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Appendix 9 Pgs. 5-6
K Zhu, S Aouf, G Roisman et al. CPAP Treatment Efficacy with Pressure-Relief Features
Table 3 —Comparison of pressure-relief features in autotitrating continuous positive airway pressure mode: residual apnea- hypopnea index, apnea index, and pressures during a 4.2-h obstructive apnea sequence (initial apnea index = 58.6/h). Residual AHI (events/h) Residual AI (events/h) Median Pressure (cmH 2 O) a Bench Device Bench Device Bench Device p b Remstar Auto Conv. APAP 9.1 ± 5.7 5.0 ± 3.0 0.5 3.7 ± 2.1 10.4 ± 0.9 10.3 ± 0.8 NS C-Flex 3 13.4 ± 4.8 5.4 ± 1.7 0.5 5.2 ± 1.7 9.7 ± 0.6 9.7 ± 0.6 NS A-Flex 3 7.5 ± 3.7 4.6 ± 1.8 1.4* 4.6 ± 1.8 9.3 ± 0.3 11.2 ± 0.4 0.002 P-Flex 20.6 ± 0.3* 13.8 ± 2.6* 1.8 ± 0.1* 13.8 ± 2.6** 8.5* 11.3 ± 0.1* < 0.001 AirSense 10 AutoSet Conv. APAP 1.3 ± 0.5 0.8 ± 0.1 0.2 0.7 10.5 ± 0.1 10.5 ± 0.1 NS EPR 3 1.4 10.2 ± 0.6** c 0.7* 1.4* 10.2 ± 0.1** 12.7 ± 0.1** < 0.001 Prisma 20A Conv. APAP 2.4 ± 1.3 1.0 0.5 1.0 10.0 ± 0.1 10.0 NS SoftPAP 2 2.1 ± 1.3 2.3 ± 1.2 0.6 ± 0.1 1.0 9.9 ± 0.2 10.5 ± 0.5 NS SoftPAP 3 4.0 ± 1.2 3.7 ± 0.6* 0.5 1.0 9.6 ± 0.2* 10.5** 0.04 Results are given as mean ± standard deviation (n = 3). a For Remstar Auto, mean pressure was noted instead of median pressure. Conventional APAP: APAP without pressure-relief feature. b For the comparison of median/mean pressures between bench and device report. Statistical analysis: one-way analysis of variance preceded by Levene’s test for equality of variance; Kruskal-Wallis test was applied if Levene’s test was positive. c Large difference in residual AHI between the bench and the device, such as observed in EPR 3, was due to the difference in the definition of baseline that applied for sleep disordered breathing event scoring: for the bench, the baseline was considered as the 6-min normal breathing session at the beginning during which the pressure-relief feature was not activated; whereas for the device such as AirSense 10 AutoSet, a real-time baseline was utilized. Of note, this baseline could later be increased by “pressure supports” that were generated by the pressure-relief features such as EPR 3. *p < 0.05; **p < 0.01: comparison between pressure-relief and conventional APAP. APAP, autotitrating continuous positive airway pressure; NS, nonsignificant.
to conventional CPAP, the residual AHI significantly increased when the following pressure-relief features were turned on: C-Flex+ 3, P-Flex, and EPR 3. Compared to conventional APAP, the residual AHI only increased with P-Flex by 11.5/h in a 4.2-h breathing sequence with successive obstructive apneas. Pressure-relief therapy features are developed to overcome patient difficulty of exhaling against a fixed pressure during CPAP treatment and improve the treatment adherence. How- ever, for C-Flex, better adherence has not been proved consis - tently in clinical studies, 4,8,9,11–14,16,17 and the majority reported similar adherence 4,9,14,17 and treatment efficacy 9 between CPAP with and without C-Flex. Adherence and treatment ef - ficacy are not reported in the literature for the other pressure- relief features. According to our results, we confirm the efficacy of C-Flex in fixed CPAP treatment. 9 However, obstructive SDB events remained untreated with C-Flex+ 3, P-Flex, and EPR 3, as a consequence of actual therapeutic pressure being lower than the titration pressure ( Table 2 ). In short, these three modali - ties converted the pressure profiles into a “bilevel PAP” for the purpose of relieving the patient exhalation. C-Flex+ and P-Flex consist of an inspiratory positive airway pressure (IPAP) iden - tical to the titration pressure of CPAP but an expiratory positive airway pressure (EPAP) at least 2 cmH 2 O lower, with a further pressure decrease at the beginning of exhalation ( Figure 1A ). This modality of pressure delivery was not efficient to main - tain the airway patency when apnea occurred ( Figure 1B , col- umn 2 and 3). For EPR 3, the therapeutic pressure decreased by 3 cmH 2 O and apneas thus persisted ( Figure 1B , column 4). Because it has been demonstrated that apneas begin with upper airway narrowing at end-expiration and followed by
collapse during ensuing inspiratory effort, 28 an airway pres- sure equal or higher than the full opening pressure, i.e., the conventionally titrated CPAP, should be applied to keep the airway patency during the end-expiration and the inspiration, as in the curves of C-Flex 3 and SoftPAP 2 and 3 shown in Figure 1B (Columns 1, 5, and 6). Alternatively, the airway patency can be achieved with a “bilevel PAP” pattern, with an EPAP that at least can alleviate the airway obstruction at end-expiration and allow sufficient patient-generated inspira - tory airflow to trigger IPAP. 29 In this case, the EPAP must be higher than the critical closing pressure, and most importantly, the IPAP must be able to overcome the negative intraluminal pressure caused by the inspiratory effort and keep the upper airway patency during the remainder of inspiration. In CPAP mode, C-Flex+ 3 and EPR 3 might lower the treat - ment efficacy on apneas if the device pressure is kept as same as that just sufficient to abolish flow limitations in conventional CPAP. As shown in Figures 2A and 2B , the device pressure should be set higher to reach the same treatment efficacy as conventional CPAP. Accordingly, in the case of APAP with A- Flex 3 (A-Flex shares the same principle as C-Flex+) and EPR 3, the device autotitration pressure reported as the mean/median value was higher than that of the conventional APAP ( Table 3 ) in order to compensate for the pressure reduction caused by the pressure relief. Consequently, similar bench-measured mean/median pressures and residual AHI were obtained be - tween APAPs with and without A-Flex 3 and EPR 3 ( Table 3 ). It should be highlighted that the device-reported pressures in conventional and pressure-relief APAPs are not comparable. On the contrary, P-Flex APAP appeared to underperform in terms of residual AHI as well as in its response to apneas.
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Journal of Clinical Sleep Medicine, Vol. 12, No. 3, 2016
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