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Communications to the Editor |

SNAP Technology and Sleep Apnea FREE TO VIEW

Thomas J. Kehoe, MD, FCCP
Author and Funding Information

Affiliations: Evanston Northwestern Healthcare, Evanston, IL,  Rhode Island Hospital, Providence, RI,  The Johns Hopkins University, Baltimore, MD

Correspondence to: Thomas J. Kehoe, MD, FCCP, Assistant Professor in Clinical Medicine, Feinberg School of Medicine, Northwestern University Medical School, 2650 Ridge Ave, Evanston, IL 60201; e-mail: Tkehoe@ENH.org



Chest. 2005;127(4):1465-1467. doi:10.1378/chest.127.4.1465
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Published online

To the Editor:

As a Fellow of the American College of Chest Physicians, a medical adviser to SNAP Laboratories, and a SNAP Laboratories test user of many years, I read with surprise the study by Liesching et al (March 2004),1as well as the accompanying editorial by Collop.2

Using data derived from a poorly designed study, Liesching et al unjustifiably concluded that the agreement between the apnea-hypopnea index determined by SNAP testing and polysomnography can only be characterized as “fair.” The authors then offered the opinion that SNAP studies may not accurately assess the severity of obstructive sleep apnea. In an additional reply to this article, Collop2 correctly pointed out that “the study is not without faults.”

As noted, the study by Liesching et al1 was a retrospective comparison of nonsimultaneous studies performed in the laboratory with those performed at home. In actuality, the mean time frame between tests that were compared was 5 months. The decision to compare data collected from different and nonsequential nights is a major flaw. Despite the rebuttal of one study by Liesching et al, there is a substantial body of research35 that documents the first-night and night-to-night variability of sleep apnea. This variability is compounded by the week-to-week or month-to-month variability inherent in their study. Therefore, their data were clearly impacted by variables such as changes in body mass index, medications, and site of testing. In addition, of the original 39 subjects, only 31 had complete data for analysis. Considering the limitations of the study, it is remarkable that it was considered to be an empirical foundation for any conclusions. A more appropriate conclusion, if any were to be drawn, would be that SNAP home testing variability is no greater than that documented between nights in a sleep center.

In addition to pointing out this study’s shortcomings, Collop has noted previously6that “given the outdated sleep staging rules, inconsistent equipment between labs, variable scoring parameters … it is a wonder that there can be any consistent scoring of PSGs [between trained sleep professionals].” In another publication7 Collop concluded that “clinicians should be aware that there is tremendous variability among polysomnography technologists regarding the scoring of polysomnography.” Given the disagreement levels reported by Collop in this study (eg, the record of the same patient yielded apnea-hypopnea index scores of 5 and 74 by two differently trained technicians), the SNAP results criticized by Liesching et al,1 are in fact impressive. Thus, even if the SNAP test had been in perfect agreement with the scoring done by the Brown Sleep Laboratory physician used in this study, scoring by personnel at another laboratory would in all likelihood differ. This would lead Liesching et al1 to the same conclusions that they reached in their study.

SNAP testing is being held to a different standard from that the sleep industry sets for itself. The sleep medicine community has been aware for years of the high level of disagreement between two trained professionals scoring the same record on the same night. Why then should they be surprised when SNAP results vary between a review by one technician and that of another technician performed months later in an entirely different environment? Perhaps one should question why we should subject patients to laboratory-based polysomnography at significantly greater expense and inconvenience when same-test scoring agreement is no more accurate than that reported by a SNAP home test.

The SNAP test is not a “black box,” as suggested in the editorial by Collop,2 but instead requires a full night of continuous recording of at least four data channels. These raw data are analyzed by a trained technician who analyzes the full night of digitally recorded raw data, just as is done in the sleep laboratory. All data with marked events are available to the referring physician on request. The SNAP test technology and scoring procedure have been validated on five separate occasions by accredited sleep centers. All of these studies used a protocol of recording SNAP data and conventional polysomnography data on the same night in sleep laboratories, with quite impressive results. Previous attempts to publish these side-by-side blind studies have been met with strong resistance by journals with review committees dominated by sleep specialists. In other cases, after the data were collected and analyzed, the sleep laboratory involved in the study simply refused to submit the results for publication.

