Certain Sleep Related Breathing Disorders occur when the ventilatory control mechanisms of breathing fails to maintain adequate ventilation during sleep (and sometimes during wake). Unlike the mechanical changes that cause Obstructive events, these changes are caused by abnormalities in the communications between the higher control centres of ventilation. They are referred to as Central events, and include conditions such as Central Sleep Apnoea, Obesity Hypoventilation Syndrome and COPD/OSA overlap syndrome.
The diminished effort to breath during sleep, causing a hypopnoea or an apnoea. Causes can be classified as either hypercapnic or non-hypercapnic. Hypercapnic CSA is often associated with conditions that cause daytime hypoventilation which decreases the ventilatory response to carbon dioxide, for example neuromuscular disorders, chronic lung disease and obesity. Non-hypercapnic CSA is not associated with daytime hypoventilation. Causes include congestive heart failure and high altitude.
Obstructive Sleep Apnoea and Central Sleep Apnoea are likely to present in a very similar way in terms of presenting symptoms. In addition, they will appear to be very similar on a simple overnight sleep study. Whilst Obstructive Sleep Apnoea is the most common sleep related breathing disorder, it is important to be aware of the conditions associated with Central Sleep Apnoea when assessing a patient with excessive daytime sleepiness. These conditions are managed in very different ways, for example the discovery of Central Sleep Apnoea can lead to a discovery of a more sinister underlying disease, such as heart failure.