Acoustic Pharyngometers and SNAP Testing System

Number: 0336


Aetna considers acoustic pharyngometry (e.g., Eccovision Acoustic Pharyngometer), and versions of  the SNAP Testing System using fewer than 3 channels, experimental and investigational for screening, diagnosis, treatment planning, or prediction of surgical success 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 Eccovision™ 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.

Acoustic Pharyngometry for Screening of Obstructive Sleep Apnea

Kendzerska et al (2016) stated that owing to resource limitations, the testing of patients for obstructive sleep apnea (OSA) is often delayed.  There is a need to accurately triage and expedite testing in those with a high pretest probability of OSA.  Acoustic pharyngometry (AP) is a simple, non-invasive technique used to assess the upper airway cross-sectional area (UA-CSA), which is known to be reduced in those with OSA.  These researchers determined the discriminative ability and predictive value of UA-CSA measurements by AP for OSA.  They carried out a cross-sectional study with a clinical cohort of consecutive adults with suspected OSA who had undergone both polysomnography and AP; OSA was defined as an apnea-hypopnea index (AHI) of greater than or equal to 5.  Multi-variable logistic regression analyses and receiver operating characteristic curves were used.  The cohort included 576 subjects, 87 % of whom had OSA and 64 % of whom were men.  The subjects' median body mass index (BMI) was 30.3 kg/m2, and their median age was 57 years.  The median UA-CSA at FRC when sitting was significantly smaller in those with OSA compared with those without OSA (3.3 cm2 [interquartile range [IQR], 2.7 to 3.8] versus 3.7 cm2 [IQR, of 2.9 to 4.2]).  When the analysis was controlled for age, sex, BMI, and co-morbidities, the odds of OSA increased for every 1-cm2 decrease in the mean UA-CSA FRC when sitting (odds ratio [OR], 1.62; 95 % confidence interval [CI]: 1.23 to 2.13).  The mean UA-CSA provided fair discrimination for OSA (area under the curve, 0.60).  A cut-off value of 3.75 cm2, the point with the best sum of sensitivity and specificity, had sensitivity of 73 % and specificity of 46 % . The magnitude of the incremental discriminative value of UA-CSA over clinical variables (age, sex, BMI, and co-morbidities) was small and non-significant (p = 0.5).  The authors concluded that the mean UA-CSA at FRC when sitting or supine provided no further significant advantage over clinical variables for the discernment of OSA; thus, it is probably of no clinical utility in this setting.

Tekin et al (2016) noted that chronic otitis media (COM) is a disorder characterized by perforation of the eardrum and hearing loss following chronic inflammation of the middle ear cavity, ossicules, and mastoid cells.  Eustachian dysfunction plays an important role in COM etiopathogenesis and postoperative prognosis.  The determinants of postoperative prognosis are still being researched.  These researchers examined the prognostic value of acoustic rhinometry (ARM) and rhinomanometry (RMM) in COM surgery in terms of eradication of the infection after operation, graft success, and hearing gain in operated cases.  This study included 58 patients who underwent surgery with a diagnosis of COM.  Patients were assessed in terms of age, gender, COM type, treatment methods used, eradication of infection, graft success, and hearing gain.  ARM and RMM measurements were performed in the pre-operative period; ARM and RMM values were statistically compared in terms of the existence of post-operative infection, graft success, and hearing gain.  In terms of ARM and RMM measurements, there was no statistically significant difference between cases where post-operative infection control was assured and cases with ongoing infection; successful and failed cases in terms of grafting; or successful and failed cases in terms of post-operative hearing.  When pre-operative and post-operative air-bone gap averages were compared, statistically significant differences were observed.  The authors concluded that in the presence of a nasal obstruction in cases with chronic otitis, elimination of this situation was the first-line of treatment.  Infection control, graft success, and improvement of hearing will be possible to a greater extent in the post-operative period for patients with the nasal pathology remedied.  This study examined the use of acoustic rhinometry and rhinomanometry for chronic otitis media; it did not address the use of acoustic pharyngometry for screening of OSA.

