Intermittent hypoxia damages cerebellar cortex and deep nuclei

Intermittent hypoxia in neonatal rodents affects facial bone growth

Preterm human infants often show periodic breathing (PB) or apnea of prematurity (AOP), breathing patterns which are accompanied by intermittent hypoxia (IH). We examined cause-effect relationships between transient IH and reduced facial bone growth using a rat model. Neonatal pups from 14 timed pregnant Sprague-Dawley rats were randomly assigned to an IH condition, with oxygen altering between 10% and 21% every 4 min for 1 h immediately after birth, or to a litter-matched control group. The IH pups were compared with their age- and sex-matched control groups in body weight (WT), size of facial bones and nor-epinephrine (NE) levels in blood at 3, 4, and 5-weeks. Markedly increased activity of osteoclasts in sub-condylar regions of 3-week-old IH-treated animals appeared, as well as increased numbers of sympathetic nerve endings in the same region of tissue sections. Male IH-pups showed significantly higher levels of NE levels in sera at 3, 4 as well as 5-week-old time points. NE levels in 4- and-5-week-old female pups did not differ significantly. Intercondylar Width, Mandible Length and Intermolar Width measures consistently declined after IH insults in 3- and 4-week-old male as well as female animals. Three-week-old male IH-pups only showed a significantly reduced (p < 0.05) body weight compared to those of 3-week controls. However, female IH-pups were heavier than age-matched controls at all 3 time-points. Trabecular bone configuration, size of facial bones, and metabolism are disturbed after an IH challenge 1 h immediately after birth. The findings raise the possibility that IH, introduced by breathing patterns such as PB or AOP, induce significantly impaired bone development and metabolic changes in human newborns. The enhanced NE outflow from IH exposure may serve a major role in deficient bone growth, and may affect bone and other tissue influenced by that elevation.

Effects of a single night of continuous positive airway pressure on spontaneous brain activity in severe obstructive sleep apnea

This study aimed to investigate the effect of a single night of continuous positive airway pressure (CPAP) treatment on spontaneous brain activity and the underlying neuropathological mechanisms in patients with severe obstructive sleep apnea (OSA). The study involved 30 severe OSA patients and 19 healthy controls (HC). Fractional amplitude of low-frequency fluctuation (fALFF) and regional homogeneity (ReHo) methods were employed to evaluate spontaneous brain activity in all participants. Following a single night of CPAP treatment, ReHo values increased in the bilateral caudate and decreased in the right superior frontal gyrus. The fALFF values increased in the left orbital part of the middle frontal gyrus and the right orbital of the inferior frontal gyrus (Frontal_Inf_Orb_R). However, fALFF values decreased in the medial part of the left superior frontal gyrus and the right supramarginal part of the inferior parietal lobe. Pearson correlation analysis revealed a positive relationship between the change in the fALFF in the Frontal_Inf_Orb_R and the change in REM sleep duration (r = 0.437, p = 0.016) following a single night of CPAP treatment. We concluded that observing changes in abnormal fALFF and ReHo in OSA patients before and after a single night of CPAP treatment may enhance our understanding of the neurological mechanisms in patients with severe OSA.

Exploring the brain with sleep-related injuries, and fixing it

The focus of my research efforts rests with determining dysfunctional neural systems underlying disorders of sleep, and identifying interventions to overcome those disorders. Aberrant central and physiological control during sleep exerts serious consequences, including disruptions in breathing, motor control, blood pressure, mood, and cognition, and plays a major role in sudden infant death syndrome, congenital central hypoventilation, and sudden unexpected death in epilepsy, among other concerns. The disruptions can be traced to brain structural injury, leading to inappropriate outcomes. Identification of failing systems arose from the assessment of single neuron discharge in intact, freely moving and state-changing human and animal preparations within multiple systems, including serotonergic action and motor control sites. Optical imaging of chemosensitive, blood pressure and other breathing regulatory areas, especially during development, were useful to show integration of regional cellular action in modifying neural output. Identification of damaged neural sites in control and afflicted humans through structural and functional magnetic resonance imaging procedures helped to identify the sources of injury, and the nature of interactions between brain sites that compromise physiological systems and lead to failure. Interventions to overcome flawed regulatory processes were developed, and incorporate noninvasive neuromodulatory means to recruit ancient reflexes or provide peripheral sensory stimulation to assist breathing drive to overcome apnea, reduce the frequency of seizures, and support blood pressure in conditions where a failure to perfuse can lead to death.

Relationships between brain tissue damage, oxygen desaturation, and disease severity in obstructive sleep apnea evaluated by diffusion tensor imaging

STUDY OBJECTIVES

Patients with obstructive sleep apnea (OSA) show brain injury in sites responsible for autonomic, cognitive, and respiratory functions. Brain changes in OSA may vary with disease severity as assessed by the apnea-hypopnea index (AHI), which does not provide information about the apnea depth and length in contrast to oxygen desaturation. Although significant associations with brain injury and AHI are known in OSA, it is unclear whether AHI or the extent of oxygen desaturations better correlate with brain damage. We evaluated associations between brain changes, AHI, and oxygen desaturation using diffusion tensor imaging-based measures.

METHODS

We acquired diffusion tensor imaging data from 19 patients with OSA using a 3.0-Tesla MRI scanner and calculated, normalized, and smoothed mean, axial, and radial diffusivity maps that were used for correlations between brain changes, oxygen desaturation, and AHI values.

RESULTS

Positive correlations with extent of injury (mean, axial, and radial diffusivity values) and AHI appeared in the frontal areas, cingulate and insula, amygdala, hippocampus, and basal pons, and negative associations emerged in the putamen, internal-capsule, globus-pallidus, and cerebellar cortices. Regional diffusivity values and oxygen desaturation showed positive correlations in the cingulate, frontal, putamen, and cerebellar sites, and negative relationships in several areas, including the occipital cortex.

CONCLUSIONS

Patients with OSA show negative and positive correlations, indicated by increased and decreased diffusivity values, resulting from chronic and acute changes in those areas. The extent of injury in OSA partially depends on the extent of AHI and oxygen desaturation, with the effects representing continued development from acute to chronic processes.

CITATION

Sahib A, Roy B, Kang D, Aysola RS, Wen E, Kumar R. Relationships between brain tissue damage, oxygen desaturation, and disease severity in obstructive sleep apnea evaluated by diffusion tensor imaging. J Clin Sleep Med. 2022;18(12):2713-2721.

Brain tissue integrity mapping in adults with obstructive sleep apnea using T1-weighted and T2-weighted images

BACKGROUND

Obstructive sleep apnea (OSA) is accompanied by both gray and white matter differences in brain areas that regulate autonomic, cognitive, and mood functions, which are deficient in the condition. Such tissue changes have been examined through diffusion tensor and diffusion kurtosis imaging-based procedures. However, poor in-plane spatial resolution of these techniques precludes precise determination of the extent of tissue injury. Tissue texture maps derived from the ratio of T1-weighted and T2-weighted images can provide more adequate in-plane assessment of brain tissue differences.

OBJECTIVES

To examine brain tissue integrity in recently diagnosed, treatment-naïve OSA subjects, relative to age- and sex-comparable control subjects using T1-weighted and T2-weighted images.

DESIGN

A cross-sectional study.

METHODS

We examined the extent of tissue changes in 106 OSA over 115 control subjects using high-resolution T1- and T2-weighted images collected from a 3.0-Tesla scanner (analysis of covariance; covariates: age, sex, body-mass-index, Pittsburgh sleep quality index, Epworth sleepiness scale, Beck Anxiety Inventory, and Beck Depression Inventory II; false discovery rate corrected; p < 0.01).

