Modeling of sleep-induced changes in airway function: implication for nocturnal worsening of bronchial asthma

Resolution of daytime and night-time respiratory symptoms but persistent sleep apnea in severe asthma with the add-on of benralizumab

Introduction

The relationship between asthma and obstructive sleep apnea (OSA) is a widely debated topic in the scientific literature with the controversy surrounding the bi-directional nature of the correlation.

Case presentation

We report the case of a 59-year-old male being affected by severe allergic eosinophilic asthma and severe OSA (apnea-hypopnea index [AHI] 32 ev·hr^-1). Due to a clinical worsening of asthma (aggravation of dyspnea, chest constriction and night-time respiratory symptoms), despite the optimal therapy for asthma and recurrent administration of systemic corticosteroids, we have added-on treatment with benralizumab (monoclonal anti-interleukin 5 antibody). After eight months, the patient reported an improvement in asthma control (asthma control test [ACT]= 25 points), in pulmonary function and a good control of nocturnal symptoms of both diseases (i.e., wheezing, snoring, etc.). Then, the follow up polysomnography (PSG) was performed resulting in a high reduction of OSA severity (~18% AHI) even if obstructive events persisted and almost resolution of nocturnal hypoxemia. So, a trial with positive airway pressure (PAP) was proposed to the patient, who declined.

Conclusions

In consideration of our experience, we suggest that the nocturnal profile of patients with severe asthma should be always studied by a sleep investigation to prevent the negative effects of interaction with OSA. However, further studies on larger samples are needed to better understand the pathophysiological mechanisms underlying the beneficial effects of benralizumab on obstructive events during sleep.

Inspiratory-Activated Airway Vagal Preganglionic Neurones Excited by Thyrotropin-Releasing Hormone via Multiple Mechanisms in Neonatal Rats

The airway vagal preganglionic neurons (AVPNs) providing projections to intrinsic tracheobronchial ganglia are considered to be crucial to modulation of airway resistance in physiological and pathological states. AVPNs classified into inspiratory-activated AVPNs (IA-AVPNs) and inspiratory-inhibited AVPNs (II-AVPNs) are regulated by thyrotropin-releasing hormone (TRH)-containing terminals. TRH causes a direct excitatory current and attenuates the phasic inspiratory glycinergic inputs in II-AVPNs, however, whether and how TRH influences IA-AVPNs remains unknown. In current study, TRH regulation of IA-AVPNs and its mechanisms involved were investigated. Using retrogradely fluorescent labeling method and electrophysiology techniques to identify IA-AVPNs in brainstem slices with rhythmic inspiratory hypoglossal bursts recorded by a suction electrode, the modulation of TRH was observed with patch-clamp technique. The findings demonstrate that under voltage clamp configuration, TRH (100 nM) caused a slow excitatory inward current, augmented the excitatory synaptic inputs, progressively suppressed the inhibitory synaptic inputs and elicited a distinctive electrical oscillatory pattern (OP). Such a current and an OP was independent of presynaptic inputs. Carbenoxolone (100 μM), a widely used gap junction inhibitor, fully suppressed the OP with persistence of TRH-induced excitatory slow inward current and augment of the excitatory synaptic inputs. Both tetrodotoxin (1 μM) and riluzole (20 μM) functioned to block the majority of the slow excitatory inward current and prevent the OP, respectively. Under current clamp recording, TRH caused a slowly developing depolarization and continuously progressive oscillatory firing pattern sensitive to TTX. TRH increased the firing frequency in response to injection of a square-wave current. The results suggest that TRH excited IA-AVPNs via the following multiple mechanisms: (1) TRH enhances the excitatory and depresses the inhibitory inputs; (2) TRH induces an excitatory postsynaptic slow inward current; (3) TRH evokes a distinctive OP mediated by gap junction.

Mechanical properties of the upper airway

The importance of the upper airway (nose, pharynx, and larynx) in health and in the pathogenesis of sleep apnea, asthma, and other airway diseases, discussed elsewhere in the Comprehensive Physiology series, prompts this review of the biomechanical properties and functional aspects of the upper airway. There is a literature based on anatomic or structural descriptions in static circumstances, albeit studied in limited numbers of individuals in both health and disease. As for dynamic features, the literature is limited to studies of pressure and flow through all or parts of the upper airway and to the effects of muscle activation on such features; however, the links between structure and function through airway size, shape, and compliance remain a topic that is completely open for investigation, particularly through analyses using concepts of fluid and structural mechanics. Throughout are included both historically seminal references, as well as those serving as signposts or updated reviews. This article should be considered a resource for concepts needed for the application of biomechanical models of upper airway physiology, applicable to understanding the pathophysiology of disease and anticipated results of treatment interventions.

