Effects of Exposure to Intermittent Hypoxia on Oxidative Stress and Acute Hypoxic Ventilatory Response in Humans

Autonomic nervous system and mediating role of respiratory function in patients with ALS

Patients with Amyotrophic Lateral Sclerosis (ALS) exhibit altered patterns of respiratory rate and heart rhythm that are directly related to autonomic nervous system (ANS) activity. This study aimed to analyze the role of the ANS in respiratory function, cognition, functionality, and antioxidant capacity in patients with ALS through a predictive model that assesses the mediating activity of respiration. This quantitative, observational, analytical, and cross-sectional clinical study was conducted using a sample of 75 patients diagnosed with ALS. ANS activity, respiratory function, cognition, functionality, and antioxidant capacity were also measured. Using these values, a structural equation model was developed using AMOS V.23 software. The mediational predictive model showed that increased sympathetic nervous system (SNS) activity, in turn, increased respiratory function, whereas the role of the parasympathetic nervous system in respiration was very weak and had the opposite effect. Furthermore, SNS activity increased respiratory function values, which, in turn, improved functional capacity, cognition, and antioxidant power in patients with ALS, with respiratory function playing a mediating role. The mediating effect of respiratory function was observed primarily between ANS and functional disability. For oxidative stress, respiratory function showed a high mediating effect, such that greater respiratory function corresponded to greater antioxidant capacity. Additionally, for cognitive activity, a moderate direct effect of the ANS was observed; however, it was greatly enhanced by respiratory disability. Finally, differences were only found based on sex, with respiratory capacity and antioxidant power being higher in men.

Sexual Dimorphism in Cardiometabolic Diseases: From Development to Senescence and Therapeutic Approaches

The global incidence and prevalence of cardiometabolic disorders have risen significantly in recent years. Although lifestyle choices in adulthood play a crucial role in the development of these conditions, it is well established that events occurring early in life can have an important effect. Recent research on cardiometabolic diseases has highlighted the influence of sexual dimorphism on risk factors, underlying mechanisms, and response to therapies. In this narrative review, we summarize the current understanding of sexual dimorphism in cardiovascular and metabolic diseases in the general population and within the framework of the Developmental Origins of Health and Disease (DOHaD) concept. We explore key risk factors and mechanisms, including the influence of genetic and epigenetic factors, placental and embryonic development, maternal nutrition, sex hormones, energy metabolism, microbiota, oxidative stress, cell death, inflammation, endothelial dysfunction, circadian rhythm, and lifestyle factors. Finally, we discuss some of the main therapeutic approaches, responses to which may be influenced by sexual dimorphism, such as antihypertensive and cardiovascular treatments, oxidative stress management, nutrition, cell therapies, and hormone replacement therapy.

Oxidative stress and nitric oxide metabolism responses during prolonged high-altitude exposure in preterm born adults

BACKGROUND

Prematurely-born individuals tend to exhibit higher resting oxidative stress, although evidence suggests they may be more resistant to acute hypoxia-induced redox balance alterations. We aimed to investigate the redox balance changes across a 3-day hypobaric hypoxic exposure at 3375 m in healthy adults born preterm (gestational age ≤ 32 weeks) and their term-born (gestational age ≥ 38 weeks) counterparts.

METHODS

Resting venous blood was obtained in normoxia (prior to altitude exposure), immediately upon arrival to altitude, and the following 3 mornings. Antioxidant (superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and ferric reducing antioxidant power (FRAP)), pro-oxidant (xanthine oxidase (XO) and myeloperoxidase (MPO)) enzyme activity, oxidative stress markers (advanced oxidation protein product (AOPP) and malondialdehyde (MDA)), nitric oxide (NO) metabolites (nitrites, nitrates, and total nitrite and nitrate (NOx)), and nitrotyrosine were measured in plasma.

RESULTS

SOD increased only in the preterm group (p < 0.05). Catalase increased at arrival in preterm group (p < 0.05). XO activity increased at Day 3 for the preterm group, while it increased acutely (arrival and Day 1) in control group. MPO increased in both groups throughout the 3 days (p < 0.05). AOPP only increased at arrival in the preterm (p < 0.05) whereas it decreased at arrival up to Day 3 (p < 0.05) for control. MDA decreased in control group from arrival onward. Nitrotyrosine decreased in both groups (p < 0.05). Nitrites increased on Day 3 (p < 0.05) in control group and decreased on Day 1 (p < 0.05) in preterm group.

CONCLUSION

These data indicate that antioxidant enzymes seem to increase immediately upon hypoxic exposure in preterm adults. Conversely, the blunted pro-oxidant enzyme response to prolonged hypoxia exposure suggests that these enzymes may be less sensitive in preterm individuals. These findings lend further support to the potential hypoxic preconditioning effect of preterm birth.

The histone demethylase KDM6B links obstructive sleep apnea to idiopathic pulmonary fibrosis

Obstructive sleep apnea (OSA) is increasingly recognized for its link to idiopathic pulmonary fibrosis (IPF), though the underlying mechanisms remain poorly understood. Histone lysine demethylase 6B (KDM6B) may either prevent or promote organ fibrosis, but its specific role in IPF is yet to be clarified. This study aimed to investigate the function and mechanisms of KDM6B in IPF and the exacerbating effects of OSA. We assessed KDM6B levels in lung tissues from IPF patients, IPF mouse models, and a dual-hit model combining OSA-associated intermittent hypoxia (IH) with bleomycin (BLM) or TGF-β1. We evaluated pulmonary fibrosis, myofibroblast activation, and oxidative stress. KDM6B levels were elevated in lung tissues from IPF patients and BLM-treated mice, as well as in TGF-β1-stimulated myofibroblasts. Importantly, IH significantly worsened BLM-induced pulmonary fibrosis and TGF-β1-induced myofibroblast activation, further amplifying KDM6B expression both in vivo and in vitro. Inhibition of KDM6B reduced pulmonary fibrosis and decreased fibroblast activation and migration in IPF and dual-hit models. Mechanistically, KDM6B inhibition led to decreased NOX4 expression and reduced oxidative stress. KDM6B plays a critical role in promoting pulmonary fibrosis and mediating the exacerbating effects of OSA on this condition. Our findings identify KDM6B as a novel potential therapeutic target for IPF.

Influence of the partner's obstructive sleep apnea on metabolic syndrome in couples

OBJECTIVES

This study investigates the relationship between the risk of obstructive sleep apnea, as assessed by the STOP-Bang questionnaire, and metabolic syndrome among couples. It also examines how snoring and observed apnea are associated with metabolic syndrome in couples.

STUDY DESIGN

Cross-sectional study using data from 2436 couples in the Korea National Health and Nutrition Examination Survey (2019-2021). A high risk of obstructive sleep apnea was defined as a STOP-Bang score of 3 or more (excluding the hypertension item).

MAIN OUTCOME MEASURES

Metabolic syndrome in couples.

RESULTS

47.6 % of husbands and 5.7 % of wives had a high risk of obstructive sleep apnea. The prevalence of metabolic syndrome was 45.5 % among husbands and 24.7 % among wives. After adjusting for sociodemographic factors and health behaviors, wives whose husbands were at high risk of obstructive sleep apnea or who reported snoring or observed apnea had 1.4-1.5 times higher odds of metabolic syndrome. Conversely, husbands' metabolic syndrome was not significantly associated with their wives' risk of obstructive sleep apnea and sleep behaviors. The adjusted odds of metabolic syndrome in both partners were 2.8-4.4 times higher when only husbands had a high risk of obstructive sleep apnea or snoring, and 2.3-2.9 times higher when only wives had these sleep issues, compared with couples without such problems.

CONCLUSIONS

This study reveals a gender disparity in the impact of a spouse's risk of obstructive sleep apnea on metabolic syndrome, emphasizing the need for a couple-focused approach in managing these health issues.

Menstrual cycle does not impact the hypoxic ventilatory response and acute mountain sickness prediction

The relationship between the variations in ovarian hormones (i.e., estrogens and progesterone) and the hypoxic ventilatory response (HVR) remains unclear. HVR is a key adaptive mechanism to high altitude and has been proposed as a predictor for acute mountain sickness (AMS). This study aimed to explore the effects of hormonal changes across the menstrual cycle on HVR. Additionally, it assessed the predictive capacity of HVR for AMS and examined whether a particular menstrual phase could enhance its predictive accuracy. Thirteen eumenorrheic women performed a pure nitrogen breathing test near sea level, measuring HVR and cerebral oxygenation in early follicular, late follicular, and mid-luteal phases. Oxidative stress and ovarian hormone levels were also measured. AMS symptoms were evaluated after spending 14 h, including one overnight, at an altitude of 3,375 m. No differences in HVR, ventilation, peripheral oxygen saturation, or cerebral oxygenation were observed between the three menstrual cycle phases. Moreover, these parameters and the oxidative stress markers did not differ between the women with or without AMS (31% vs 69%), regardless of the menstrual cycle phase. In conclusion, ventilatory responses and cerebral oxygenation in normobaric hypoxia were consistent across the menstrual cycle. Furthermore, these parameters did not differentiate women with or without AMS.

