Diagnosis of Obstructive Sleep Apnea Syndrome Using Overnight Oximetry Measurement

Youn, T; Park, D H; Choi, K H; Kim, Y S; Woo, J I; Kwon, J S; Ha, K S; Jeong, D U

Abstract

OBJECTIVES
The gold standard for diagnosing obstructive sleep apnea syndrome (OSAS) is nocturnal polysomnography (NPSG). This is rather expensive and somewhat inconvenient, however, and consequently simpler and cheaper alternatives to NPSG have been proposed. Oximetry is appealing because of its widespread availability and ease of application. In this study, we have evaluated whether oximetry alone can be used to diagnose or screen OSAS. The diagnostic performance of an analysis algorithm using arterial oxygen saturation (SaO2)base on 'dip index', mean of SaO2, and CT90 (the percentage of time spent at SaO2<90%)was compared with that of NPSG.
METHODS
Fifty-six patients referred for NPSG to the Division of Sleep Studies at Seoul National University Hospital, were randomly selected. For each patient, NPSG with oximetry was carried out. We obtained three variables from the oximetry data such as the dip index most linearly correlated with respiratory disturbance index(RDI) from NPSG, mean SaO2, and CT90 with diagnosis from NPSG. In each case, sensitivity, specificity and positive and negative predictive values of oximetry data were calculated.
RESULTS
Thirty-nine patients out of fifty-six patients were diagnosed as OSAS with NPSG. Mean RDI was 17.5, mean SaO2 was 94.9%, and mean CT90 was 5.1%. The dip index [4%-4sec] was most linearly correlated with RDI (r=0.861). With dip index [4%-4sec]> or =2 as diagnostic criteria, we obtained sensitivity of 0.95, specificity of 0.71, positive predictive value of 0.88, and negatives predictive value of 0.86. Using mean SaO2< or =97%, we obtained sensitivity of 0.95, specificity of 0.41, positive predictive value of 0.79, and negative predictive value of 0.78. Using CT90> or =5%, we obtained sensitivity of 0.28, specificity of 1.00, positive predictive value of 1.00, and negative predictive value of 0.38.
CONCLUSIONS
The dip index [4%-4sec] and mean SaO2< or =97% obtained from nocturnal oximetry data are helpful in diagnosis of OSAS. CT90< or =5% can be alo used in excluding OSAS.