Kim et al (2020) noted that combining AP parameters with cephalon-metric and clinical parameters could improve the predictive power for significant OSA in a Korean population.  A total of 229 consecutive adult patients with suspected OSA were enrolled.  The predictability for significant OSA using AP or cephalon-metric parameters or combining these parameters and clinical factors was calculated and compared using multi-variate logistic regression and receiver operating characteristic (ROC) curves.  In multi-variate logistic regression, age, sex, minimum upper airway cross-sectional area (UA-CSA), and mandibular plane to hyoid distance (MPH) were all significant independent predictors of significant OSA.  The minimum UA-CSA of 0.85 cm2 provided fair discrimination for OSA [area under the curve (AUC): 0.60, 95 % confidence interval (CI): 0.52 to 0.67].  The MPH of 18.75 mm provided fair discrimination for OSA (AUC; 0.65, 95 % CI: 0.58 to 0.72).  The discriminative ability of the final model of multi-variate ROC curve analyses that included the minimum UA-CSA, age, sex, body mass index (BMI), and MPH was better than the minimum UA-CSA alone (AUCs: 0.77 versus 0.60).  Optimal cut-off values of predictors for discriminating significant OSA were as follows: male for sex, 40 years for age, 25.5 kg/m2 for BMI, 1.06 cm2 for minimum UA-CSA, and 18 mm for MPH.  The authors concluded that minimum UA-CSA measured using AP while sitting might be a useful method to predict OSA; and combining minimum UA-CSA with age, sex, BMI and MPH improved the predictive value for significant OSA.

Kochar et al (2019) examined the stability of pharyngeal airway space changes with the use of AP 1 year after bilateral sagittal split ramus osteotomy for mandibular advancement in patients with skeletal Class II malocclusion.  The sample comprised 16 patients (mean age of 21.26 ± 1.86 years).  Acoustic pharyngometry measurements were recorded 1 week before surgery (T0), 2 months after surgery (T1), and 1 year after surgery (T2).  Parameters were compared by means of repeated-measures analysis of variance (ANOVA).  Significant increase was observed in minimum CSA 2 months after surgery (p < 0.001).  Relapse of 12.6 % was observed within 1 year after surgery (p < 0.001).  Statistically significant increase, i.e., 31.5 %, was observed in mean CSA 2 months after surgery (p < 0.001), which relapsed by 7.9 % 1 year after surgery (p < 0. 0.001).  Significant increase in mean volume from 30.32 ± 2.2 cm3 before surgery to 38.91 ± 2.73 cm3 2 months after surgery (p < 0.001) was observed.  Mean volume relapsed 3.9 % 1 year after surgery (p < 0.001).  The authors concluded that changes in pharyngeal airway space dimensions in patients subjected to isolated surgical mandibular advancement on 1 year follow-up showed encouraging results.  This was a small (n = 16) study with short-term follow-up (1 year).  These researchers also noted that AP is limited to providing measurements of CSA and volume according to distance along the airway; it does not provide high resolution imaging of anatomic or soft tissue structures.