Clinicopathological Aspects of Dilation and Curettage (D&C) Biopsies Taken from Patients Living at High Altitude in Taif, KSA, with a Special Emphasis on Chronic Endometritis

BACKGROUND

Chronic endometritis (CE) is a persistent inflammation of the uterine lining. Although it has a minimal clinical presentation, CE adversely affects the reproductive ability of women. The aims of this study were to detect pathological endometrial patterns in D&C biopsies and to evaluate chronic endometritis in patients living in a high-altitude area (1800 m above sea level) in order to determine the clinical pathological features and prevalence.

MATERIALS AND METHODS

A cross-sectional study conducted at King Faisal Maternity Hospital included 100 samples of D&C biopsies from women complaining of various gynecological symptoms not due to gestational causes. The biopsies underwent tissue processing, H&E staining, and CD138 detection. Blood samples were taken for serological detection of infectious diseases, complete blood count, and chemical parameters.

RESULTS

The mean age of women in the study with CE was 48.5 ± 8.5 years, and that of those without CE was 46.9 ± 9.7 years. The most common complaints were abnormal uterine bleeding, accounting for 83%. CE was present in 8% of cases, and there was a nonsignificant difference in hematological parameters between women with CE and those with other pathological diagnoses. There were also nonsignificant differences in chemical parameters, except for FSH and LH levels, which showed a significant difference, with p-values of 0.05 and 0.02, respectively. It can be concluded that the most common gynecological complaint of women in this study was abnormal uterine bleeding.

CONCLUSIONS

The most commonly diagnosed pathological endometrial disorder in D&C biopsies was disordered proliferative endometrium, followed by endometrial polyps and endometrial hyperplasia. All of these are usually associated with hormonal disturbance, which appeared to be very common in the women in this study. The prevalence of chronic endometritis detected in our study was 8%, which is relatively high.

Characteristics of obstructive sleep apnea related to insulin resistance

BACKGROUND

Obstructive sleep apnea (OSA) is associated with multiple comorbidities, including diabetes. Its development is preceded by alterations in the initial phase of carbohydrate metabolism characterized by insulin resistance. This study aims to evaluate the role of intermittent hypoxia and sleep fragmentation characteristic of OSA on the risk of insulin resistance among apneic patients without diabetes.

METHODOLOGY

92 consecutive patients with OSA without evidence of diabetes were recruited. Overnight video polysomnography was performed and, the following morning, fasting blood glucose, insulin and glycosylated hemoglobin were determined. Insulin resistance was measured using the HOMA-IR index.

RESULTS

Insulin resistance was present in 52.2% of OSA patients. In these subjects, insulin resistance was independently associated to the apnea index during REM sleep (adjusted odds ratio [aOR] 1.09; 95% CI, 1.03 to 1.16; p = 0.004), desaturation index (aOR 1.08; 95% CI: 1.04 to 1.13; p = 0.027), and sleep time with oxygen saturation below 90% (aOR 1.04; 95% CI 1.00 to 1.08; p = 0.049). Furthermore, the HOMA-IR level was also directly related to the desaturation index (standardized regression coefficient [B] = 0.514, p < 0.001) and to the apnea index during REM sleep (B = 0.344, p = 0.002).

CONCLUSIONS

Intermittent hypoxia and disturbances in REM sleep emerge as main contributors to insulin resistance in OSA patients yet to experience diabetes onset.

The hypoxic respiratory response of the pre-Bötzinger complex

Since the discovery of the pre-Bötzinger Complex (preBötC) as a crucial region for generating the main respiratory rhythm, our understanding of its cellular and molecular aspects has rapidly increased within the last few decades. It is now apparent that preBötC is a highly flexible neuronal network that reconfigures state-dependently to produce the most appropriate respiratory output in response to various metabolic challenges, such as hypoxia. However, the responses of the preBötC to hypoxic conditions can be varied based on the intensity, pattern, and duration of the hypoxic challenge. This review discusses the preBötC response to hypoxic challenges at the cellular and network level. Particularly, the involvement of preBötC in the classical biphasic response of the respiratory network to acute hypoxia is illuminated. Furthermore, the article discusses the functional and structural changes of preBötC neurons following intermittent and sustained hypoxic challenges. Accumulating evidence shows that the preBötC neural circuits undergo substantial changes following hypoxia and contribute to several types of the respiratory system's hypoxic ventilatory responses.

Advancements in the neurocirculatory reflex response to hypoxia

Hypoxia is a pivotal factor in the pathophysiology of various clinical conditions, including obstructive sleep apnea, which has a strong association with cardiovascular diseases like hypertension, posing significant health risks. Although the precise mechanisms linking hypoxemia-associated clinical conditions with hypertension remains incompletely understood, compelling evidence suggests that hypoxia induces plasticity of the neurocirculatory control system. Despite variations in experimental designs and the severity, frequency, and duration of hypoxia exposure, evidence from animal and human models consistently demonstrates the robust effects of hypoxemia in triggering reflex-mediated sympathetic activation. Both acute and chronic hypoxia alters neurocirculatory regulation and, in some circumstances, leads to sympathetic outflow and elevated blood pressures that persist beyond the hypoxic stimulus. Dysregulation of autonomic control could lead to adverse cardiovascular outcomes and increase the risk of developing hypertension.

Intermittent hypoxia: a call for harmonization in terminology

Mild intermittent hypoxia may be a potent novel strategy to improve cardiovascular function, motor and cognitive function, and altitude acclimatization. However, there is still a stigma surrounding the field of intermittent hypoxia (IH). Major contributors to this stigma may be due to the overlapping terminology, heterogeneous methodological approaches, and an almost dogmatic focus on different mechanistic underpinnings in different fields of research. Many clinicians and investigators explore the pathophysiological outcomes following long-term exposure to IH in an attempt to improve our understanding of sleep apnea (SA) and develop new treatment plans. However, others use IH as a tool to improve physiological outcomes such as blood pressure, motor function, and altitude acclimatization. Unfortunately, studies investigating the pathophysiology of SA or the potential benefit of IH use similar, unstandardized terminologies facilitating a confusion surrounding IH protocols and the intentions of various studies. In this perspective paper, we aim to highlight IH terminology-related issues with the aim of spurring harmonization of the terminology used in the field of IH research to account for distinct outcomes of hypoxia exposure depending on protocol and individuum.

Anemia and Hypoxia Impact on Chronic Kidney Disease Onset and Progression: Review and Updates

Chronic kidney disease (CKD) is caused by hypoxia in the renal tissue, leading to inflammation and increased migration of pathogenic cells. Studies showed that leukocytes directly sense hypoxia and respond by initiating gene transcription, encoding the 2-integrin adhesion molecules. Moreover, other mechanisms participate in hypoxia, including anemia. CKD-associated anemia is common, which induces and worsens hypoxia, contributing to CKD progression. Anemia correction can slow CKD progression, but it should be cautiously approached. In this comprehensive review, the underlying pathophysiology mechanisms and the impact of renal tissue hypoxia and anemia in CKD onset and progression will be reviewed and discussed in detail. Searching for the latest updates in PubMed Central, Medline, PubMed database, Google Scholar, and Google search engines were conducted for original studies, including cross-sectional studies, cohort studies, clinical trials, and review articles using different keywords, phrases, and texts such as "CKD progression, anemia in CKD, CKD, anemia effect on CKD progression, anemia effect on CKD progression, and hypoxia and CKD progression". Kidney tissue hypoxia and anemia have an impact on CKD onset and progression. Hypoxia causes nephron cell death, enhancing fibrosis by increasing interstitium protein deposition, inflammatory cell activation, and apoptosis. Severe anemia correction improves life quality and may delay CKD progression. Detection and avoidance of the risk factors of hypoxia prevent recurrent acute kidney injury (AKI) and reduce the CKD rate. A better understanding of kidney hypoxia would prevent AKI and CKD and lead to new therapeutic strategies.

