Pathogenesis of cognitive dysfunction in patients with obstructive sleep apnea: a hypothesis with emphasis on the nucleus tractus solitarius

Mediating role of obstructive sleep apnea in altering slow-wave activity and elevating Alzheimer's disease risk: Pilot study from a northern Taiwan cohort

OBJECTIVES

Obstructive sleep apnea is associated with alterations in slow-wave activity during sleep, potentially increasing the risk of Alzheimer's disease. This study investigated the associations between obstructive sleep apnea manifestations such as respiratory events, hypoxia, arousal, slow-wave patterns, and neurochemical biomarker levels.

METHODS

Individuals with suspected obstructive sleep apnea underwent polysomnography. Sleep disorder indices, oxygen metrics, and slow-wave activity data were obtained from the polysomnography, and blood samples were taken the following morning to determine the plasma levels of total tau (T-Tau) and amyloid beta-peptide 42 (Aβ42) by using an ultrasensitive immunomagnetic reduction assay. Subsequently, the participants were categorized into groups with low and high Alzheimer's disease risk on the basis of their computed product Aβ42 × T-Tau. Intergroup differences and the associations and mediation effects between sleep-related parameters and neurochemical biomarkers were analyzed.

RESULTS

Forty-two participants were enrolled, with 21 assigned to each of the low- and high-risk groups. High-risk individuals had a higher apnea-hypopnea index, oxygen desaturation index (≥3%, ODI-3%), fraction of total sleep time with oxygen desaturation (SpO2-90% TST), and arousal index and greater peak-to-peak amplitude and slope in slow-wave activity, with a correspondingly shorter duration, than did low-risk individuals. Furthermore, indices such as the apnea-hypopnea index, ODI-3% and SpO2-90% TST were found to indirectly affect slow-wave activity, thereby raising the Aβ42 × T-Tau level.

CONCLUSIONS

Obstructive sleep apnea manifestations, such as respiratory events and hypoxia, may influence slow-wave sleep activity (functioning as intermediaries) and may be linked to elevated neurochemical biomarker levels. However, a longitudinal study is necessary to determine causal relationships among these factors.

STATEMENT OF SIGNIFICANCE

This research aims to bridge gaps in understanding how obstructive sleep apnea is associated with an elevated risk of Alzheimer's disease, providing valuable knowledge for sleep and cognitive health.

Sleep Disordered Breathing and Neurocognitive Disorders

Sleep-disordered breathing (SDB), which includes conditions such as obstructive sleep apnea (OSA) and central sleep apnea (CSA), is an independent risk factor for cerebral small vessel disease (CSVD), stroke, heart failure, arrhythmias, and other cardiovascular disorders. The influence of OSA on brain structure and cognitive function has become an essential focus in the heart-brain axis, given its potential role in developing neurocognitive abnormalities. In this review, we found that OSA plays a significant role in the cardio-neural pathway that leads to the development of cerebral small vessel disease and neurocognitive decline. Although data is still limited on this topic, understanding the critical role of OSA in the heart-brain axis could lead to the utilization of imaging modalities to simultaneously identify early signs of pathology in both organ systems based on the known OSA-driven pathological pathways that result in a disease state in both the cardiovascular and cerebrovascular systems. This narrative review aims to summarize the current link between OSA and neurocognitive disorders, cardio-neural pathophysiology, and the treatment options available for patients with OSA-related neurocognitive disorders.

Obstructive sleep apnea and attention deficits: A systematic review of magnetic resonance imaging biomarkers and neuropsychological assessments

BACKGROUND AND OBJECTIVE

Obstructive sleep apnea (OSA) is a common sleep disorder that causes intermittent hypoxia and sleep fragmentation, leading to attention impairment and other cognitive deficits. Magnetic resonance imaging (MRI) is a powerful modality that can reveal the structural and functional brain alterations associated with attention impairment in OSA patients. The objective of this systematic review is to identify and synthesize the evidence on MRI biomarkers and neuropsychological assessments of attention deficits in OSA patients.

METHODS

We searched the Scopus and PubMed databases for studies that used MRI to measure biomarkers related to attention alteration in OSA patients and reported qualitative and quantitative data on the association between MRI biomarkers and attention outcomes. We also included studies that found an association between neuropsychological assessments and MRI findings in OSA patients with attention deficits.

