Airway and alveolar nitric oxide measurements in obstructive sleep apnea syndrome

Exhaled Nitric Oxide fraction in asthma and obstructive sleep apnea among children at high altitudes. A cross-sectional study

INTRODUCTION

Exhaled nitric oxide fraction (FeNO) is employed for the diagnosis and phenotyping of asthma as an inflammatory biomarker of the airway. Limited evidence exists regarding its behavior in the presence of asthma and obstructive sleep apnea (OSA). Our objective was to determine whether FeNO levels are associated with the severity of OSA or the coexistence of asthma and OSA in residents at high altitudes.

MATERIALS AND METHODS

Observational, analytical, cross-sectional study in children aged 5-16 years residing at 2600 m above sea level treated at a Sleep Study Center between 2019 and 2021. We conducted a medical history, polysomnogram, and measurement of FeNO levels. The children were categorized into four groups: OSA, asthma, asthma with OSA, and controls (without asthma or OSA). FeNO levels among the groups were compared using the Kruskal-Wallis test, and correlations were explored using the Spearman correlation coefficient. Analyses considered statistical significance at a two-tailed p-value <0.05.

RESULTS

Among the 261 included children, 68 (26.1 %) had OSA, 42 (16.1 %) were diagnosed with asthma, 109 (41.8 %) had both asthma and OSA, and 42 (16.1 %) were controls. Their FeNO medians were 10 ppb, 18.5 ppb, 15 ppb, and 14 ppb, respectively, with no significant differences between the evaluated groups (p = 0.263). We found no correlation between FeNO and apnea-hypopnea index and obstructive apnea index even for the groups of patients with FeNO >20 ppb and FeNO >35 ppb (>75th percentile). In the adjusted model, a significant association was observed between asthma and FeNO levels.

CONCLUSIONS

Our findings suggest that FeNO measurements in children would not allow establishing this biomarker as part of the diagnosis of OSA. However, these findings may be related to high altitude.

Fractional nitric oxide measurement in exhaled air (FeNO): perspectives in the management of respiratory diseases

Exhaled nitric oxide (NO) production, upregulated by inflammatory cytokines and mediators in central and peripheral airways, can be easily and non-invasively detected in exhaled air in asthma and other respiratory conditions as a promising tool for disease monitoring. The American Thoracic Society and European Respiratory Society released recommendations that standardize the measurement of the fractional exhaled NO (FeNO). In asthma, increased FeNO reflects eosinophilic-mediated inflammatory pathways and, as a biomarker of T2 inflammation can be used to identify asthma T2 phenotype. In this setting its measurement has shown to be an important tool especially in the diagnostic process, in the assessment and evaluation of poor adherence or predicting positive response to inhaled corticosteroids treatment, in phenotyping severe asthma patients and as a biomarker to predict the response to biologic treatments. The discovery of the role of NO in the pathogenesis of different diseases affecting the airways and the possibility to estimate the predominant site of increased NO production has provided new insight on its regulatory role in the airways, making it suitable for a potential extended use in clinical practice for different pulmonary diseases, even though its role remains less clear than in asthma. Monitoring FeNO in pulmonary obstructive lung diseases including chronic bronchitis and emphysema, interstitial lung diseases, obstructive sleep apnea and other pulmonary diseases is still under debate but has opened up a window to the role NO may play in the management of these diseases. The use of FeNO is reliable, cost effective and recommendable in both adults and children, and should be implemented in the management of patients with asthma and other respiratory conditions.

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.

WAO-ARIA consensus on chronic cough - Part II: Phenotypes and mechanisms of abnormal cough presentation - Updates in COVID-19

BACKGROUND

Chronic cough can be triggered by respiratory and non-respiratory tract illnesses originating mainly from the upper and lower airways, and the GI tract (ie, reflux). Recent findings suggest it can also be a prominent feature in obstructive sleep apnea (OSA), laryngeal hyperresponsiveness, and COVID-19. The classification of chronic cough is constantly updated but lacks clear definition. Epidemiological data on the prevalence of chronic cough are informative but highly variable. The underlying mechanism of chronic cough is a neurogenic inflammation of the cough reflex which becomes hypersensitive, thus the term hypersensitive cough reflex (HCR). A current challenge is to decipher how various infectious and inflammatory airway diseases and esophageal reflux, among others, modulate HCR.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on classification, epidemiology, presenting features, and mechanistic pathways of chronic cough in airway- and reflux-related cough phenotypes, OSA, and COVID-19. The interplay of cough reflex sensitivity with other pathogenic mechanisms inherent to airway and reflux-related inflammatory conditions was also analyzed.

OUTCOMES

Currently, it is difficult to clearly ascertain true prevalence rates in epidemiological studies of chronic cough phenotypes. This is likely due to lack of standardized objective measures needed for cough classification and frequent coexistence of multi-organ cough origins. Notwithstanding, we emphasize the important role of HCR as a mechanistic trigger in airway- and reflux-related cough phenotypes. Other concomitant mechanisms can also modulate HCR, including type2/Th1/Th2 inflammation, presence or absence of deep inspiration-bronchoprotective reflex (lower airways), tissue remodeling, and likely cough plasticity, among others.

Clinical Values of Nitric Oxide Parameters from the Respiratory System

BACKGROUND

Fractional exhaled nitric oxide (FENO) concentration reliably reflects central airway inflammation, but it is not sensitive to changes in the NO dynamics in the lung periphery. By measuring FENO at several different flow rates one can estimate alveolar NO concentration (C_ANO), bronchial NO flux (J_awNO), bronchial wall NO concentration (C_awNO) and the bronchial diffusivity of NO (D_awNO).

OBJECTIVE

We aimed to describe the current knowledge and clinical relevance of NO parameters in different pulmonary diseases.

METHODS

We conducted a systematic literature search to identify publications reporting NO parameters in subjects with pulmonary or systemic diseases affecting the respiratory tract. A narrative review was created for those with clinical relevance.

RESULTS

Estimation of pulmonary NO parameters allows for differentiation between central and peripheral inflammation and a more precise analysis of central airway NO output. C_ANO seems to be a promising marker of parenchymal inflammation in interstitial lung diseases and also a marker of tissue damage and altered gas diffusion in chronic obstructive pulmonary disease and systemic diseases affecting the lung. In asthma, C_ANO can detect small airway involvement left undetected by ordinary FENO measurement. Additionally, C_awNO and D_awNO can be used in asthma to assess if FENO is increased due to enhanced inflammatory activity (increased C_awNO) or tissue changes related to bronchial remodelling (altered D_awNO).

CONCLUSION

NO parameters may be useful for diagnosis, prediction of disease progression and prediction of treatment responses in different parenchymal lung and airway diseases. Formal trials to test the added clinical value of NO parameters are needed.