Investigating the Relationship between Obstructive Sleep Apnoea, Inflammation and Cardio-Metabolic Diseases

Obstructive sleep apnoea (OSA) is a prevalent underdiagnosed disorder whose incidence increases with age and weight. Uniquely characterised by frequent breathing interruptions during sleep-known as intermittent hypoxia (IH)-OSA disrupts the circadian rhythm. Patients with OSA have repeated episodes of hypoxia and reoxygenation, leading to systemic consequences. OSA consequences range from apparent symptoms like excessive daytime sleepiness, neurocognitive deterioration and decreased quality of life to pathological complications characterised by elevated biomarkers linked to endocrine-metabolic and cardiovascular changes. OSA is a well-recognized risk factor for cardiovascular and cerebrovascular diseases. Furthermore, OSA is linked to other conditions that worsen cardiovascular outcomes, such as obesity. The relationship between OSA and obesity is complex and reciprocal, involving interaction between biological and lifestyle factors. The pathogenesis of both OSA and obesity involve oxidative stress, inflammation and metabolic dysregulation. The current medical practice uses continuous positive airway pressure (CPAP) as the gold standard tool to manage OSA. It has been shown to improve symptoms and cardiac function, reduce cardiovascular risk and normalise biomarkers. Nonetheless, a full understanding of the factors involved in the deleterious effects of OSA and the best methods to eliminate their occurrence are still poorly understood. In this review, we present the factors and evidence linking OSA to increased risk of cardiovascular conditions.

Relationship between obstructive sleep apnea, insulin resistance, and metabolic syndrome: a nationwide population-based survey

We aimed to identify the association between obstructive sleep apnea (OSA), insulin resistance (IR), and metabolic syndrome (MetS) in a nationwide population-based sample. A total of 7,900 adults with information on the STOP-Bang score and MetS (3,341 men and 4,469 women) were identified from the dataset of the Korea National Health and Nutrition Examination Survey 2019-2020. The association between OSA, IR, MetS, and its components was estimated using complex sample logistic regression analysis with adjustments for age, body mass index, residence, smoking status, alcohol consumption, household income, education, and the presence of diabetes. Participants with a high OSA score were more likely to have IR (odds ratio [OR] 2.78, 95% confidence interval [CI] 1.96-3.95 in men and OR 2.64, 95% CI 0.55-12.80 in women), MetS (OR 6.05, 95% CI 4.23-8.69 in men and OR 4.20, 95% CI 1.23-15.70 in women), and components of MetS, compared to individuals with a low OSA score. Compared to premenopausal women, postmenopausal women had a more intense association between OSA and IR (OR 1.78, 95% CI 0.13-24.43 for premenopausal women and OR 3.64, 95% CI 0.60-22.28 for postmenopausal women) and MetS (OR 2.58, 95% CI 0.23-29.55 for premenopausal women and OR 5.36, 95% CI 1.42-20.21 for postmenopausal women). OSA was associated with abdominal obesity and hypertension in premenopausal women, while all components of MetS were associated with OSA in postmenopausal women. Further studies are necessary to elucidate the underlying mechanisms of these findings.

Effects of a Maximal Exercise Followed by a Submaximal Exercise Performed in Normobaric Hypoxia (2500 m), on Blood Rheology, Red Blood Cell Senescence, and Coagulation in Well-Trained Cyclists

Acute normoxic exercise impacts the rheological properties of red blood cells (RBC) and their senescence state; however, there is a lack of data on the effects of exercise performed in hypoxia on RBC properties. This crossover study compared the effects of acute hypoxia vs. normoxia on blood rheology, RBC senescence, and coagulation during exercise. Nine trained male cyclists completed both a session in normoxia (FiO₂ = 21%) and hypoxia (FiO₂ = 15.3% ≈ 2500 m). The two sessions were randomly performed, separated by one week, and consisted of an incremental and maximal exercise followed by a 20 min exercise at the first ventilatory threshold (VT1) on a home-trainer. Blood samples were taken before and after exercise to analyze hematological parameters, blood rheology (hematocrit, blood viscosity, RBC deformability and aggregation), RBC senescence markers (phosphatidylserine (PS) and CD47 exposure, intraerythrocyte reactive oxygen species (ROS), and calcium content), and blood clot viscoelastic properties. Hemoglobin oxygen saturation (SpO₂) and blood lactate were also measured. In both conditions, exercise induced an increase in blood viscosity, hematocrit, intraerythrocyte calcium and ROS content, and blood lactate concentration. We also observed an increase in blood clot amplitude, and a significant drop in SpO₂ during exercise in the two conditions. RBC aggregation and CD47 exposure were not modified. Exercise in hypoxia induced a slight decrease in RBC deformability which could be related to the slight increase in mean corpuscular hemoglobin concentration (MCHC). However, the values of RBC deformability and MCHC after the exercise performed in hypoxia remained in the normal range of values. In conclusion, acute hypoxia does not amplify the RBC and coagulation changes induced by an exercise bout.

Experimental Models to Study End-Organ Morbidity in Sleep Apnea: Lessons Learned and Future Directions

Sleep apnea (SA) is a very prevalent sleep breathing disorder mainly characterized by intermittent hypoxemia and sleep fragmentation, with ensuing systemic inflammation, oxidative stress, and immune deregulation. These perturbations promote the risk of end-organ morbidity, such that SA patients are at increased risk of cardiovascular, neurocognitive, metabolic and malignant disorders. Investigating the potential mechanisms underlying SA-induced end-organ dysfunction requires the use of comprehensive experimental models at the cell, animal and human levels. This review is primarily focused on the experimental models employed to date in the study of the consequences of SA and tackles 3 different approaches. First, cell culture systems whereby controlled patterns of intermittent hypoxia cycling fast enough to mimic the rates of episodic hypoxemia experienced by patients with SA. Second, animal models consisting of implementing realistic upper airway obstruction patterns, intermittent hypoxia, or sleep fragmentation such as to reproduce the noxious events characterizing SA. Finally, human SA models, which consist either in subjecting healthy volunteers to intermittent hypoxia or sleep fragmentation, or alternatively applying oxygen supplementation or temporary nasal pressure therapy withdrawal to SA patients. The advantages, limitations, and potential improvements of these models along with some of their pertinent findings are reviewed.

Sleep-disordered breathing in high-risk pregnancies is associated with elevated arterial stiffness and increased risk for preeclampsia

BACKGROUND

Impaired vascular function is a central feature of pathologic processes preceding the onset of preeclampsia. Arterial stiffness, a composite indicator of vascular health and an important vascular biomarker, has been found to be increased throughout pregnancy in those who develop preeclampsia and at the time of preeclampsia diagnosis. Although sleep-disordered breathing in pregnancy has been associated with increased risk for preeclampsia, it is unknown if sleep-disordered breathing is associated with elevated arterial stiffness in pregnancy.

OBJECTIVE

This prospective observational cohort study aimed to evaluate arterial stiffness in pregnant women, with and without sleep-disordered breathing and assess the interaction between arterial stiffness, sleep-disordered breathing, and preeclampsia risk.

STUDY DESIGN

Women with high-risk singleton pregnancies were enrolled at 10 to 13 weeks' gestation and completed the Epworth Sleepiness Score, Pittsburgh Sleep Quality Index, and Restless Legs Syndrome questionnaires at each trimester. Sleep-disordered breathing was defined as loud snoring or witnessed apneas (≥3 times per week). Central arterial stiffness (carotid-femoral pulse wave velocity, the gold standard measure of arterial stiffness), peripheral arterial stiffness (carotid-radial pulse wave velocity), wave reflection (augmentation index, time to wave reflection), and hemodynamics (central blood pressures, pulse pressure amplification) were assessed noninvasively using applanation tonometry at recruitment and every 4 weeks from recruitment until delivery.

RESULTS

High-risk pregnant women (n=181) were included in the study. Women with sleep-disordered breathing (n=41; 23%) had increased carotid-femoral pulse wave velocity throughout gestation independent of blood pressure and body mass index (P=.042). Differences observed in other vascular measures were not maintained after adjustment for confounders. Excessive daytime sleepiness, defined by Epworth Sleepiness Score >10, was associated with increased carotid-femoral pulse wave velocity only in women with sleep-disordered breathing (P_interaction=.001). Midgestation (first or second trimester) sleep-disordered breathing was associated with an odds ratio of 3.4 (0.9-12.9) for preeclampsia, which increased to 5.7 (1.1-26.0) in women with sleep-disordered breathing and hypersomnolence, whereas late (third-trimester) sleep-disordered breathing was associated with an odds ratio of 8.2 (1.5-39.5) for preeclampsia.

CONCLUSION

High-risk pregnant women with midgestational sleep-disordered breathing had greater arterial stiffness throughout gestation than those without. Sleep-disordered breathing at any time during pregnancy was also associated with increased preeclampsia risk, and this effect was amplified by hypersomnolence.