Molfenter et al (2019) stated that pharyngeal lumen volume is prone to increase as a consequence of pharyngeal muscle atrophy in aging.  Yet, the impact of this on swallowing mechanics and function is poorly understood.  These researchers examined the relationship between pharyngeal volume and pharyngeal swallowing mechanics and function in a sample of healthy community-dwelling seniors.  Data were collected from 44 healthy seniors (21 men, mean age of 76.9, SD = 7.1).  Each participant swallowed 9 boluses of barium (3 × 5 ml thin, 3 × 20 ml thin, 3 × 5 ml nectar).  Pharyngeal shortening, pharyngeal constriction, pyriform sinus and vallecular residue were quantified from lateral view videofluorosopic swallowing studies.  Pharyngeal lumen volume was captured during an oral breathing task with AP.  In addition, within-participant measures of strength and anthropometrics were collected.  Four linear mixed effects regression models were run to study the relationship between pharyngeal volume and pharyngeal constriction, pharyngeal shortening, pyriform sinus residue, and vallecular residue while controlling for bolus condition, age, sex, and posterior tongue strength.  Increasing pharyngeal lumen volume was significantly related to worse constriction and vallecular residue.  In general, larger and thicker boluses resulted in worse pharyngeal constriction and residue.  Pharyngeal shortening was only significantly related to posterior tongue strength.  The authors concluded that they had confirmed that age-related pharyngeal atrophy in healthy seniors significantly (and negatively) impacted pharyngeal biomechanics and function.  Specifically, these investigators had demonstrated that larger pharyngeal lumen volume was associated with worse pharyngeal constriction and greater vallecular residue.  These relationships were established in healthy aging individuals without complaint of dysphagia and thus exercises targeting pharyngeal muscle strengthening appear to hold promise as preventative and/or rehabilitative exercises to combat age-related dysphagia.  This was a "feasibility" study carried out in 44 healthy elderly subjects.

The authors stated that this study had several drawbacks.  First, the interpretations were limited to their narrow range of stimuli and future work should expand this study to a larger range of textures and volumes.  In addition, these researchers acknowledged that the walls of the pharyngeal lumen are composed of more than just the constrictor and longitudinal muscles of the pharynx.  The anterior portion of the lumen is composed of the base of the tongue as well as supraglottic larynx.  They recognized that these structures are also prone to age-related changes that may contribute to increases in pharyngeal volume.  The inclusion of posterior tongue strength was a deliberate choice to attempt to control for a portion of this variation.  Further, two-dimensional (2D) measures of pharyngeal constriction are limited in detecting degree of constriction.  They stated that future research should confirm the relationship between expanding pharyngeal lumen volume and worsening pharyngeal function using high-resolution manometry.  With respect to future studies, particularly significant contributions would be to establish a threshold of pharyngeal lumen volume that appears to result in functional impairment and to examine swallowing exercises that can reverse or counter-act pharyngeal atrophy.

Furthermore, an UpToDate review on "Clinical presentation and diagnosis of obstructive sleep apnea in adults" (Kline, 2020) does not mention acoustic pharyngometry as a diagnostic tool.

Acoustic Pharyngometry for Facilitation of Oral Appliance Therapy

Opsahl and colleagues (2021) noted that there is lack of reliable and accurate methods to predict treatment outcomes of oral appliance (OA) treatment; AP is a non-invasive technique to evaluate the volume and minimal CSA of the UA, which may prove useful to locate the optimal position of OAs.  In a retrospective study, these researchers examined the effect of applying AP to OA treatment of patients with OSA.  All patients (n = 244) treated with OAs following an AP protocol at 2 dental clinics between 2013 and 2018 were invited to participate.  A total of 129 patients accepted the invitation, and 120 patients (75 men, and 45 women) were included in the analyses.  Mean baseline age, BMI and AHI were 59.1 ± 0.9 years, 27.8 ± 0.4, and 21.9 ± 1.1, respectively.  Mean follow-up time was 318 ± 24 days.  AHI at follow-up was 6.4 ± 0.7, resulting in a treatment success rate of 86.7 % (greater than or equal to 50 % reduction of baseline AHI).  The number of failures (less than 50 % reduction of baseline AHI) did not differ significantly among patients with mild, moderate and severe OSA; 87.6 % of the patients reported OA usage every night, and 95.5 % reported greater than 5 hours usage per night, when worn.  The authors concluded that the AP protocol applied appeared to contribute to the excellent effect of OA treatment in this study.  Moreover, these researchers stated that further research on the application of AP in OA treatment is necessary in order to clarify its possible beneficial contribution to improving OA therapy.

