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

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.

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 H₂O/expiratory positive airway pressure 5 cm H₂O, T_I1.0 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 H₂O, resistance 5 cm H₂O/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 (P₃₀₀ ms, P₅₀₀ ms), and inspiratory flow at 80% of the set T_I(F₈₀%T_I) were derived from all breath cycles.

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, F₈₀%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; F₈₀%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, P₃₀₀ ms was preserved across firmware versions, whereas F₈₀%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.

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.