Characterization of the Impacts of Living at High Altitude in Taif: Oxidative Stress Biomarker Alterations and Immunohistochemical Changes

At high elevations, the human body experiences a number of pathological, physiological, and biochemical changes, all of which have adverse impacts on human health and organ vitality. This study aimed to investigate the alterations in the liver and kidney biomarkers, oxidative stress markers, gene expression, and cellular histology of rats maintained at high altitudes and normal sea level. A total of twenty male Wistar rats at 2 months of age were randomly assigned to two groups. The rats in group A were maintained at normal sea level in Jeddah, whereas rats in group B were maintained in an area in Taif 2600 m above sea level. After 2 months of housing, orbital blood samples were collected for the analysis of significant biochemical indicators of oxidative stress biomarkers of the liver and kidneys. Liver and kidney tissues from both groups were taken to examine the hepatorenal changes occurring at the biochemical, histological, immunohistochemical, and genetic levels. The results revealed substantial increases in the serum levels of liver and kidney biomarkers (GPT, GOT, urea, and creatinine) and decreases in the serum levels of antioxidant biomarkers (SOD, catalase, GSH, and NO). In parallel, the levels of the malondialdehyde (MDA) tissue damage marker and inflammatory cytokines (IL-1β, TNF-α, and IFN-γ) were increased in the high-altitude group compared to the normal sea level group. In addition, there were significant alterations in the oxidative and inflammatory status of rats that lived at high altitude, with considerable upregulation in the expression of hepatic VEGF, type 1 collagen, Cox-2, TNF-α, and iNOS as well as renal EPASI, CMYC, HIF-α, and EGLN-2 genes in the high-altitude group compared with controls housed at normal sea level. In conclusion, living at high altitude induces hepatorenal damage and biochemical and molecular alterations, all of which may serve as critical factors that must be taken into account for organisms living at high altitudes.

Oxygen saturation as a predictor of inflammation in obstructive sleep apnea

PURPOSE

Obstructive sleep apnea (OSA) is a chronic sleep disorder, and its prevalence is increasing worldwide. This disorder has been consistently associated with several comorbidities. Although it is clear that obstructive sleep apnea severity is associated with inflammation, the trigger for this phenomenon continues to puzzle scientists. Here, we investigated the relationship between obstructive sleep apnea severity and immune parameters.

METHODS

In this cross-sectional epidemiological research, we analyzed the immune profile of 461 adults according to OSA severity (mild, moderate, and severe) and oxygen saturation.

RESULTS

The hallmark of OSA severity - the apnea-hypopnea index (AHI) - weakly correlated with an inflammatory profile. However, individuals who experienced lower oxygen saturation were more likely to exhibit higher total leukocyte and neutrophil counts, a higher neutrophil-lymphocyte ratio (NLR), and an increased concentration of C-reactive protein.

CONCLUSION

Our findings indicated that oxygen saturation is a predictor of inflammation during OSA and should be considered crucial in disease diagnostic and treatment strategies.

Risk for Cardiovascular Disease and One-Year Mortality in Patients With Chronic Obstructive Pulmonary Disease and Obstructive Sleep Apnea Syndrome Overlap Syndrome

Background: Patients with chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSAS) overlap syndrome (OS) are thought to be at increased risk for cardiovascular diseases.

Objective: To evaluate the burden of cardiovascular diseases and long-term outcomes in patients with OS.

Methods: This was a retrospective cohort study. The prevalence of cardiovascular diseases and 1-year mortality were compared among patients diagnosed with OS (OS group), COPD alone (COPD group) and OSAS alone (OSAS group), and Cox proportional hazards models were used to assess independent risk factors for all-cause mortality.

Results: Overall, patients with OS were at higher risk for pulmonary hypertension (PH), heart failure and all-cause mortality than patients with COPD or OSAS (all p < 0.05). In multivariate Cox regression analysis, the Charlson comorbidity index (CCI) score [adjusted hazard ratio (aHR): 1.273 (1.050–1.543); p = 0.014], hypertension [aHR: 2.006 (1.005–4.004); p = 0.048], pulmonary thromboembolism (PTE) [aHR: 4.774 (1.335–17.079); p = 0.016] and heart failure [aHR: 3.067 (1.521–6.185); p = 0.002] were found to be independent risk factors for 1-year all-cause mortality.

Conclusion: Patients with OS had an increased risk for cardiovascular diseases and 1-year mortality. More efforts are needed to identify the causal relationship between OS and cardiovascular diseases, promoting risk stratification and the management of these patients.

Impact of intermittent hypoxia on human vascular responses during sleep

Exposure to intermittent hypoxia (IH) ≥15 times per hour is believed to be the primary mechanism for the increased risk of cerebrovascular and cardiovascular disease in patients with moderate to severe sleep apnea. Human experimental models of IH used to investigate this link have been predominantly employed during wakefulness, which limits extrapolation of findings to sleep apnea where IH occurs during sleep. Moreover, how IH impacts vascular regulation during sleep has not been measured quantitatively. Therefore, the objective of this study was to assess the impact sleep accompanied by IH on vascular responses to hypoxia and hypercapnia during sleep. Ten males performed two randomly scheduled 6-h overnight sleep studies. One sleep study was performed in room air (normoxia) and the other sleep study was performed during isocapnic IH (60 s hypoxia-60 s normoxia). On each night, cerebrovascular (peak blood velocity through the middle cerebral artery (V¯_P); transcranial Doppler ultrasound) and cardiovascular (blood pressure, heart rate) responses to hypoxia and hypercapnia were measured before sleep onset (PM-Awake), within the first 2 h of sleep (PM-Asleep), in the 5th (out of 6) hours of sleep (AM-Asleep) and after being awoken in the morning (AM-Awake). Sleep accompanied by IH had no impact on the V¯_P and blood pressure responses to hypoxia and hypercapnic at any timepoint (p ≥ 0.103 for all responses). However, the AM-Awake heart rate response to hypoxia was greater following sleep in IH compared to sleep in normoxia. Independent of the sleep environment, the V¯_P response to hypoxia and hypercapnia were reduced during sleep. In conclusion, cerebral blood flow responses are reduced during sleep compared to wakefulness, but 6 h of sleep accompanied by IH does not alter cerebrovascular and cardiovascular response to hypoxia and hypercapnia during wakefulness or sleep in healthy young humans. However, it is likely that longer exposure to IH during sleep (i.e., days-to-weeks) is required to better elucidate IH's impact on vascular regulation in humans.

Sleep-disordered breathing is independently associated with reduced atrial connexin 43 expression

BACKGROUND

Patients with atrial fibrillation (AF) exhibit decreased atrial expression of connexin (Cx), which has been causally linked to a proarrhythmogenic substrate. Interestingly, patients with sleep-disordered breathing (SDB) are at increased risk of AF, but the mechanisms remain unclear.

OBJECTIVE

We tested the hypothesis that patients with SDB have reduced atrial Cx expression independent of important comorbidities.

METHODS

We analyzed right atrial appendage biopsies from 77 patients undergoing coronary artery bypass grafting. Patients were tested for SDB by polygraphy before surgery. Expression of Cx40 and Cx43 messenger RNA was quantified using real-time quantitative polymerase chain reaction and Western blot (Cx43). Structural atrial remodeling was investigated histologically and by quantitative polymerase chain reaction. Postoperative AF was assessed by 12-lead electrocardiography.

RESULTS

Patients were stratified according to apnea-hypopnea index (SDB if apnea-hypopnea index ≥15 per hour, n = 32 vs n = 45). Patients with SDB had significantly lower atrial Cx43 expression, which was negatively correlated with apnea-hypopnea index and oxygen desaturation index. No significant increase in atrial fibrosis or expression of hypertrophy and inflammatory markers was observed. Interestingly, SDB remained the strongest independent predictor of decreased atrial Cx43 expression in a multivariate logistic regression model including age, sex, diabetes, and heart failure with reduced ejection fraction (odds ratio 7.58; 95% confidence interval 1.891-30.375; P = .004). Moreover, reduced atrial Cx43 expression was strongly associated with the occurrence of postoperative AF (odds ratio 15.749; 95% confidence interval 1.072-231.472; P = .044).

CONCLUSION

Patients with SDB exhibited decreased atrial Cx43 expression, which correlated with the severity of SDB. This correlation was independent of several concomitant diseases and may be linked to an increased risk of AF after cardiac surgery.

Whole-genome association analyses of sleep-disordered breathing phenotypes in the NHLBI TOPMed program

BACKGROUND

Sleep-disordered breathing is a common disorder associated with significant morbidity. The genetic architecture of sleep-disordered breathing remains poorly understood. Through the NHLBI Trans-Omics for Precision Medicine (TOPMed) program, we performed the first whole-genome sequence analysis of sleep-disordered breathing.

METHODS

The study sample was comprised of 7988 individuals of diverse ancestry. Common-variant and pathway analyses included an additional 13,257 individuals. We examined five complementary traits describing different aspects of sleep-disordered breathing: the apnea-hypopnea index, average oxyhemoglobin desaturation per event, average and minimum oxyhemoglobin saturation across the sleep episode, and the percentage of sleep with oxyhemoglobin saturation < 90%. We adjusted for age, sex, BMI, study, and family structure using MMSKAT and EMMAX mixed linear model approaches. Additional bioinformatics analyses were performed with MetaXcan, GIGSEA, and ReMap.

