The OSADA (Obstructive Sleep Apnoea in Difficult Asthma) trial is an open-label, randomized control trial investigating the impact of diagnosing and treating obstructive sleep apnoea (OSA) on a asthma control in patients with difficult-to-control asthma.

Participants will undergo home-based sleep studies to assess for OSA and are then allocated to one of three arms: 1) Patients with OSA treated with CPAP (intervention group), 2) Patients with OSA not treated for OSA (control group) and 3) Patients without OSA (reference group).

The primary objective is to evaluate whether treating OSA improves asthma control, symptom burden, and quality of life compared to untreated OSA and to patients without OSA. Secondary outcomes include exacerbation rates, sleep quality, and healthcare utilization.

This trial aims to clarify the contribution of OSA to poor asthma control and the potential benefits of integrated sleep and respiratory care in this complex population.

Obstructive sleep apnoea (OSA) and asthma are two of the most common respiratory disorders worldwide, with asthma estimated to affect 300 million, and OSA in the region of 1 billion people. As a result, these two disorders frequently coexist in the same person. Whilst most people with asthma achieve successful control of their condition with straightforward inhaler therapy, approximately 20% have Difficult Asthma, characterised by persistent symptoms despite high dose inhaler usage. These patients experience a significant degree of morbidity due to their asthma, with increased healthcare utilisation, limitations in activities of daily living, and an increased need for systemic corticosteroids compared to those with milder asthma. Although novel biologic therapies have improved outcomes for some of these patients, there remain significant unmet needs in the care of many.

OSA is consistently listed as an important comorbidity in Difficult Asthma, with the suggestion being that it may have a significant detrimental impact on the ability to successfully achieve asthma control. However, there is a lack of systematic assessments of the relationship between the presence and severity of OSA on asthma symptoms in Difficult Asthma cohorts, and very little is known about the effect that treating OSA has in terms of airflow variability and asthma control.

The investigators aim to conduct an open-label randomized controlled trial to study patients attending Difficult Asthma clinics. Participants will undergo home sleep studies to investigate for an underlying concurrent diagnosis of sleep apnoea. The investigators will examine baseline and longitudinal relationships between OSA and asthma exacerbations, variability of airflow (via home peak flow monitoring), patient-reported asthma control, lung function, and markers of airway inflammation over a 3-month period, allowing a comparison of patients with OSA and those without.

Patients with confirmed OSA, as defined as an apnoea-hypopnea index of ≥10 events/hour will be randomized into treatment [continuous positive airway pressure (CPAP) therapy] and no treatment groups. Again, airflow variability, exacerbation frequency, asthma control, lung function and airway inflammation will be compared between OSA patients who receive CPAP therapy and those who do not.

Inclusion Criteria:

• Patients must have a clinical diagnosis of asthma with supportive objective diagnostics including but not limited to, variable airflow obstruction, bronchial-hyper responsiveness and demonstrable eosinophilic inflammation via fractional exhaled nitric oxide or peripheral eosinophilia
• Patients receiving step 4 or step 5 of 'The Global Initiative for Asthma' (GINA) treatment guidelines will be selected
• Between the ages of 18 to 90 years of age

Exclusion Criteria:

• Patients with previous sleep study investigations
• Excessive daytime sleepiness; ESS >17
• Previous diagnosis of a sleep disorder
• Resting hypoxaemia or need for long-term oxygen therapy
• Inability to provide informed consent