RESULTS

We included 19 studies that met our inclusion criteria and extracted the relevant data from each study. We categorized the studies into three groups based on the MRI modality and the cognitive domain they used: structural and diffusion tensor imaging MRI findings, functional, perfusion, and metabolic MRI findings, and neuropsychological assessment findings.

CONCLUSIONS

We found that OSA is associated with structural, functional, and metabolic brain alterations in multiple regions and networks that are involved in attention processing. Treatment with continuous positive airway pressure can partially reverse some of the brain changes and improve cognitive function in some domains and in some studies. This review suggests that MRI techniques and neuropsychological assessments can be useful tools for monitoring the progression and response to treatment of OSA patients.

Effects of continuous positive airway pressure on comprehensive geriatric assessment and cognitive function in elderly patients with obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) can lead to cognitive impairment and depression affecting memory, attention, and executive functions. Continuous positive airway pressure (CPAP) treatment seems to be able to revert changes in brain networks and neuropsychological tests correlated to OSAS. The aim of the present study was to evaluate the effects of a 6-month treatment with CPAP on functional, humoral and cognitive parameters in a cohort of elderly OSAS patients with several comorbidities. We enrolled 360 elderly patients suffering from moderate to severe OSAS and indication for nocturnal CPAP. At baseline the Comprehensive Geriatric Assessment (CGA) revealed a borderline Mini-Mental State Examination (MMSE) score that improved after 6-month treatment with CPAP (25.3 ± 1.6 vs 26 ± 1.5; p < 0.0001), as well as the Montreal Cognitive Assessment (MoCA) showed a mild improvement (24.4 ± 2.3 vs 26.2 ± 1.7; p < 0.0001). Moreover, functionality activities increased after treatment, as documented by a short physical performance battery (SPPB) (6.3 ± 1.5 vs 6.9 ± 1.4; p < 0.0001). Reduction of the Geriatric Depression Scale (GDS) from 6.0 ± 2.5 to 4.6 ± 2.2 (p < 0.0001) was also detected. Changes of homeostasis model assessment (HOMA) index, oxygen desaturation index (ODI), sleep-time spent with saturation below 90% (TC90), peripheral arterial oxyhaemoglobin saturation (SpO2), apnea-hypopnea index (AHI) and estimation of glomerular filtration rate (eGFR), contributed, respectively, to 27.9%, 9.0%, 2.8%, 2.3%, 1.7% and 0.9% of MMSE variability for a total of 44.6% of MMSE variations. GDS score changes were due to the improvement of AHI, ODI and TC90, respectively, for 19.2%, 4.9%, 4.2% of the GDS variability, cumulative responsible for 28.3% of GDS modifications. The present real-world study shows that CPAP treatment is able to improve cognition and depressive symptoms in OSAS elderly patients.

The 6-Minute Walk Test and Anthropometric Characteristics as Assessment Tools in Patients with Obstructive Sleep Apnea Syndrome. A Preliminary Report during the Pandemic

Patients with obstructive sleep apnea syndrome (OSAS) exhibit low cardio-fitness impact, attributed to fragmented sleep architecture and associated pathophysiological sequelae. The purpose of our study was to investigate fitness indicators during 6-min walk test (6MWT) and oxidative stress markers in apnea-hypopnea index (AHI) in OSAS patients stratified by severity. A total of 37 newly diagnosed patients, comorbidity-free, were divided into two groups: (Moderate OSAS (n = 12), defined as ≥ 15 AHI < 30 events per hour; Age: 50.7 ± 7.2 years, BMI: 32.5 ± 4.0 kg/m2 vs. Severe OSAS (n = 25), defined as AHΙ ≥ 30 events per hour; Age: 46.3 ± 10.4 years, BMI: 33.3 ± 7.9 kg/m2). Measurements included demographics, anthropometric characteristics, body composition, blood sampling for reactive oxygen metabolites' levels (d-ROM) and plasma antioxidant capacity (PAT), and followed by a 6MWT. AHI was significantly associated with d-ROMs levels, chest circumference in maximal inhalation and exhalation (Δchest), neck circumference, as well as 6MWT-derived indices. In conclusion, our study determines bidirectional interrelationships between OSAS severity and anthropometrics, body composition, and fitness metrics. These findings indicate that the impact of OSAS should be evaluated well beyond polysomnography-derived parameters.