RESULTS

OSA subjects showed significantly lowered tissue integrity in several brain regions, including the frontal, cingulate and insular cortices, cingulum bundle, thalamus, corpus callosum, caudate and putamen, pons, temporal, occipital, and parietal sites, cerebellar peduncles, and medial medullary sites, compared with controls.

CONCLUSION

OSA subjects show widespread lowered tissue integrity in autonomic, mood, and cognitive control sites over healthy controls. The pathological processes contributing to the alterations may include repetitive hypoxic and hypercarbic processes and excitotoxic injury, leading to altered brain tissue integrity in OSA.

Baroreflex sensitivity during rest and pressor challenges in obstructive sleep apnea patients with and without CPAP

INTRODUCTION

Obstructive sleep apnea (OSA) increases sympathetic vasoconstrictor drive and reduces baroreflex sensitivity (BRS), the degree to which blood pressure changes modify cardiac output. Whether nighttime continuous positive airway pressure (CPAP) corrects BRS in the awake state in OSA remains unclear. We assessed spontaneous BRS using non-invasive continuous BP and ECG recordings at rest and during handgrip and Valsalva challenges, maneuvers that increase vasoconstrictor drive with progressively higher BP, in untreated OSA (unOSA), CPAP-treated OSA (cpOSA) and healthy (CON) participants.

METHODS

In a cross-sectional study of 104 participants, 34 unOSA (age mean±std, 50.6±14.1years; Respiratory Event Index [REI] 21.0±15.3 events/hour; 22male), 31 cpOSA (49.6±14.5years; REI 23.0±14.2 events/hour; 22male; self-report 4+hours/night,5+days/week,6months), and 39 CON (42.2±15.0years; 17male), we calculated BRS at rest and during handgrip and Valsalva. Additionally, we correlated BP variability (BPV) with BRS during these protocols.

RESULTS

BRS in unOSA, cpOSA and CON was, respectively (mean±sdv in ms/mmHg), at rest: 14.8±11.8, 15.8±17.0, 16.1±11.3; during handgrip 13.3±7.6, 12.7±8.4, 16.4±8.7; and during Valsalva 12.7±8.0, 11.5±6.6, 15.1±8.9. BRS was lower in cpOSA than CON for handgrip (p=0.04) and Valsalva (p=0.03). BRS was negatively correlated with BPV in unOSA during Valsalva and handgrip for cpOSA, both R=-0.4 (p=0.02). BRS was negatively correlated with OSA severity (levels: none, mild, moderate, severe) at R=-0.2 (p=0.04,n=104).

CONCLUSIONS

As expected, BRS was lower and BPV higher in OSA during the pressor challenges, and disease severity negatively correlated with BRS. In this cross-sectional study, both CPAP-treated (self-reported) and untreated OSA showed reduced BRS, leaving open whether within-person CPAP improves BRS.

Neuromodulatory Support for Breathing and Cardiovascular Action During Development

Neonatal survival requires precise control of breathing and cardiovascular action, with fatal consequences or severe injury without support. Prematurity presents multiple opportunities to disrupt cardiorespiratory regulation, leading to expressions of apnea of prematurity, periodic breathing, and inappropriate cardiovascular responses to apnea. Failed breathing control can result from altered breathing drives, typically arising from untimely development of sensory or motor coordination processes. Some drives, such as temperature, are a special concern in neonates with low body mass, enhancing susceptibility to rapid body cooling. Chemical drives, such as pH or CO2 or O2, may be inadequately developed; in some conditions, such as congenital central hypoventilation syndrome (CCHS), breathing responses to CO2 or low O2 may be reduced or absent, and coupling of cardiovascular responses to breathing changes are abolished. Sleep states exert profound influences on both chemical and temperature drives, with rapid eye movement (REM) sleep potentially modifying descending temperature influences, and state transitions significantly altering respiratory responses to chemical stimuli. In addition, neonates spend the majority of time in REM sleep, a state which induces a generalized inhibition of skeletal muscle activity that abolishes muscle tone to upper airway and thoracic wall muscles, enhancing the likelihood for obstructive sleep apnea. Although disrupted regulatory drives can often be replaced by positive (or negative) pressure ventilation, such as continuous positive airway pressure or enhanced by manipulating neurotransmitter action via caffeine, those approaches may exert negative consequences in the long term; the lungs of neonates, especially premature infants, are fragile, and easily injured by positive pressure. The consequences of caffeine use, acting directly on neural receptors, although seemingly innocuous in the near-term, may have long-term concerns and disrupts the integrity of sleep. The developmental breathing field needs improved means to support ventilation when one or more drives to respiration fail, and when the cardiovascular system, depending heavily on interactions with breathing, is compromised. Neuromodulatory procedures which manipulate the vestibular system to stabilize breathing or use tactile or proprioceptive stimuli to activate long-established reflexive mechanisms coupling limb movement with respiratory efforts can provide support for central and obstructive apnea, as well as for periodic breathing and cardiovascular action, particularly during sleep.

The Impact of Obstructive Sleep Apnea on Balance, Gait, and Falls Risk: A Narrative Review of the Literature

Falls-related hospitalization and injury rates are steadily increasing globally due to a growth in the aging population, and the associated health problems that increase risk of falls. One such associated health problem is sleep disturbances and disorders. Recent cohort studies have shown that subjectively reported poor quality sleep is associated with an increased risk of falls. Obstructive sleep apnea (OSA) is a common sleep disorder characterized by the repetitive reductions, or cessation, of airflow. Some studies have shown that OSA impairs posture/balance and gait with nocturnal hypoxemia the likely main cause. Emerging evidence suggests that treating OSA by continuous positive airway pressure (CPAP) can improve gait, but no studies to date have examined the effect of CPAP on posture/balance. The overall control of balance relies on a complex interaction between several physiological functions including vestibular, muscle, visual, and cognitive functions. We postulate that OSA impacts balance by affecting these different systems to various degrees, with the nocturnal hypoxic burden likely playing an important role. Importantly, these impairments in balance/posture and possible falls risk may be alleviated by OSA treatment. Larger mechanistic studies are needed to properly elucidate how OSA affects falls risk and future large-scale randomized control trials are needed to determine the effectiveness of OSA treatment in reducing the risk of falls.

Peri-ictal hypoxia is related to extent of regional brain volume loss accompanying generalized tonic-clonic seizures

OBJECTIVES

Hypoxia, or abnormally low blood-oxygen levels, often accompanies seizures and may elicit brain structural changes in people with epilepsy which contribute to central processes underlying sudden unexpected death in epilepsy (SUDEP). The extent to which hypoxia may be related to brain structural alterations in this patient group remains unexplored.

METHODS

We analyzed high-resolution T1-weighted magnetic resonance imaging (MRI) to determine brain morphometric and volumetric alterations in people with generalized tonic-clonic seizures (GTCS) recorded during long-term video-electroencephalography (VEEG), recruited from two sites (n = 22), together with data from age- and sex-matched healthy controls (n = 43). Subjects were sub-divided into those with mild/moderate (GTCS-hypox-mild/moderate, n = 12) and severe (GTCS-hypox-severe, n = 10) hypoxia, measured by peripheral oxygen saturation (SpO2 ) during VEEG. Whole-brain voxel-based morphometry (VBM) and regional volumetry were used to assess group comparisons and correlations between brain structural measurements as well as the duration and extent of hypoxia during GTCS.

RESULTS

Morphometric and volumetric alterations appeared in association with peri-GTCS hypoxia, including volume loss in the periaqueductal gray (PAG), thalamus, hypothalamus, vermis, cerebellum, parabrachial pons, and medulla. Thalamic and PAG volume was significantly reduced in GTCS patients with severe hypoxia compared with GTCS patients with mild/moderate hypoxia. Brainstem volume loss appeared in both hypoxia groups, although it was more extensive in those with severe hypoxia. Significant negative partial correlations emerged between thalamic and hippocampal volume and extent of hypoxia, whereas vermis and accumbens volumes declined with increasing hypoxia duration.

