Classification of sleep-disordered breathing

Increasing recognition of sleep-disordered breathing (SDB) and its morbidit y have prompted reevaluation of techniques to identify respiratory events d uring sleep. The present study was designed to evaluate the utility of vari ous metrics of SDB and to identify the optimal respiratory metric that obje ctively correlates to symptoms of excessive daytime somnolence (EDS). Metri cs were derived from combinations of conventional apnea/hypopnea, flow limi tation events (transient elevated upper airway resistance identified by cha racteristic flattening on the flow/time tracing, using a noninvasive nasal cannula technique), desaturation, and arousal. A total of 137 subjects unde rwent clinical evaluation and nocturnal polysomnogram. In 34 randomly selec ted subjects, the best metrics for discriminating between 13 subjects with no EDS/snoring and 21 patients with EDS and snoring were identified by rece iver operator curve analysis. Of the metrics and cut points tested, a total respiratory disturbance index (RDITotal, sum of apneas, hypopnea, and flow limitation events) of 18 events/h was found to have the best discriminant ability (100% sensitivity and 96% specificity). Prospective testing of this metric was then performed with the remaining 103 subjects (14 nonsnoring n on-EDS, 21 snoring non-EDS, 68 snoring with EDS). Using this cutoff of 18 e vents/h, we obtained 71% sensitivity and 60% specificity for identifying su bjects with EDS. We conclude that, in subjects with upper airway dysfunctio n, an index that incorporates all respiratory events provides the best quan titative physiological correlate to EDS.