Unilateral vagotomy alters astrocyte and microglial morphology in the nucleus tractus solitarii of the rat

The nucleus tractus solitarii (nTS) is the initial site of integration of sensory information from the cardiorespiratory system and contributes to reflex responses to hypoxia. Afferent fibers of the bilateral vagus nerves carry input from the heart, lungs, and other organs to the nTS where it is processed and modulated. Vagal afferents and nTS neurons are integrally associated with astrocytes and microglia that contribute to neuronal activity and influence cardiorespiratory control. We hypothesized that vagotomy would alter glial morphology and cardiorespiratory responses to hypoxia. Unilateral vagotomy (or sham surgery) was performed in rats. Prior to and seven days after surgery, baseline and hypoxic cardiorespiratory responses were monitored in conscious and anesthetized animals. The brainstem was sectioned and caudal, mid-area postrema (mid-AP), and rostral sections of the nTS were prepared for immunohistochemistry. Vagotomy increased immunoreactivity (-IR) of astrocytic glial fibrillary acidic protein (GFAP), specifically at mid-AP in the nTS. Similar results were found in the dorsal motor nucleus of the vagus (DMX). Vagotomy did not alter nTS astrocyte number, yet increased astrocyte branching and altered morphology. In addition, vagotomy both increased nTS microglia number and produced morphologic changes indicative of activation. Cardiorespiratory baseline parameters and hypoxic responses remained largely unchanged, but vagotomized animals displayed fewer augmented breaths (sighs) in response to hypoxia. Altogether, vagotomy alters nTS glial morphology, indicative of functional changes in astrocytes and microglia that may affect cardiorespiratory function in health and disease.

White matter tract-specific alterations in male patients with untreated obstructive sleep apnea are associated with worse cognitive function

STUDY OBJECTIVES

Neurocognitive impairment is one of the daytime symptoms of obstructive sleep apnea (OSA). We proposed to use tract-specific statistical analysis (TSSA) to investigate whether there are fiber tract abnormalities in OSA, which may be undiscovered using voxel-based approaches, and whether such tract-specific disruptions in brain connectivity are associated with neuropsychological deficits in patients with untreated OSA.

METHODS

We enrolled 38 patients with OSA diagnosed by overnight polysomnography, and 41 healthy sleepers. Fractional anisotropy (FA) and mean diffusivity (MD) maps were obtained from whole-brain diffusion tensor imaging, and TSSA were used to assess regional deficits of white matter tracts. All participants underwent a battery of neuropsychological tests. To evaluate the association between FA values and clinical, polysomnographic, and neuropsychological parameters in the OSA group, permutation-based tests for correlation were performed preceding cluster-based statistics.

RESULTS

Compared to healthy controls, patients with OSA showed decreased values of FA in the left and right anterior thalamic radiations, and right uncinate fasciculus (UNC) (p < 0.001, p = 0.005, and p = 0.008, respectively). A lower score of digit span backward was associated with lower FA values of right UNC in the OSA group (p = 0.023). The Rey Complex Figure Test copy score revealed a positive correlation with FA values in the right UNC (p = 0.010).

CONCLUSIONS

The TSSA method indeed identified previously unrevealed tract-specific disruptions in OSA. Furthermore, reduced FA values in the frontal lobe portion of the right UNC which has been known to be involved in working memory function were significantly associated with lower cognitive performance in patients with untreated OSA.

Impact of Obstructive Sleep Apnea on Cognitive and Motor Functions in Parkinson's Disease

INTRODUCTION

Parkinson's disease (PD) is a chronic neurodegenerative disorder that presents with motor and non-motor manifestations. Amongst the non-motor features, various forms of sleep disturbances can occur, and obstructive sleep apnea (OSA) is considered to be a common comorbidity. We conducted this systematic review and meta-analysis to assess the impact of OSA on cognitive and motor functions in PD.

METHODS

The information sources of for this systematic review and meta-analysis were PubMed, SCOPUS, Web of Science, and ScienceDirect. Studies meeting the following criteria were included: (1) studies including idiopathic PD patients, (2) studies using polysomnography to categorize PD patients into PD with OSA and PD without OSA, and (3) studies with observational designs (case-control, cohort, or cross-sectional). Data analysis was performed using RevMan.