RESULTS

We identified a multi-ethnic set-based rare-variant association (p = 3.48 × 10-8) on chromosome X with ARMCX3. Additional rare-variant associations include ARMCX3-AS1, MRPS33, and C16orf90. Novel common-variant loci were identified in the NRG1 and SLC45A2 regions, and previously associated loci in the IL18RAP and ATP2B4 regions were associated with novel phenotypes. Transcription factor binding site enrichment identified associations with genes implicated with respiratory and craniofacial traits. Additional analyses identified significantly associated pathways.

CONCLUSIONS

We have identified the first gene-based rare-variant associations with objectively measured sleep-disordered breathing traits. Our results increase the understanding of the genetic architecture of sleep-disordered breathing and highlight associations in genes that modulate lung development, inflammation, respiratory rhythmogenesis, and HIF1A-mediated hypoxic response.

The role of NADPH oxidase in chronic intermittent hypoxia-induced respiratory plasticity in adult male mice

Reactive oxygen species (ROS) are proposed as mediators of chronic intermittent hypoxia (CIH)-induced respiratory plasticity. We sought to determine if NADPH oxidase 2 (NOX2)-derived ROS underpin CIH-induced maladaptive changes in respiratory control. Adult male mice (C57BL/6 J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) given in the drinking water throughout exposure to CIH. In addition, we studied sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Whole-body plethysmography was used to measure breathing and metabolic parameters. Ventilation (V̇_I/V̇CO₂) during normoxia was unaffected by CIH, but apnoea index was increased, which was prevented by apocynin, but not by NOX2 deletion. The ventilatory response to hypercapnia following exposure to CIH was potentiated in NOX2-null mice. Our results reveal ROS-dependent influences on the control of breathing and point to antioxidant intervention as a potential adjunctive therapeutic strategy in respiratory control disorders.

Daytime Napping Duration Is Positively Associated With Risk of Hyperuricemia in a Chinese Population

CONTEXT

Loss of sleep or disturbance of sleep-wake cycles has been related to metabolic impairments. However, few studies have investigated the association between daily sleep duration and hyperuricemia.

OBJECTIVE

We investigated daily sleep duration (daytime napping and nocturnal sleep) with hyperuricemia risk.

METHODS

We cross-sectionally analyzed data from the China Multi-Ethnic Cohort (CMEC), Yunnan region. A total of 22 038 participants aged 30 to 79 years were recruited in 2018. Hyperuricemia was defined as serum uric acid (SUA) above 7.0 mg/dL in men and above 6.0 mg/dL in women. Outcomes were associations between daily sleep duration and hyperuricemia.

RESULTS

We found that the longest daytime napping duration was associated with a higher risk of hyperuricemia in the crude model (odds ratio [OR] [95% CI], 2.22 [1.88-2.61], P < .001) and in a multivariable adjustment model (OR, 1.69; 95% CI, 1.41-2.01, P < .001) after adjusting for demographic, sleep habits, and metabolic risk factors. The association was moderately attenuated with additionally adjusted for serum creatinine (OR, 1.54; 95% CI, 1.28-1.86, P < .001). Longer daytime napping duration was also related to higher risk of hyperuricemia combined with metabolic syndrome (MetS). Respondents in the group with daytime napping duration greater than or equal to 90 minutes presented with a higher risk of hyperuricemia combined with MetS (OR, 1.39; 95% CI, 1.06-1.79; P < .001) in the fully adjusted model. We did not observe any relation between nocturnal sleep duration and risk of hyperuricemia in the study.

CONCLUSION

Longer daytime napping duration (but not nocturnal sleep duration) was independently associated with risk of hyperuricemia in a Chinese population.

The relationship between metabolic syndrome and obstructive sleep apnea syndrome: a nationwide population-based study

There has been a need for research on the association between metabolic syndrome (MetS) and obstructive sleep apnea syndrome (OSAS) using large data such as nationwide population-based data that adjusts important confounding factors. Therefore, we investigated the relationship between MetS and OSAS. The data source we used was the National Health Insurance Service claims database managed by the Republic of Korea government, in which 10,113,560 individuals were enrolled in 2009 and followed up until 2018. The independent association of MetS with the risk of OSAS was determined using a Cox proportional hazards model with adjustment for age, sex, smoking status, alcohol consumption, regular physical exercise, and body mass index. Our results showed that MetS were strongly associated to OSAS which was adjusted for several confounding factors. Also, we found men, increased waist circumference and increased triglyceride are important risk factors for OSAS.

A comprehensive review of respiratory, autonomic and cardiovascular responses to intermittent hypoxia in humans

This review explores forms of respiratory and autonomic plasticity, and associated outcome measures, that are initiated by exposure to intermittent hypoxia. The review focuses primarily on studies that have been completed in humans and primarily explores the impact of mild intermittent hypoxia on outcome measures. Studies that have explored two forms of respiratory plasticity, progressive augmentation of the hypoxic ventilatory response and long-term facilitation of ventilation and upper airway muscle activity, are initially reviewed. The role these forms of plasticity might have in sleep disordered breathing are also explored. Thereafter, the role of intermittent hypoxia in the initiation of autonomic plasticity is reviewed and the role this form of plasticity has in cardiovascular and hemodynamic responses during and following intermittent hypoxia is addressed. The role of these responses in individuals with sleep disordered breathing and spinal cord injury are subsequently addressed. Ultimately an integrated picture of the respiratory, autonomic and cardiovascular responses to intermittent hypoxia is presented. The goal of the integrated picture is to address the types of responses that one might expect in humans exposed to one-time and repeated daily exposure to mild intermittent hypoxia. This form of intermittent hypoxia is highlighted because of its potential therapeutic impact in promoting functional improvement and recovery in several physiological systems.

Pro-Oxidant/Antioxidant Balance during a Prolonged Exposure to Moderate Altitude in Athletes Exhibiting Exercise-Induced Hypoxemia at Sea-Level

This study examined to what extent athletes exhibiting exercise-induced hypoxemia (EIH) possess an altered redox status at rest, in response to exercise at sea level (SL) and during moderate altitude exposure. EIH was defined as a fall in arterial O₂ saturation of at least 4% during exercise. Nine endurance athletes with EIH and ten without (NEIH) performed a maximal incremental test under three conditions: SL, one (H1) and five (H2) days after arrival to 2400 m. Gas exchange and peripheral capillary oxygen saturation (SpO₂) were continuously monitored. Blood was sampled before exercise and after exercise cessation. Advanced oxidation protein products (AOPP), catalase, ferric-reducing antioxidant power, glutathione peroxidase, superoxide dismutase (SOD) and nitric oxide metabolites (NOx) were measured in plasma by spectrophotometry. EIH athletes had higher AOPP and NOx concentrations at pre- and post-exercise stages compared to NEIH at SL, H2 but not at H1. Only the EIH group experienced increased SOD activity between pre- and post-exercise exercise at SL and H2 but not at H1. EIH athletes had exacerbated oxidative stress compared to the NEIH athletes at SL and H2. These differences were blunted at H1. Oxidative stress did not alter the EIH groups’ aerobic performance and could lead to higher minute ventilation at H2. These results suggest that higher oxidative stress response EIH athletes could be involved in improved aerobic muscle functionality and a greater ventilatory acclimatization during prolonged hypoxia.

The effects of normoxic endurance exercise on erythropoietin (EPO) production and the impact of selective β1 and non-selective β1 + β2 adrenergic receptor blockade

PURPOSE

Habitual endurance exercise results in increased erythropoiesis, which is primarily controlled by erythropoietin (EPO), yet studies demonstrating upregulation of EPO via a single bout of endurance exercise have been equivocal. This study compares the acute EPO response to 30 min of high versus 90 min of moderate-intensity endurance exercise and whether that response can be upregulated via selective adrenergic receptor blockade.

METHODS

Using a counterbalanced, cross-over design, fifteen participants (age 28 ± 8) completed two bouts of running (30-min, high intensity vs 90-min, moderate intensity) matched for overall training stress. A separate cohort of fourteen participants (age 31 ± 6) completed three bouts of 30-min high-intensity cycling after ingesting the preferential β₁-adrenergic receptor (AR) antagonist bisoprolol, the non-preferential β₁ + β₂ antagonist nadolol or placebo. Venous blood was collected before, during, and after exercise, and serum EPO levels were determined by ELISA.

RESULTS

No detectable EPO response was observed during or after high intensity running, however, in the moderate-intensity trial EPO was significantly elevated at both during-exercise timepoints (+ 6.8% ± 2.3% at 15 min and + 8.7% ± 2.2% at 60 min). No significant change in EPO was observed post-cycling or between the trials involving βAR blockade.

