K Zhu, S Aouf, G Roisman et al. CPAP Treatment Efficacy with Pressure-Relief Features
Table 1 —Pressure evolution of studied pressure-relief features during one breathing cycle (summarized from the provider manuals of the CPAP devices and reference 15).
Pressure during the transition to expiration
Pressure during the beginning of expiration
Pressure at the end expiration
Pressure during inspiration
Remstar Auto C-Flex Level 1, 2 and 3
Pressure drops proportional to expiratory flow (3 levels of settings for C-Flex and C-Flex+/A-Flex).
1 (if set pressure = 5) or 2 cmH 2 O (if set pressure ≥ 6) below the set pressure. Up to 4 cmH 2 O below the set pressure.
C-Flex+ (for fixed CPAP) and A-Flex (for APAP) Levels 1, 2, and 3
Pressure drops by 1 (if set pressure = 5) or 2 cmH 2 O (if set pressure ≥ 6). Pressure drops by up to 4 cmH 2 O depending on the set pressure. b
P-Flex (only for APAP) a
AirSense 10 AutoSet EPR Level 1, 2 and 3
Pressure drops by 3 levels: 1, 2, or 3 cmH 2 O (3 levels of settings), but remains ≥ 4 cmH 2 O.
Prisma 20A SoftPAP Level 1 and 2
Pressure drops depending on the set pressure (2 levels of settings). b
SoftPAP Level 3
Set pressure with supplementary pressure support.
Pressure drops as the same way as SoftPAP 2 does.
Set pressure: user-set pressure for fixed continuous positive airway pressure (CPAP); device-ordered autotitration pressure for autotitration continuous positive airway pressure (APAP). a P-Flex is exclusive for the French market. b Values undisclosed by the manufacturers.
titration when the patient complains of excessive pressure. In addition, most studies on such therapy feature are restricted to C-Flex (Philips Respironics, Murrysville, PA, USA), and the literature does not consistently support its usefulness. 8–16 For other pressure-relief features available on the market, the ad- ditional benefits still remain unclear. 3,17 Bench studies have been proposed to evaluate the responses of APAP devices in different conditions, such as the pres- ence of predefined sleep disordered breathing (SDB) patterns and air leak, 18–25 whereas no such study to date has focused on pressure-relief CPAPs and APAPs. We investigated seven pressure-relief features developed by three CPAP device man- ufacturers with a previously reported bench model. 25 METHODS Bench Model and Simulation of Obstructive Apneas Evaluations were carried out on a previously described bench model. 25 Consisting of an active lung model and a Starling resistor, the bench model is able to simulate different SDB patterns such as obstructive apneas, hypopneas, and flow limi - tations. The human upper airway is mimicked by the Starling resistor, and the control of airway patency can be achieved by adjusting the pressure inside the resistor. The CPAP device and the bench are connected by a standard tubing (1.8 m long and 22 mm in diameter), and a calibrated leak port (24 L/min at 10 cmH 2 O) is presented in order to mimic the intentional leak in nasal masks. Mask pressure (P m ) and airflow (V’) are recorded for further analyses.
During obstructive apnea simulation, the breathing effort is generated by the piston movement. The pressure inside the Starling resistor is set at 9 cmH 2 O, and the critical closing and full opening pressures were measured at around 6 and 11 cmH 2 O, respectively. Studied Pressure-Relief Features Three CPAP devices were included in the current study: Remstar Auto P-Flex (Philips Respironics), AirSense 10 AutoSet (Resmed, Sydney, Australia) and Prisma 20A (Weinmann, Hamburg, Germany). Studied pressure-relief features and their principles are shown in Table 1 . During the test, each feature was set at the maximum level if adjust - able, i.e., achieving the maximally reduced pressure during expiration. Pressure-Relief CPAP/APAP Efficacy Protocol F ixed CPAP: With simulated apneas, a manual titration of pressure was first conducted to obtain the therapeutic pres - sure for each CPAP device with pressure-relief features dis- abled (conventional CPAP): the pressure was increased from 4 cmH 2 O in a stepwise manner with a minimum increment (0.5 cmH 2 O for Remstar Auto and Prisma 20A, 0.2 cmH 2 O for AirSense 10 AutoSet) until the breathing flow was fully normalized. Afterward, the devices were set at obtained titra- tion pressure, and subjected to a predefined short obstructive apnea sequence with pressure-relief features enabled. The short breathing sequence lasted 10 min, which was considered
Journal of Clinical Sleep Medicine, Vol. 12, No. 3, 2016
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