Imagine suddenly waking up in the middle of the night, gasping for breath, because your throat muscles have blocked your airway during your sleep. This is the terrifying reality for people living with obstructive sleep apnoea (OSA).
OSA occurs when the muscles in the back of their throat (supporting the soft palate, the uvula, the tonsils and the tongue) relax too much to allow normal breathing. The airway then narrows or even closes as they breathe in, preventing normal respiratory airflow and leading to a buildup of carbon dioxide in the blood. The brain responds to this by momentarily waking the sufferer so that they can reopen their airway and restore normal flow. A pattern which repeats itself between five and thirty times each hour, throughout just one night.1–3 Hundreds of apnoeas may therefore occur over the course of weeks and months and in doing so, lead to other health complications. These may include insulin resistance, arterial hypertension, daytime sleepiness, memory and cognitive deficits and arteriosclerosis.4
OSA is one of the most common respiratory disorders worldwide, alongside asthma and COPD. For years, both asthma and COPD have been associated with poor sleep quality and sleep-related problems, but only recently have studies begun to indicate that there is a reciprocal reaction and overlap between these conditions and sleep-related disorders. There is now evidence to suggest that chronic lung disease predisposes people to OSA, and OSA worsens control and outcomes in people with chronic lung disease.5,6
But we’re still not entirely sure how these diseases interact. Obesity and gastro-esophageal reflux are both known risk factors for OCS, asthma and COPD, but how does the overlap syndrome occur? Possible pathophysiological interactions between OSA and asthma and COPD include lower airways inflammation and remodeling; while asthma and COPD are thought to interact with OSA through sleep deprivation, nasal and mucosal inflammation, and local myopathy, amongst other mechanisms.5
With current demographic and environmental changes, the prevalence of all three diseases is likely to increase. Their coexistence can create an overlap syndrome with unique and potentially fatal symptoms, yet accurate diagnosis is frequently lacking in the clinic.5 For those with asthma, healthcare professionals’ evaluation must include a targeted sleep history and an investigation of nocturnal symptom control. If there are indications of possible OSA, then objective measurements such as the Pittsburgh Sleep Quality Index or Epworth Sleepiness Scale should be considered before polysomnography, or a sleep study, is required. For those with COPD, clinicians should ensure they question their patient about sleep issues, with a focus on daytime hypersomnolence, morning headaches, snoring, and witnessed apnoeas. If symptoms of OSA are found, the patient should then undergo polysomnography. However, if hypoxaemia or right heart failure develops in the presence of relatively mild airflow limitation, the GOLD guidelines recommend evaluation by polysomnography prior to initial questioning (as an overlap with OSA may contribute to pulmonary artery pressure elevations).3,6
Despite this diagnostic advice, knowledge of the overlap syndrome between OSA and chronic respiratory disease is still lacking in comparison with other areas of sleep and respiratory medicine. There is a huge amount of research still required to properly understand the interactions between the conditions, their similarities and differences. Accurate diagnosis is vital to avoid unnecessary escalation of respiratory treatments, and to ensure appropriate treatment of OSA with positive airway pressure, with the potential to improve respiratory control, quality of life and even mortality.5,6