CONCLUSION

Neither training mode (running or cycling), nor beta-blockade significantly influenced the EPO response to 30 min of high-intensity exercise, however, 90 min of moderate-intensity running elevated EPO during exercise, returning to baseline immediately post-exercise. Identifying the optimal mode, duration and intensity required to evoke an EPO response to exercise may help tailor exercise prescriptions designed to maximize EPO response for both performance and clinical applications.

Interstitial lung disease and obstructive sleep apnea

Obstructive sleep apnea (OSA) is one of the most common comorbidities in patients with interstitial lung disease (ILD). Growing evidence highlights the significance of sleep disturbance on health outcomes in this population. The relationships between ILD and OSA are complex and possibly bidirectional, with multiple mechanisms postulated for the pathogenic and physiologic links. This review synthesizes current evidence and hypotheses regarding different aspects of the relationships between ILD and OSA, emphasizing the interactions between epidemiology, pathogenesis, and pathophysiology.

Histogenous Hypoxia and Acid Retention in Schizophrenia: Changes in Venous Blood Gas Analysis and SOD in Acute and Stable Schizophrenia Patients

Background: Oxidative stress may play an important role in the pathogenesis of schizophrenia (SCH), and there is considerable indirect evidence that hypoxia is closely related to SCH, but direct evidence of hypoxia in SCH has never been found. Methods:In this study, superoxide dismutase (SOD), venous blood gas, and Positive and Negative Syndrome Scale (PANSS) were examined in 40 SCH patients and compared with those of 40 healthy controls. The patients were treated with combination of atypical antipsychotics and Ditan Huayu Lishen decoction (a Chinese medicine decoction) and examined in the acute and stable period, respectively. Comparisons of indicators between two groups were performed using an independent-samples t-test, comparison of indicators between the acute and stable periods in the SCH group was performed using paired-samples t-test. Pearson correlation and multiple linear regression analyses were performed to investigate the relationships between the effect indicators. Results: Higher venous pH, PvO₂, and fasting blood glucose levels and lower SOD, lactic acid, and PvCO₂ levels were found in SCH patients compared with the control group; SOD was negatively correlated with the general psychopathology subscale score (PANSS-G), and PvO₂ levels were closely related to venous pH in SCH and related to PvCO₂ in the control group. It was also found that SOD activity showed no significant difference in acute and stable period, whereas PvO₂ showed a downward trend, and venous pH was decreased significantly after treatment. Both the venous pH and PvO₂ were higher in patients with SCH than that in healthy controls. Conclusion: It suggests that histogenous hypoxia and acid retention exist in relation to SCH, and there is an improvement of acid retention and a downward trend in histogenous hypoxia after combination treatment. Venous pH, PvO₂, and PvCO₂ are trait variables, but not state variables of SCH. The theory of histogenous hypoxia and acid retention can well explain the decrease in pH value and the increase in lactic acid in brain tissue of patients with SCH. Histogenous hypoxia and acid retention closely related to glucose metabolism. So they may play an important role in pathophysiology for SCH.

Skin sympathetic nerve activity in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with increased cardiac arrhythmia and sudden cardiac death. We recently developed a new method (neuECG) to noninvasively measure electrocardiogram and skin sympathetic nerve activity (SKNA).

OBJECTIVE

The purpose of this study was to test the hypothesis that SKNA measured during sleep study is higher in patients with OSA than in those without OSA.

METHODS

We prospectively recorded neuECG and polysomnography in 26 patients undergoing a sleep study. Sleep stages were scored into rapid eye movement (REM), and non-REM sleep stages 1 (N1), 2 (N2), and 3 (N3). Average voltage of skin sympathetic nerve activity (aSKNA) and SKNA burst area were calculated for quantification. Apnea/hypopnea index (AHI) >5 per hour was used to diagnose OSA.

RESULTS

There was a positive correlation (r = 0.549; P = .018) between SKNA burst area and the arousal index in OSA but not in the control group. aSKNA during sleep was 0.61 ± 0.09 μV in OSA patients (n = 18) and 0.53 ± 0.04 μV in control patients (n = 8; P = .025). Burst area was 3.26 (1.90-4.47) μV·s/min in OSA patients and 1.31 (0.67-1.94) μV·s/min in control (P = .047). More apparent differences were found during N2, when the burst area in OSA (3.06 [1.46-5.52] μV·s/min) was much higher than that of the control (0.89 [0.79-1.65] μV·s/min; P = .03).

CONCLUSION

OSA patients have higher SKNA activity than control patients, with the most pronounced differences observed during N2. Arousal at the end of apnea episodes is associated with large SKNA bursts. Overlaps of aSKNA and SKNA burst area between groups suggest that not all OSA patients have increased sympathetic tone.

Understanding the pathophysiological mechanisms of cardiometabolic complications in obstructive sleep apnoea: towards personalised treatment approaches

In January 2019, a European Respiratory Society research seminar entitled "Targeting the detrimental effects of sleep disturbances and disorders" was held in Dublin, Ireland. It provided the opportunity to critically review the current evidence of pathophysiological responses of sleep disturbances, such as sleep deprivation, sleep fragmentation or circadian misalignment and of abnormalities in physiological gases such as oxygen and carbon dioxide, which occur frequently in respiratory conditions during sleep. A specific emphasis of the seminar was placed on the evaluation of the current state of knowledge of the pathophysiology of cardiovascular and metabolic diseases in obstructive sleep apnoea (OSA). Identification of the detailed mechanisms of these processes is of major importance to the field and this seminar offered an ideal platform to exchange knowledge, and to discuss pitfalls of current models and the design of future collaborative studies. In addition, we debated the limitations of current treatment strategies for cardiometabolic complications in OSA and discussed potentially valuable alternative approaches.

Case Studies in Physiology: Sympathetic neural discharge patterns in a healthy young male during end-expiratory breath hold-induced sinus pause

This case study reports the efferent muscle sympathetic nerve activity (MSNA) discharge patterns during a sinus pause observed during a maximal end-expiratory apnea in a young healthy male (age = 26 yr). During a 15.3-s end-expiratory apnea following a bout of intermittent hypercapnic hypoxia, we observed a 5.2-s (R-R interval) sinus pause and integrated MSNA recording, demonstrating a square-wave discharge pattern atypical of sharp MSNA burst peaks entrained to cardiac cycles or during preventricular contractions. This abnormal MSNA discharge pattern was observed again during a follow-up experiment, where an end-expiratory apnea at baseline resulted in pronounced bradycardia (R-R intervals >2.5-s) but failed to reproduce the 5.2-s sinus pause. Action potential (AP) discharge patterns during MSNA bursts were detected using a continuous wavelet transform approach. AP discharge increased by 300% during the end-expiratory apnea with 5.2-s sinus pause compared with baseline and involved increased firing (i.e., rate-coding) of AP clusters (bins of AP with similar morphology) already present during baseline and pronounced recruitment of larger-amplitude AP clusters not present at baseline. Large-amplitude AP clusters continued to discharge during sinus pause. In summary, we show MSNA discharge during sinus pause and pronounced bradycardia during end-expiratory apnea, which demonstrates a square-wave discharge with recruitment of latent larger-amplitude AP clusters. The MSNA discharge was terminated before systole following sinus pause potentially through an inhibitory influence of inspiration, or cardiac mechanoreceptor feedback causing burst termination.NEW & NOTEWORTHY We characterize the occurrence of a square-wave discharge pattern of efferent muscle sympathetic nerve activity during a sinus pause in a young healthy male. This discharge pattern comprised large recruited action potential clusters undetected at baseline that continuously discharged during the sinus pause. Notably, this discharge pattern was still contained within a single cardiac cycle.

Cardiovascular and metabolic responses to passive hypoxic conditioning in overweight and mildly obese individuals

Although severe intermittent hypoxia (IH) is well known to induce deleterious cardiometabolic consequences, moderate IH may induce positive effects in obese individuals. The present study aimed to evaluate the effect of two hypoxic conditioning programs on cardiovascular and metabolic health status of overweight or obese individuals. In this randomized single-blind controlled study, 35 subjects (54 ± 9.3 yr, 31.7 ± 3.5 kg/m²) were randomized into three 8-wk interventions (three 1-h sessions per week): sustained hypoxia (SH), arterial oxygen saturation ([Formula: see text]) = 75%; IH, 5 min [Formula: see text] = 75% - 3 min normoxia; normoxia. Ventilation, heart rate, blood pressure, and tissue oxygenation were measured during the first and last hypoxic conditioning sessions. Vascular function, blood glucose and insulin, lipid profile, nitric oxide metabolites, and oxidative stress were evaluated before and after the interventions. Both SH and IH increased ventilation in hypoxia (+1.8 ± 2.1 and +2.3 ± 3.6 L/min, respectively; P < 0.05) and reduced normoxic diastolic blood pressure (-12 ± 15 and -13 ± 10 mmHg, respectively; P < 0.05), whereas changes in normoxic systolic blood pressure were not significant (+3 ± 9 and -6 ± 13 mmHg, respectively; P > 0.05). IH only reduced heart rate variability (e.g., root-mean-square difference of successive normal R-R intervals in normoxia -21 ± 35%; P < 0.05). Both SH and IH induced no significant change in body mass index, vascular function, blood glucose, insulin and lipid profile, nitric oxide metabolites, or oxidative stress, except for an increase in superoxide dismutase activity following SH. This study indicates that passive hypoxic conditioning in obese individuals induces some positive cardiovascular and respiratory improvements despite no change in anthropometric data and even a reduction in heart rate variability during IH exposure.