Exhaled Nitric Oxide as a Surrogate Marker for Obstructive Sleep Apnea Severity Grading: An In-Hospital Population Study

PURPOSE

Our study aimed to evaluate the relationship between exhaled nitric oxide (eNO) markers and obstructive sleep apnea (OSA) severity and verify the changes in eNO profiles among mild, moderate, and severe OSA subgroups.

METHODS

This study was a cross-sectional and in-hospital population-based study. We investigated 123 OSA patients (17 mild, 23 moderate and, 83 severe OSA) in the department of respiratory diseases. Studied data included anthropometry, respiratory polygraphy, biological markers, spirometry, and multi-flow eNO measurements. Data analysis implied linear correlation, non-parametric ANOVA, and pair-wise comparison.

RESULTS

No significant difference could be found among 3 OSA severity subgroups for FENO at - four sampling flow rates (50-350 mL/s). The bronchial production rate of NO (J'awNO) was proportionally increased, with median values of 11.2, 33.9, and 36.2 in mild, moderate, and severe OSA, respectively (p=0.010). The alveolar concentration of NO (CANO) changed with a non-linear pattern; it was increased in moderate (6.49) vs mild (7.79) OSA but decreased in severe OSA (5.20, p = 0.015). The only correction that could be established between OSA severity and exhaled nitric oxide markers is through J'AWNO (rho=0.25, p=0.02) and CANO (rho= 0.18, p=0.04). There was no significant correlation between FENO measured at three different flow rates and the OSA severity. We also found a weak but significant correlation between FENO 100 and averaged SpO2 (rho = 0.07, p= 0.03).

CONCLUSION

The present study showed that J'AWNO, which represents eNO derived from the central airway, is proportionally increased in more severe OSA, while eNO from alveolar space, indicated by CANO, was also associated with OSA severity and relatively lower in the most severe OSA patients. In contrast, stand-alone FENO metrics did not show a clear difference among the three severity subgroups.

Extended Exhaled Nitric Oxide Analysis in Interstitial Lung Diseases: A Systematic Review

Fractional exhaled nitric oxide (FeNO) is a well-known and widely accepted biomarker of airways inflammation that can be useful in the therapeutic management, and adherence to inhalation therapy control, in asthmatic patients. However, the multiple-flows assessment of FeNO can provide a reliable measurement of bronchial and alveolar production of NO, supporting its potential value as biomarker also in peripheral lung diseases, such as interstitial lung diseases (ILD). In this review, we first discuss the role of NO in the pathobiology of lung fibrosis and the technique currently approved for the measurement of maximum bronchial flux of NO (J'awNO) and alveolar concentration of NO (CaNO). We systematically report the published evidence regarding extended FeNO analysis in the management of patients with different ILDs, focusing on its potential role in differential diagnosis, prognostic evaluation and severity assessment of disease. The few available data concerning extended FeNO analysis, and the most common comorbidities of ILD, are explored too. In conclusion, multiple-flows FeNO analysis, and CaNO in particular, appears to be a promising tool to be implemented in the diagnostic and prognostic pathways of patients affected with ILDs.

Effects of chronic intermittent hypoxia caused by obstructive sleep apnea on lipopolysaccharide-induced acute lung injury

AIM OF THE STUDY

Obstructive sleep apnea (OSA) is a common disease associated with significant morbidity and mortality. Sleep quality is an important issue; some patients with acute lung injury (ALI) have underlying OSA. However, the potential influences of OSA on ALI have not been reported until now. In this study, we evaluated the impact of preceding intermittent hypoxia (IH), a typical characteristic of OSA, on lipopolysaccharide (LPS)-induced ALI in a mouse model.

METHODS

C57BL/6J mice were randomly divided into four groups: room air-control (RA-CTL), intermittent hypoxia-control (IH-CTL), room air-lipopolysaccharide (RA-LPS), and intermittent hypoxia-lipopolysaccharide (IH-LPS) groups. The mice were exposed to RA or IH (20 cycles/h, FiO₂ nadir 7 ± 0.5%, 8 h/day) for 30 days. The LPS groups received intratracheal LPS on day 28.

RESULTS

The IH-LPS group tended to exhibit more severe inflammation, fibrosis, and oxidative stress compared to the other groups, including the RA-LPS group. Total cell, neutrophil, and eosinophil counts in bronchoalveolar lavage fluid increased significantly in the IH-LPS group compared to the RA-LPS group. Compared to the RA-LPS group, the hydroxyproline level increased significantly in the IH-LPS group. In addition, the IH-LPS group exhibited significantly more terminal deoxynucleotidyl transferase dUTP nick end labeled-positive cells compared to the RA-LPS group.

CONCLUSIONS

We found that prior IH may negatively impact LPS-induced ALI in a mouse model. This result suggests that ALI in patients with OSA may be more of a concern. Further research into the mechanisms underlying the effects of IH on ALI is needed.

Evaluation of preoperative and postoperative serum interleukin-6, interleukin-8, tumor necrosis factor α and raftlin levels in patients with obstructive sleep apnea

BACKGROUND

Raftlin is a large, major lipid raft protein of cell membranes. Raftlin levels have not been previously examined in patients with obstructive sleep apnea (OSA). Our study aimed to evaluate the changes in raftlin, interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor alpha (TNFα) values from the preoperative state to the third month postoperatively in patients undergoing expansion sphincter pharyngoplasty for OSA.

METHODS

Of 60 patients, 10 patients had mild OSA (AHI 5-14), 10 moderate (AHI 15-29), 10 severe (AHI ≥ 30), and 30 with AHI < 5 formed a control group. Preoperatively and at 3 months post-operatively, IL-6, IL-8, TNFα, and raftlin values were measured.

RESULTS

Preoperatively, mean raftlin levels were 914.4 ± 62.7 pg/mL for controls, 910.0 ± 42.5 pg/mL in mild, 1000.5 ± 63.3 pg/mL in moderate, and 1386.3 ± 101.4 pg/mL in severe groups, with moderate and severe groups significantly elevated compared to controls (p < 0.001). Preoperatively to 3 months post-operatively, raftlin levels decreased significantly in each OSA group (p < 0.05). Levels of IL-6, IL-8 and TNFα followed similar patterns at baseline and after surgical intervention.

CONCLUSIONS

Raftlin levels at the third postoperative month decreased significantly compared with preoperative levels in parallel with other markers of inflammation.

How to apply the personalized medicine in obesity-associated asthma?

INTRODUCTION

Obesity-associated asthma (OA) is frequently severe, with an increased rate of hospitalizations, numerous comorbidities and low response to corticosteroids. Despite progress in applying for personalized medicine in asthma, no specific recommendations exist for the management of OA.