Despite these obstacles, a recent study performed at the University of Chicago was published8 that simultaneously compared SNAP to PSG, as was suggested by Liesching et al. The authors concluded that “the results of this validation study demonstrate that there is good correlation between SNAP and PSG in quantifying RDI with reliable sensitivity, specificity, positive and negative predictive values in a laboratory setting.” Thus “SNAP is an excellent tool for the diagnosis of OSAS.”

As a medical adviser I have been assured by SNAP Laboratories of their willingness to participate in any well-designed, objective study that will yield a fair and accurate assessment of SNAP sleep testing.

Liesching, TN, Carlisle, C, Marte, A, et al (2004) Evaluation of the accuracy of SNAP technology sleep sonography in detecting obstructive sleep apnea in adults compared to standard polysomnography.Chest125,886-891. [CrossRef] [PubMed]
 
Collop, NA Portable monitoring for diagnosing obstructive sleep apnea.Chest2004;125,809-811. [CrossRef] [PubMed]
 
Lord, S, Sawyer, B, O’Connell, D, et al Night-to-night variability of disturbed breathing during sleep in an elderly community sample.Sleep1991;14,252-258. [PubMed]
 
Mosko, SS, Dickel, MJ, Ashurst, J Night-to-night variability in sleep apnea and sleep-related periodic leg movements in the elderly.Sleep1998;11,340-348
 
Moser, NJ, Phillips, BA, Berry, DT What is hypopnea anyway?Chest1994;105,426-428. [CrossRef] [PubMed]
 
Collop, NA Consistency crucial to polysomnography scoring.Adv Managers Respir Care2004;13,13-16
 
Collop, NA Scoring variability between polysomnography technologists in different sleep laboratories.Sleep Med2002;3,43-47. [CrossRef] [PubMed]
 
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 Surg2004;131,844-850. [CrossRef] [PubMed]
 
To the Editor:

We read with interest Dr. Kehoe’s letter regarding our study entitled “Evaluation of the Accuracy of SNAP Technology Sleep Sonography in Detecting Obstructive Sleep Apnea in Adults Compared to Standard Polysomnography” (March 2004).1 As the medical advisor to SNAP laboratories, I can understand Dr. Kehoe’s concerns and interest in our article. I think it is important for all to understand our rationale for initiating this study and submitting it for publication in CHEST.

At the Sleep Disorders Center of Lifespan Hospitals in Rhode Island, we started to get referrals from several primary care physicians who had performed SNAP studies on their patients with presumed obstructive sleep apnea. We only were referred patients who had positive SNAP sleep study results that were consistent with obstructive sleep apnea. Since there was nothing in the peer reviewed published literature about SNAP technology, we attempted to find out how the recordings were done and how they were scored. When Dr. Liesching, then a fellow in our laboratory, tried to call SNAP Technology about their analysis method, he was told that this information was “proprietary.” Since we did not know whether SNAP was accurate in this or not, we felt that we had to perform a full attended polysomnography on all of these patients. When we began to see that sleep apnea severity, as determined by polysomnography, did not correlate with the results of the SNAP evaluation, we started to take a more systematic approach to accessing the results of SNAP. The SNAP reports also recommend a starting continuous positive airway pressure (CPAP), and we again found that this did not correlate with the actual determined CPAP pressure during a titration in our laboratory.

If SNAP had been demonstrated to have been clearly evaluated and published in peer reviewed journals, we would never have initiated an analysis of our data compared to data from SNAP technology. Our article went through vigorous peer review to be accepted in CHEST, including multiple revisions. We understand that there are limitations to our study, and we clearly noted these in our article. I understand Dr. Kehoe’s frustration with our article being the first study published about this technology, as there have been no published validation studies to date. We also hope that there will be a future well-designed objective study that will yield a fair and accurate assessment of SNAP sleep technology.

