Acoustic Pharyngometers and SNAP Testing System

Number: 0336


Aetna considers acoustic pharyngometry (e.g., EccovisionTM Acoustic Pharyngometer), and versions of  the SNAP Testing System using fewer than 3 channels, experimental and investigational for screening, diagnosis, or treatment planning in persons with suspected or known obstructive sleep apnea (OSA) and for all other indications because their effectiveness has not been established.

Aetna considers SNAP Testing using 3 or more channels a medically necessary device for home diagnosis of OSA in adults, according to the criteria in CPB 0004 - Obstructive Sleep Apnea in Adults.

See also CPB 0700 - Rhinometry and Rhinomanometry.


Multiple methods that detect structural and functional abnormalities of the upper airway implicated as risk factors for obstructive sleep apnea (OSA) continue to stimulate interest because it is hoped that they may allow physicians to more easily distinguish patients with OSA from those without it, and therefore reduce the number of unnecessary sleep studies.

The EccovisionTM  Acoustic Reflection Pharyngometer (Hood Laboratories, Pembroke, MA) provides a non-invasive assessment of the dimensions, structure and physiological behavior of the upper airway from the oral cavity to the hypopharnyx while the patient breathes.  Computer processing of the incident and reflected sound waves from the airways provides an area distance curve representing the lumen from which minimal cross-sectional area and volume can be derived.  This device is marketed as a screening method to quickly assess a patient for potential sites of sleep-related upper airway obstruction, and to better determine whether an oral appliance or continuous positive airway pressure is more appropriate for the patient.

In a study to ascertain whether the Eccovision reflectance pharyngometer could assess the anatomical structure of the upper airway in young children, Hatzakis et al (2003) found that the Eccovision pharyngometer does not reliably assess pharyngeal volumes in a pediatric population.

Gelardi et al (2007) assessed variations of pharyngometric parameters in patients with sleep disorders and established a correlation between morpho-volumetric variations of oro-pharyngo-laryngeal spaces and the presence and severity of disease.  A total of 110 patients, of which 70 with sleep disorders and 40 healthy patients as a control group, were analyzed.  All patients underwent acoustic pharyngometry to evaluate the mouth and hypopharynx based on an explanatory chart.  A significant difference in parameters was observed between sleep disorder patients and the control group, especially in the amplitude of the I wave (significantly lower in patients with macroglossia), the extension of the O-F segment, and the amplitude of the O-F segment and hypopharyngeal area.  The authors concluded that although not a standardized test, acoustic pharyngometry was proven to be a useful method both in the diagnosis and severity of OSA, and in post-operative monitoring of upper airway surgery in patients with sleep disorders.  The findings of this study need to be validated by well-designed studies.

The SNAP Testing System (SNAP Laboratories, Wheeling, IL) is another type of reflective acoustic device marketed as a screening and analysis system to locate the source of snoring and detect sleep apnea conditions.  These devices were approved by the Food and Drug Administration based on 510(k) premarket notifications; thus, the manufacturers were not required to submit the evidence of efficacy necessary to support a premarket approval application.

There is insufficient evidence that versions of the home SNAP testing device using fewer than 3 channels are as good as conventional sleep studies for diagnosis and treatment planning in patients with OSA.

Liesching and colleagues (2004) compared the SNAP testing system to standard polysomnography to determine the accuracy of the SNAP testing system in detecting OSA.  The investigators concluded that SNAP studies do not appear to accurately assess the severity of OSA.  The investigators performed polysomnography on 31 consecutive patients referred to a sleep disorder clinic on the basis of SNAP testing.  The investigators reported that the severity criteria reported in the SNAP study accurately assessed the true severity confirmed by polysomnography in only 11 of 31 patients.  SNAP study severity scores were over-estimated in 13 of 31 patients, compared to the polysomnography results.  In 8 of the 11 over-estimated patients, the SNAP study diagnosed OSA when the patient had a normal polysomnography finding.  One potential factor contributing to the poor correlation between SNAP testing and polysomnography was that the tests were not performed simultaneously; the mean follow-up time between the 2 studies was 5 months.  The investigators concluded that, although there may be some variability from night to night in measurements, "these results suggest that SNAP studies do not accurately assess the severity of OSA."

Galer and associates (2007) examined the clinical significance of the acoustic data channel (single channel) recorded by the SNAP home polysomnography system in a retrospective comparison involving 59 patients.  The investigators reported that snoring did not correlate with anthropometric variables such as body mass index and neck circumference.  Statistical analysis showed no correlation between respiratory disturbance index (RDI) and the maximum or average loudness of snoring.  Average loudness was predictive of the presence of sleep apnea.  Spectral analysis of snoring sonography found that the proportion of snoring events associated with a palatal source correlated strongly with the loudness of snoring.  The investigators concluded that these findings suggest that analysis of snoring has limited utility in the evaluation of the patient with sleep apnea but may be able to select patients who would benefit from palatal procedures to reduce snoring.

Guidelines on the use of portable monitoring devices for the diagnosis of obstructive sleep apnea from the American Academy of Sleep Medicine, the American Thoracic Society, and the American College of Chest Physicians (Chesson et al, 2004) stated that type 4 monitoring devices are not recommended in the attended or unattended setting.  The guideline definition of type 4 monitoring devices would include the SNAP Testing System using less than 3 channels and acoustic pharyngometry.