AREAS COVERED

The aim of this review is to summarize recent data about the relationship obesity-asthma, describe clinical characteristics, potential mechanisms involved and possible therapeutic interventions to improve OA outcomes. Extensive research in the PubMed was performed using the following terms: "asthma and obesity" and "obese asthma" in combination with "phenotypes", "airway inflammation", "biomarkers", "lung function", "weight loss", "lifestyle interventions", "therapies" Currently two phenotypes are described. Early-onset atopic asthma is conventional allergic asthma aggravated by the pro-inflammatory properties of adipose tissue in excess, while late-onset non-atopic asthma is due to airway dysfunction as a consequence of the chronic lung compression caused by the obese chest walls. Previous data showed that different therapeutic strategies used in weight loss have a positive impact on OA outcomes.

EXPERT OPINION

The presence of a multidisciplinary team (chest physician, nutritionist, exercise physiologist, physiotherapist, psychologist, bariatric surgeon) and the collaboration between different specialists are mandatory to optimize the management and to apply the personalized medicine in OA.

Olfactory Function in Patients With Obstructive Sleep Apnea Using Positive Airway Pressure

Previous studies reported that positive airway pressure (PAP) treatment may improve olfaction function in patients with obstructive sleep apnea (OSA) through various mechanisms. Olfactory function before and after PAP treatment is understudied regarding patient group at issue. The aim of this study is to investigate the contribution of PAP to olfactory function in patients with OSA. The study was conducted on 26 patients with OSA (10 females and 16 males, mean age 50.1 [9.3] years) who scheduled for PAP treatment. The Connecticut Chemosensory Clinical Research Center odor test was performed before and 4 months after PAP treatment. Patients were grouped (normal, anosmia, mild hyposmia, moderate hyposmia, and severe hyposmia) with respect to olfactory function by measuring odor test parameters, including threshold determination and identification. The odor test average scores of the patients after 4-month PAP treatment compared to pretreatment scores were increased and the difference was statistically significant (P = .002). In the apnea hypopnea index groups, statistically significant difference was found in the threshold and discrimination values regarding before PAP treatment (P = .038, P = .022, respectively). This study revealed that improvement in olfactory thresholds in patients with OSA receiving PAP treatment seems to improve olfactory dysfunction. This provides minimization of OSA consequences, including progressive upper airway inflammation, cognitive impairment, and associated olfactory dysfunction. Resolving the associations between olfactory function and PAP treatment is an important area for future research.

Exhaled Breath Analysis in Obstructive Sleep Apnea Syndrome: A Review of the Literature

Background and Objectives: Obstructive sleep apnea syndrome (OSAS) represents an independent risk factor for cardiovascular, metabolic and neurological events. Polysomnography is the gold-standard for the diagnosis, however is expensive and time-consuming and not suitable for widespread use. Breath analysis is an innovative, non-invasive technique, able to provide clinically relevant information about OSAS. This systematic review was aimed to outline available evidence on the role of exhaled breath analysis in OSAS, taking into account the techniques' level of adherence to the recently proposed technical standards. Materials and Methods: Articles reporting original data on exhaled breath analysis in OSAS were identified through a computerized and manual literature search and screened. Duplicate publications, case reports, case series, conference papers, expert opinions, comments, reviews and meta-analysis were excluded. Results: Fractional exhaled Nitric Oxide (FeNO) is higher in OSAS patients than controls, however its absolute value is within reported normal ranges. FeNO association with AHI is controversial, as well as its change after continuous positive airway pressure (C-PAP) therapy. Exhaled breath condensate (EBC) is acid in OSAS, cytokines and oxidative stress markers are elevated, they positively correlate with AHI and normalize after treatment. The analysis of volatile organic compounds (VOCs) by spectrometry or electronic nose is able to discriminate OSAS from healthy controls. The main technical issues regards the dilution of EBC and the lack of external validation in VOCs studies. Conclusions: Exhaled breath analysis has a promising role in the understanding of mechanisms underpinning OSAS and has demonstrated a clinical relevance in identifying individuals affected by the disease, in assessing the response to treatment and, potentially, to monitor patient's adherence to mechanical ventilation. Albeit the majority of the technical standards proposed by the ERS committee have been followed by existing papers, further work is needed to uniform the methodology.

Measurement of nitric oxide and assessment of airway diseases in children: an update

INTRODUCTION

Nitric oxide (NO) is a gas synthesized by the inducible NO synthase enzyme in airway cells and it is thought to make important functions in the airway inflammation of several respiratory diseases.

EVIDENCE ACQUISITION

This current study is a review of the literature from 1990 to present about NO and its use in clinical practice. The databases used were PubMed, Scopus, and Cochrane Library.

EVIDENCE SYNTHESIS

At the respiratory level there are three different measurements sites of NO: nNO (nasal nitric oxide), FeNO (exhaled fraction of nitric oxide), CaNO (alveolar nitric oxide). Each of them is produced at different levels of the respiratory tract and is involved in various diseases. nNO finds its use, principally, in the allergic rhinitis in fact it can be used as a measure of therapeutic efficacy, but not for the evaluation of the severity; also in primary ciliary dyskinesia (PCD), where high levels exclude the disease, and in chronic rhinosinusitis, but it is not currently used as a diagnostic or prognostic marker. FeNO has a greatest use in bronchial asthma, particularly, it is considered a non-invasive biomarker to identify and to monitor airway inflammation but currently, there is not a consensus on the use of the FeNO in the management of asthma treatment. Finally, CaNO is the least used in clinical practice, because lack of standardization of measurement techniques.

CONCLUSIONS

Nitric oxide is a sensitive indicator of the presence of airway inflammation and ciliary dysfunction, although some studies have shown varying or conflicting results.

Impact of PAP therapy on hospitalization rates in Medicare beneficiaries with COPD and coexisting OSA

OBJECTIVE

Growing evidence supports that patients with chronic obstructive pulmonary disease (COPD) and coexisting obstructive sleep apnea (OSA) have poor prognosis. This association is described as overlap syndrome. Positive airway pressure (PAP) therapy is now the preferred treatment for OSA. We hypothesized that use of PAP therapy in elderly patients with overlap syndrome would be associated with lower healthcare utilization.

METHODS

In this retrospective cohort study, we analyzed data from 5% national sample of fee-for-service Medicare beneficiaries with a diagnosis of COPD who were newly started on PAP therapy in 2011. We examined the effect of PAP therapy on emergency room (ER) visits and hospitalizations for all-cause and COPD-related conditions in the 1 year pre- and 1 year post-initiation of PAP therapy.

RESULTS

In year 2011, we identified 319 patients with overlap syndrome who were new users of PAP therapy. In this cohort of patients, hospitalization rates for COPD-related conditions were significantly lower in the 1 year post-initiation of PAP therapy compared to the 1-year pre-initiation period (19.4 vs 25.4%, P value = 0.03). However, ER visits (for any cause or COPD-related conditions) and hospitalization rates for any cause did not differ significantly in the pre- and post-initiation periods. PAP therapy was more beneficial in older adults, those with higher COPD complexity, and those with three or more comorbidities.