SIGNIFICANCE

Brain structural alterations in patients with GTCS are related to the extent of hypoxia in brain sites that serve vital functions. Although the changes are associative only, they provide evidence of injury to regulatory brain sites related to respiratory manifestations of seizures.

The association of sleep-disordered breathing and white matter hyperintensities in heart failure patients

Heart failure patients often manifest white matter hyperintensites on brain magnetic resonance imaging (MRI). White matter hyperintnsities have also been linked with cognitive problems in patients with heart failure. Sleep disordered breathing may contribute to structural brain changes in heart failure. The purpose of this study was to test the extent to which the apnea hypopnea index is associated with global and regional white matter hyperintensities, and is a moderating factor in the relationship between age and white matter hyperintensites. A total of 28 HF patients [mean age (SD) = 67.89 (5.8)] underwent T1-weighted and T2FLAIR MRI and a home sleep monitoring study. The apnea hypopnea index cut off of 10 was used to compare between higher and lower risks of sleep disordered breathing. Regression analysis was used to test the association between apnea hypopnea index and both global and regional white matter hyperintensities. The interaction term was entered to identify the moderation effect. Apnea hypopnea index was associated with higher regional white matter hyperintensities but not global white matter hyperintensities. There was a significant interaction between the apnea hypopnea index and age, such that older participants with the apnea hypopnea index ≥10 showed greater regional white matter hyperintensities than those with the apnea hypopnea index <10. The results of this preliminary study indicate that a higher apnea hypopnea index is associated with more white matter hyperintensities. The age-related white matter hyperintensities appear to be exacerbated by apnea hypopnea index in our individuals with heart failure. Future studies are needed to further investigate the underlying mechanisms.

Neuropathological Developments in Sudden Infant Death Syndrome

A wide variety of neuropathological abnormalities have been investigated in infants who have died of sudden infant death syndrome (SIDS). Issues which detracted from early studies included failure to use uniform definitions of SIDS and lack of appropriately matched control populations. Development of the triple risk model focused attention on the concept of an inherent susceptibility to unexpected death in certain infants, with research demonstrating a role for the neurotransmitter serotonin within the brainstem. However, it now appears that neuropathological abnormalities in SIDS infants are more complex than a simple serotonergic deficiency in certain medullary nuclei but instead could involve failure of an integrated network of neurochemical transmitters in a variety of subcortical locations. The following overview examines recent research developments looking particularly at the potential role of the peptide neurotransmitter substance P and its neurokinin-1 receptor in multiple nuclei within the brainstem, asymmetry and microdysgenesis of the hippocampus, and decreased orexin levels within dorsomedial, perifornical, and lateral levels in the hypothalamus. Whether such research will lead to identifiable biomarker for infants at risk of SIDS is yet to be established. Use of standardized and consistent methods of classifying and categorizing infant deaths will be pivotal in generating reproducible research results.

Linoleic acid participates in the response to ischemic brain injury through oxidized metabolites that regulate neurotransmission

Linoleic acid (LA; 18:2 n-6), the most abundant polyunsaturated fatty acid in the US diet, is a precursor to oxidized metabolites that have unknown roles in the brain. Here, we show that oxidized LA-derived metabolites accumulate in several rat brain regions during CO2-induced ischemia and that LA-derived 13-hydroxyoctadecadienoic acid, but not LA, increase somatic paired-pulse facilitation in rat hippocampus by 80%, suggesting bioactivity. This study provides new evidence that LA participates in the response to ischemia-induced brain injury through oxidized metabolites that regulate neurotransmission. Targeting this pathway may be therapeutically relevant for ischemia-related conditions such as stroke.

A prospective observational cohort study of exposure to womb-like sounds to stabilize breathing and cardiovascular patterns in preterm neonates

PURPOSE

We exposed premature infants to womb-like sounds to evaluate such exposure on breathing and cardiovascular patterns. We hypothesized that these sounds would reduce apnea and intermittent hypoxemia, enhance parasympathetic outflow, and improve cardiovascular patterns.

METHODS

A total of 20 cases and 5 control infants at ≤32-36 weeks corrected gestational age participated in a prospective observational cohort study. Twenty-four hours of continuous ECG, respiratory and oxygen saturation data were collected in all infants. Womb-like sounds were played intermittently in 6-hour blocks. Salivary samples were collected at study beginning and end for cortisol. Apnea, intermittent hypoxemia, and bradycardia were evaluated, and heart rate variability was assessed by time domain and spectral techniques.

RESULTS

Intermittent hypoxemia and bradycardia significantly declined after sound exposure. No significant differences in apnea, cortisol levels, or heart rate variability were evident among the study infants.

CONCLUSIONS

Exposing premature infants to womb-like sounds has the potential to reduce hypoxemic and bradycardic events, and be used as an intervention to stabilize breathing and cardiac control in preterm infants.

Mechanisms of microglial activation in models of inflammation and hypoxia: Implications for chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) is a hallmark of sleep apnoea, a condition associated with diverse clinical disorders. CIH and sleep apnoea are characterized by increased reactive oxygen species formation, peripheral and CNS inflammation, neuronal death and neurocognitive deficits. Few studies have examined the role of microglia, the resident CNS immune cells, in models of CIH. Thus, little is known concerning their direct contributions to neuropathology or the cellular mechanisms regulating their activities during or following pathological CIH. In this review, we identify gaps in knowledge regarding CIH-induced microglial activation, and propose mechanisms based on data from related models of hypoxia and/or hypoxia-reoxygenation. CIH may directly affect microglia, or may have indirect effects via the periphery or other CNS cells. Peripheral inflammation may indirectly activate microglia via entry of pro-inflammatory molecules into the CNS, and/or activation of vagal afferents that trigger CNS inflammation. CIH-induced release of damage-associated molecular patterns from injured CNS cells may also activate microglia via interactions with pattern recognition receptors expressed on microglia. For example, Toll-like receptors activate mitogen-activated protein kinase/transcription factor pathways required for microglial inflammatory gene expression. Although epigenetic effects from CIH have not yet been studied in microglia, potential epigenetic mechanisms in microglial regulation are discussed, including microRNAs, histone modifications and DNA methylation. Epigenetic effects can occur during CIH, or long after it has ended. A better understanding of CIH effects on microglial activities may be important to reverse CIH-induced neuropathology in patients with sleep disordered breathing.

Accelerated Echo Planer J-resolved Spectroscopic Imaging of Putamen and Thalamus in Obstructive Sleep Apnea

Obstructive sleep apnea syndrome (OSAS) leads to neurocognitive and autonomic deficits that are partially mediated by thalamic and putamen pathology. We examined the underlying neurochemistry of those structures using compressed sensing-based 4D echo-planar J-resolved spectroscopic imaging (JRESI), and quantified values with prior knowledge fitting. Bilaterally increased thalamic mI/Cr, putamen Glx/Cr, and Glu/Cr, and bilaterally decreased thalamic and putamen tCho/Cr and GABA/Cr occurred in OSAS vs healthy subjects (p < 0.05). Increased right thalamic Glx/Cr, Glu/Cr, Gln/Cr, Asc/Cr, and decreased GPC/Cr and decreased left thalamic tNAA/Cr, NAA/Cr were detected. The right putamen showed increased mI/Cr and decreased tCho/Cr, and the left, decreased PE/Cr ratio. ROC curve analyses demonstrated 60–100% sensitivity and specificity for the metabolite ratios in differentiating OSAS vs. controls. Positive correlations were found between: left thalamus mI/Cr and baseline oxygen saturation (SaO₂); right putamen tCho/Cr and apnea hypopnea index; right putamen GABA/Cr and baseline SaO₂; left putamen PE/Cr and baseline SaO₂; and left putamen NAA/Cr and SaO₂ nadir (all p < 0.05). Negative correlations were found between left putamen PE/Cr and SaO₂ nadir. These findings suggest underlying inflammation or glial activation, with greater alterations accompanying lower oxygen saturation. These metabolite levels may provide biomarkers for future neurochemical interventions by pharmacologic or other means.