A newer version of the SNAP testing system has been developed that records patient airflow, oxygen saturation, pulse rate, and respiratory effort, respiratory sounds and body position.  Su et al (2004) examined correlations between polysomnography and SNAP testing done in a laboratory in 60 consecutive patients referred to a sleep disorder clinic.  For an RDI of greater than or equal to 15, the sensitivity, specificity, positive predictive value and negative predictive value of SNAP versus polysomnography as the gold standard was 83.9 %, 75.9 %, 78.8 % and 81.5 %, respectively.  For RDI greater than equal to 15, using polysomography as the gold standard, 20 % of patients would be incorrectly classified using the SNAP testing system.

Michaelson et al (2006) examined correlations between polysomnography and SNAP testing done in a laboratory in 59 consecutive patients referred to a sleep disorder clinic.  For an apnea-hypopnea index (AHI) of greater than or equal to 15, the sensitivity, specificity, positive predictive value and negative predictive value of SNAP versus polysomnography (using Medicare criteria for hypopnea) was 100 %, 88.5 %, 57 % and 100 %, respectively.  For an AHI of greater than or equal to 5, the corresponding numbers were 94 %, 86.8 %, 76 %, and 97 %.

Friedman et al (2014) examined the role of regional upper airway obstruction measured with acoustic pharyngometry as a determinant of oral appliances (OAs) success.  This retrospective case-series included patients with OSA-hypopnea syndrome at a tertiary care center.  Patients were fitted with a custom OA between July 1, 2011, and January 1, 2012.  Regions of maximal upper airway collapse were determined on acoustic pharyngometry: retro-palatal, retro-glossal, or retro-epiglottic.  Apnea-hypopnea index improvement at titration polysomnography was assessed against regional collapse.  A total of 75 patients (56 [75 %] men; mean [SD] age of 49.0 [13.6] years; mean body mass index [calculated as weight in kilograms divided by height in meters squared] of 29.4 [5.2]; and mean AHI of 30.6 [20.0]) were assessed, and data were grouped on the basis of region of maximal collapse at pharyngometry (retro-palatal in 29 patients, retro-glossal in 28, and retro-epiglottic in 18).  The overall reduction in AHI at OA titration showed no significant difference between groups. There was no significant difference in the response rate to treatment, defined as more than 50% AHI reduction plus an AHI of less than 20 (response rate, 69% for retro-palatal, 75% for retro-glossal, and 83% for retro-epiglottic collapse; p = 0.55) or the cure rate, defined as an AHI of less than 5 (cure rate, 52 % for retro-palatal, 43 % for retro-glossal, and 72 % for retro-epiglottic collapse; p = 0.15).  The correlation between minimal cross-sectional area and response trended toward significance (r = 0.20; range of -0.03 to 0.41; p < 0.10).  The authors concluded that OA therapy achieved reasonable response and cure rates in patients with primary retro-palatal, retro-glossal, or retro-epiglottic obstruction at the time of initial titration polysomnography.  However, success is not predicted by identification of the region of maximal upper airway collapse measured with acoustic pharyngometry.

CPT Codes / HCPCS Codes / ICD-10 Codes
Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":
ICD-10 codes will become effective as of October 1, 2015 :
Acoustic pharyngometry:
No specific code
ICD-10 codes not covered for indications listed in the CPB (not all-inclusive):
F51.8 Other sleep disorders not due to a substance or known physiological condition
Sleep disorders
G47.31 - G47.39 Organic sleep apnea
P28.4 Other apnea of newborn
SNAP Testing system using 3 or more channels:
HCPCS codes covered if selection criteria are met:
G0400 Home sleep test (HST) with type IV portable monitor, unattended; minimum of 3 channels [covered for adults only]
ICD-10 codes covered if selection criteria are met:
F51.03 - F51.05
F51.13 - F51.19
Insomnia and hypersomnia not due to a substance or known physiological condition
F51.8 Other sleep disorders not due to a substance or known physiological condition
G47.00 - G47.39
G47.50 - G47.9
Sleep disorders
R06.83 - R06.89
Abnormalities of breathing
R06.81 Apnea, not elsewhere classified

The above policy is based on the following references:
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    15. U.S. Food and Drug Administration (FDA), Center for Devices and Radiologic Health (CDRH). Eccovision Acoustic Diagnostic Imaging Acoustic Pharyngometer. 510(k) No. K011329. Rockville, MD: FDA; July 26, 2002.
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    20. Galer C, Yonkers A, Duff W, Heywood B. Clinical significance of SNAP somnography test acoustic recording. Otolaryngol Head Neck Surg. 2007;136(2):241-245.
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    24. Flemons WW, Littner MR, Rowley JA, et al. Home diagnosis of sleep apnea: A systematic review of the literature. An evidence review cosponsored by the American Academy of Sleep Medicine, the American College of Chest Physicians, and the American Thoracic Society. Chest. 2003;124(4):1543-1579.
    25. Gelardi M, Del Giudice AM, Cariti F, et al. Acoustic pharyngometry: Clinical and instrumental correlations in sleep disorders. Rev Bras Otorrinolaringol (Engl Ed). 2007;73(2):257-265.
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    27. Deyoung PN, Bakker JP, Sands SA, et al. Acoustic pharyngometry measurement of minimal cross-sectional airway area is a significant independent predictor of moderate-to-severe obstructive sleep apnea. J Clin Sleep Med. 2013;9(11):1161-1164.
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