CONCLUSION

Initiation of PAP therapy in elderly patients with overlap syndrome is associated with a reduction in hospitalization for COPD-related conditions, but not for all-cause hospitalizations and ER visits.

Fractional Exhaled Nitric Oxide Measurements and Screening of Obstructive Sleep Apnea in a Sleep-Laboratory Setting: A Cross-Sectional Study

PURPOSE

Obstructive sleep apnea (OSA) is a common condition characterized by repetitive collapse of the upper airways and intermittent oxygen desaturation, which may lead to airway inflammation. Here, we explored whether fractional exhaled nitric oxide (FeNO) levels provide a non-invasive screening tool of OSA.

METHODS

Over a 3-month period, FeNO levels were measured in consecutive non-smoking patients referred for a sleep laboratory. All patients underwent full polysomnography. OSA severity was classified based on the apnea/hypopnea index: ≥ 5.0/h as any OSA, ≥ 15.0/h as moderate/severe OSA, and ≥ 30.0/h as severe OSA. FeNO was measured by a portable device (NIOX-MINO®; Aerocrine AB, Solna, Sweden) and expressed as parts per billion (ppb). Discrimination by area under the curve (AUC) and binary logistic regression were performed.

RESULTS

A total of 229 subjects were evaluated. Mean FeNO values were similar among subjects without OSA or with OSA: 16.9 ± 10.6 ppb versus 20.2 ± 14.5 ppb, p = 0.221; respectively. FeNO was not an inclusionary parameter to predict any OSA, moderate/severe OSA, and severe OSA: odds ratio (OR) 1.023 (95% confidence interval [CI]: 0.986-1.062); OR 1.012 (95% CI: 0.991-1.034); and OR 0.999 (95% CI: 0.980-1.018), respectively. The AUC values for FeNO in the diagnosis of any OSA, moderate/severe OSA, and severe OSA showed no discriminatory properties: AUC: 0.567 (95% CI: 0.464-0.670), AUC: 0.541 (95% CI: 0.465-0.618), and AUC: 0.535 (95% CI: 0.459-0.610); respectively.

CONCLUSIONS

In a sleep-lab setting, our findings suggest that FeNO measurements are inconsequential in the screening of OSA in adults.

Decreased Ambient Oxygen Tension Alters the Expression of Endothelin-1, iNOS and cGMP in Rat Alveolar Macrophages

Background: Hypoxia plays an important role in the vascular tone of pulmonary circulation via the vasculature and parenchymal tissue. Endothelin-1 (ET-1), a potent vasoconstrictive peptide, plays a role in inflammation in mononuclear cells. Nitric oxide synthase (NOS), which generates nitric oxide (NO)/cyclic 3', 5'-monophosphate (cGMP), is coexpressed with ET-1 in many cell types. The aim of this study was to assess whether hypoxia induces the production of ET-1 and associated expression of NOS, NO/cGMP and chemokines in rat alveolar macrophages (AMs). Methods: NR8383 cells were cultured under hypoxic (1% oxygen) conditions for 0, 2, 4, 8 and 12 hours. Levels of ET-1, inducible NOS (iNOS), phosphorylated iNOS (p-iNOS), nitrite/nitrate (NOx), cGMP and monocyte chemoattractant protein-1 (MCP-1) were measured. Results: ET-1, p-iNOS, NOx, and cGMP increased significantly in AMs after 4 hours of hypoxia (p < 0.05). ET-1 and MCP-1 mRNA increased after 8 hours (p < 0.05). The protein expression of ET-1, MCP-1, and p-iNOS increased in a time-dependent manner, while iNOS expression decreased with time. Conclusions: The changes in ET-1, p-iNOS, and the NO/cGMP pathway in AMs may help elucidate the mechanisms in the hypoxic lung. Understanding changes in the endothelin axis in hypoxic AMs is a crucial first step to unravel its role in pulmonary circulation.

Does Continuous Positive Airway Pressure (CPAP) treatment of obstructive sleep apnoea (OSA) improve asthma-related clinical outcomes in patients with co-existing conditions?- A systematic review

INTRODUCTION

A high prevalence of OSA has been observed in asthma populations, with detrimental impact on clinical outcomes.

AIM

To determine if CPAP treatment of co-existing OSA improves asthma-related symptoms and quality of life.

METHODS

Literature review of EMBASE and MEDLINE databases prior to July 2017. Study populations included asthmatics with co-existing OSA treated with CPAP, and ≥1 asthma-related clinical outcome measure.

RESULTS

12 studies; 8 prospective quasi-experimental and 4 observational. Mean CPAP duration; 19.5 (2-100) weeks. Meta-analysis demonstrated significant improvement in mean Asthma Quality of Life Questionnaire scores (AQLQ and mini-AQLQ); 0.59 (95%CI; 0.25, 0.92), p = 0.0006. No significant improvement was demonstrated in forced expiratory volume in 1 s (FEV1)% predicted; 0.32 (95%CI; -2.84, 3.47), p = 0.84. Asthma Control Test/Asthma Control Questionnaire improved in 2 studies, with no improvement in 1 study. 4 studies demonstrated improvement in asthma daytime/night-time symptoms, and 3 studies showed improved asthma severity.

CONCLUSION

Asthmatics with co-existing OSA can experience improved quality of life with CPAP treatment. This effect appears more pronounced in severe OSA or poorly controlled asthma.

Gestational Obstructive Sleep Apnea: Biomarker Screening Models and Lack of Postpartum Resolution

STUDY OBJECTIVES

To measure prevalence and severity of third trimester obstructive sleep apnea and evaluate postpartum resolution. To assess a novel biomarker for screening for obstructive sleep apnea in pregnancy.

METHODS

This prospective observational study was performed at Wake Forest School of Medicine obstetrics clinics between April 2014 and December 2015. Fractional exhaled nitric oxide measurements and sleep studies were obtained and compared at 32 0/7 to 35 6/7 weeks gestation and postpartum. Exhaled nitric oxide and risk factors for the development of gestational sleep apnea were evaluated for predictive ability independently and in screening models.

RESULTS

Of 76 women enrolled, 73 performed valid sleep studies in pregnancy and 65 had an additional valid study 6 to 15 weeks postpartum. Twenty-four women (37%) had gestational sleep apnea compared with 23 (35%) with postpartum sleep apnea (P > .99). Eight of 11 women (73%) retested 6 to 8 months postpartum had persistent sleep apnea. Exhaled nitric oxide had moderate discrimination screening for sleep apnea in pregnancy (area under the receiver operating characteristic curve = 0.64). A model utilizing exhaled nitric oxide, pregnancy-specific screening, and Mallampati score improved ability to identify women at risk for gestational sleep apnea (sensitivity = 46%, specificity = 91% and likelihood ratio = 5.11, area under receiver operating characteristic curve = 0.75).

