Model study on the change of the pressure applied by automatic CPAP devices when subjected to simulated respiratory events with and without increases in upper airway resistance

Introduction: Automatic continuous positive airway pressure (CPAP) devices are increasingly being used for treating patients with obstructive sleep apnoea syndrome (OSAS). Most of these devices are based on detecting respiratory events from the analysis of the breathing flow shape and/or snoring. However, other devices also include the detection of upper airway resistance increases for identifying obstructive events. The differences in the detection method of these devices may influence their strategy for modifying the applied CPAP during treatment, specifically in the presence of central and obstructive events. The aim of this bench study was to evaluate the response of different commercial automatic CPAP devices to simulated respiratory events with and without increases in upper airway resistance during sleep. Methods: A patient simulator was used for evaluating the automatic CPAP devices in the bench in a systematic and controlled way. The patient simulator was able to reproduce any type of flow waveform (Farré et al. Am J Respir Crit Care Med 2002; 166: 469–73) and included a servocontrolled valve capable of reproducing precisely the increases in airway resistance typically found in patients with OSAS (J. Rigau et al. Eur Respir J 2003; 22(45): 181s). Three devices with detection algorithms based on the flow shape and snoring were analyzed: REMstar auto (Respironics, USA), Autoset Spirit (Resmed, Australia), PV10i (Breas, Sweden). Two additional devices, which detect also increases in airway resistance, were analyzed: SOMNOsmart 2 (Weinmann, Germany) and Autoset II Plus (ResMed, Australia). Each device was connected to the patient simulator and was submitted to hypopnoea flow patterns with different flattened inspiratory contours and apnoea flow patterns with simultaneous increases in the airway resistance (obstructive hypopnoeas and apnoeas) and without increases in airway resistance (central hypopnoeas and apnoeas), continuously repeated regardless of the device reaction. Results: In the presence of obstructive apnoeas with a resistance of around 75 cmH2O s/L, all the devices modified the applied pressure at different rates. The time required for each device for increasing the pressure from 4 to 10 cmH2O was 4min for Autoset II Plus, 5min for Autoset Spirit, 7min for PV10i, 12min for REMstar Auto and 13min for SOMNOsmart 2. When the same apnoea pattern was reproduced without an increase of airway obstruction (central apnoeas), the Autoset Spirit, the PV10i and the REMstar Auto devices increased the applied CPAP exactly in the same way as during the obstructive apnoeas. However, the SOMNOsmart 2 and the Autoset II Plus, did not modify the pressure, keeping the initial CPAP of 4 cmH2O. The different flattened inspiratory flow shapes were evaluated by the devices in a different way leading to pressure changes in a pattern specific subgroup of devices only. The pressure reaction was independent of simulated partial airway obstructions in the devices without resistance detection and also in Autoset II Plus, since this device detects obstructions only during apnoeas. The SOMNOsmart2, which detects airway resistance continuously, altered its pressure response when no obstruction was present. Discussion: The automatic CPAP devices including the detection of increases in the upper airway resistance are able to differentiate central from obstructive respiratory events. This allows avoiding an unnecessary increase in the applied CPAP in the presence of central events characterised by an absence of airway obstruction.

Supported in part by Measure, Check & Control, GmbH & Co. KG.