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.