The authors stated that the uncertainty of the reproducibility and validity of AP measures was a limitation of the technique.  The results of the treatment indicated that AP improved OA treatment compared to standard OA treatment, when performed by 2 calibrated and experienced clinicians.  The current study was, however, not performed with a randomized design including a control group, and direct comparison with other studies was not possible due the differences in case selection, etc.  The clinicians performing the AP and the positioning of OAs in this study were highly skilled in using the technique, and the results could not directly be extrapolated in the hands of lesser experienced dentists; therefore, this will require further investigations.  There was also an uncertainty regarding the reproducibility of the modified Mueller maneuver, and the fact that the measures were performed awake and in a seated position.  The rationale for using the modified Mueller maneuver when demonstrating collapsibility of the UA was that this technique was previously shown to demonstrate a reduction in pharyngeal CSA in OSA patients, which was not present in non‐OSA subjects.  As the subjects in above‐mentioned studies were seated and awake during AP measures, this was applied in this study’s protocol as well.  The reproducibility of total lung capacity and residual volume had previously been shown to have acceptable intra‐class correlation.  Some of the included patients were diagnosed with OSA some years prior to the OA treatment.  This meant that, in some patients, the true AHI at baseline might have been different at the start of OA treatment, due to, for example, greater age and changed BMI.  This was possibly the case in 3 patients where the initial follow‐up AHI with OA was higher than the baseline AHI.  In those patients, a new ambulatory polygraphic recording was carried out without the OA and the results showed an aggravation of the OSA diagnosis compared to that at the referral time.  Still, in those 3 patients, these investigators used the original baseline diagnosis and AHI in the analyses, and all of them consequently became treatment failures, as reported in the results.  Nonetheless, this uncertainty would in most cases only generated false‐negative rather than false‐positive results, due to the unlikelihood of reduced AHI in the absence of intensive lifestyle interventions.  Furthermore, there was some uncertainty about using different diagnostic devices for baseline and follow‐up sleep recordings.  All follow‐up registrations were made with the same type III devices, which had previously been shown to have comparable accuracy in diagnosing OSA with a type IV device (Embletta), and with polysomnographic examination.  The type III devices used have shown a slight tendency to over-estimate AHI compared to Embletta at lower values, when using autoscore, but this would be correctly adjusted as the present type III reports were manually scored in this study, and would also, if AHI was over-estimated, resulted in false‐negative results.

Acoustic Pharyngometry in the Treatment of Obstructive Sleep Apnea Patients with Expansion Sphincter Pharyngoplasty Surgery

Masiyev and colleagues (2022) noted that expansion sphincter pharyngoplasty (ESP) is a common surgery for patients with OSA that aims to correct the obstruction at the palatal level.  The effectiveness of ESP has been widely shown in the literature using surgical success rates, but to the authors’ knowledge, there is no research that objectively documented the changes in the UA anatomy.  These investigators examined the effectiveness of ESP using AP; they also evaluated the possible use of AP in predicting surgical outcomes.  Pre- and post-operative AP and polysomnography data of patients who underwent ESP were compared prospectively.  Minimum CSA (MCSA) and total volume of the pharynx (TPV), AHI, and surgical success rates were evaluated.  A total of 52 patients with OSA were invited to this study, and 35 patients who agreed to participate were enrolled.  All patients underwent ESP surgery.  Surgical success rate was 63 % according to Sher's criteria.  The mean AHI of the patients decreased from 29.6 ± 16.3 to 18.3 ± 18.1.  MCSA increased from 1.1 ± 0.4 to 2.3 ± 0.4 cm2, and TPV increased from 21.1 ± 6.9 to 31.7 ± 5.5 cm3.  Comparative analysis of the successful and unsuccessful groups yielded no significant differences between the groups concerning pre- and post-operative MCSA and TPV or in mean changes in MCSA and TPV achieved with the surgery.  The authors concluded that improvement in the UA anatomy by ESP can be clearly demonstrated using AP.  Moreover, AP findings were quite similar in patients with successful and unsuccessful outcomes; thus, AP findings could not be used to predict surgical success; and surgical success could not be solely attributed to the changes in MCSA and TPV.

Table: CPT Codes / HCPCS Codes / ICD-10 Codes
Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":

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
P28.40 - P28.49 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
R06.00 - R06.09
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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