The introduction of various novel approaches to quantify pulse oximetric information requires an evaluation of the relative utility of derived indexes in the diagnosis of sleep-disordered breathing. In the current issue of CHEST (see page 1694), Magalang and coworkers report a systematic comparison of several indexes derived from computer-assisted nocturnal pulse oximetry. Three large cohorts of patients with suspected sleep apnea were examined at two different institutions. The investigation confirms that the Delta index (Table 1)
, and desaturation indexes that reflect the variability of oxygen saturation, have a similarly high diagnostic accuracy for detection of patients with the obstructive sleep apnea syndrome. Moreover, the authors demonstrate that combining several pulse oximetry-derived variables to an aggregated model enhances the diagnostic yield over that of individual indexes. The study represents an important contribution to the validation of computerized analysis and interpretation of nocturnal pulse oximetry. Nevertheless, the efforts to get the most out of this fascinating noninvasive technique should continue. With further technical developments, and the advancement in our understanding of sleep apnea, new questions arise. For example, it is not clear to what extent the dynamic response characteristics,16–
artifact detection and rejection algorithms,17
and other technical specifications that differ among various brands of pulse oximeters affect their performance in sleep apnea diagnosis. Finally, the principal discussion over the reference standard against which novel techniques in sleep apnea diagnostic should be evaluated is also relevant for pulse oximetry. It seems that future evaluations of pulse oximetry would be more meaningful if performed in regard to major clinical outcomes of sleep apnea rather than in comparisons with polysomnography, a technique that has its own limitations, and depends itself on pulse oximetry for the detection of breathing disturbances.