I appreciate that Dr. Kehoe feels that SNAP technology meets the level of rigorous testing. Unfortunately, it is very difficult to judge, because there are no peer-reviewed published articles on SNAP. I think he is incorrect in stating that SNAP validation studies have not been published because the review committees on journals are dominated by sleep specialists. There have been multiple other portable sleep units that have gone through vigorous validation and have had their data published. In fact, our laboratory did a thorough evaluation of the Edentec Monitoring System, Model 4700 scanner (Mallinckrodt-Nellcor Puritan Bennett; St. Louis, MO) and showed that it compared favorably to simultaneous in-laboratory polysomnography.2 In that study, we also performed home studies using the same equipment, and showed that there was no significant night-to-night variability using that equipment in the laboratory and subsequently at home. We did the study and had it accepted for publication prior to using the equipment in subsequent epidemiologic evaluations and in our hospital for inpatients with suspected sleep apnea.

I agree that there is variability in interpreting polysomnography findings and that in-laboratory polysomnography may not be the “gold standard.” In fact, our laboratory has previously published a study in CHEST3that showed that one should probably repeat a sleep study in a patient with negative all-night polysomnography findings and a high clinical suspicion for sleep apnea. In addition, it is possible that more accurate and consistent studies could be obtained in the home setting. The professional pulmonary and sleep societies in this country having been trying for years to determine whether the diagnosis of sleep apnea can be made more accurately and be less costly in the home. All the data on portable recording has been vigorously reviewed by these groups46 and now most recently by Medicare. The general consensus is that type 3 recording devices, which would include SNAP, are not recommended to rule in or rule out a diagnosis of obstructive sleep apnea in unattended settings at the present time.

I would welcome well-done validation studies of SNAP and other technologies because I still feel there is a potential role for portable studies in select patients with a high pretest clinical suspicion for obstructive sleep apnea.7 Until that has been done, I am going to continue to perform full polysomnography in a laboratory setting.

References
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.Chest2004;125,886-891. [CrossRef] [PubMed]
 
Redline, S, Tosteson, T, Boucher, MA, et al Measurement of sleep-related breathing disturbances in epidemiologic studies: assessment of the validity and reproducibility of a portable monitoring device.Chest1992;100,1281-1286
 
Meyer, T, Eveloff, SE, Kline, L, et al One negative polysomnography does not exclude obstructive sleep apnea.Chest1993;103,756-760. [CrossRef] [PubMed]
 
Ferber, A, Millman, RP, Coppola, M, et al Portable recording in the assessment of obstructive sleep apnea: ASDA standards of practice.Sleep1994;17,378-392. [PubMed]
 
Chesson, AL, Berry, RB, Pack, A Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults.Sleep2003;26,907-913. [PubMed]
 
ATS/ACCP/AASM Taskforce Steering Committee.. Executive summary on the systematic review and practice parameters for portable monitoring in the investigation of suspected sleep apnea in adults.Am J Respir Crit Care Med2004;169,1160-1163. [CrossRef] [PubMed]
 
Millman, RP, Neumeyer, D, Kramer, NR Diagnostic strategies.Semin Respir Crit Care Med1998;19,133-138
 
To the Editor:

I thank Dr. Kehoe for his letter concerning my editorial (March 2004)1on the article by Liesching et al2 entitled “Evaluation of the Accuracy of SNAP Technology in Detecting Obstructive Sleep Apnea in Adults Compared to Standard Polysomnography.” As noted, I agreed in my editorial that the study by Liesching et al2 had several flaws. However, despite the many flaws in the study, I would still challenge the idea that the SNAP device is a “black box” since there is no published literature on its scoring or reliability. I find it hard to believe that of five separate studies, no sleep centers or journals would publish the information if it was sound, unbiased research. I am anxious to read their upcoming study when published in a peer-reviewed journal.