Clinical neurocardiology defining the value of neuroscience-based cardiovascular therapeutics

The autonomic nervous system regulates all aspects of normal cardiac function, and is recognized to play a critical role in the pathophysiology of many cardiovascular diseases. As such, the value of neuroscience-based cardiovascular therapeutics is increasingly evident. This White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology, pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.

Neuromodulation of Limb Proprioceptive Afferents Decreases Apnea of Prematurity and Accompanying Intermittent Hypoxia and Bradycardia

BACKGROUND

Apnea of Prematurity (AOP) is common, affecting the majority of infants born at <34 weeks gestational age. Apnea and periodic breathing are accompanied by intermittent hypoxia (IH). Animal and human studies demonstrate that IH exposure contributes to multiple pathologies, including retinopathy of prematurity (ROP), injury to sympathetic ganglia regulating cardiovascular action, impaired pancreatic islet cell and bone development, cerebellar injury, and neurodevelopmental disabilities. Current standard of care for AOP/IH includes prone positioning, positive pressure ventilation, and methylxanthine therapy; these interventions are inadequate, and not optimal for early development.

OBJECTIVE

The objective is to support breathing in premature infants by using a simple, non-invasive vibratory device placed over limb proprioceptor fibers, an intervention using the principle that limb movements trigger reflexive facilitation of breathing.

METHODS

Premature infants (23-34 wks gestational age), with clinical evidence of AOP/IH episodes were enrolled 1 week after birth. Caffeine treatment was not a reason for exclusion. Small vibration devices were placed on one hand and one foot and activated in 6 hour ON/OFF sequences for a total of 24 hours. Heart rate, respiratory rate, oxygen saturation (SpO2), and breathing pauses were continuously collected.

RESULTS

Fewer respiratory pauses occurred during vibration periods, relative to baseline (p<0.005). Significantly fewer SpO2 declines occurred with vibration (p<0.05), relative to control periods. Significantly fewer bradycardic events occurred during vibration periods, relative to no vibration periods (p<0.05).

CONCLUSIONS

In premature neonates, limb proprioceptive stimulation, simulating limb movement, reduces breathing pauses and IH episodes, and lowers the number of bradycardic events that accompany aberrant breathing episodes. This low-cost neuromodulatory procedure has the potential to provide a non-invasive intervention to reduce apnea, bradycardia and intermittent hypoxia in premature neonates.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02641249.

The Cerebellum and SIDS: Disordered Breathing in a Mouse Model of Developmental Cerebellar Purkinje Cell Loss during Recovery from Hypercarbia

The cerebellum assists coordination of somatomotor, respiratory, and autonomic actions. Purkinje cell alterations or loss appear in sudden infant death and sudden death in epilepsy victims, possibly contributing to the fatal event. We evaluated breathing patterns in 12 wild-type (WT) and Lurcher mutant mice with 100% developmental cerebellar Purkinje cell loss under baseline (room air), and recovery from hypercapnia, a concern in sudden death events. Six mutant and six WT mice were exposed to 4-min blocks of increasing CO₂ (2, 4, 6, and 8%), separated by 4-min recovery intervals in room air. Breath-by-breath patterns, including depth of breathing and end-expiratory pause (EEP) durations during recovery, were recorded. No baseline genotypic differences emerged. However, during recovery, EEP durations significantly lengthened in mutants, compared to WT mice, following the relatively low levels of CO₂ exposure. Additionally, mutant mice exhibited signs of post-sigh disordered breathing during recovery following each exposure. Developmental cerebellar Purkinje cell loss significantly affects compensatory breathing patterns following mild CO₂ exposure, possibly by inhibiting recovery from elevated CO₂. These data implicate cerebellar Purkinje cells in the ability to recover from hypercarbia, suggesting that neuropathologic changes or loss of these cells contribute to inadequate ventilatory recovery to increased environmental CO₂. Multiple disorders, including sudden infant death syndrome (SIDS) and sudden unexpected death in epilepsy (SUDEP), appear to involve both cardiorespiratory failure and loss or injury to cerebellar Purkinje cells; the findings support the concept that such neuropathology may precede and exert a prominent role in these fatal events.

Obstructive sleep apnea is associated with low GABA and high glutamate in the insular cortex

The insular cortex is injured in obstructive sleep apnea (OSA) and responds inappropriately to autonomic challenges, suggesting neural reorganization. The objective of this study was to assess whether the neural changes might result from γ-aminobutyric acid (GABA) and glutamate alterations. We studied 14 OSA patients [mean age ± standard deviation (SD): 47.5 ± 10.5 years; nine male; apnea-hypopnea index (AHI): 29.5 ± 15.6 events h(-1) ] and 22 healthy participants (47.5 ± 10.1 years; 11 male), using magnetic resonance spectroscopy to detect GABA and glutamate levels in insular cortices. We localized the cortices with anatomical scans, and measured neurochemical levels from anterior to mid-regions. Left and right anterior insular cortices showed lower GABA and higher glutamate in OSA versus healthy subjects [GABA left: OSA n = 6: 0.36 ± 0.10 (mean ± SD), healthy n = 5: 0.62 ± 0.18; P < 0.05), right: OSA n = 11: 0.27 ± 0.09, healthy n = 14: 0.45 ± 0.16; P < 0.05; glutamate left: OSA n = 6: 1.61 ± 0.32, healthy n = 8: 0.94 ± 0.34; P < 0.05, right: OSA n = 14: 1.26 ± 0.28, healthy n = 19: 1.02 ± 0.28; P < 0.05]. GABA and glutamate levels were correlated only within the healthy group in the left insula (r: -0.9, P < 0.05). The altered anterior insular levels of GABA and glutamate may modify integration and projections to autonomic areas, contributing to the impaired cardiovascular regulation in OSA.

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.

Water Exchange across the Blood-Brain Barrier in Obstructive Sleep Apnea: An MRI Diffusion-Weighted Pseudo-Continuous Arterial Spin Labeling Study

BACKGROUND AND PURPOSE

Obstructive sleep apnea (OSA) subjects show brain injury in sites that control autonomic, cognitive, and mood functions that are deficient in the condition. The processes contributing to injury may include altered blood-brain barrier (BBB) actions. Our aim was to examine BBB function, based on diffusion-weighted pseudo-continuous arterial spin labeling (DW-pCASL) procedures, in OSA compared to controls.

METHODS

We performed DW-pCASL imaging in nine OSA and nine controls on a 3.0-Tesla MRI scanner. Global mean gray and white matter arterial transient time (ATT, an index of large artery integrity), water exchange rate across the BBB (Kw, BBB function), DW-pCASL ratio, and cerebral blood flow (CBF) values were compared between OSA and control subjects.

RESULTS

Global mean gray and white matter ATT (OSA vs. controls; gray matter, 1.691 ± .120 vs. 1.658 ± .109 second, P = .49; white matter, 1.700 ± .115 vs. 1.650 ± .114 second, P = .44), and CBF values (gray matter, 57.4 ± 15.8 vs. 58.2 ± 10.7 ml/100 g/min, P = .67; white matter, 24.2 ± 7.0 vs. 24.6 ± 6.7 ml/100 g/min, P = .91) did not differ significantly, but global gray and white matter Kw (gray matter, 158.0 ± 28.9 vs. 220.8 ± 40.6 min(-1) , P = .002; white matter, 177.5 ± 57.2 vs. 261.1 ± 51.0 min(-1) , P = .006), and DW-pCASL ratio (gray matter, .727 ± .076 vs. .823 ± .069, P = .011; white matter, .722 ± .144 vs. .888 ± .100, P = .004) values were significantly reduced in OSA over controls.

