SLEEP- RELATED BREATHING DISORDERS (SRBDs)
The most important cause of sleep disruption is sleep-disordered breathing. The term "sleep-disordered breathing" prima rily refers to the sleep apnea syndromes, but also includes disorders that result in noc turnal hypoventilation and hypoxemia such as restrictive and parenchymal pulmonaty diseases. While well known to cause exces sive daytime sleepiness, the sleep apnea syn dromes, both central and obstructive, are also important contributors to difficulty initiating and maintaining sleep because of frequent nocturnal arousals. Current defi nitions that have the most widespread clini cal use are based on guidelines provided by the Center for Medicare and Medicaid Services (CMS)
Apnea: An apnea is defined as the ab sence airflow for at least 10 seconds. There are three types:
Obstructive apnea: Absence of airflow for at least 10 seconds with evidence of persistent respiratory effort.
Central apnea: Absence of airflow for 10 seconds without evidence of any of respiratory effort.
Mixed Apnea: Absence of airflow for 10 seconds with initial absence of effort followed by a return of respi ratory effort before resumption of airflow.
Hypopnea: The term hypopnea refers to a decrease in airflow. By CMS criteria: "Hypopnea in adult patients is defined as an abnormal respiratoty event last ing at least 10 seconds with at least a 30% reduction in thorocoabdorninal movement or airflow as compared to baseline, and with at least a 4% oxy gen desaturation."2
Apnea Hypopnea Index (AHI): The total number of apneas and hypopneas are summed and divided by the number of hours of sleep. When used with the definitions above, the index is useful as a stan dardized measure that reflects sever