CONCLUSIONS

Obstructive sleep apnea is common in the early postpartum period and often persisted at least 6 months. Exhaled nitric oxide as a sole biomarker to screen for sleep apnea in pregnancy has only modest discrimination. Combined with additional parameters sensitivity and specificity improved.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov, Identifier: NCT02100943, Title: Exhaled Nitric Oxide as a Biomarker of Gestational Obstructive Sleep Apnea and Persistence Postpartum, URL: https://clinicaltrials.gov/ct2/show/NCT02100943.

Role of lung volume and airway inflammation in obstructive sleep apnea

Obstructive sleep apnea (OSA) is a prevalent disorder that affects not only the upper airways but also the intrathoracic airways. In this review, we summarize the results of studies on lung function and airway inflammation. We provide evidence that the alterations in intrathoracic airways observed in OSA are not purely consequences of mechanical trauma and oxidative stress during apneic events but have a causal role in the structural changes associated with OSA and increasing severity of this disorder.

Asthma outcomes improve with continuous positive airway pressure for obstructive sleep apnea

BACKGROUND

Continuous positive airway pressure (CPAP) in asthma patients with concomitant obstructive sleep apnea syndrome (OSAS) seems to have a favorable impact on asthma, but data are inconsistent due to methodological limitations of previous studies.

METHODS

Prospective, multicenter study. We examined asthma outcomes after 6 months of CPAP in 99 adult asthma patients (mean age 57 years) with OSAS (respiratory disturbance index ≥20). Asthma control and quality of life were assessed with the Asthma Control Questionnaire (ACQ) and the Mini Asthma Quality of Life Questionnaire (MiniAQLQ), respectively. Data were analyzed by intention-to-treat basis.

RESULTS

The mean ± SD score of the ACQ decreased from 1.39 ± 0.91 at baseline to 1.0 ± 0.78 at 6 months (P = 0.003), the percentage of patients with uncontrolled asthma from 41.4% to 17.2% (P = 0.006), and the percentage of patients with asthma attacks in the 6 months before and after treatment from 35.4% to 17.2% (P = 0.015). The score of the mAQLQ increased from 5.12 ± 1.38 to 5.63 ± 1.17 (P = 0.009). There were also significant improvements in symptoms of gastroesophageal reflux and rhinitis, bronchial reversibility, and exhaled nitric oxide values (all P < 0.05). No significant changes were observed in drug therapy for asthma or their comorbidities nor in the patients' weight.

CONCLUSIONS

Asthma control (both actual and future risk), quality of life, and lung function improved after starting continuous positive airway pressure in asthmatics with moderate to severe obstructive sleep apnea syndrome.

Measurement of exhaled nitric oxide concentration in patients with obstructive sleep apnea: A meta-analysis

BACKGROUND

Exhaled nitric oxide (eNO) has been proposed as a noninvasive measure of airway inflammation. However, its value in patients with obstructive sleep apnea (OSA) is still controversial. The authors aim to assess the difference in eNO levels between patients with OSA and controls by a meta-analysis.

METHODS

A systematic search was performed in the PubMed, EMBASE, the Cochrane Library, and MEDLINE databases to collect relevant studies published from 1996 to 2016. Eligible studies that reported eNO levels in patients with OSA were included. STATA (version 12.0) was used for data analysis.

RESULTS

Two hundred eighty-four studies were reviewed for inclusion, with 16 studies pooled for analysis (16 studies for fractional exhaled nitric oxide [FENO], 5 for alveolar nitric oxide [CANO], and 4 for the maximum airway wall flux of nitric oxide [J'awNO]). The FENO levels were significantly higher in patients with OSA compared with that in the control groups (6.32 ppb, 95% confidence interval [CI] 4.46-8.33, P < 0.001). Furthermore, FENO was significantly increased (4.00 ppb, 95% CI 1.74-6.27, P = 0.001) after overnight sleep in patients with OSA, but not in healthy controls. Additionally, long-term continuous positive airway pressure (CPAP) therapy reduced FENO levels (-5.82 ppb, 95% CI -9.6 to -2.01, P < 0.001). However, the CANO (-0.01 ppb, 95% CI -1.66 to 1.64, P = 0.989) and J'awNO levels (220.32 pl/s, 95% CI -49.31 to 489.94, P = 0.109) were not significantly different between the OSA groups and non-OSA groups.

CONCLUSION

The results of the meta-analysis suggest that OSA is significantly associated with airway inflammation and elevated FENO levels can be modified by long-term CPAP therapy. J'awNO and CANO levels were not significantly different between the OSA groups and control groups.

Nasal nitric oxide improved by continuous positive airway pressure therapy for upper airway inflammation in obstructive sleep apnea

PURPOSE

In this report, we examined the association between obstructive sleep apnea (OSA) and upper and lower airway inflammation based on nitric oxide (NO) measurements.

METHODS

Study subjects included 51 consecutive participants. Sleep-disordered breathing was evaluated by a type 3 portable monitor and quantified by respiratory disturbance index (RDI). Airway inflammation was noninvasively analyzed by the measurement of nasally and orally exhaled NO; nasal value was presented as nasally exhaled NO minus orally exhaled NO. In 15 patients prescribed nasal continuous positive airway pressure (nCPAP) therapy, exhaled NO was re-evaluated in 10.7 ± 6.3 months after nCPAP therapy.

RESULTS

Nasal NO was significantly higher in patients with severe OSA (RDI ≥ 30/h) than those with non-OSA (RDI < 10/h) (76.9 ± 26.0 ppb vs. 47.9 ± 22.0 ppb, respectively, p = 0.016) and correlated with RDI (rho = 0.36, p = 0.0099), whereas orally exhaled NO did not differ between non-OSA and OSA patients and was not correlated with RDI. In 15 patients, nasal NO after nCPAP therapy was significantly decreased than that before nCPAP therapy (81.9 ± 31.2 ppb vs. 53.7 ± 27.2 ppb, respectively, p = 0.0046); in 11 patients having good compliance to nCPAP therapy (nCPAP use >4 h per night on more than 70% of nights), this association was more remarkable.

CONCLUSIONS

In OSA, upper but not lower airway inflammation can be increased by repetitive collapse of the upper airway. Future studies are required to determine the role of nasal NO in OSA.

Intermittent Hypoxia Contributes to the Lung Damage by Increased Oxidative Stress, Inflammation, and Disbalance in Protease/Antiprotease System

INTRODUCTION

Intermittent hypoxia as a surrogate of obstructive sleep apnea is associated with different cardiovascular complications. However, the effects of intermittent hypoxia on the lung tissue are less known. Therefore, the aim of our present study was to investigate if intermittent hypoxia may influence oxidative stress, inflammation, and protease/antiprotease system in the lung. Additionally, potential protective properties of anti-inflammatory and anti-oxidative drugs have been evaluated.