Oximetry Signal Processing Identifies REM Sleep-Related Vulnerability Trait in Asthmatic Children

Rationale. The sleep-related factors that modulate the nocturnal worsening of asthma in children are poorly understood. This study addressed the hypothesis that asthmatic children have a REM sleep-related vulnerability trait that is independent of OSA. Methods. We conducted a retrospective cross-sectional analysis of pulse-oximetry signals obtained during REM and NREM sleep in control and asthmatic children (n = 134). Asthma classification was based on preestablished clinical criteria. Multivariate linear regression model was built to control for potential confounders (significance level P ≤ 0.05). Results. Our data demonstrated that (1) baseline nocturnal respiratory parameters were not significantly different in asthmatic versus control children, (2) the maximal % of SaO₂ desaturation during REM, but not during NREM, was significantly higher in asthmatic children, and (3) multivariate analysis revealed that the association between asthma and REM-related maximal % SaO₂ desaturation was independent of demographic variables. Conclusion. These results demonstrate that children with asthma have a REM-related vulnerability trait that impacts oxygenation independently of OSA. Further research is needed to delineate the REM sleep neurobiological mechanisms that modulate the phenotypical expression of nocturnal asthma in children.

Nocturnal phenotypical features of obstructive sleep apnea (OSA) in asthmatic children

BACKGROUND

Asthma and obstructive sleep apnea (OSA) often coexists during childhood. To delineate this clinical association, we investigated the phenotypical features of OSA in asthmatic children. Specifically, we hypothesized that asthmatic children have a distinct OSA phenotype that involves a higher prevalence of Rapid-Eye-Movement (REM)-related breathing abnormalities relative to children with OSA alone.

METHODS

We conducted a retrospective cross-sectional analysis of 141 children aged 2-12 years with OSA diagnosed by polysomnography (PSG) in our sleep center. Outcomes included PSG parameters, maximal %SaO2 REM desaturations and prevalence of REM-related OSA. Multivariate linear regression model or logistic regression model was built to study the joint effect of asthma and OSA parameters with control for potential confounders (significance level P < 0.05).

RESULTS

Baseline respiratory parameters, obstructive apnea-hypopnea index (OAHI) severity, and oxygenation during NREM sleep were unaffected by the presence of asthma in children with OSA. In contrast, maximal %SaO2 REM desaturation, REM-OAHI and prevalence of REM-related OSA in children with moderate-severe OSA were significantly increased in asthmatic children with OSA compared to subjects with OSA alone. Multivariate analysis revealed that the association between asthma and REM-related OSA parameters is independent of asthma control, BMI, age, and gender. The presence of REM-related OSA in asthmatics was unaffected by rhinitis or atopic status.

CONCLUSION

These results demonstrate that asthma is associated with REM-related breathing abnormalities in children with moderate-severe OSA. The link between asthma and REM-related OSA is independent of asthma control and obesity. Further research is needed to delineate the REM-sleep biological mechanisms that modulate the phenotypical expression of OSA in asthmatic children.

Obstructive sleep apnea is associated with reduced quality of life in adult patients with asthma

BACKGROUND

Recent data suggest that obstructive sleep apnea (OSA) is an important contributor to severe uncontrolled asthma.

OBJECTIVE

To investigate the clinical characteristics, asthma control, and asthma-related quality of life in adult patients with asthma at a high risk for OSA.

METHODS

A total of 217 patients with asthma who visited our tertiary-care clinic were randomly recruited. They completed the Berlin questionnaire, which screens for OSA risk, a quality-of-life questionnaire for adult Korean patients with asthma (QLQAKA), and underwent an asthma control test (ACT). Fraction of exhaled nitric oxide (FeNO), lung function, blood lipid profiles, and body composition were evaluated.

RESULTS

The mean age was 58.4 ± 15.4, and 91 (41.9%) were male. Eighty-nine subjects (41.0%) were classified as high risk for OSA from the Berlin questionnaire. Patients with a high OSA risk were significantly older, had a higher prevalence of hypertension, higher BMI, non-atopic predisposition, and longer asthma treatment duration in the baseline clinical characteristics. The high OSA risk group had a lower ACT score than the low OSA risk group, but it was not statistically significant (20.9 ± 3.6 vs 21.5 ± 3.3, P = .091). The QLQAKA score was significantly lower in the high OSA risk group compared with the low OSA risk group (64.4 ± 10.9 vs 68.1 ± 11.1, P = .026), especially in the activity-domain (P = .005). The FeNO was not significantly different between the 2 groups.