RESULTS

Our meta-analysis showed that OSA was associated with significantly lower scores of Montreal Cognitive Assessments (MoCA) (mean difference (MD) = -0.70, 95% confidence interval (CI) [-1.28, -0.13], P = 0.01) and Mini-Mental State Examination (MMSE) (MD = -0.69, 95% CI [-1.17, -0.21], P = 0.005). Moreover, the score of the motor part of the Unified Parkinson's Disease Rating Scale (UPDRS III) was significantly higher in PD patients with OSA as compared with those without OSA (MD = 1.63, 95% CI [0.03, 3.23], P = 0.049).

CONCLUSIONS

OSA is associated with increased severity of PD-associated cognitive dysfunction and motor symptoms. However, further studies are needed to corroborate these findings, assess the underlying mechanisms by which OSA influences the motor and cognitive functions in PD, and investigate whether OSA can accelerate the neurodegenerative process of PD. © 2020 International Parkinson and Movement Disorder Society.

Effects of levothyroxine on lung inflammation, oxidative stress and pathology in a rat model of Alzheimer's disease

BACKGROUND

In this study, the effect of levothyroxine (L-T4) on tracheal responsiveness, lung inflammation, oxidative stress and pathological features in a rat model of Alzheimer's disease (AD), was evaluated.

METHODS

An animal model of AD was established by intracerebroventricular injection of streptozotocin (STZ) (3 mg/kg) in rats. The rats were then treated for 3 weeks with L-T4 (10 and 100 μg/kg).

RESULTS

In AD animals, tracheal responsiveness to methacholine and ovalbumin (p < 0.05), white blood cell (WBC) count (p < 0.05 to p < 0.01), malondialdehyde (MDA) concentration (p < 0.05) and inflammation score (p < 0.01) were increased, but superoxide dismutase (SOD) activity and total thiol content (for both cases p < 0.05) were decreased compared to the controls. Tracheal responsiveness to methacholine and MDA concentration (p < 0.05) were decreased in AD animals treated with T4 compared to the AD group. Bronchial inflammation in terms of total and some differential WBC in the BALF and inflammatory score, was significantly worsened in AD animals treated with high dose of T4 (p < 0.05 to p < 0.001) compared to the controls.

CONCLUSION

Alzheimer's disease may cause lung inflammation and treatment with low dose of T4 improved MDA level and lung inflammation.

Bone Metabolic Markers in Patients with Obstructive Sleep Apnea Syndrome

Background:

Obstructive sleep apnea syndrome (OSAS) is prevalent in obesity and is associated with many metabolic abnormalities. The relationship between OSAS and bone metabolism is still unclear. The aim of this study was to investigate the relationship between the severity of OSAS and bone metabolic markers.

Methods:

A total of 119 obese males were enrolled in this study in spring months from 2015 to 2017. All candidates underwent polysomnography, and their bone mineral density (BMD) and the serum levels of total procollagen type 1 N-terminal propeptide (t-P1NP), N-terminal midfragment of osteocalcin (N-MID), β-C-terminal telopeptide of type 1 collagen (β-CTX), vitamin D (VD), and parathyroid hormone (PTH) were measured. The analysis of variance and Pearson correlation analysis were performed for data analyses.

Results:

No significant differences in the mean values of BMD were observed among the obesity, mild-to-moderate OSAS, and severe OSAS groups; and the serum levels of t-P1NP and β-CTX in the severe OSAS group were significantly higher than those in the obesity group (48.42 ± 23.78 ng/ml vs. 31.98 ± 9.85 ng/ml, P < 0.001; 0.53 ± 0.24 ng/ml vs. 0.41 ± 0.13 ng/ml, P = 0.011, respectively). The serum level of VD in the obesity group was significantly higher than those in the mild-to-moderate and severe OSAS groups (both P < 0.001), and decreased as the severity of OSAS increased (P < 0.001). The serum level of PTH in the severey and mild-to-moderate OSAS groups (both P < 0.001). The results of correlation analysis indicated that the level of apnea-hypopnea index (AHI) was correlated with the levels of t-P1NP (r = 0.396, P < 0.001), VD (r = –0.404, P < 0.001), and PTH (r = 0.400, P < 0.001), whereas the level of minimum O₂ saturation (SaO₂ min) was correlated with the levels of VD (r = 0.258, P = 0.016) and PTH (r = –0.376, P < 0.001).