A combined γ-H2AX and 53BP1 approach to determine the DNA damage-repair response to exercise in hypoxia

This study examines the interplay between exercise and hypoxia in relation to the DNA damage-repair response; with specific interest to DNA double strand damage. Following two V̇O_2max tests, 14 healthy, male participants completed two exercise trials (hypoxia; 12% FiO₂, normoxia; 20.9% FiO₂) consisting of cycling for 30-min at 80-85% of V̇O_2max relative to the environmental condition. Blood was sampled pre-, immediately post-, 2-, and 4-h post-exercise with additional blood cultured in vitro for 24-, 48-, and 72-h following the experimental trial. Samples were analysed for single- and double-strand DNA damage, FPG-sensitive sites, lipid hydroperoxides, lipid soluble antioxidants, and the ascorbyl free radical quantified by EPR. Exercise increased single strand breaks and FPG-sensitive sites (P < 0.05) which was exacerbated following hypoxia (P = 0.02) and a similar increase in DNA double strand breaks occurred as a result of hypoxia per se (P < 0.000). With respect to the DNA damage-repair response, single strand breaks, FPG-sensitive sites, and double strand lesions were fully repaired by the 4- (in vivo), 24-, and 48-h (in vitro) time-points respectively. Changes in lipid hydroperoxides (P = 0.001), the ascorbyl free radical (P = 0.02), and lipid soluble antioxidants (P > 0.05), were also observed following exercise in hypoxia. These findings highlight significant single- and double strand DNA damage and oxidative stress as a function of high-intensity exercise, which is substantially exacerbated in hypoxia and may be attributed to multiple mechanisms of ROS generation. In addition, full repair of DNA damage (SSB, DSB, and FPG-sensitive sites) was observed within 24- and 48-h of normoxic and hypoxic exercise, respectively.

Obstructive Sleep Apnea and Circulating Biomarkers of Oxidative Stress: A Cross-Sectional Study

Oxidative stress (OS) drives cardiometabolic diseases. Intermittent hypoxia consistently increases oxidative stress markers. Obstructive sleep apnea (OSA) patients experience intermittent hypoxia and an increased rate of cardiovascular disease, however, the impact of OSA on OS markers is not clear. The objective was to assess relationships between OSA severity and biomarker levels. Patients with suspected OSA referred for a polysomnogram (PSG) provided fasting blood sample. Plasma levels of 8-isoprostane, 8-hydroxydeoxyguanosine (8-OHdG), and superoxide dismutase (SOD) were measured. The relationship between OSA and OS was assessed both before and after controlling for confounders (age, sex, smoking history, history of cardiovascular disease, ethnicity, diabetes, statin usage, body mass index (BMI)). 402 patients were studied (68% male, mean age ± SD = 50.8 ± 11.8 years, apnea-hypopnea index (AHI) = 22.2 ± 21.6 events/hour, BMI = 31.62 ± 6.49 kg/m²⁾. In a multivariable regression, the AHI significantly predicted 8-isoprostane levels (p = 0.0008) together with age and statin usage; AHI was not a predictor of 8-OHdG or SOD. Female sex (p < 0.0001) and no previous history of cardiovascular disease (p = 0.002) were associated with increased antioxidant capacity. Circulating 8-isoprostane levels may be a promising biomarker of the severity of oxidative stress in OSA patients. Prospective studies are needed to determine whether this biomarker is associated with long-term cardiometabolic complications in OSA.

Effect of increasing feed intake during late gestation on piglet performance at parturition in commercial production enterprises

The present study was conducted to investigate effects of feed intake during late gestation on piglet birth weight and reproductive performance of sows. At d 90 of gestation (Gd90), a total of 397 Landrance × Large White gilts (parity 1) and sows (parities 2, 3, and 4) were randomly assigned to three groups according to feed intake, 2.8 kg/d (energy maintenance requirement for gilts and sows, 8.40 Mcal/d ME), 3.6 kg/d (10.26 Mcal/d ME), and 4.0 kg/d (11.40 Mcal/d ME), respectively. All gilts and sows were individually fed. Results indicate the increase in feed intake had no effect on birth weight and uniformity of piglet weight at parturition for sows with different backfat thickness (BF) at Gd90 or with different parities. Additionally, lactation body weight (BW) loss was greater (P < 0.05) in response to the greater feed intake during late gestation. Furthermore, there were no correlations between feed intake during late gestation and litter weight, average piglet birth weight, coefficient variation of within-litter birth weight (CVB), number of piglets with birth weight < 1.00 kg, and piglet weaning weight. In addition, the greater feed intake during late gestation led to a marked increase in reactive oxygen species and malondialdehyde (P < 0.05) and glutamine peroxidase tended to be less (P =  0.08) in plasma at parturition. In conclusion, the greater feed intake (exceeding energy requirement for maintenance) during late gestation had no effect on piglet birth weight or weaning weight, and led to greater oxidative stress at parturition and greater BW loss during lactation.

Cardio-respiratory, oxidative stress and acute mountain sickness responses to normobaric and hypobaric hypoxia in prematurely born adults

PURPOSE

We compared the effects of hypobaric and normobaric hypoxia on select cardio-respiratory responses, oxidative stress and acute mountain sickness (AMS) severity in prematurely born individuals, known to exhibit blunted hypoxic ventilatory response.

METHODS

Sixteen prematurely born but otherwise healthy males underwent two 8-h hypoxic exposures under: (1) hypobaric hypoxic [HH; terrestrial altitude 3840 m; P_iO₂:90.2 (0.5) mmHg; BP: 478 (2) mmHg] and (2) normobaric hypoxic [NH; P_iO₂:90.6 (0.9) mmHg; F_iO₂:0.142 (0.001)] condition. Resting values of capillary oxyhemoglobin saturation (SpO₂), heart rate (HR) and blood pressure were measured before and every 2 h during the exposures. Ventilatory responses and middle cerebral artery blood flow velocity (MCAv) were assessed at rest and during submaximal cycling before and at 4 and 8 h. Plasmatic levels of selected oxidative stress and antioxidant markers and AMS symptoms were also determined at these time points.

RESULTS

HH resulted in significantly lower resting (P = 0.010) and exercise (P = 0.004) SpO₂ as compared to NH with no significant differences in the ventilatory parameters, HR or blood pressure. No significant differences between conditions were found in resting or exercising MCAv and measured oxidative stress markers. Significantly lower values of ferric-reducing antioxidant power (P = 0.037) were observed during HH as opposed to NH. AMS severity was higher at 8 h compared to baseline (P = 0.002) with no significant differences between conditions.

CONCLUSION

These data suggest that, in prematurely born adults, 8-h exposure to hypobaric, as opposed to normobaric hypoxia, provokes greater reductions in systemic oxygenation and antioxidant capacity. Further studies investigating prolonged hypobaric exposures in this population are warranted.

REGISTRATION

NCT02780908 (ClinicalTrials.gov).

Effect of pre-term birth on oxidative stress responses to normoxic and hypoxic exercise

Pre-term birth is a major health concern that occurs in approximately 10% of births worldwide. Despite high incidence rate, long-term consequences of pre-term birth remain unclear. Recent evidence suggests that elevated oxidative stress observed in pre-term born infants could persist into adulthood. Given that oxidative stress is known to play an important role in response to physical activity and hypoxia, we investigated whether oxidative stress responses to acute exercise in normoxia and hypoxia may be differently modulated in pre-term vs. full-term born adults. Twenty-two pre-term born and fifteen age-matched full-term born controls performed maximal incremental cycling tests in both normoxia (FiO2: 0.21) and normobaric hypoxia (FiO2: 0.13; simulated altitude of 3800 m) in blinded and randomized manner. Plasma levels of oxidative stress (advanced oxidation protein products [AOPP] and malondialdehyde), antioxidant (ferric reducing antioxidant power, glutathione peroxidase, catalase [CAT] and superoxide dismutase [SOD]) and nitrosative stress markers (nitrotyrosine, nitrite and total nitrite and nitrate [NOx]) were measured before and immediately after each test. AOPP (+24%, P<0.001), CAT (+38%, P<0.001) and SOD (+12%, P=0.018) and NOx (+17%, P=0.024) significantly increased in response to exercise independently of condition and birth status. No difference in response to acute exercise in normoxia was noted between pre-term and full-term born adults in any of measured markers. Hypoxic exposure during exercise resulted in significant increase in AOPP (+45%, P=0.008), CAT (+55%, P=0.019) and a trend for an increase in nitrite/nitrate content (+35%, P=0.107) only in full-term and not pre-term born individuals. These results suggest that prematurely born adult individuals exhibit higher resistance to oxidative stress response to exercise in hypoxia.