METHODS

32 mice were divided into four groups: (1) intermittent hypoxia, (2) intermittent hypoxia with infliximab, (3) intermittent hypoxia with L-glutathione, and (4) normoxia. After 4 weeks, lungs and blood were collected. Levels of reactive oxygen species in the lung were calculated by L-O12-enhanced chemiluminescence. CD68-positive lung macrophages were detected by immunofluorescence. Concentrations of elastase and desmosine in lung and of alpha-1-antitrypsin in blood were calculated by means of enzyme-linked immunosorbent assay.

RESULTS

Compared to a control, intermittent hypoxia augmented the release of free oxygen radicals, expression of CD68+ macrophages, and concentration of elastase in the lung tissue. Despite increased blood levels of protective alpha-1-antitrypsin, concentrations of desmosine-degradation product of elastin were higher versus control. The application of anti-inflammatory infliximab und anti-oxidative L-glutathione prevented at least partly the above-observed hypoxia-associated changes.

CONCLUSIONS

Intermittent hypoxia contributes to the lung damage by increased oxidative stress, inflammation, and disbalance in protease/antiprotease system. Infliximab and L-glutathione may prevent adverse hypoxia-induced lung alternations.

Effect of Continuous Positive Airway Pressure on Airway Inflammation and Oxidative Stress in Patients with Obstructive Sleep Apnea

Background. Airway inflammation and oxidative stress may be linked in obstructive sleep apnea (OSA) patients. We determined the effectiveness of continuous positive airway pressure (CPAP) therapy in reducing fractional exhaled nitric oxide (FeNO) and malondialdehyde (MDA) levels in OSA patients. Methods. Thirteen patients with OSA and 13 normal controls were recruited. FeNO and MDA levels were measured in the controls and in OSA patients before and after three months of CPAP therapy. Results. FeNO and MDA levels were higher in the patients compared to the age and gender matched controls (FeNO: 25.9 ± 5.0 versus 17.5 ± 5.9 ppb, P < 0.001; MDA: 14.6 ± 7.8 versus 2.1 ± 0.3 μmol/L, P < 0.001). FeNO and MDA levels were lower post-CPAP compared to pre-CPAP (FeNO: 25.9 ± 5.0 versus 17.0 ± 2.3 ppb, P < 0.001; MDA: 14.6 ± 7.8 versus 10.0 ± 6.4 μmol/L, P < 0.01). Apnea-hypopnea index (15.9 ± 6.6 versus 4.1 ± 2.1/h, P < 0.001) and mean arterial pressure (P < 0.01) decreased following CPAP treatment. Daytime mean SpO₂ (P < 0.05) increased. Conclusion. Our study demonstrates that CPAP therapy yields clinical benefits by reducing upper airway inflammation and oxidative stress in OSA patients.

Inflammatory Role of ROS-Sensitive AMP-Activated Protein Kinase in the Hypersensitivity of Lung Vagal C Fibers Induced by Intermittent Hypoxia in Rats

Obstructive sleep apnea (OSA), manifested by airway exposure to intermittent hypoxia (IH), is associated with excess reactive oxygen species (ROS) production in airways, airway inflammation, and hyperreactive airway diseases. The cause-effect relationship for these events remains unclear. We investigated the inflammatory role of ROS-sensitive AMP-activated protein kinase (AMPK) in IH-induced airway hypersensitivity mediated by lung vagal C fibers (LVCFs) in rats. Conscious rats were exposed to room air (RA) or IH with or without treatment with N-acetyl-L-cysteine (NAC, an antioxidant), Compound C (an AMPK inhibitor), ibuprofen (a cyclooxygenase inhibitor), or their vehicles. Immediately after exposure (24 h), we found that intravenous capsaicin, phenylbiguanide, or α,β-methylene-ATP evoked augmented LVCF-mediated apneic responses and LVCF afferent responses in rats subjected to IH exposure in comparison with those in RA rats. The potentiating effect of IH on LVCF responses decreased at 6 h after and vanished at 12 h after the termination of IH exposure. The potentiating effect of IH on LVCF-mediated apneic and LVCF afferent responses was significantly attenuated by treatment with NAC, compound C, or ibuprofen, but not by their vehicles. Further biochemical analysis revealed that rats exposed to IH displayed increased lung levels of lipid peroxidation (an index of oxidative stress), AMPK phosphorylation (an index of AMPK activation), and prostaglandin E₂ (a cyclooxygenase metabolite), compared with those exposed to RA. IH-induced increase in lipid peroxidation was considerably suppressed by treatment with NAC but not by compound C or ibuprofen. IH-induced increase in AMPK phosphorylation was totally abolished by NAC or compound C but not by ibuprofen. IH-induced increase in prostaglandin E₂ was considerably prevented by any of these three inhibitor treatments. The vehicles of these inhibitors exerted no significant effect on the three IH-induced responses. These results suggest that 24-h IH exposure sensitizes LVCFs, leading to an exaggerated reflex and afferent responses to chemical stimulants in rats. Moreover, this IH-induced LVCF sensitization is mediated through a cascade of inflammatory responses in the airways involving increases in ROS, AMPK activation, and cyclooxygenase metabolite release.

Study of Exhaled Nitric Oxide in Subjects with Suspected Obstructive Sleep Apnea: A Pilot Study in Vietnam

Background and Objective. The concentration of exhaled nitric oxide (eNO), reflecting the activity of inducible NO synthase in airway epithelium, has been found to increase in patients with obstructive sleep apnea (OSA). This study aimed to measure eNO concentration in patients with suspected OSA and to correlate different eNO parameters with clinical and sleep apnea characteristics. Methods. In this cross-sectional study, all patients underwent in-lab overnight polysomnography (PSG) and eNO measurement using a method of multiple flow rates before and after PSG (pre- and post-PSG). Results. According to the result of PSG, 82 persons were divided into two groups: control subjects (n = 30; 54 ± 14 years) and patients with OSA defined as apnea-hypopnea index (AHI) ≥ 5/hour (n = 52; 53 ± 12 years). Body mass index (BMI) and neck and abdomen circumferences of OSA patients were significantly higher than those from control subjects. In OSA group, post-PSG alveolar NO concentration (CANO) (5.3 ± 1.9 ppb) was significantly higher than pre-PSG CANO (4.0 ± 1.7 ppb; P < 0.001). Significant correlations have been found between CANO and AHI (P < 0.001) and between CANO and nadir SpO₂ (P < 0.05). The daytime CANO value of more than 4.1 ppb can be used to screen symptomatic subjects for the presence of OSA with a high specificity of 93.3%. Conclusion. Our findings indicate CANO as a surrogate marker for OSA in persons with suggestive symptoms.