Conclusions:

The levels of bone resorption and formation markers in patients with severe OSAS were significantly increased compared to obese men, and the severity of OSAS was correlated with the serum levels of t-P1NP, VD, and PTH.

Contribution of Oxidative Stress and Inflammation to the Neurogenic Hypertension Induced by Intermittent Hypoxia

Chronic intermittent hypoxia (CIH), the hallmark of obstructive sleep apnea, is the main risk factor to develop systemic hypertension. Oxidative stress, inflammation, and sympathetic overflow have been proposed as possible mechanisms underlying the CIH-induced hypertension. CIH potentiates the carotid body (CB) chemosensory discharge leading to sympathetic overflow, autonomic dysfunction, and hypertension. Oxidative stress and pro-inflammatory molecules are involved in neurogenic models of hypertension, acting on brainstem and hypothalamic nuclei related to the cardiorespiratory control, such as the nucleus of the solitary tract, which is the primary site for the afferent inputs from the CB. Oxidative stress and pro-inflammatory molecules contribute to the activation of the CB chemoreflex pathway in CIH-induced hypertension. In this brief review, we will discuss new evidence for a critical role of oxidative stress and neuro-inflammation in development of the CIH-induced hypertension through activation of the CB chemoreflex pathway.

Sleep Disorders Associated With Alzheimer's Disease: A Perspective

Sleep disturbances, as well as sleep-wake rhythm disturbances, are typical symptoms of Alzheimer's disease (AD) that may precede the other clinical signs of this neurodegenerative disease. Here, we describe clinical features of sleep disorders in AD and the relation between sleep disorders and both cognitive impairment and poor prognosis of the disease. There are difficulties of the diagnosis of sleep disorders based on sleep questionnaires, polysomnography or actigraphy in the AD patients. Typical disturbances of the neurophysiological sleep architecture in the course of the AD include deep sleep and paradoxical sleep deprivation. Among sleep disorders occurring in patients with AD, the most frequent disorders are sleep breathing disorders and restless legs syndrome. Sleep disorders may influence circadian fluctuations of the concentrations of amyloid-β in the interstitial brain fluid and in the cerebrovascular fluid related to the glymphatic brain system and production of the amyloid-β. There is accumulating evidence suggesting that disordered sleep contributes to cognitive decline and the development of AD pathology. In this mini-review, we highlight and discuss the association between sleep disorders and AD.

Improvement of postoperative cognitive dysfunction and attention network function of patients with ischemic cerebrovascular disease via dexmedetomidine

The protective effect of dexmedetomidine on cognitive dysfunction and decreased attention network function of patients with ischemic cerebrovascular disease after stenting was investigated. Fifty-eight patients with ischemic cerebrovascular disease undergoing stenting in Guizhou Provincial People's Hospital were selected and randomly divided into control group (n=29) and dexmedetomidine group (n=29). The dexmedetomidine group was treated with dexmedetomidine before induced anesthesia, while the control group was given the same dose of normal saline; and the normal volunteers of the same age were selected as the normal group (n=29). At 3 days after operation, the levels of serum S100B and nerve growth factor (NGF) in each group were detected using the enzyme-linked immunosorbent assay, and the level of brain-derived neurotrophic factor (BDNF) was detected via western blotting. Montreal cognitive assessment (MoCA) and attention network test (ANT) were performed. Moreover, the cognitive function and attention network function, and the effects of dexmedetomidine on cognitive function and attention network function were evaluated. The concentrations of serum S100B and NGF in dexmedetomidine group was lower than those in control group (P<0.01). The results of western blotting showed that the levels of serum BDNF in control group and dexmedetomidine group were significantly lower than that in normal group (P<0.01), and it was higher in dexmedetomidine group than that in control group (P<0.01). Besides, both MoCA and ANT results revealed that the visual space and executive function scores, attention scores, delayed memory scores, targeted network efficiency and executive control network efficiency in dexmedetomidine group were obviously higher than those in control group (P<0.01). The cognitive function and attention network function of patients with ischemic cerebrovascular disease have a certain degree of damage, and the preoperative administration of dexmedetomidine can effectively improve the patient's cognitive dysfunction and attention network function after operation.

