Obstructive sleep apnea

Along with an increasingly sophisticated scientific ap-proach to obstructive sleep apnea has come contro-versy over its true definition. By convention, the apnea– hypopnea index has been used to characterize obstructive sleep apnea. This index measures the frequency of reduc-tions in airflow associated with upper-airway collapse or narrowing that occurs with the state change from wakeful-ness to sleep. The term sleep-disordered breathing encom-passes these phenomena. However, a rigid diagnostic stan-dard has not been applied to the apnea–hypopnea index. As a result, its definition differs among sleep laboratories and in the medical literature. A consensus statement was developed over 5 years ago in an attempt to standardize these criteria in human research (1), and although many sleep laboratories have adopted these recommendations, di-agnostic variability remains. According to this statement, an apnea involves upper-airway collapse and is defined as nearly complete cessation of airflow associated with oxygen desaturation or an arousal from sleep. Hypopneas, which are associated with partial collapse of the upper airway, should be considered as existing on a pathologic continuum with apneas and may be clinically more important because they may make up the majority of disordered breathing events in a given night (2). The apnea–hypopnea index measures the frequency of disordered breathing events but does not quantify other processes that may be operative in the pathophysiology of obstructive sleep apnea, such as the degree of oxygen de-saturation. Moreover, the total number of arousals, some of which may occur in the absence of frank breathing ab-normalities, may be a superior marker of sleep fragmenta-tion than is the apnea–hypopnea index and may better explain daytime sleepiness (3). Nevertheless, no other met