Diagnosis of obstructive sleep apnea usually involves polysomnograpy, an overnight sleep test in a sleep clinic or lab. Results of a new study indicate that a take-home sleep test is just as effective as a polysomnography and is less expensive while providing timely results.
Obstructive sleep apnea (OSA) is a common medical condition that occurs in approximately nine to 24 percent of the population and can lead to hypertension, heart problems, and stroke. The effects of untreated OSA are responsible for a two-fold increase in traffic accidents, a decrease in the quality of life of affected patients, and billions of dollars of healthcare costs annually in the US. Obtaining an accurate and timely diagnosis is imperative, but is becoming more difficult as awareness of the disorder grows and more patients require overnight sleep lab tests.
Polysomnography, the gold standard for diagnosis of OSA, is an expensive test that can only be done in a sleep center that accommodates overnight testing. In addition to requiring an overnight stay, some patients may be limited by geographic accessibility to an appropriate sleep lab.
Researchers set out to determine the validity of the SNAP test, a take-home sleep test and whether or not it would produce effective results that could be used as an alternative diagnostic or screening tool for OSA. The study ¡°Validations of a Portable Home Sleep Study with 12-Lead Polysomnography: Comparisons and Insights into a Variable Gold Standard,¡± is authored by Peter G. Michaelson, MD, Patrick F. Allan, MD, John C. Chaney, MD, and Eric A. Mair, MD, of the Department of Otolaryngology¡ªHead and Neck Surgery and Department of Pulmonary/Critical Care and Sleep Medicine at Wilford Hall USAF Medical Center in San Antonio, Texas. Their findings are being presented at the American Academy of Otolaryngology-Head and Neck Surgery Foundation Annual Meeting & OTO EXPO, being held September 19-22, 2004, at the Jacob K. Javits Convention Center, New York City, NY.
Methodology:
This comparison study included 59 adult patients (49 men and 10 women) who presented at Wilford Hall USAF Medical Center (WHMC) Sleep Laboratory for polysomnography (PSG) evaluation between June and August 2003. Average male age was 37.8 with an average body mass index (BMI) of 27 while average female age was 50 years old with a BMI of 24.4. To mirror the population who commonly receive PSG, the only exclusion criteria were: those who did not wish to undergo trial enrolment, those presenting to the sleep laboratory only for a titration (determination of air pressure needed for effective control of OSA) of CPAP (continuous positive airway pressure), and all patients younger than 18 years of age.
Patients underwent a PSG and SNAP test simultaneously during the first half of the night to evaluate for OSA. Those who were determined to have OSA then underwent a CPAP titration for the remainder of the night. The PSG raw data were read in an independent, blinded fashion, by a separate, board-certified group of sleep physicians at WHMC, PSG1, and at an external center, PSG2. SNAP data were read by two independent readers (SNAP1 and SNAP2) at the SNAP laboratories. Since multiple variables are recorded during both tests, a determination was made to use the apnea/hypoxnia index (AHI), the most commonly used variable of sleep characteristics to test for OSA severity, for comparison between the two tests. Several other relationships were calculated, including Pearson correlation coefficients (CC), receiver operating characteristic (ROC) curve, sensitivity, specificity, positive and negative predictive value and Bland-Altman curves. To analyze inter-reader variability, multiple relationships were also calculated between PSG reads (PSG1 and PSG2) and SNAP reads (SNAP1 and SNAP2).
Results:
The average PSG recording time was 256 minutes; average SNAP recording time was 250 minutes. Due to the high correlation coefficient, ROC curve areas and Bland-Altman relationship, both SNAP reads (SNAP1 and SNAP2) were considered interchangeable and SNAP1 was used for further comparison against the PSG data. Comparison of both PSG reads indicated a weaker relationship between different reads.