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 %.

CPT Codes / HCPCS Codes / ICD-9 Codes
There are no specific codes for acoustic pharyngometry:
ICD-9 codes not covered for indications listed in the CPB (not all-inclusive):
327.20 - 327.29 Organic sleep apnea
770.82 Other apnea of newborn
780.51 - 780.59 Sleep disturbances
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-9 codes covered if selection criteria are met:
327.00 - 327.8 Organic sleep disorders
780.50 - 780.59 Sleep disturbances
786.03 Apnea
786.09 Other dyspnea and respiratory abnormality

The above policy is based on the following references:
    1. Walker RP, Gatti WM, Poirier N, et al. Objective assessment of snoring before and after laser-assisted uvulopalatoplasty. Laryngoscope. 1996;106(11):1372-1377.
    2. Weingarten CZ, Raviv G. Evaluation of criteria for uvulopalatoplasty (UPP) patient selection using acoustic analysis of oronasal respiration (SNAP testing). J Otolaryngol. 1995;24(6):352-357.
    3. Mathur R, Douglas NJ. Family studies in patients with the sleep apnea-hypopnea syndrome. Ann Intern Med. 1995;122(3):174-178.
    4. Zhou Y, Daubenspeck JA. Measurement of upper airway movement by acoustic reflection. Ann Biomed Eng. 1995;23(1):85-94.
    5. Louis B, Glass G, Kresen B, et al. Airway area by acoustic reflection: The two-microphone method. J Biomech Eng. 1993;115(3):278-285.
    6. Young T, Palta M, Dempsey J, et al. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med. 1993;328(17):1230-1205.
    7. Shepard JW Jr, Gefter WB, Guilleminault C, et al. Evaluation of the upper airway in patients with obstructive sleep apnea. Sleep. 1991;14(4):361-371.
    8. Hoffstein V, Wright S, Zamel N, et al. Pharyngeal function and snoring characteristics in apneic and nonapneic snorers. Am Rev Respir Dis. 1991;143(6):1294-1299.
    9. Hoffstein V, Fredberg JJ. The acoustic reflection technique for non-invasive assessment of upper airway area. Eur Respir J. 1991;4(5):602-611.
    10. Wiesmuller GA, Steup A, Ranft U, et al. Value of acoustic rhinometry in environmental medicine. Int J Hyg Environ Health. 2000;203(1):55-64.
    11. Huang J, Itai N, Hoshiba T, et al. A new nasal acoustic reflection technique to estimate pharyngeal cross-sectional area during sleep. J Appl Physiol. 2000;88(4):1457-1466.
    12. Hatzakis GE, Karsan N, Cook J, et al. Acoustic reflectance of pharyngeal structures in children. Int J Pediatr Otorhinolaryngol. 2003;67(4):373-381.
    13. Liesching TN, 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(3):886-891.
    14. Kehoe TJ. SNAP technology and sleep apnea [letter]. Chest. 2005;127(4):1465-1466; author reply 1466-1467.
    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.
    16. U.S. Food and Drug Administration (FDA), Center for Devices and Radiologic Health (CDRH). Snap Model 5. Apnea/snoring.recording and analysis device and oximeter. 510(k) No. K992322. Rockville, MD: FDA; February 2, 2000.
    17. SNAP Laboratories. Sleep apnea and snoring analysis [website]. Wheeling, IL: SNAP Laboratories; 2005. Available at: Accessed May 12, 2005. 
    18. Hood Laboratories. Eccovision Acoustic Pharyngometer [website]. Pembroke, MA: Hood Laboratories; 2004. Available at: Accessed May 12, 2005.
    19. Raviv G. Is SNAP technology accurate in the diagnosis of obstructive sleep apnea? Chest. 2006;129(1):214; author reply 214-215.
    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.
    21. Michaelson PG, Allan P, Chaney J, Mair EA. Validations of a portable home sleep study with twelve-lead polysomnography: Comparisons and insights into a variable gold standard. Ann Otol Rhinol Laryngol. 2006;115(11):802-809.
    22. Su S, Baroody FM, Kohrman M, Suskind D. A comparison of polysomnography and a portable home sleep study in the diagnosis of obstructive sleep apnea syndrome. Otolaryngol Head Neck Surg. 2004;131(6):844-850.
    23. Chesson AL Jr, Berry RB, Pack A; American Academy of Sleep Medicine; American Thoracic Society; American College of Chest Physicians. Practice parameters for the use of portable monitoring devices in the investigational of suspected obstructive sleep apnea in adults. Sleep. 2003;26(7):907-913.
    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.
    26. Trikalinos TA, Ip S, Raman G, et al. Home diagnosis of obstructive sleep apnea-hypopnea syndrome. Technology Assessment. Prepared for the Agency for Healthcare Research and Quality (AHRQ) by the Tufts-New England Medical Center Evidence-based Practice Center (EPC). Rockville, MD: AHRQ; 2007.
    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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