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.

Decreased Regional Cerebral Perfusion in Moderate-Severe Obstructive Sleep Apnoea during Wakefulness

STUDY OBJECTIVES

To investigate gray matter volume and concentration and cerebral perfusion in people with untreated obstructive sleep apnea (OSA) while awake.

DESIGN

Voxel-based morphometry to quantify gray matter concentration and volume. Arterial spin labeling perfusion imaging to quantify cerebral perfusion.

SETTING

Lying supine in a 3-T magnetic resonance imaging scanner in the early afternoon.

PARTICIPANTS

19 people with OSA (6 females, 13 males; mean age 56.7 y, range 41-70; mean AHI 18.5, range 5.2-52.8) and 19 controls (13 females, 6 males; mean age: 50.0 y, range 41-81).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

There were no differences in regional gray matter concentration or volume between participants with OSA and controls. Neither was there any difference in regional perfusion between controls and people with mild OSA (n = 11). However, compared to controls, participants with moderate-severe OSA (n = 8) had decreased perfusion (while awake) in three clusters. The largest cluster incorporated, bilaterally, the paracingulate gyrus, anterior cingulate gyrus, and subcallosal cortex, and the left putamen and left frontal orbital cortex. The second cluster was right-lateralized, incorporating the posterior temporal fusiform cortex, parahippocampal gyrus, and hippocampus. The third cluster was located in the right thalamus.

CONCLUSIONS

There is decreased regional perfusion during wakefulness in participants with moderate-severe obstructive sleep apnea, and these are in brain regions which have shown decreased regional gray matter volume in previous studies in people with severe OSA. Thus, we hypothesize that cerebral perfusion changes are evident before (and possibly underlie) future structural changes.

Heart failure and Alzheimer's disease

It has recently been proposed that heart failure is a risk factor for Alzheimer's disease. Decreased cerebral blood flow and neurohormonal activation due to heart failure may contribute to the dysfunction of the neurovascular unit and cause an energy crisis in neurons. This leads to the impaired clearance of amyloid beta and hyperphosphorylation of tau protein, resulting in the formation of amyloid beta plaques and neurofibrillary tangles. In this article, we will summarize the current understanding of the relationship between heart failure and Alzheimer's disease based on epidemiological studies, brain imaging research, pathological findings and the use of animal models. The importance of atherosclerosis, myocardial infarction, atrial fibrillation, blood pressure and valve disease as well as the effect of relevant medications will be discussed.

Chronic functional bowel syndrome enhances gut-brain axis dysfunction, neuroinflammation, cognitive impairment, and vulnerability to dementia

The irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder world wide that lasts for decades. The human gut harbors a diverse population of microbial organisms which is symbiotic and important for well being. However, studies on conventional, germ-free, and obese animals have shown that alteration in normal commensal gut microbiota and an increase in pathogenic microbiota-termed "dysbiosis", impact gut function, homeostasis, and health. Diarrhea, constipation, visceral hypersensitivity, and abdominal pain arise in IBS from the gut-induced dysfunctional metabolic, immune, and neuro-immune communication. Dysbiosis in IBS is associated with gut inflammation. Gut-related inflammation is pivotal in promoting endotoxemia, systemic inflammation, and neuroinflammation. A significant proportion of IBS patients chronically consume alcohol, non-steroidal anti-inflammatories, and fatty diet; they may also suffer from co-morbid respiratory, neuromuscular, psychological, sleep, and neurological disorders. The above pathophysiological substrate is underpinned by dysbiosis, and dysfunctional bidirectional "Gut-Brain Axis" pathways. Pathogenic gut microbiota-related systemic inflammation (due to increased lipopolysaccharide and pro-inflammatory cytokines, and barrier dysfunction), may trigger neuroinflammation enhancing dysfunctional brain regions including hippocampus and cerebellum. These as well as dysfunctional vago-vagal gut-brain axis may promote cognitive impairment. Indeed, inflammation is characteristic of a broad spectrum of neurodegenerative diseases that manifest demntia. It is argued that an awareness of pathophysiological impact of IBS and implementation of appropriate therapeutic measures may prevent cognitive impairment and minimize vulnerability to dementia.

