Oral pressure therapy (winx) for obstructive sleep apnea: a meta-analysis updating the systematic review

Letter to the editor: We read with great interest the recent systematic review by Dr. Nigam and colleagues evaluating the effect of oral pressure therapy (Winx® Sleep Therapy System by ApniCureTM Redwood City, CA, USA) on obstructive sleep apnea (OSA) outcomes [1]. We commend the authors for their role in advancing the academic literature regarding treatment for OSA. We believe this article would be strengthened by inclusion of a meta-analysis of the data, as has previously been published for other medical treatments (e.g. myofunctional therapy [2] and nasal expiratory positive airway pressure devices [3] (Provent ®)) and surgical treatments (e.g. hyoid surgery [4] and supraglottoplasty surgery [5]) for OSA. We, therefore, offer this additional statistical analysis for oral pressure therapy. In order to perform the meta-analysis, we first reviewed the article by Dr. Nigam and colleagues and downloaded the included manuscripts. Subsequently, M.C. and S.A.S. performed an updated search through February 10, 2016 to ensure there were no additional studies. We found no additional studies. We reviewed the studies and did our best to exclude studies if they had potentially duplicate data. Next, we used STATA 14.1 (StataCorp, College Station, Texas, USA) and Review Manager Software (REVMAN) version 5.3 (Copenhagen: The Nordic Cochrane Centre: The Cochrane Collaboration, 2014) to perform the statistical analysis and the meta-analysis with random effects modeling. In total, 140 patients had pre and post-oral pressure therapy data for evaluation. The means and standard deviations for apnea-hypopnea index (AHI) preand post-oral pressure therapy treatment for adults was 37.18 ± 24.94 and 21.35 ± 23.72 events/h (relative reduction: 42.6 %). Random effects modeling was performed for the studies providing means and standard deviations in 139 patients (1 patient was excluded as a case report since case reports have no mean and standard deviation, therefore, case reports cannot be analyzed in REVMAN). For AHI, the mean difference was −16.11 [95 % Confidence Interval (CI) -21.53, −10.68] events/h, overall effect z = 5.83, p < 0.00001. The Cochrane Q-statistic for mean difference in AHI was 0.40 (no statistically significant heterogeneity) and the I was 0 % (no inconsistency). The standardized mean difference for AHI was −0.69 [95 % CI −0.97, −0.41], which corresponds to a moderate magnitude of effect using Cohen’s guidelines. The Cochrane Q-statistic for standardized mean difference was 0.31 (no statistically significant heterogeneity) and the I was 16 % (no to low inconsistency). Figure 1 summarizes the mean difference and standardized mean difference data comparing oral pressure therapy to baseline values as treatment for obstructive sleep apnea. Review of the individual studies’ outcomes does not clearly demonstrate whether select groups would most benefit from oral pressure therapy based on OSA severity (mild, moderate or severe); however, as summarized by Nigam et al. BOPT success rate varied in the range of 27-43% for mild OSA, 42-71% for moderate OSA, and 23-50% for severe OSA^. [1]. The first limitation in this meta-analysis is that the majority of the original work evaluating oral pressure therapy has been performed by a select few investigators using industry funded * Macario Camacho drcamachoent@yahoo.com