Are We Underestimating the Central Components of the Mixed Apneas?-A Hypothesis for Revised Scoring.

PURPOSE Apneas are classified in three categories, as obstructive, central, and mixed types. Mixed apneas are calculated together with the obstructive events in diagnosing obstructive sleep apnea syndrome (SAS). The clinical significance of mixed apneas needs to be specified. METHODS Patients with obstructive SAS having an index of mixed apneas ≥5/hour were evaluated. A new approach was developed to score the mixed apneas, and calculated them together with either obstructive or central type of events, depending on their obstructive and central components. The relationship between the development of complex SAS and the indices of abnormal respiratory events per standard and revised scoring was evaluated. RESULTS Ten of 56 patients (17.9%) developed complex SAS at titration polysomnography. The mean index of mixed apneas per standard scoring was significantly higher in patients who did not develop complex SAS (P = 0.006). The use of newly developed method in scoring mixed apneas resulted that three patients (5.4%) fulfilled the diagnostic criteria for the central SAS at first-night polysomnography (P < 0.001), and all of them had developed complex SAS at titration night requiring other modes of positive airway pressure therapy than the continuous mode (P = 0.004). Curve estimation models showed that the change from mixed apneas to central apneas was highly significant in patients developing complex SAS (r2 = 0.501; P = 0.022). CONCLUSIONS Our study showed that the summation of mixed apneas with the obstructive events conventionally underestimates the central components and the diagnosis of central SAS, which are fundamental in the risk stratification of complex SAS.