Respironics v60

Due to the resource scarcity the patients were supported by several types of ventilators including the Puritan Bennet 840® (Medtronic, Minneapolis MN), the Dräger Evita V500® (Draeger Inc. Telford PA), the Maquet Servo-i® (Getinge LLC, Wayne NJ), the Respironics V60®, the Phillips EVO Trilogy (both Koninklijke Philips N.V.), and the LTV 1000® (Vyaire, Mettawa IL). Standard principles of protective ventilation strategies including the limitation of plateau airway pressures to < 30 cm H₂O and tidal volumes of 6–8 cc/kg ideal body weight guided therapy. Moderate hypercapnia was tolerated provided the pH was > 7.20.

The HFNC device (Airvo-2^™; Fisher & Paykel Healthcare, Auckland, New Zealand) consisted of a flow generator (up to 60 L/min), an air–oxygen blender that allows for adjustment of FiO₂ from 21 to 100%, and an auto-fill MR 290 heated chamber. The gas mixture at 34–37 °C was delivered via a single-limb heated breathing tube to the patient via the Optiflow™ nasal cannula (Fisher & Paykel, Auckland, New Zealand). The dedicated NIV machine (BIPAP Vivo 40; Breas Medical AB, Mölnlycke, Sweden or Respironics V60; Philips Healthcare, Best, the Netherlands) was applied via an oronasal mask and was connected to an active humidification system (VH2000, VADI Medical Technology, Taoyuan, Taiwan). An appropriately sized oronasal mask was chosen to minimize leaks and to optimize patient comfort. The NIV settings, including inspiratory positive airway pressure, expiratory positive airway pressure, respiratory rate, and FiO₂, were clinically adjusted by an attending physician and not modified during the study period.

One week before the start of aerobic training, each subject underwent measurements of SV, CO, arterial blood pressure (BP) and heart rate (HR) during NPPV at pressure levels of 0, 4, 8, 12 cmH₂O in the supine position. The above parameters were recorded 5 minutes after steady-state breathing at the selected NPPV level. Artificial ventilation (Respironics V60; Philips, Amsterdam, Holland) was used in all subjects with a nasal mask, and the ventilator mode was set to continues positive airway pressure (CPAP) throughout the study. CO and SV were measured by the impedance method (Noninvasive Continuous Cardiac Output Monitor MCO-101; Medisens, Tokyo). HR was obtained from the R-R interval of the electrocardiogram (Stress Test System ML-9000; Fukuda Denshi, Tokyo) and BP was measured manually by a sphygmomanometer.