Comparison of AutoSet (TM) and polysomnography for the detection of apnea-hypopnea events

The use of the flow vs time relationship obtained with the nasal prongs of the AutoSet(TM) (AS) system (diagnosis mode) has been proposed to detect ap neas and hppopneas in patients with reasonable nasal patency. Our aim was t o compare the accuracy of AS to that of a computerized polysomnoeraphic (PS G) system. The study was conducted on 56 individuals (45 men) with clinical characteristics of obstructive sleep apnea (OSA), Their mean (+/- SD) age was 44.6 +/- 12 years and their body mass index was 31.3 +/- 7 kg/m(2). Dat a were submitted to parametric analysis to determine the agreement between methods and the intraclass correlation coefficient was calculated. The Stud ent t-test and Bland and Altman plots were also used. Twelve patients had a n apnea-hypopnea index (AHI) <10 in bed and 20 had values >40. The mean (+/ - SD) AHI(PSG) index of 37.6 (28.8) was significantly lower (P = 0.0003) th an AHI(AS) (41.8 (25.3)), but there was a high intraclass correlation coeff icient (0.93), with 0.016 variance. For a threshold of AHI of 20, AS showed 73.0% accuracy, 97% sensitivity and 60% specificity, with positive and neg ative predictive values of 78% and 93%, respectively. Sensitivity, specific ity and negative predictive values increased in parallel to the increase in AHI threshold for detecting OSA. However, when the differences of AHI(PSG- AS) were plotted against their means, the limits of agreement between the m ethods (95% of the differences) were +13 and -22, showing the discrepancy b etween the AHI values obtained with PSG and AS. Finally, cubic regression a nalysis was used to better predict the result of AHI(PSG) as a function of the method proposed, i.e., AHI(AS). We conclude that, despite these differe nces, AHI measured by AutoSet(TM) can be useful for the assessment of patie nts with high pre-test clinical probability of OSA, for whom standard PSG i s not possible as an initial step in diagnosis.