CONCLUSIONS

OSA subjects show compromised BBB function, but intact large artery integrity. The BBB alterations may introduce neural damage contributing to abnormal functions in OSA, and suggest a need to repair BBB function with strategies commonly used in other fields.

Cocaine promotes oxidative stress and microglial-macrophage activation in rat cerebellum

Different mechanisms have been suggested for cocaine neurotoxicity, including oxidative stress alterations. Nuclear factor kappa B (NF-κB), considered a sensor of oxidative stress and inflammation, is involved in drug toxicity and addiction. NF-κB is a key mediator for immune responses that induces microglial/macrophage activation under inflammatory processes and neuronal injury/degeneration. Although cerebellum is commonly associated to motor control, muscular tone, and balance. Its relation with addiction is getting relevance, being associated to compulsive and perseverative behaviors. Some reports indicate that cerebellar microglial activation induced by cannabis or ethanol, promote cerebellar alterations and these alterations could be associated to addictive-related behaviors. After considering the effects of some drugs on cerebellum, the aim of the present work analyzes pro-inflammatory changes after cocaine exposure. Rats received daily 15 mg/kg cocaine i.p., for 18 days. Reduced and oxidized forms of glutathione (GSH) and oxidized glutathione (GSSG), glutathione peroxidase (GPx) activity and glutamate were determined in cerebellar homogenates. NF-κB activity, CD68, and GFAP expression were determined. Cerebellar GPx activity and GSH/GSSG ratio are significantly decreased after cocaine exposure. A significant increase of glutamate concentration is also observed. Interestingly, increased NF-κB activity is also accompanied by an increased expression of the lysosomal mononuclear phagocytic marker ED1 without GFAP alterations. Current trends in addiction biology are focusing on the role of cerebellum on addictive behaviors. Cocaine-induced cerebellar changes described herein fit with previosus data showing cerebellar alterations on addict subjects and support the proposed role of cerebelum in addiction.

Chronic obstructive pulmonary disease and cerebrovascular disease: A comprehensive review

Along with the aging population, the public health burden of cerebrovascular disease is increasing. Cerebral small vessel disease and accumulation of brain pathology associate with cognitive decline and can lead to clinical outcomes, such as stroke and dementia. Chronic Obstructive Pulmonary Disease (COPD) is a common respiratory disease among elderly. The quality of life and prognosis of patients with COPD is greatly determined by the presence of comorbidities including stroke and cognitive impairment. Despite the clinical relevance of cerebral small vessel disease, stroke and (vascular) cognitive impairment in patients with COPD, literature is scarce and underlying mechanisms are unknown. The aim of the present review is therefore to summarize current scientific knowledge, to provide a better understanding of the interplay between COPD and the aging brain and to define remaining knowledge gaps. This narrative review article 1) overviews the epidemiology of cerebral small vessel disease, stroke and cognitive impairment in patients with COPD; 2) discusses potential underlying mechanisms including aging, smoking, systemic inflammation, vasculopathy, hypoxia and genetic susceptibility; and 3) highlights areas requiring further research.

Neuroprotective mechanism of Lycium barbarum polysaccharides against hippocampal-dependent spatial memory deficits in a rat model of obstructive sleep apnea

Chronic intermittent hypoxia (CIH) is a hallmark of obstructive sleep apnea (OSA), which induces hippocampal injuries mediated by oxidative stress. This study aims to examine the neuroprotective mechanism of Lycium barbarum polysaccharides (LBP) against CIH-induced spatial memory deficits. Adult Sprague–Dawley rats were exposed to hypoxic treatment resembling a severe OSA condition for a week. The animals were orally fed with LBP solution (1mg/kg) daily 2 hours prior to hypoxia or in air for the control. The effect of LBP on the spatial memory and levels of oxidative stress, inflammation, endoplasmic reticulum (ER) stress, apoptosis and neurogenesis in the hippocampus was examined. There was a significant deficit in the spatial memory and an elevated level of malondialdehyde with a decreased expression of antioxidant enzymes (SOD, GPx-1) in the hypoxic group when compared with the normoxic control. In addition, redox-sensitive nuclear factor kappa B (NFКB) canonical pathway was activated with a translocation of NFКB members (p65, p50) and increased expression levels of NFКB-dependent inflammatory cytokines and mediator (TNFα, IL-1β, COX-2); also, a significantly elevated level of ER stress (GRP78/Bip, PERK, CHOP) and autophagic flux in the hypoxic group, leading to neuronal apoptosis in hippocampal subfields (DG, CA1, CA3). Remarkably, LBP administration normalized the elevated level of oxidative stress, neuroinflammation, ER stress, autophagic flux and apoptosis induced by hypoxia. Moreover, LBP significantly mitigated both the caspase-dependent intrinsic (Bax, Bcl2, cytochrome C, cleaved caspase-3) and extrinsic (FADD, cleaved caspase-8, Bid) signaling apoptotic cascades. Furthermore, LBP administration prevented the spatial memory deficit and enhanced the hippocampal neurogenesis induced by hypoxia. Our results suggest that LBP is neuroprotective against CIH-induced hippocampal-dependent spatial memory deficits by promoting hippocampal neurogenesis and negatively modulating the apoptotic signaling cascades activated by oxidative stress and inflammation.

Brain metabolites in autonomic regulatory insular sites in heart failure

Autonomic, pain, and neuropsychologic comorbidities appear in heart failure (HF), likely resulting from brain changes, indicated as loss of structural integrity and functional deficits. Among affected brain sites, the anterior insulae are prominent in serving major regulatory roles in many of the disrupted functions commonly seen in HF. Metabolite levels, including N-acetylaspartate (NAA), creatine (Cr), choline (Cho), and myo-inositol (MI), could indicate the nature of anterior insula tissue injury in HF. The study aim was to assess anterior insular metabolites to determine processes mediating autonomic, pain, and neuropsychologic disruptions in HF. We performed magnetic resonance spectroscopy in bilateral anterior insulae in 11 HF and 53 controls, using a 3.0-Tesla magnetic resonance imaging scanner. Peaks for NAA at 2.02 ppm, Cr at 3.02 ppm, Cho at 3.2 ppm, and MI at 3.56 ppm were assigned, peak areas were calculated, and metabolites were expressed as ratios, including NAA/Cr, Cho/Cr, and MI/Cr. HF patients showed significantly increased Cho/Cr ratios, indicative of glial proliferation or injury, on the left anterior insula, and reduced NAA/Cr levels, suggesting neuronal loss/dysfunction, on the right anterior insula over controls. No differences in MI/Cr ratios appeared between groups. Right anterior insular neuronal loss and left glial alterations may contribute to distorted autonomic, pain, and neuropsychologic functions found in HF.

No changes in cerebellar microvessel length density in sudden infant death syndrome: implications for pathogenetic mechanisms

Sudden infant death syndrome (SIDS) is the leading cause of mortality in infants younger than 1 year in developed countries, but its primary cause remains unknown. Some studies suggest that there may be hypoxia in the cerebellum in SIDS subjects, but mean total Purkinje cell numbers in SIDS versus controls was recently found not to be different. Probably the best marker for chronic hypoxia in a brain region is the microvessel length per unit volume of tissue, that is, the microvessel length density (MLD). Here, we investigated MLDs using a rigorous design-based stereologic approach in all cell layers and white matter in postmortem cerebella from 9 SIDS cases who died between ages 2 and 10 months and from 14 control children, 9 of which were age- and sex- matched to the SIDS cases. We found no differences either in mean MLDs in the cerebellar layers between the SIDS cases and the controls or between controls with a low likelihood of hypoxia and those with a higher likelihood of hypoxia. Immunohistochemical detection of the astrocytosis marker glial fibrillary acidic protein showed no differences between the SIDS and the matched control cases. These data indicate that there is no association of chronic hypoxia in the cerebellum with SIDS.

