinical marker of cognitive decline in Down syndrome: A review of theory and proposed mechanisms

Down syndrome (DS) is the most common genetic cause of intellectual disability in children. With aging, DS is associated with an increased risk for Alzheimer's disease (AD). The development of AD neuropathology in individuals with DS can result in further disturbances in cognition and behavior and may significantly exacerbate caregiver burden. Early detection may allow for appropriate preparation by caregivers. Recent literature suggests that declines in gait may serve as an early marker of AD-related cognitive disorders; however, this relationship has not been examined in individuals with DS. The theory regarding gait dyspraxia and cognitive decline in the general population is reviewed, and potential applications to the population with individuals with DS are highlighted. Challenges and benefits in the line of inquiry are discussed. In particular, it appears that gait declines in aging individuals with DS may be associated with known declines in frontoparietal gray matter, development of AD-related pathology, and white matter losses in tracts critical to motor control. These changes are also potentially related to the cognitive and functional changes often observed during the same chronological period as gait declines in adults with DS. Gait declines may be an early marker of cognitive change, related to the development of underlying AD-related pathology, in individuals with DS. Future investigations in this area may provide insight into the clinical changes associated with development of AD pathology in both the population with DS and the general population, enhancing efforts for optimal patient and caregiver support and propelling investigations regarding safety/quality of life interventions and disease-modifying interventions.

Age protects from harmful effects produced by chronic intermittent hypoxia

Obstructive sleep apnoea (OSA) affects an estimated 3–7% of the adult population, the frequency doubling at ages >60–65 years. As it evolves, OSA becomes frequently associated with cardiovascular, metabolic and neuropsychiatric pathologies defining OSA syndrome (OSAS). Exposing experimental animals to chronic intermittent hypoxia (CIH) can be used as a model of the recurrent hypoxic and O2 desaturation patterns observed in OSA patients. CIH is an important OSA event triggering associated pathologies; CIH induces carotid body (CB)-driven exaggerated sympathetic tone and overproduction of reactive oxygen species, related to the pathogenic mechanisms of associated pathologies observed in OSAS. Aiming to discover why OSAS is clinically less conspicuous in aged patients, the present study compares CIH effects in young (3–4 months) and aged (22–24 months) rats. To define potential distinctive patterns of these pathogenic mechanisms, mean arterial blood pressure as the final CIH outcome was measured. In young rats, CIH augmented CB sensory responses to hypoxia, decreased hypoxic ventilation and augmented sympathetic activity (plasma catecholamine levels and renal artery content and synthesis rate). An increased brainstem integration of CB sensory input as a trigger of sympathetic activity is suggested. CIH also caused an oxidative status decreasing aconitase/fumarase ratio and superoxide dismutase activity. In aged animals, CIH minimally affected CB responses, ventilation and sympathetic-related parameters leaving redox status unaltered. In young animals, CIH caused hypertension and in aged animals, whose baseline blood pressure was augmented, CIH did not augment it further. Plausible mechanisms of the differences and potential significance of these findings for the diagnosis and therapy of OSAS are discussed.

Tumor circulating DNA profiling in xenografted mice exposed to intermittent hypoxia

Intermittent hypoxia (IH) a hallmark characteristic of obstructive sleep apnea (OSA), is proposed as a major determinant of processes involving tumor growth, invasion and metastasis. To examine whether circulating DNA (cirDNA) in blood plasma reflects changes in tumor cells under IH conditions, we used a xenografted murine model. Mice engrafted with TC1 epithelial lung cancer cells and controls were exposed to IH or room air (RA) conditions. Plasma cirDNA amounts were significantly increased in mice exposed to IH (p<0.05). Significant associations between plasma cirDNA concentrations and tumor size, weight and invasiveness also emerged (p<0.05). Using a methylation microarray-based approach, we identified 2,094 regions showing significant differential cirDNA modifications. Systems biology analyses revealed an association with molecular pathways deregulated in cancer progression and with distal and TSS-associated transcription factor binding sites. We detected clusters of highly variable regions in chromosomes 7, 13, 14 and X, which may highlight hotspots for DNA deletions. Single locus displayed high intragroup variation, suggesting cellular heterogeneity within the tissue may be associated to cirDNA release. Thus, exposures to IH increase the shedding of cirDNA into circulation, which carries epigenetic modifications that may characterize cell populations within the tumor that preferentially release their DNA upon IH exposure.

