Firmware-Dependent Changes in Pressurization and Tidal Volume Delivery During Passive Leak Ventilation

Abstract

Background: Portable home ventilators operating in pressure-targeted passive leak mode are widely prescribed for patients with neuromuscular disease (NMD). In this passive ventilation configuration, delivered tidal volume (V Ti ) is determined not by clinician-set parameters alone but by device-specific pressurization algorithms. Inter-device V Ti variability has been demonstrated in cross-sectional bench studies; however, whether firmware updates alter these characteristics longitudinally—and whether such alterations are clinically important—has not been systematically examined. NMD is a progressive condition in which respiratory system compliance deteriorates over time, further amplifying the clinical relevance of device pressurization characteristics. Methods: We performed bench testing of portable home ventilators in 3 measurement cohorts: 2018 (no. = 7 devices), 2020 (no. = 3 devices), and 2021 (no. = 4 devices). All cohorts used an identical protocol: single-limb passive leak circuit (Intersurgical), 1.8-m corrugated tubing, SmartLung test lung (IMT Analytics, Buchs, Switzerland), inspiratory positive airway pressure (IPAP) 15 cm H 2 O/expiratory positive airway pressure 5 cm H 2 O, T I 1.0 s, breathing frequency 10 breaths/min, rise time fastest, and Body Temperature, Pressure, Saturated (BTPS) correction. Three test conditions simulated NMD mechanics (C30/R5: compliance 30 mL/cm H 2 O, resistance 5 cm H 2 O/L/s), high airway resistance (C30/R50), and low compliance (C20/R5). Data were logged continuously for each condition for 60 min at a 10-Hz output interval (CITREX H4 analyzer; IMT Analytics), yielding ∼590 complete breath cycles per condition. Ensemble-averaged V Ti , pressurization indices at 300 and 500 ms (P 300 ms, P 500 ms), and inspiratory flow at 80% of the set T I (F 80 %T I ) were derived from all breath cycles. Results: Under C30/R5 in the 2018 cohort, inter-device V Ti ranged from 308 to 424 mL (range 116 mL; 32.7% of the cohort mean). Devices were classified into 2 flow profile categories: high late-T I flow (VOCSN, F 80 %T I = 11.3 L/min; Vivo 60, 9.8 L/min) and early flow decay (Stellar 100 [VELIA], Trilogy 100, PB560, Astral 150, A40; F 80 %T I 3.0–7.2 L/min). Longitudinal comparison revealed clinically important V Ti reduction following firmware updates: VOCSN decreased from 424 ± 4.8 mL (v4.01.06R, 2018) to 269 ± 4.5 mL (v4.13.00R, 2021), a reduction of 155 mL (−37%); Trilogy EVO decreased from 396 ± 2.0 mL (v1.01, 2020) to 275 ± 1.2 mL (v1.04.06, 2021), a reduction of 121 mL (−31%); and Vivo 45LS decreased from 515 ± 2.6 mL (early lot, 2020) to 316 ± 3.0 mL (revised firmware, 2021), a reduction of 199 mL (−39%). In each case, P 300 ms was preserved across firmware versions, whereas F 80 %T I fell sharply (VOCSN: 11.3 to 1.4 L/min; Trilogy EVO: 8.3 to 2.0 L/min; Vivo 45LS: 21.5 to −0.5 L/min), consistent with compromised pressure maintenance fidelity during the latter phase of inspiration. Under C20/R5, V Ti converged to 114–134 mL across all devices and cohorts regardless of firmware version. Conclusions: Inter-device V Ti variability of up to 32.7% under identical settings indicates that device selection directly influences ventilation adequacy in passive NMD ventilation. Firmware updates produced a clinically important 31–39% reduction in V Ti without any modification of clinician-set parameters, with altered pressure maintenance fidelity in the latter phase of inspiration demonstrated as the primary mechanism. These changes reflect proprietary algorithm modifications that were implemented, typically not detailed in standard firmware release notes available to clinicians. In patients with low respiratory system compliance, device substitution is unlikely to resolve the V Ti deficit; IPAP adjustment represents a primary strategy within the existing circuit. Clinicians managing ventilator-dependent NMD patients should be aware that the V Ti actually delivered may not correspond to expectations based on set parameters and should verify V Ti delivery after firmware updates. Knowledge of device-specific pressurization characteristics should inform ventilator selection commensurate with disease severity and progression.