Analysis of the vertebrobasilar system in patients with obstructive sleep apnea

We conducted a prospective study to evaluate the vertebrobasilar system in adults with and without obstructive sleep apnea (OSA). Our study population was made up of 48 patients with OSA and 21 healthy volunteers who served as controls; the OSA patients were subdivided into one group with mild or moderate OSA (n = 22) and another with severe OSA (n = 26). Each participant underwent Doppler ultrasonography three times to measure the diameter of the vertebral artery, the peak systolic velocity (PSV), the resistive index (RI), and the vertebral artery flow volume; the mean of the three measurements was calculated for each patient, for the OSA and control groups, and for various subgroups. No significant differences in vessel diameter, PSV, or RI were seen among any of the subgroups. Overall, the vertebral artery flow volume was slightly, but not significantly, higher in all patients with OSA (206 ml/min) than in the control group (177 ml/min); this difference might reflect the body's daytime response to the chronic apneic events experienced during sleep. The only statistically significant difference we found was in vertebral artery flow volume between the controls and the subgroup with mild or moderate OSA (p = 0.026); no difference was seen between the controls and the patients with severe OSA (p = 0.318). Likewise, no significant difference in any of the four parameters was seen when patients were subclassified by body mass index and arterial oxygen saturation level.

Insular cortex metabolite changes in obstructive sleep apnea

STUDY OBJECTIVE

Adults with obstructive sleep apnea (OSA) show significant autonomic and neuropsychologic deficits, which may derive from damage to insular regions that serve those functions. The aim was to assess glial and neuronal status from anterior insular metabolites in OSA versus controls, using proton magnetic resonance spectroscopy (PMRS), and thus to provide insights for neuroprotection against tissue changes, and to reduce injury consequences.

DESIGN

Cross-sectional study.

SETTING

University-based medical center.

PARTICIPANTS

Thirty-six patients with OSA, 53 controls.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

We performed PMRS in bilateral anterior insulae using a 3.0-Tesla magnetic resonance imaging scanner, calculated N-acetylaspartate/creatine (NAA/Cr), choline/creatine (Cho/Cr), myo-inositol/creatine (MI/Cr), and MI/NAA metabolite ratios, and examined daytime sleepiness (Epworth Sleepiness Scale, ESS), sleep quality (Pittsburgh Sleep Quality Index, PSQI), and neuropsychologic status (Beck Depression Inventory II [BDI-II] and Beck Anxiety Inventory [BAI]). Body mass index, BAI, BDI-II, PSQI, and ESS significantly differed between groups. NAA/ Cr ratios were significantly reduced bilaterally, and left-sided MI/Cr and MI/NAA ratios were increased in OSA over controls. Significant positive correlations emerged between left insular MI/Cr ratios and apnea-hypopnea index values, right insular Cho/Cr ratios and BDI-II and BAI scores, and negative correlations appeared between left insular NAA/Cr ratios and PSQI scores and between right-side MI/Cr ratios and baseline and nadir change in O2 saturation.

CONCLUSIONS

Adults with obstructive sleep apnea showed bilaterally reduced N-acetylaspartate and left-side increased myo-inositol anterior insular metabolites, indicating neuronal damage and increased glial activation, respectively, which may contribute to abnormal autonomic and neuropsychologic functions in the condition. The activated glial status likely indicates increased inflammatory action that may induce more neuronal injury, and suggests separate approaches for glial and neuronal protection.

Affective brain areas and sleep-disordered breathing

The neural damage accompanying the hypoxia, reduced perfusion, and other consequences of sleep-disordered breathing, found in obstructive sleep apnea, heart failure, and congenital central hypoventilation syndrome (CCHS), appears in areas that serve multiple functions, including emotional drives to breathe, and involve systems that serve affective, cardiovascular, and breathing roles. The damage, assessed with structural magnetic resonance imaging (MRI) procedures, shows tissue loss or water content and diffusion changes indicative of injury, and impaired axonal integrity between structures; damage is preferentially unilateral. Functional MRI responses in affected areas also are time- or amplitude-distorted to ventilatory or autonomic challenges. Among the structures injured are the insular, cingulate, and ventral medial prefrontal cortices, as well as cerebellar deep nuclei and cortex, anterior hypothalamus, caudal raphé, ventrolateral medulla, portions of the basal ganglia and, in CCHS, the locus coeruleus. Caudal raphé and locus coeruleus injury have the potential to modify serotonergic and adrenergic modulation of upper airway and arousal characteristics, as well as affective drive to breathe. Since both axons and gray matter show injury, the consequences to function, especially to autonomic, cognitive, and mood regulation, are major. Several of the affected rostral sites mediate aspects of dyspnea, especially in CCHS, while others participate in initiation of inspiration after central breathing pauses, and the medullary injury can impair baroreflex and breathing control. The ancillary injury associated with sleep-disordered breathing to central structures can elicit multiple other distortions in cardiovascular, cognitive, and emotional functions in addition to effects on breathing regulation.

Effects of chronic sleep fragmentation on wake-active neurons and the hypercapnic arousal response

STUDY OBJECTIVES

Delayed hypercapnic arousals may occur in obstructive sleep apnea. The impaired arousal response is expected to promote more pronounced oxyhemoglobin desaturations. We hypothesized that long-term sleep fragmentation (SF) results in injury to or dysfunction of wake-active neurons that manifests, in part, as a delayed hypercapnic arousal response.

DESIGN

Adult male mice were implanted for behavioral state recordings and randomly assigned to 4 weeks of either orbital platform SF (SF4wk, 30 events/h) or control conditions (Ct4wk) prior to behavioral, histological, and locus coeruleus (LC) whole cell electrophysiological evaluations.

MEASUREMENTS AND RESULTS

SF was successfully achieved across the 4 week study, as evidenced by a persistently increased arousal index, P < 0.01 and shortened sleep bouts, P < 0.05, while total sleep/wake times and plasma corticosterone levels were unaffected. A multiple sleep latency test performed at the onset of the dark period showed a reduced latency to sleep in SF4wk mice (P < 0.05). The hypercapnic arousal latency was increased, Ct4wk 64 ± 5 sec vs. SF4wk 154 ± 6 sec, P < 0.001, and remained elevated after a 2 week recovery (101 ± 4 sec, P < 0.001). C-fos activation in noradrenergic, orexinergic, histaminergic, and cholinergic wake-active neurons was reduced in response to hypercapnia (P < 0.05-0.001). Catecholaminergic and orexinergic projections into the cingulate cortex were also reduced in SF4wk (P < 0.01). In addition, SF4wk resulted in impaired LC neuron excitability (P < 0.01).

CONCLUSIONS

Four weeks of sleep fragmentation (SF4wk) impairs arousal responses to hypercapnia, reduces wake neuron projections and locus coeruleus neuronal excitability, supporting the concepts that some effects of sleep fragmentation may contribute to impaired arousal responses in sleep apnea, which may not reverse immediately with therapy.