Effects of chronic obstructive pulmonary disease and obstructive sleep apnea on cognitive functions: evidence for a common nature

Patients with chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea syndrome (OSAS) show similar neurocognitive impairments. Effects are more apparent in severe cases, whereas in moderate and mild cases the effects are equivocal. The exact mechanism that causes cognitive dysfunctions in both diseases is still unknown and only suggestions have been made for each disease separately. The primary objective of this review is to present COPD and OSAS impact on cognitive functions. Secondly, it aims to examine the potential mechanisms by which COPD and OSAS can be linked and provide evidence for a common nature that affects cognitive functions in both diseases. Patients with COPD and OSAS compared to normal distribution show significant deficits in the cognitive abilities of attention, psychomotor speed, memory and learning, visuospatial and constructional abilities, executive skills, and language. The severity of these deficits in OSAS seems to correlate with the physiological events such as sleep defragmentation, apnea/hypopnea index, and hypoxemia, whereas cognitive impairments in COPD are associated with hypoventilation, hypoxemia, and hypercapnia. These factors as well as vascocerebral diseases and changes in systemic hemodynamic seem to act in an intermingling and synergistic way on the cause of cognitive dysfunctions in both diseases. However, low blood oxygen pressure seems to be the dominant factor that contributes to the presence of cognitive deficits in both COPD and OSAS.

Role of stress, depression, and aging in cognitive decline and Alzheimer's disease

Late-onset Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most common cause of progressive cognitive dysfunction and dementia. Despite considerable progress in elucidating the molecular pathology of this disease, we are not yet close to unraveling its etiopathogenesis. A battery of neurotoxic modifiers may underpin neurocognitive pathology via deleterious heterogeneous pathologic impact in brain regions, including the hippocampus. Three important neurotoxic factors being addressed here include aging, stress, and depression. Unraveling "upstream pathologies" due to these disparate neurotoxic entities, vis-à-vis cognitive impairment involving hippocampal dysfunction, is of paramount importance. Persistent systemic inflammation triggers and sustains neuroinflammation. The latter targets several brain regions including the hippocampus causing upregulation of amyloid beta and neurofibrillary tangles, synaptic and neuronal degeneration, gray matter volume atrophy, and progressive cognitive decline. However, what is the fundamental source of this peripheral inflammation in aging, stress, and depression? This chapter highlights and delineates the inflammatory involvement-i.e., from its inception from gut to systemic inflammation to neuroinflammation. It highlights an upregulated cascade in which gut-microbiota-related dysbiosis generates lipopolysaccharides (LPS), which enhances inflammation and gut's leakiness, and through a Web of interactions, it induces stress and depression. This may increase neuronal dysfunction and apoptosis, promote learning and memory impairment, and enhance vulnerability to cognitive decline.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Depressive symptoms and childhood sleep apnea syndrome

BACKGROUND

The relationship between sleep and mood regulation is well known, and some reports suggest a key role of sleep-related breathing disorders (SRBD) in the development of the symptomatology of depression, even if no conclusive data are actually found in the clinical literature. The aim of this study was to assess the relationship between SRBD and depressive symptoms in a population of school-aged children.

METHODS

The study population comprised 94 children affected by SRBD and 107 healthy children. To identify the severity of SRBD, an overnight respiratory evaluation was performed. All subjects filled out the Italian version of the Children Depression Inventory (CDI) to screen for the presence of depressive symptoms.

RESULTS

The group with SRBD showed higher CDI scores than the group without SRBD, with a positive correlation found between CDI scores, apnea-hypopnea index, and oxygen desaturation index values. Logistic regression showed that an apnea-hypopnea index ≥ 3 and an oxygen desaturation index ≥ 1 could be risk factors for development of depressive symptoms. According to receiver-operating characteristic curve analysis, the cutoff point for the apnea-hypopnea index that could cause a pathological CDI score (≥19) was >5.66, and the cutoff point for the oxygen desaturation index was >4.2. The limitations of this study are that our data are derived from one single psychometric test and not from a complete psychiatric evaluation, and our subjects came from a small group in southern Italy.

CONCLUSION

Our results suggest the importance of mood assessment in children affected by SRBD.