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07 November 2012

Electronic nose helps sniff out sleep apneoa

An "electronic nose" can distinguish between patients with obstructive sleep apneoa syndrome and healthy controls.

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The Cyranose 320 (Smiths Detection Group Ltd, Watford, UK) "electronic nose" can distinguish between patients with obstructive sleep apneoa syndrome (OSAS) and healthy controls "with high accuracy," a study from Germany found.

The researchers say to their knowledge this is the first study in which the "smellprints" of OSAS patients have been compared to healthy subjects.

Polysomnography, the current gold standard to confirm OSAS, is technically demanding, time-consuming and labour- and cost-intensive, and not available everywhere, as Dr Timm Greulich from University Hospital of Giessen and Marburg and colleagues noted online in the ERJ Express.

"The measurement of volatile organic compounds by an electronic nose is an innovative method that determines distinct molecular patterns of exhaled breath in different patient groups," they say.

How the study was done

The researchers used the Cyranose 320 to analyse exhaled breath of 40 OSAS patients (before receipt of CPAP therapy) and 20 healthy controls.

They report that linear discriminant analysis (LDA) scores of OSAS patients and healthy controls differed significantly, and the Cyranose 320 accurately separated OSAS patients from healthy controls (p<0.0001). The Mahalanobis distance between the two groups was 1.88 and the cross-validation value was 79.5%.

The corresponding area under the receiver operating curve was 0.85, indicating a sensitivity of 0.93 and specificity of 0.70. In addition, the LDA was significantly correlated with the apnea hypopnoea index (p<0.001), indicating a "dose-response" relationship, the investigators say.

The electronic nose could also discriminate the state before and after treatment with CPAP, indicating that specific volatile organic compound patterns in exhaled breath are associated with untreated OSAS," the authors report.

"In pharyngeal washing fluids of OSAS patients, we observed higher levels of alpha-1-antitrypsin and markers of extracellular remodelling compared to controls," they report.

The authors think the eNose could be useful in two settings. First, it could help rule out OSAS in a low prevalence population, such as a general practitioners office where the prevalence of OSAS is around 2% to 4%. A negative result would have a negative predictive value of 99.6%, providing a high degree of certainty, the researchers say.

Second, the device could help make decisions regarding overnight polysomnography. In a population with a high prevalence of OSAS (as high as 35% in obese, snoring subjects), a positive result would have a positive predictive value of 62.4% and would pave the way toward overnight polysomnography. On the other hand, a negative result would have a negative predictive value of 94.5%, thus directing attention to diagnoses other than OSAS.

The researchers emphasise that their results "have to be validated in a separate cohort, possibly in an independent center."

The study was supported by the German Research Foundation and the Behring-Roentgen Foundation. The paper lists no relevant disclosures.

(Reuters Health, November 2012)

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