Regarding the issue of variability, as long as we continue to use a sleep-disordered breathing index to make this diagnosis, there will always be significant variability, whether we are looking at standard polysomnography or portable monitoring. Polysomnography has the significant advantage of the measurement of sleep and its architecture, and will always be better than portable monitoring because of the multiplicity of channels and the attendance by a technician. Few data are available regarding the use of portable monitoring in patients other than middle-aged white men. An evidence review,3a study on practice parameters,4 and, more recently, a panel from CMS, concluded that there is not enough support in the literature to allow portable monitoring (specifically, unattended level 3 systems) to be utilized indiscriminately for the diagnosis of sleep apnea. Portable monitoring will be acceptable, in my eyes, when these devices have been thoroughly validated and when the populations in which sleep apnea can be accurately diagnosed using these devices have been defined.

References
Collop, NA Portable monitoring for diagnosing obstructive sleep apnea: not yet ready for primetime.Chest2004;125,809-811. [CrossRef] [PubMed]
 
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.Chest2004;125,886-891. [CrossRef] [PubMed]
 
Flemons, W, Littner, M, Rowley, J, 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.Chest2003;124,1543-1579. [CrossRef] [PubMed]
 
Chesson, A, Berry, R, Pack, A Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults.Sleep2003;26,1-7
 

Figures

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References

Liesching, TN, Carlisle, C, Marte, A, et al (2004) Evaluation of the accuracy of SNAP technology sleep sonography in detecting obstructive sleep apnea in adults compared to standard polysomnography.Chest125,886-891. [CrossRef] [PubMed]
 
Collop, NA Portable monitoring for diagnosing obstructive sleep apnea.Chest2004;125,809-811. [CrossRef] [PubMed]
 
Lord, S, Sawyer, B, O’Connell, D, et al Night-to-night variability of disturbed breathing during sleep in an elderly community sample.Sleep1991;14,252-258. [PubMed]
 
Mosko, SS, Dickel, MJ, Ashurst, J Night-to-night variability in sleep apnea and sleep-related periodic leg movements in the elderly.Sleep1998;11,340-348
 
Moser, NJ, Phillips, BA, Berry, DT What is hypopnea anyway?Chest1994;105,426-428. [CrossRef] [PubMed]
 
Collop, NA Consistency crucial to polysomnography scoring.Adv Managers Respir Care2004;13,13-16
 
Collop, NA Scoring variability between polysomnography technologists in different sleep laboratories.Sleep Med2002;3,43-47. [CrossRef] [PubMed]
 
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 Surg2004;131,844-850. [CrossRef] [PubMed]
 
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.Chest2004;125,886-891. [CrossRef] [PubMed]
 
Redline, S, Tosteson, T, Boucher, MA, et al Measurement of sleep-related breathing disturbances in epidemiologic studies: assessment of the validity and reproducibility of a portable monitoring device.Chest1992;100,1281-1286
 
Meyer, T, Eveloff, SE, Kline, L, et al One negative polysomnography does not exclude obstructive sleep apnea.Chest1993;103,756-760. [CrossRef] [PubMed]
 
Ferber, A, Millman, RP, Coppola, M, et al Portable recording in the assessment of obstructive sleep apnea: ASDA standards of practice.Sleep1994;17,378-392. [PubMed]
 
Chesson, AL, Berry, RB, Pack, A Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults.Sleep2003;26,907-913. [PubMed]
 
ATS/ACCP/AASM Taskforce Steering Committee.. Executive summary on the systematic review and practice parameters for portable monitoring in the investigation of suspected sleep apnea in adults.Am J Respir Crit Care Med2004;169,1160-1163. [CrossRef] [PubMed]
 
Millman, RP, Neumeyer, D, Kramer, NR Diagnostic strategies.Semin Respir Crit Care Med1998;19,133-138
 
Collop, NA Portable monitoring for diagnosing obstructive sleep apnea: not yet ready for primetime.Chest2004;125,809-811. [CrossRef] [PubMed]
 
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.Chest2004;125,886-891. [CrossRef] [PubMed]
 
Flemons, W, Littner, M, Rowley, J, 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.Chest2003;124,1543-1579. [CrossRef] [PubMed]
 
Chesson, A, Berry, R, Pack, A Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults.Sleep2003;26,1-7
 
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