Exhaled nitric oxide from the central airway and alveoli in OSAHS patients: the potential correlations and clinical implications

BACKGROUND

The aim of the study was to evaluate exhaled nitric oxide (eNO) derived from different areas of airway in obstructive sleep apnea hypopnea syndrome (OSAHS) patients with NO exchange model and investigate the potential application and interpretation of eNO in clinical setting.

METHODS

This study was divided into two parts. Firstly, we performed a case control study in 32 OSAHS patients and 27 non-OSAHS participants. Fractional eNO (FeNO) and eNO from the central airway (J'awNO) and from alveoli (CANO) were compared in OSAHS and control groups. Also, correlation of eNO to severity of OSAHS was analyzed. Secondly, a prospective study was conducted in 30 severe OSAHS patients who received a short-term nasal continuous positive airway pressure (nCPAP) treatment. We evaluated eNO, plasma ET-1 concentration, and echocardiography during the treatment process and explored the potential relationship among them.

RESULTS

FeNO and J'awNO were higher in OSAHS and associated with disease severity, while CANO was relatively lower. After nCPAP treatment in severe OSAHS patients, FeNO and J'awNO decreased and CANO increased significantly. Substantial agreement was shown between the elevation of CANO and the decrease of plasma ET-1 concentration after nCPAP by Kappa analysis for consistency. Tei index, which is considered indicative of global right ventricular function, might be predicted by plasma ET-1 levels in severe OSAHS patients.

CONCLUSIONS

NO exchange model provides us with more information of eNO derived from different areas. eNO is not only confirmed to be an effective method for airway inflammation evaluation in the follow-up of OSAHS, CANO may also serve as a useful marker in monitoring endothelial function, resistance of pulmonary circulation, and right ventricular function for clinical implication.

Cough in obstructive sleep apnoea

Obstructive Sleep Apnoea (OSA) has recently been reported to be a cause of chronic cough. It should be considered when cough remains unexplained following investigations and treatments for common causes. The presence of nocturnal cough, snoring and gastro-oesophageal reflux may be helpful in identifying patients who require further investigation. Daytime somnolence is often absent. Continuous positive airway pressure (CPAP) therapy has been reported to be effective in alleviating cough. Therapy for gastro-oesophageal reflux disease, if present, should be optimised. The mechanism of the association between OSA and cough is not clear, but airway inflammation, gastro-oesophageal reflux disease, increased cough reflex sensitivity and tracheobronchomalacia are possible explanations. Further studies should identify clinical predictors of OSA-cough, establish mechanisms and the optimal therapy.

Predicting sleep disordered breathing in outpatients with suspected OSA

OBJECTIVE

To validate the utilities of Berlin, STOP and STOP-BANG Questionnaires, other patient characteristics, comorbidities, Epworth Sleepiness Scale (ESS), fractional exhaled nitric oxide (FENO) and blood markers for the prediction of sleep disordered breathing (SDB) on limited polygraphy.

SETTING

North Glasgow Sleep Service (a tertiary referral centre).

PARTICIPANTS

129 consecutive patients, aged ≥16 years, referred to the sleep clinic for assessment of possible obstructive sleep apnoea.

INTERVENTIONS

We selected cut-points of apnoea hypopnoea index (AHI) of ≥5 and ≥15/h from their home polygraphy and determined associations of these with individual symptoms, questionnaire scores and other results. Receiver operating characteristic analysis and univariate and multivariate logistic regression were used to explore these.

PRIMARY AND SECONDARY OUTCOMES MEASURES

Primary: The utility of STOP, STOP-BANG and Berlin Questionnaires for prediction of SDB. Secondary: The utility of other measures for prediction of SDB.

RESULTS

AHI was ≥5 in 97 patients and ≥15 in 56 patients. STOP and STOP-BANG scores were associated with both AHI cut-points but results with ESS and Berlin Questionnaire scores were negative. STOP-BANG had a negative predictive value 1.00 (0.77-1.00) for an AHI ≥15 with a score ≥3 predicting AHI ≥5 with sensitivity 0.93 (95% CI 0.84 to 0.98) and accuracy 79%, while a score ≥6 predicted AHI ≥15 with specificity 0.78 (0.65 to 0.88) and accuracy 72%. Neck circumference ≥17 inch and presence of witnessed apnoeas were independent predictors of SDB.

CONCLUSIONS

STOP and STOP-BANG Questionnaires have utility for the prediction of SDB in the sleep clinic population. Modification of the STOP-BANG Questionnaire merits further study in this and other patient groups.

Utility of continuous positive airway pressure therapy for treating chronic coughs in patients with obstructive sleep apnea

We experienced two patients with chronic coughs whose symptoms persisted after initial treatment under a diagnosis of suspected upper airway cough syndrome or cough variant asthma. Neither patient exhibited daytime somnolence, although both were subsequently found to have severe obstructive sleep apnea. Following the administration of nocturnal continuous positive airway pressure therapy, the cough symptoms rapidly improved in both cases. These cases represent the first reports of obstructive sleep apnea-induced chronic cough in Japan.

Obstructive sleep apnea and asthma: associations and treatment implications

Obstructive sleep apnea (OSA) and asthma are highly prevalent respiratory disorders and are frequently co-morbid. Risk factors common to the two diseases include obesity, rhinitis, and gastroesophageal reflux (GER). Observational and experimental evidence implicates airways and systemic inflammation, neuromechanical effects of recurrent upper airway collapse, and asthma-controlling medications (corticosteroids) as additional explanatory factors. Therefore, undiagnosed or inadequately treated OSA may adversely affect control of asthma and vice versa. It is important for clinicians to be vigilant and specifically address weight-control, nasal obstruction, and GER in these populations. Utilizing validated screening instruments to affirm high risk of co-morbid OSA or asthma in persistently symptomatic patients will allow clinicians to cost-effectively test and treat appropriate patients, potentially improving outcomes. While non-invasive ventilation in acute asthma improves outcomes, the role of chronic continuous positive airway pressure (CPAP; the first-line treatment for OSA) in improving long-term asthma control is not known. Future research should focus on the impact of optimal CPAP therapy and adherence on asthma symptoms and outcomes.

Long-term continuous positive airway pressure therapy normalizes high exhaled nitric oxide levels in obstructive sleep apnea

STUDY OBJECTIVES

Upper airway inflammation and oxidative stress have been implicated in the pathogenesis of obstructive sleep apnea (OSA) and may be linked to cardiovascular consequences. We prospectively examined fraction of exhaled nitric oxide (FENO), a surrogate marker of upper airway inflammation using a portable nitric oxide analyzer (NIOX MINO).

DESIGN

In consecutive adult nonsmokers with suspected OSA, FENO was measured immediately before and after polysomnographic studies, and within 1-3 months following continuous positive airway pressure (CPAP) therapy.