CONCLUSION

Quality of life is significantly decreased in adult patients with asthma with a high risk of OSA. Special consideration is needed for the care and treatment of patients with asthma who have a high risk of OSA.

Nocturnal asthma

PURPOSE OF REVIEW

The aim is to review pathophysiological mechanisms and treatment of nocturnal asthma.

RECENT FINDINGS

Physiologic changes accompanying sleep, as well as the nocturnal phase of circadian rhythms, may have an adverse effect on asthma control. Chronotherapeutic principles, which consider circadian variation in relevant biologic rhythms, may improve asthma outcomes. Administration of long-acting bronchodilators and inhaled corticosteroids which achieve maximum efficacy at night may improve nocturnal asthma. Comorbid conditions that may contribute to nocturnal asthma should be considered. The prevalence of obstructive sleep apnea is greater in a cohort of patients with severe asthma than in moderate asthma and in BMI and age matched nonasthmatic controls, suggesting a link between these diseases. A large trial concluded that esomeprazole did not improve asthma control even with comorbid acid reflux, questioning the importance of acid reflux in asthma. The role of polymorphisms of the β2-adrenergic receptor and their relationship with nocturnal asthma remain controversial.

SUMMARY

Sleep is a time of vulnerability to respiratory compromise, especially in asthma patients experiencing nocturnal exacerbations. This asthma phenotype is associated with poorer control, reduced sleep quality, daytime somnolence and increased morbidity and mortality. Nocturnal asthma is a common but under-recognized problem.

Prevalence of obstructive sleep apnea-hypopnea in severe versus moderate asthma

BACKGROUND

Previous studies have suggested a link between obstructive sleep apnea and poor asthma control, which may be mediated through airway inflammation, obesity, and other mechanisms.

OBJECTIVE

To test the hypothesis that the prevalence and severity of sleep apnea is greater among patients with severe compared with moderate asthma and controls without asthma.

METHODS

Complete overnight home polysomnography was performed in 26 patients with severe asthma consecutively recruited to a difficult asthma program, 26 patients with moderate asthma, and 26 controls without asthma of similar age and body mass index. Flow rates and Juniper asthma control and quality of life questionnaires were also obtained.

RESULTS

Obstructive sleep apnea-hypopnea, defined by an Apnea-Hypopnea Index > or = 15 events/h of sleep scored using Chicago criteria, was present in 23 of 26 (88%) patients with severe asthma, 15 of 26 (58%) patients with moderate asthma, and 8 of 26 (31%) controls without asthma (chi(2): P < .001). Using the more restrictive scoring criteria applied in the Wisconsin cohort study, Apnea-Hypopnea Index > or = 5/h was present in 50% (severe), 23% (moderate), and 12% (control) of subjects (P = .007). Mean nocturnal arterial oxygen saturation was significantly lower in patients with severe asthma versus controls, and apnea-hypopnea severity measures were significantly worse for both asthmatic groups compared with controls. Among subjects with asthma, no significant correlations were identified between the severity of sleep-disordered breathing and asthma severity or control measures (FEV(1), Juniper scores).

CONCLUSIONS

Obstructive sleep apnea-hypopnea was significantly more prevalent among patients with severe compared with moderate asthma, and more prevalent for both asthma groups than controls without asthma. These observations suggest potential pathophysiologic interactions between obstructive sleep apnea-hypopnea and asthma severity and control.

Recent findings on the pathogenesis of bronchial asthma. Part I. Asthma as a neurohumoral disorder, a pathological vago-vagal axon reflex

The novel data on the pathogenesis of asthma are summarized in this three-part review. Its immunological background is well established but it is more than an immunological disorder. Multiple lines indicate that both peripheral and central neural mechanisms are also involved in the pathogenesis of asthma. In the present first part of the review asthma is described as vago-vagal axon reflex brought about by multiple positive feed-back mechanisms, receptor upregulation, wind-up, phenotypic switch and formation of a pathological conditioned reflex. In the coming second part the main dispositional (mostly hormonal) and external contributing factors are reviewed, while the third part deals with the role of inheritance, i.e., with gene alleles leading to enhanced production of mediators of asthma.