Oximetry spectral analysis in the diagnosis of obstructive sleep apnoea

Using spectral analysis of oximetry data, we prospectively evaluated the va lidity of this methodology in patients clinically suspected of suffering fr om obstructive sleep apnoea (OSA). A total of 233 outpatients were stud led . Nocturnal oximetry was performed simultaneously with conventional polysom nography for all participants. The power density of oxygen saturation was a nalysed using Fast-Fourier transformation of the oximetric signal. Nocturna l oximetry test results were considered as abnormal (suspicion of OSA) if a peak in the spectrum between the period boundaries 30 and 70 s was observe d. A normal test result was defined as the absence of the 30-70 s peak from the spectrum. Single-blind evaluation was performed by three independent o bservers, and agreement of two or more of these was considered definitive. The peak amplitude and the ratio of the area enclosed in the 30-70 s peak t o the total area of the spectrum (rs) were measured. The presence of a peak has a sensitivity of 78%, a specificity of 89%, a positive predictive valu e of 89% and a negative predictive value of 78%. Apnoea-hypopnoea indexes w ere correlated significantly with peak amplitude (r = 0.74; P < 0.001)and w ith r(s) (r = 0.69; P < 0.001). For a peak amplitude threshold of 0.7%(2), the sensitivity was 94% and the specificity was 65% for OSA diagnosis. Usin g a threshold for r(S) of 0.15, the sensitivity was 91% and the specificity was 67%. Thus the spectral analysis of nocturnal oximetry and identificati on of a peak at 30-70 s could be useful as a diagnostic technique for OSA s ubjects.