Chronic intermittent hypoxia exerts CNS region-specific effects on rat microglial inflammatory and TLR4 gene expression

Intermittent hypoxia (IH) during sleep is a hallmark of sleep apnea, causing significant neuronal apoptosis, and cognitive and behavioral deficits in CNS regions underlying memory processing and executive functions. IH-induced neuroinflammation is thought to contribute to cognitive deficits after IH. In the present studies, we tested the hypothesis that IH would differentially induce inflammatory factor gene expression in microglia in a CNS region-dependent manner, and that the effects of IH would differ temporally. To test this hypothesis, adult rats were exposed to intermittent hypoxia (2 min intervals of 10.5% O₂) for 8 hours/day during their respective sleep cycles for 1, 3 or 14 days. Cortex, medulla and spinal cord tissues were dissected, microglia were immunomagnetically isolated and mRNA levels of the inflammatory genes iNOS, COX-2, TNFα, IL-1β and IL-6 and the innate immune receptor TLR4 were compared to levels in normoxia. Inflammatory gene expression was also assessed in tissue homogenates (containing all CNS cells). We found that microglia from different CNS regions responded to IH differently. Cortical microglia had longer lasting inflammatory gene expression whereas spinal microglial gene expression was rapid and transient. We also observed that inflammatory gene expression in microglia frequently differed from that in tissue homogenates from the same region, indicating that cells other than microglia also contribute to IH-induced neuroinflammation. Lastly, microglial TLR4 mRNA levels were strongly upregulated by IH in a region- and time-dependent manner, and the increase in TLR4 expression appeared to coincide with timing of peak inflammatory gene expression, suggesting that TLR4 may play a role in IH-induced neuroinflammation. Together, these data indicate that microglial-specific neuroinflammation may play distinct roles in the effects of intermittent hypoxia in different CNS regions.

Heart rate responses to autonomic challenges in obstructive sleep apnea

Obstructive sleep apnea (OSA) is accompanied by structural alterations and dysfunction in central autonomic regulatory regions, which may impair dynamic and static cardiovascular regulation, and contribute to other syndrome pathologies. Characterizing cardiovascular responses to autonomic challenges may provide insights into central nervous system impairments, including contributions by sex, since structural alterations are enhanced in OSA females over males. The objective was to assess heart rate responses in OSA versus healthy control subjects to autonomic challenges, and, separately, characterize female and male patterns. We studied 94 subjects, including 37 newly-diagnosed, untreated OSA patients (6 female, age mean ± std: 52.1 ± 8.1 years; 31 male aged 54.3 ± 8.4 years), and 57 healthy control subjects (20 female, 50.5 ± 8.1 years; 37 male, 45.6 ± 9.2 years). We measured instantaneous heart rate with pulse oximetry during cold pressor, hand grip, and Valsalva maneuver challenges. All challenges elicited significant heart rate differences between OSA and control groups during and after challenges (repeated measures ANOVA, p<0.05). In post-hoc analyses, OSA females showed greater impairments than OSA males, which included: for cold pressor, lower initial increase (OSA vs. control: 9.5 vs. 7.3 bpm in females, 7.6 vs. 3.7 bpm in males), OSA delay to initial peak (2.5 s females/0.9 s males), slower mid-challenge rate-of-increase (OSA vs. control: -0.11 vs. 0.09 bpm/s in females, 0.03 vs. 0.06 bpm/s in males); for hand grip, lower initial peak (OSA vs. control: 2.6 vs. 4.6 bpm in females, 5.3 vs. 6.0 bpm in males); for Valsalva maneuver, lower Valsalva ratio (OSA vs. control: 1.14 vs. 1.30 in females, 1.29 vs. 1.34 in males), and OSA delay during phase II (0.68 s females/1.31 s males). Heart rate responses showed lower amplitude, delayed onset, and slower rate changes in OSA patients over healthy controls, and impairments may be more pronounced in females. The dysfunctions may reflect central injury in the syndrome, and suggest autonomic deficiencies that may contribute to further tissue and functional pathologies.

Visual assessment of brain magnetic resonance imaging detects injury to cognitive regulatory sites in patients with heart failure

BACKGROUND

Heart failure (HF) patients exhibit depression and executive function impairments that contribute to HF mortality. Using specialized magnetic resonance imaging (MRI) analysis procedures, brain changes appear in areas regulating these functions (mammillary bodies, hippocampi, and frontal cortex). However, specialized MRI procedures are not part of standard clinical assessment for HF (which is usually a visual evaluation), and it is unclear whether visual MRI examination can detect changes in these structures.

METHODS AND RESULTS

Using brain MRI, we visually examined the mammillary bodies and frontal cortex for global and hippocampi for global and regional tissue changes in 17 HF and 50 control subjects. Significantly global changes emerged in the right mammillary body (HF 1.18 ± 1.13 vs control 0.52 ± 0.74; P = .024), right hippocampus (HF 1.53 ± 0.94 vs control 0.80 ± 0.86; P = .005), and left frontal cortex (HF 1.76 ± 1.03 vs control 1.24 ± 0.77; P = .034). Comparison of the visual method with specialized MRI techniques corroborates right hippocampal and left frontal cortical, but not mammillary body, tissue changes.

CONCLUSIONS

Visual examination of brain MRI can detect damage in HF in areas regulating depression and executive function, including the right hippocampus and left frontal cortex. Visual MRI assessment in HF may facilitate evaluation of injury to these structures and the assessment of the impact of potential treatments for this damage.

Regional cerebral blood flow alterations in obstructive sleep apnea

Obstructive sleep apnea (OSA) is a condition characterized by upper airway muscle atonia with continued diaphragmatic efforts, resulting in repeated airway obstructions, periods of intermittent hypoxia, large thoracic pressure changes, and substantial shifts in arterial pressure with breathing cessation and resumption. The hypoxic exposure and hemodynamic changes likely induce the structural and functional deficits found in multiple brain areas, as shown by magnetic resonance imaging (MRI) procedures. Altered cerebral blood flow (CBF) may contribute to these localized deficits; thus, we examined regional CBF, using arterial spin labeling procedures, in 11 OSA (age, 49.1±12.2 years; 7 male) and 16 control subjects (42.3±10.2 years; 6 male) with a 3.0-Tesla MRI scanner. CBF maps were calculated, normalized to a common space, and regional CBF values across the brain quantified. Lowered CBF values emerged near multiple bilateral brain sites in OSA, including the corticospinal tracts, superior cerebellar peduncles, and pontocerebellar fibers. Lateralized, decreased CBF appeared near the left inferior cerebellar peduncles, left tapetum, left dorsal fornix/stria terminalis, right medial lemniscus, right red nucleus, right midbrain, and midline pons. Regional CBF values in OSA are significantly reduced in major sensory and motor fiber systems and motor regulatory sites, especially in structures mediating motor coordination; those reductions are often lateralized. The asymmetric CBF declines in motor regulatory areas may contribute to loss of coordination between upper airway and diaphragmatic musculature, and lead to further damage in the syndrome.

Sleep-disordered breathing: effects on brain structure and function

Sleep-disordered breathing is accompanied by neural injury that affects a wide range of physiological systems which include processes for sensing chemoreception and airflow, driving respiratory musculature, timing circuitry for coordination of breathing patterning, and integration of blood pressure mechanisms with respiration. The damage also occurs in regions mediating emotion and mood, as well as areas regulating memory and cognitive functioning, and appears in structures that serve significant glycemic control processes. The injured structures include brain areas involved in hormone release and action of major neurotransmitters, including those playing a role in depression. The injury is reflected in a range of structural magnetic resonance procedures, and also appears as functional distortions of evoked activity in brain areas mediating vital autonomic and breathing functions. The damage is preferentially unilateral, and includes axonal projections; the asymmetry of the injury poses unique concerns for sympathetic discharge and potential consequences for arrhythmia. Sleep-disordered breathing should be viewed as a condition that includes central nervous system injury and impaired function; the processes underlying injury remain unclear.

