Researchers Examine Effectiveness of New Home Test for Sleep Apnea
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Source: American Academy of Otolaryngology Head and Neck Surgery (AAOHNS)
Newswise — Sleep disordered breathing (SDB) is a spectrum of diseases that includes snoring, upper airway resistance syndrome, and obstructive sleep apnea (OSA). Obstructive sleep apnea is a common sleep disorder that can have a negative impact on the cardiovascular and respiratory systems, neuro-cognitive function, as well as a strong link to hypertension. Past research studies have found a relative risk of 2.38 for congestive heart failure and 1.58 for cerebrovascular disease in patients with obstructive sleep apnea when compared to normal patients. Therefore, it should be an essential public health priority to identify patients with OSA in order to prevent subsequent cardiovascular and cerebrovascular morbidity and mortality.
The good news is that public awareness of this disorder has grown in the last decade. Unfortunately, the demand for diagnostic procedures/devices for patients with suspected OSA exceeds the available supply. The gold standard for diagnosing OSA (the attended overnight Level I polysomnogram or PSG) is expensive, labor-intensive, and cumbersome; this has resulted in long waiting lists for studies. Consequently, an option that has emerged is the use of single and/or multiple channel ambulatory monitoring systems, which assess the presence and severity of OSA. Most of these devices are still undergoing validation.
Most specialists who treat sleep disorders agree that the ideal screening device for OSA should be inexpensive, widely accessible, easily used with minimal instructions, have no risk or side effects to the patient, and be accurate. The screening device should be capable of being issued by relatively unskilled staff, and even sent through the mail in order to reduce patient travel and staff costs.
One such device introduced in 2002 was called the SleepStripâ„¢. A team of researchers set out to examine ad validate the reliability and predictive capability of the SleepStripâ„¢. Their findings appear in the study, "A Comparison of Polysomnography and the SleepStrip in the Diagnosis of OSA" authored by Kenny P. Pang, FRCSEd FRCSI(OTO) FAMS(ORL), Thomas A. Dillard MD, Amy R. Blanchard MD, Christine G. Gourin MD FACS, Robert Podolsky PhD, David J. Terris, MD FACS, all with the Medical College of Georgia, Augusta, GA. Their findings are to be presented at the 109th Annual Meeting & OTO EXPO of the American Academy of Otolaryngology—Head and Neck Surgery Foundation, being held September 25-28, 2005, at the Los Angeles Convention Center, Los Angeles, CA.
Methodology: Thirty-nine consecutive adult patients referred to the Georgia Sleep Center for an attended overnight Level I polysomnography were prospectively enrolled over a two-month period. All wore the SleepStripTM device at home the night after the PSG. The procedure of use was explained to each patient individually according to the instruction guidelines provided with the device.
The apnea-hypopnea index (AHI) (the number of apneas and hypopneas divided by the time in bed) determined by PSG was compared to the results of the SleepStrip recording.
Results: A total of 39 patients (17 men and 22 women) were recruited for the study, the mean age was 52.1 ± 12.2 years (range, 18 to 79 years), and the mean body mass index was 35.7 ± 5.2 (range, 17.7 to 46.8). The mean Epworth sleepiness score was 14.9 ± 3.5 out of a possible 24 (range of 2 to 20). A total of 37 SleepStripTMs were returned. One patient had a suspected adhesive allergy and withdrew from the study; one patient could not be contacted. One patient had to repeat the study as the SleepStripTM fell off after one hour of commencing the study. Although there was one patient with a mustache, he was able to complete the study. Three patients reported that they had poor sleep quality on the night of the SleepStripTM; they slept a mean of 5.4 hours. One SleepStripTM indicator light did not flash throughout the night, however, it did give a display result of "0" .
Five SleepStripTMs reported an "E" (error) on the SleepStripTM (13.5 percent), while the other 32 gave a reading of, either "0" , "1" , "2" or "3" (Table 1). There were 17 (53.2 percent) SleepStripTM results with a "0" reading, 5 (15.6 percent) SleepStripTM results with a "1" , 5 (15.6 percent) SleepStripTM results with a "2" , and 5 (15.6 percent) SleepStripTM results with a "3" .
The mean AHI was 32.1 ± 20.2, with a range of 0.4 to 111.2, while the mean AHI was 11.3 ± 6.5, with a range of 0.1 to 74.9. The overall agreement, using the Cohen's Kappa value, between the AHI and the SleepStripTM results was 0.139 (p=0.19) (Table 1). The sensitivity and specificity for diagnosing OSA (AHI >15) were 54.6 percent and 70 percent respectively (p=0.26). When the threshold for OSA was set at an AHI >25, the sensitivity was 43.8 percent and the specificity was 81.3 percent (p=0.25). For diagnosing severe OSA (AHI >40), the sensitivity was 33.3 percent and the specificity was 95 percent (p=0.05) (Table 2). The mean patient-reported sleep time for the SleepStripTM was higher at 6.25 ± 1.01 hours, while the mean sleep time for the polysomnography was 5.73 ± 1.12 hours (p=0.052).
The data revealed an overall lack of agreement between the PSG and the SleepStripTM, with a correlation of only 0.139 (p=0.19). The sensitivities at AHI >15, >25 and >40 were poor, as were the specificity at AHI >15 and AHI >25. It was only useful in excluding severe OSA (AHI>40) for which a specificity of 95 percent was achieved. We observed an overall under-estimate of the severity of the OSA in the SleepStripTM compared to the Level I PSG. This discrepancy could not be explained by the sleep times, as the mean patient reported sleep time for the SleepStripTM was higher (6.25 +/- 1.01 hours), than that of the polysomnography (5.73 +/- 1.12 hours) (p=0.052).
The researchers cite the number of limitations to the current study; the most significant limitation of this study is that the SleepStripTM device and the PSG could not be conducted simultaneously. They were unable to eliminate the night-to-night variability as a potential confounding factor, which may have contributed to the difference in the tests results. However, they do assert that there are numerous studies that have shown that the night-to-night variability in sleep studies is modest.
Another limitation that merits consideration, and which is inherent with all portable home monitoring devices, is the fact that the total sleep time for the portable home device may not reflect the true sleep time. In a portable home monitoring device, it is self-administered and not supervised by a sleep technician; as a result, the onset of sleep may not be accurately determined, unlike the EEG-monitored laboratory PSG. This limitation may result in a tendency for the SleepStripTM to underestimate the AHI.
Conclusions: Given the high prevalence of OSA and limited capacity for sleep laboratory testing, there is a clear need for home diagnostic screening tests. The SleepStripTM is small, lightweight, inexpensive, easy-to-use, and safe. However, it demonstrates low sensitivity and specificity for diagnosing mild (AHI >15) and moderate (AHI>25) OSA. The SleepStripTM only demonstrated usefulness in excluding severe OSA (AHI>40). The researchers believe that further prospective investigation must be accomplished before the SleepStripTM can be recommended as a screening device for OSA.
Note: The American Academy of Otolaryngology—Head and Neck Surgery Foundation Annual Meeting and OTO EXPO is a venue for the presentation of scientific and medical research findings to its members. The findings and opinions reached in this research study are those of the authors only, and do not necessarily reflect those of the American Academy of Otolaryngology—Head and Neck Surgery, its Foundation, or its officers.
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