GRK5 deficiency leads to susceptibility to intermittent hypoxia-induced cognitive impairment

Obstructive sleep apnea (OSA) leads to cognitive impairment in about 25% patients, though it remains elusive what makes one more susceptible than the other to be cognitively impaired. G protein-coupled receptor kinase-5 (GRK5) deficiency is recently found to render subjects more susceptible to cognitive impairment triggered by over-expression of Swedish mutant ß-amyloid precursor protein. This study is to determine whether GRK5 deficiency also renders subjects more susceptible to the OSA-triggered cognitive impairment. Both wild type (WT) and GRK5 knockout (KO) mice were placed in conditions absence and presence of intermittent hypoxia (IH) with 8%/21% O2 90-s cycle for 8h a day for a month, and then followed by behavioral assessments with battery of tasks. We found that the selected IH condition only induced marginally abnormal behavior (slightly elevated anxiety with most others unchanged) in the WT mice but it caused significantly more behavioral deficits in the KO mice, ranging from elevated anxiety, impaired balancing coordination, and impaired short-term spatial memory. These results suggest that GRK5 deficiency indeed makes the mice more susceptible to wide range of behavioral impairments, including cognitive impairments.

The Cognitive Effects of Obstructive Sleep Apnea: An Updated Meta-analysis

This meta-analysis set out to ascertain the cognitive function of obstructive sleep apnea (OSA) patients as measured through objective neuropsychological tests. The meta-analysis investigated the cognitive functioning of these patients prior to them receiving any treatment such as continuous positive airway pressure (CPAP). A total of 19 studies met the study inclusion criteria. Results revealed statistically significant negative effect sizes in the cognitive domains of non-verbal memory, concept formation, psychomotor speed, construction, executive functioning, perception, motor control and performance, attention, speed of processing, working and verbal memory, verbal functioning and verbal reasoning. The clinical implication of these results, the possible causal mechanisms of the cognitive impairments and the implication of these for future research were each discussed. Despite a number of important limitations, the analysis highlights the need for clinicians to comprehensively explore complaints about sleep disturbance, particularly OSA, in all clinical assessments to ensure control for this important confounder in order to ensure appropriate attribution of the source of any observed cognitive compromise.

Cognitive deficits in adults with obstructive sleep apnea compared to children and adolescents

Obstructive sleep apnea (OSA) can negatively affect the patient's physical and psychological functioning, as well as their quality of life. A major consequence of OSA is impaired cognitive functioning. Indeed, several studies have shown that OSA mainly leads to deficits in executive functions, attention, and memory. As OSA can present in all age groups, these associated cognitive deficits have been observed in adults, as well as in children and adolescents. However, these cognitive deficits may have a different clinical picture in young patients compared to adults. In this review, we analyze the most affected cognitive domains in adults and children/adolescents with OSA, as evaluated by neuropsychological and neuroimaging studies. We found that deficits in working memory, attention, or executive functions cognitive domains are found in both adults and children with OSA. However, children with OSA also show changes in behavior and phonological processing necessary for proper development. Moreover, we examine the possible OSA treatments in children and adults that can have a positive influence on cognition, and therefore, improve patients' general functioning and quality of life.

Regional Cerebral Blood Flow during Wakeful Rest in Older Subjects with Mild to Severe Obstructive Sleep Apnea

OBJECTIVES

To evaluate changes in regional cerebral blood flow (rCBF) during wakeful rest in older subjects with mild to severe obstructive sleep apnea (OSA) and healthy controls, and to identify markers of OSA severity that predict altered rCBF.

DESIGN

High-resolution (99m)Tc-HMPAO SPECT imaging during wakeful rest.

SETTING

Research sleep laboratory affiliated with a University hospital.

PARTICIPANTS

Fifty untreated OSA patients aged between 55 and 85 years, divided into mild, moderate, and severe OSA, and 20 age-matched healthy controls.

INTERVENTIONS

N/A.

MEASUREMENTS

Using statistical parametric mapping, rCBF was compared between groups and correlated with clinical, respiratory, and sleep variables.

RESULTS

Whereas no rCBF change was observed in mild and moderate groups, participants with severe OSA had reduced rCBF compared to controls in the left parietal lobules, left precentral gyrus, bilateral postcentral gyri, and right precuneus. Reduced rCBF in these regions and in areas of the bilateral frontal and left temporal cortex was associated with more hypopneas, snoring, hypoxemia, and sleepiness. Higher apnea, microarousal, and body mass indexes were correlated to increased rCBF in the basal ganglia, insula, and limbic system.

CONCLUSIONS

While older individuals with severe obstructive sleep apnea (OSA) had hypoperfusion in the sensorimotor and parietal areas, respiratory variables and subjective sleepiness were correlated with extended regions of hypoperfusion in the lateral cortex. Interestingly, OSA severity, sleep fragmentation, and obesity correlated with increased perfusion in subcortical and medial cortical regions. Anomalies with such a distribution could result in cognitive deficits and reflect impaired vascular regulation, altered neuronal integrity, and/or undergoing neurodegenerative processes.