Correlation between pulmonary function and brain volume in healthy elderly subjects

INTRODUCTION

Cigarette smoking decreases brain regional gray matter volume and is related to chronic obstructive lung disease (COPD). COPD leads to decreased pulmonary function, which is represented by forced expiratory volume in one second percentage (FEV1.0 %); however, it is unclear if decreased pulmonary function is directly related to brain gray matter volume decline. Because there is a link between COPD and cognitive decline, revealing a direct relationship between pulmonary function and brain structure is important to better understand how pulmonary function affects brain structure and cognitive function. Therefore, the purpose of this study was to analyze whether there were significant correlations between FEV1.0 % and brain regional gray and white matter volumes using brain magnetic resonance (MR) image data from 109 community-dwelling healthy elderly individuals.

METHODS

Brain MR images were processed with voxel-based morphometry using a custom template by applying diffeomorphic anatomical registration using the exponentiated lie algebra procedure.

RESULTS

We found a significant positive correlation between the regional white matter volume of the cerebellum and FEV1.0 % after adjusting for age, sex, and intracranial volume.

CONCLUSION

Our results suggest that elderly individuals who have a lower FEV1.0 % have decreased regional white matter volume in the cerebellum. Therefore, preventing decreased pulmonary function is important for cerebellar white matter volume in the healthy elderly population.

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.

Making sense of oxidative stress in obstructive sleep apnea: mediator or distracter?

Obstructive sleep apnea is increasingly recognized as an important contributor to cognitive impairment, metabolic derangements, and cardiovascular disease and mortality. Identifying the mechanisms by which this prevalent disorder influences health outcomes is now of utmost importance. As the prevalence of this disorder steadily increases, therapies are needed to prevent or reverse sleep apnea morbidities now more than ever before. Oxidative stress is implicated in cardiovascular morbidities of sleep apnea. What role oxidative stress plays in neural injury and cognitive impairments has been difficult to understand without readily accessible tissue to biopsy in persons with and without sleep apnea. An improved understanding of the role oxidative stress plays in neural injury in sleep apnea may be developed by integrating information gained examining neural tissue in animal models of sleep apnea with key features of redox biochemistry and clinical sleep apnea studies where extra-neuronal oxidative stress characterizations have been performed. Collectively, this information sets the stage for developing and testing novel therapeutic approaches to treat and prevent, not only central nervous system injury and dysfunction in sleep apnea, but also the cardiovascular and potentially metabolic conditions associated with this prevalent, disabling disorder.

Microglia-derived proinflammatory cytokines tumor necrosis factor-alpha and interleukin-1beta induce Purkinje neuronal apoptosis via their receptors in hypoxic neonatal rat brain

The developing cerebellum is extremely vulnerable to hypoxia which can damage the Purkinje neurons. We hypothesized that this might be mediated by tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) derived from activated microglia as in other brain areas. One-day-old rats were subjected to hypoxia following, which the expression changes of various proteins in the cerebellum including hypoxia inducible factor-1α, TNF-α, IL-1β, TNF-R1 and IL-1R1 were analyzed. Following hypoxic exposure, TNF-α and IL-1β immunoexpression in microglia was enhanced coupled by that of TNF-R1 and IL-1R1 in the Purkinje neurons. Along with this, hypoxic microglia in vitro showed enhanced release of TNF-α and IL-1β whose receptor expression was concomitantly increased in the Purkinje neurons. In addition, nitric oxide (NO) level was significantly increased in the cerebellum and cultured microglia subjected to hypoxic exposure. Moreover, cultured Purkinje neurons treated with conditioned medium derived from hypoxic microglia underwent apoptosis but the incidence was significantly reduced when the cells were treated with the same medium that was neutralized with TNF-α/IL-1β antibody. We conclude that hypoxic microglia in the neonatal cerebellum produce increased amounts of NO, TNF-α and IL-1β which when acting via their respective receptors could induce Purkinje neuron death.

Neuronal injury and cytogenesis after simple febrile seizures in the hippocampal dentate gyrus of juvenile rat

PURPOSE

Although simple febrile seizures are frequently described as harmless, there is evidence which suggests that hippocampal damage may occur after simple febrile seizures. This study aimed to investigate possible neuronal damages as well as alterations in cytogenesis in the hippocampal dentate gyrus following simple febrile seizures.

METHODS

Simple febrile seizure was modeled by hyperthermia-induced seizures in 22-day-old male rats. The brains were removed 2 or 15 days after hyperthermia in all rats with (n=20) and without (n=10) occurrence of seizures as well as in control animals (n=10). The sections were stained with hematoxylin and eosin to estimate the surface numerical density of dark neurons. Ki-67 immunohistochemistry was performed to evaluate changes of cytogenesis following simple febrile seizures.

RESULTS

Hyperthermia induced behavioral seizure activities in 67 % of the rats. The numerical densities of dark neurons as well as the mean Ki-67 index (the fraction of Ki-67-positive cells) were significantly increased in dentate gyrus after induction of seizures by hyperthermia compared to both controls and rats without seizure after hyperthermia. Both the seizure duration and intensity were correlated significantly with numerical densities of dark neurons (but not with Ki-67 index).

CONCLUSION

The data indicate that simple febrile seizures can cause neuronal damages and enhancement of cytogenesis in the hippocampal dentate gyrus, which were still visible for at least 2 weeks. These findings also suggest the correlation of febrile seizure intensity and duration with neuronal damage.

Altered global and regional brain mean diffusivity in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common and progressive disorder accompanied by severe cardiovascular and neuropsychological sequelae, presumably induced by brain injury resulting from the intermittent hypoxia and cardiovascular processes accompanying the syndrome. However, whether the predominant brain tissue pathology is acute or chronic in newly-diagnosed, untreated OSA subjects is unclear; this assessment is essential for revealing pathological processes. Diffusion tensor imaging (DTI)-based mean diffusivity (MD) procedures can detect and differentiate acute from chronic pathology and may be useful to reveal processes in the condition. We collected four DTI series from 23 newly-diagnosed, treatment-naïve OSA and 23 control subjects, using a 3.0-Tesla magnetic resonance imaging scanner. Mean diffusivity maps were calculated from each series, realigned, averaged, normalized to a common space, and smoothed. Global brain MD values for each subject were calculated using normalized MD maps and a global brain mask. Mean global brain MD values and smoothed MD maps were compared between groups by using analysis of covariance (covariate: age). Mean global brain MD values were significantly reduced in OSA compared with controls (P = 0.01). Multiple brain sites in OSA, including medullary, cerebellar, basal ganglia, prefrontal and frontal, limbic, insular, cingulum bundle, external capsule, corpus callosum, temporal, occipital, and corona radiata regions showed reduced regional MD values compared with controls. The results suggest that global brain MD values are significantly reduced in OSA, with certain regional sites especially affected, presumably a consequence of axonal, glial, and other cell changes in those areas. The findings likely represent acute pathological processes in newly-diagnosed OSA subjects.

Role of 5-hydroxytryptamine expression in cerebellar Purkinje cells in obstructive sleep apnea syndrome

In the present study, electrical stimulation to the rat insular cortex induced apnea or respiratory disturbance, reduced amplitude of genioglossal electromyogram, and decreased electromyogram integrals. In addition, arterial blood gas analysis showed arterial blood acidosis, reduced pH values, increased alkali reserve negative values, decreased peripheral blood 5-hydroxytryptamine content, and increased 5-hydroxytryptamine expression in cerebellar Purkinje cells. Following lidocaine injection to block the habenular nucleus, abnormalities in breath, genioglossal electromyogram, and blood gas values disappeared, and peripheral blood 5-hydroxytryptamine content returned to levels prior to electric stimulation. However, 5-hydroxytryptamine expression in cerebellar Purkinje cells remained high. The results suggested that 5-hydroxytryptamine expression in Purkinje cells did not correlate with ventilation function involving insular cortex and habenular nucleus.