•

Oxidative stress and antioxidant activity are increased in full-term and pre-term adults following normoxic exercise.

•

Plasma AOPP, catalase and NOx levels are not increased in pre-term adults following an acute exercise in hypoxia.

•

Oxidative stress is differently regulated in pre-term adults during acute physical exercise under hypoxic condition.

•

Pre-term birth may have long term consequences concerning oxidative stress regulation especially during these conditions.

Interventions targeted at oxidatively generated modifications of nucleic acids focused on urine and plasma markers

Oxidative stress is associated with the development and progression of numerous diseases. However, targeting oxidative stress has not been established in the clinical management of any disease. Several methods and markers are available to measure oxidative stress, including direct measurement of free radicals, antioxidants, redox balance, and oxidative modifications of cellular macromolecules. Oxidatively generated nucleic acid modifications have attracted much interest due to the pre-mutagenic oxidative modification of DNA into 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), associated with cancer development. During the last decade, the perception of RNA has changed from that of a 'silent messenger' to an 'active contributor', and, parallelly oxidatively generated RNA modifications measured as 8-oxo-7,8-dihydro-guanosine (8-oxoGuo), has been demonstrated as a prognostic factor for all-caused and cardiovascular related mortality in patients with type 2 diabetes. Several attempts have been made to modify the amount of oxidative nucleic acid modifications. Thus, this review aims to introduce researchers to the measurement of oxidatively generated nucleic acid modifications as well as critically review previous attempts and provide future directions for targeting oxidatively generated nucleic acid modifications.

Prevalence of Sleep Apnea in Patients with Carotid Artery Stenosis

Obstructive sleep apnea (OSA) is a common disease affecting about 13% of men and 6% of women, usually having severe cardiovascular sequalae. OSA is responsible for the systemic inflammatory response and oxidative stress and results in endothelial injury being a risk factor for atherosclerosis. The aim of this study was to estimate the prevalence of OSA among patients with severe carotid artery stenosis. Fifty-five patients (F/M-24/31, mean age 70 ± 7 years, body mass index 28.3 ± 6.3 kg/m²) were enrolled into the study. The patients were qualified for elective surgical treatment of carotid artery stenosis. Polysomnography was performed in all patients the night before surgery. Thirty-six patients underwent surgical endarterectomy and nineteen patients underwent carotid artery stenting. Sleep apnea was diagnosed in 44 (80%) of all patients. The mean apnea-hypopnea index (AHI) was 14.5 ± 12.9. The OSA severity distribution was as follows: 22 mild, 16 moderate, and 6 severe cases. We found that the percentage of carotid endarterectomies was the greatest in mild and moderate OSA. It was approximately twofold greater than that in non-OSA patients. Carotid artery stenting was performed in nearly half of the patients in each of these groups. We conclude that OSA is highly prevalent in patients with carotid artery stenosis scheduled for carotid surgery. Nonetheless, the exact pathogenetic mechanisms underlying mutual interaction between OSA and vascular wall damage remain elusive. OSA is not routinely diagnosed among patients with advanced atherosclerosis. The study results might be an argument for performing polysomnography in patients with carotid artery stenosis.

The Role of Animal Models in Developing Pharmacotherapy for Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a highly prevalent disease characterized by recurrent closure of the upper airway during sleep. It has a complex pathophysiology involving four main phenotypes. An abnormal upper airway anatomy is the key factor that predisposes to sleep-related collapse of the pharynx, but it may not be sufficient for OSA development. Non-anatomical traits, including (1) a compromised neuromuscular response of the upper airway to obstruction, (2) an unstable respiratory control (high loop gain), and (3) a low arousal threshold, predict the development of OSA in association with anatomical abnormalities. Current therapies for OSA, such as continuous positive airway pressure (CPAP) and oral appliances, have poor adherence or variable efficacy among patients. The search for novel therapeutic approaches for OSA, including pharmacological agents, has been pursued over the past years. New insights into OSA pharmacotherapy have been provided by preclinical studies, which highlight the importance of appropriate use of animal models of OSA, their applicability, and limitations. In the present review, we discuss potential pharmacological targets for OSA discovered using animal models.

Comorbidities in idiopathic pulmonary fibrosis: an underestimated issue

Idiopathic pulmonary fibrosis (IPF) is a progressive and fibrosing lung disease with a poor prognosis. Between 60% and 70% of IPF patients die of IPF; the remaining causes of death may be due to comorbidities occurring in this ageing population. Interest in the role played by comorbidities in IPF has increased in the past few years. The optimal clinical management of IPF is multifaceted and not only involves antifibrotic treatment, but also vaccinations, oxygen supplementation, evaluation of nutritional status as well as psychological support and patient education. Symptom management, pulmonary rehabilitation, palliative care and treatment of comorbidities represent further areas of clinical intervention. This review analyses the major comorbidities observed in IPF, focusing on those that have the greatest impact on mortality and quality of life (QoL). The identification and treatment of comorbidities may help to improve patients' health-related QoL (i.e. sleep apnoea and depression), while some comorbidities (i.e. lung cancer, cardiovascular diseases and pulmonary hypertension) influence survival. It has been outlined that gathering comorbidities data improves the prediction of survival beyond the clinical and physiological parameters of IPF.

Hypoxia-adaptive pathways: A pharmacological target in fibrotic disease?

Wound healing responses are physiological reactions to injuries and share common characteristics and phases independently of the injured organ or tissue. A major hallmark of wound healing responses is the formation of extra-cellular matrix (ECM), mainly consisting of collagen fibers, to restore the initial organ architecture and function. Overshooting wound healing responses result in unphysiological accumulation of ECM and collagen deposition, a process called fibrosis. Importantly, hypoxia (oxygen demand exceeds supply) plays a significant role during wound healing responses and fibrotic diseases. Under hypoxic conditions, cells activate a gene program, including the stabilization of hypoxia-inducible factors (HIFs), which induces the expression of HIF target genes counteracting hypoxia. In contrast, in normoxia, so-called HIF-prolyl hydroxylases (PHDs) oxygen-dependently hydroxylate HIF-α, which marks it for proteasomal degradation. Importantly, PHDs can be pharmacologically inhibited (PHI) by so-called PHD inhibitors. There is mounting evidence that the HIF-pathway is continuously up-regulated during the development of tissue fibrosis, and that pharmacological (HIFI) or genetic inhibition of HIF can prevent organ fibrosis. By contrast, initial (short-term) activation of the HIF pathway via PHI during wound healing seems to be beneficial in several models of inflammation or acute organ injury. Thus, timing and duration of PHI and HIFI treatment seem to be crucial. In this review, we will highlight the role of hypoxia-adaptive pathways during wound healing responses and development of fibrotic disease. Moreover, we will discuss whether PHI and HIFI might be a promising treatment option in fibrotic disease, and consider putative pitfalls that might result from this approach.

The Effect of Upper Airway Surgery on Loop Gain in Obstructive Sleep Apnea

STUDY OBJECTIVES

Controversy exists as to whether elevated loop gain is a cause or consequence of obstructive sleep apnea (OSA). Upper airway surgery is commonly performed in Asian patients with OSA who have failed positive airway pressure therapy and who are thought to have anatomical predisposition to OSA. We hypothesized that high loop gain would decrease following surgical treatment of OSA due to reduced sleep apnea severity.

METHODS

Polysomnography was performed preoperatively and postoperatively to assess OSA severity in 30 Chinese participants who underwent upper airway surgery. Loop gain was calculated using a validated clinically-applicable method by fitting a feedback control model to airflow.

RESULTS

Patients were followed up for a median (interquartile range) of 130 (62, 224) days after surgery. Apnea-hypopnea index (AHI) changed from 60.8 (33.7, 71.7) to 18.4 (9.9, 42.5) events/h (P < .001). Preoperative and postoperative loop gain was 0.70 (0.58, 0.80) and 0.53 (0.46, 0.63) respectively (P < .001). There was a positive association between the decrease in loop gain and the improvement of AHI (P = .025).

CONCLUSIONS

High loop gain was reduced by surgical treatment of OSA in our cohort. These data suggest that elevated loop gain may be acquired in OSA and may provide mechanistic insight into improvement in OSA with upper airway surgery.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov, Title: The Impact of Sleep Apnea Treatment on Physiology Traits in Chinese Patients With Obstructive Sleep Apnea, Identifier: NCT02696629, URL: https://clinicaltrials.gov/show/NCT02696629.