Objectives: The aim of our study was to assess the diagnostic characteristics of the OxiFlow (OF) device that combines oximetry with recording of thermistor airflow.
Methods: In patients referred to the sleep laboratory of an obesity clinic apnea-hypopnea index (AHI, events h(-1)) was calculated both by a full-night polysomnography (PSG) and OF on a separate night. Fifty-six patients were studied, of whom 49 had OSA defined as an AHI> or =15 events h(-1).
Results: There was an underestimation of AHI by OF when assessed by the Bland-Altman plot. Sensitivity (Se), specificity (Sp), positive (PPV) and negative (NPV) predictive values for OF-AHI thresholds (10, 15 and 20 events h(-1)), taking PSG as a gold standard with a fixed PSG-AHI threshold of 15 events h(-1), were evaluated in two groups of patients with intermediate (group A, n=18, OSA prevalence=72.2%) and high (group B, n=38, OSA prevalence=94.7%) clinical probability of OSA. Se and PPV ranged respectively from 0.77 to 0.85 and from 0.73 to 0.77 (group A); from 0.74 to 0.97 and from 0.94 to 0.98 (group B). Sp and NPV ranged respectively from 0.20 to 0.40 and from 0.33 to 0.40 (group A); from 0.50 to 0.83 and from 0.21 to 0.67 (group B). Likelihood ratios (LRs) for a positive OF result ranged from 1.06 to 1.28 (group A) and from 1.83 to 4.42 (group B).
Conclusions: We conclude that in a population with a high OSA prevalence, we have found a low agreement between PSG-AHI and OF-AHI and an underestimation of AHI by OF. The LRs of OF as a diagnostic test were of low significance, precluding its usefulness in generating significant shifts in pretest to posttest probability of OSA.