Is SNAP Technology Accurate in the Diagnosis of Obstructive Sleep Apnea?

Abstract

Dr. Kehoe’s letter (April 2005)1Kehoe T SNAP technology and sleep apnea [letter].Chest. 2005; : 1465-1466Abstract Full Text Full Text PDF Google Scholar identified serious methodological shortcomings in the study by Liesching et al2Liesching FN Carlisle C Marte A et al.Evaluation of the accuracy of SNAP technology sleep sonography in detecting obstructive sleep apnea in adults compared to standard polysomnography.Chest. 2004; 125: 886-889Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar (March 2004) and shed significant doubt on the conclusions of the study. Dr. Millman’s rebuttal (April 2005)3Millman RP Response to: SNAP technology and sleep apnea [letter].Chest. 2005; 127: 1466-1467Abstract Full Text Full Text PDF Google Scholar compelled my response. First, Millman denied the existence of published literature on SNAP test reliability. In fact, Su et al4Su S Baroody FM Kohrman M et al.Comparison of polysomnography and a portable home sleep study in the diagnosis of obstructive sleep apnea syndrome.Otolaryngol Head Neck Surg. 2004; 131: 844-850Crossref PubMed Scopus (57) Google Scholar in their study conducted at the University of Chicago, concluding the following: “The results … demonstrate… good correlation between SNAP and polysomnography in quantifying RDI [respiratory disturbance index] with new reliable sensitivity, specificity, positive and negative predictive values… [thus]… SNAP is an excellent tool for the diagnosis of OSAS [obstructive sleep apnea syndrome]… .” The article demonstrated via receiver operating characteristic curves (Fig 3, 4 in the article by Su et al4Su S Baroody FM Kohrman M et al.Comparison of polysomnography and a portable home sleep study in the diagnosis of obstructive sleep apnea syndrome.Otolaryngol Head Neck Surg. 2004; 131: 844-850Crossref PubMed Scopus (57) Google Scholar) that a SNAP test accurately identified apnea severity. Su et al4Su S Baroody FM Kohrman M et al.Comparison of polysomnography and a portable home sleep study in the diagnosis of obstructive sleep apnea syndrome.Otolaryngol Head Neck Surg. 2004; 131: 844-850Crossref PubMed Scopus (57) Google Scholar utilized a more powerful design performing both tests simultaneously. In contrast, Liesching et al2Liesching FN Carlisle C Marte A et al.Evaluation of the accuracy of SNAP technology sleep sonography in detecting obstructive sleep apnea in adults compared to standard polysomnography.Chest. 2004; 125: 886-889Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar have been soundly criticized for comparing data from the SNAP test and polysomnography findings that were collected, on average, 5 months apart.1Kehoe T SNAP technology and sleep apnea [letter].Chest. 2005; : 1465-1466Abstract Full Text Full Text PDF Google Scholar2Liesching FN Carlisle C Marte A et al.Evaluation of the accuracy of SNAP technology sleep sonography in detecting obstructive sleep apnea in adults compared to standard polysomnography.Chest. 2004; 125: 886-889Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar Given the stronger design of the study by Su et al,4Su S Baroody FM Kohrman M et al.Comparison of polysomnography and a portable home sleep study in the diagnosis of obstructive sleep apnea syndrome.Otolaryngol Head Neck Surg. 2004; 131: 844-850Crossref PubMed Scopus (57) Google Scholar the startling variant conclusions offered by Liesching et al2Liesching FN Carlisle C Marte A et al.Evaluation of the accuracy of SNAP technology sleep sonography in detecting obstructive sleep apnea in adults compared to standard polysomnography.Chest. 2004; 125: 886-889Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar should be substantially discounted. Second, Millman claimed that the initial continuous positive airway pressure derived from the clinically proven Miljeteig-Hoffstein method and reported by SNAP testing differed from the titration pressure that had been determined in his laboratory. This difference was never mentioned in his article; nor were data supporting his claim mentioned when the article was submitted for peer review. In contrast, the Miljeteig-Hoffstein formula has been well-validated.5Miljeteig H Hoffstein V Determinants of continuous positive airway pressure level for treatment of obstructive sleep apnea.Am Rev Respir Dis. 1993; 147: 1526-1530Crossref PubMed Google Scholar6Masa JF Jimenez A Duran J et al.Alternative methods of titrating continuous positive airway pressure: a large multicenter study.Am J Respir Care Med. 2004; 170: 1218-1224Crossref PubMed Scopus (264) Google Scholar Finally, in his latest reply, Millman admitted systematically excluding patients who had been found to be nonapneic by the SNAP test. Why was this not fully disclosed in the article? Eliminating nonapneic patients as well as four patients with obviously severe disease (who excluded due to a split-night polysomnography study) weighted the sample heavily toward patients with mild apnea, introducing a substantial bias given the higher night-to-night variability in that group of patients. Omitting crucial details in his article pours cold water on Millman’s defensive statement “our article went through vigorous peer review to be accepted by CHEST.”