Prediction of obstructive sleep apnea by OxiFlow in overweight patients

The aim of our study was to assess the diagnostic characteristics of the OxiFlow (OF) device that combines oximetry with recording of thermistor airflow.

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).

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).

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.