MEASUREMENT AND RESULTS

FENO levels were increased in the 75 patients with OSA compared to the 29 controls, both before sleep (13.4 ± 6.5 ppb vs. 6.5 ± 3.5; p < 0.001) and after sleep (19.0 ± 7.7 ppb vs. 6.9 ± 3.7; p < 0.001). Furthermore, in patients with OSA, FENO levels were significantly higher post-sleep than pre-sleep (19.0 ± 7.7 ppb vs. 13.4 ± 6.5; p < 0.001), while there was no significant overnight change in patients without OSA. The rise in FENO correlated with the apnea-hypopnea index (r = 0.65, p < 0.001), nadir oxygen saturation (r = 0.54, p < 0.001), and arousal index (r = 0.52, p < 0.001). Thirty-seven of these patients underwent CPAP titration and treatment. Successful titration was associated with a lower overnight increase in FENO (7.2 ± 3.3 vs. 11.0 ± 4.3, p = 0.02). FENO levels declined after 1-3 months of CPAP therapy (11.7 ± 4.4 ppb, p < 0.001).

CONCLUSIONS

FENO levels are elevated in OSA, correlate with severity, and decrease after positive pressure therapy. This study supports the role of upper airway inflammation in OSA pathogenesis and a possible role for FENO in monitoring CPAP therapy.

Obstructive sleep apnea syndrome (OSAS) and hypertension: pathogenic mechanisms and possible therapeutic approaches

Obstructive sleep apnea syndrome (OSAS), a chronic condition characterized by collapse of the pharynx during sleep, has been increasingly recognized as a health issue of growing importance over the last decade. Recently emerging evidence suggests that there is a causal link between OSAS and hypertension, and hypertension represents an independent risk factor in OSAS patients. However, the pathophysiological basis for patients with OSAS having an increased risk for hypertension remains to be elucidated. The main acute physiological outcomes of OSAS are intermittent hypoxia, intrapleural pressure changes, and arousal from sleep, which might induce endothelial dysfunction, sympathetic activation, renin-angiotensin-aldosterone system activation, lipid metabolism dysfunction, and increased oxidative stress. This brief review focuses on the current understanding of the complex association between OSAS and hypertension.

Influence of CPAP treatment on airway and systemic inflammation in OSAS patients

AIM

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent respiratory disorders in the upper airways during sleep. Although continuous positive airway pressure (CPAP) has been accepted to be the most effective treatment for OSAS, its role on inflammation remains debatable. In this study, our aim was to examine the influence of 3 months of CPAP treatment on tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), 8-isoprostane, and peroxynitrite levels in exhaled breathing condensates (EBC) and serum.

METHODS

Thirty-five patients who were newly diagnosed as moderate or severe OSAS with full night polysomnography and used CPAP therapy regularly for 3 months were included in the study. Polysomnography, spirometric tests, fasting blood samples, and EBC were ascertained on entry into the study and after 3 months of treatment. All patients were assessed monthly for treatment adherence and side effects.

RESULTS

We found that all polysomnographic parameters were normalized after CPAP therapy in the control polysomnogram. Also, all markers in EBC and nitrotyrosine and 8-isoprostane levels in serum were decreased significantly with CPAP treatment. Sedimentation rate, C-reactive protein, IL-6, and TNF-α remained unchanged in serum after treatment. We found that baseline nitrotyrosine levels were significantly correlated with apnea-hypopnea index, oxygen desaturation index, and percent time in SpO2 < 90 % (p < 0.01).

CONCLUSIONS

CPAP therapy has primarily a relevant impact on airways, and nitrotyrosine levels correlated well with severity of OSAS. This treatment decreases both inflammation and oxidative stress levels in airways in OSAS patients. Also, this treatment helps to decrease systemic oxidative stress levels in serum.

Evaluation of arterial blood gases and arterial blood pressures in brachycephalic dogs

BACKGROUND

Brachycephalic dogs (BD) are prone to congenital upper airway obstruction (brachycephalic syndrome, BS). In humans suffering from sleep apnea, upper airway obstruction is known to cause hypertension. There is no information regarding the influence of BS in dogs on cardiorespiratory physiology.

HYPOTHESIS

BD are prone to lower P(a) O(2), higher P(a) CO (2), and hypertension compared with meso- or dolicocephalic dogs (MDD).

ANIMALS

Eleven BD and 11 MDD.

METHODS

After a questionnaire was completed by the owner, a physical examination was performed. Height and thoracic circumferences were measured. Arterial blood gases, electrolyte concentrations, and packed cell volume (PCV) were measured. Systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood pressure recordings were performed.

RESULTS

A total of 7 French and 4 English bulldogs met the inclusion criteria. The control group consisted in 6 Beagles, 2 mixed breed dogs, 1 Staffordshire Bull Terrier, 1 Parson Russell Terrier, and 1 Australian Cattle Dog. Statistically, BD had lower P(a) O(2), higher P(a) CO2, and higher PCV when compared with controls (86.2 ± 15.9 versus 100.2 ± 12.6 mmHg, P = .017; 36.3 ± 4.6 versus 32.7 ± 2.6 mmHg, P = .019; 48.2 ± 3.5 versus 44.2 ± 5.4%, P = .026, respectively). Also, they had significantly higher SAP (177.6 ± 25.0 versus 153.5 ± 21.7 mmHg, P = .013), MAP (123.3 ± 17.1 versus 108.3 ± 12.2 mmHg, P = .014), and DAP (95.3 ± 19.2 versus 83.0 ± 11.5 mmHg, P = .042). BD with a P(a) CO (2) >35 mmHg were significantly older than those with a P(a) CO (2) ≤35 mmHg (58 ± 16 and 30 ± 11 months, P = .004).

CONCLUSION

Results of this study suggest that some BD are prone to lower P(a) O(2), higher P(a) CO (2), and hypertension when compared with MDD. Age may be a contributing factor.

Chronic cough and OSA: a new association?

Chronic cough is defined as cough lasting more than 2 months. Common causes for chronic cough in nonsmokers with normal chest radiographs and pulmonary functions include gastroesophageal reflux disease (GERD), cough-variant asthma (CVA), and upper airway cough syndrome (UACS). Current guidelines recommend diagnosing the etiology of chronic cough based upon the results of therapy for suspected GERD, CVA, and UACS. Despite following current recommendations for diagnosis and treatment, the cause for a significant proportion of chronic cough remains unexplained.Recent reports indicate the resolution of chronic cough following treatment of concomitantly diagnosed obstructive sleep apnea (OSA). Whether this represents a co-occurrence of two commonly prevalent disorders or a pathophysiologic relationship between OSA and cough remains unknown. This review offers insights into a pathophysiologic link between OSA and the commonly purported etiologies for cough, namely, GERD, UACS, and CVA. In addition, evidence for a relationship between airway inflammation that can trigger or perpetuate cough and OSA is discussed. This review explores mechanisms by which nocturnal continuous positive airway therapy resolves cough by improving underlying airway inflammation secondary to OSA and impacts upon GERD, CVA, and UACS.