## 2 Materials and Methods
### Control System, Safety, and Monitoring of the Ventilator  
The ventilator operates using a programmable logic controller (PLC) CP6606 (Beckhoff, Verl, Germany) powered by an ARM Cortex(tm)-A8 processor running real-time operating system Windows Embedded Compact 7 (Microsoft Corporation, Redmont, WA, USA). The ventilator control firmware was developed within the TwinCAT 3.1 programming environment (version 3.1, Beckhoff, Verl, Germany), utilizing Microsoft Visual Studio as the integrated development interface. The firmware architecture incorporates two independent threads: a primary thread, designated as high-priority, responsible for managing inspiratory and expiratory valves, processing sensor data, and evaluating alarm conditions; and a secondary thread, operating at a lower priority, which serves as the graphical user interface and facilitates bidirectional communication between the primary thread and the user. The graphical user interface displays measured parameters and active alarms and provides functionality for user parameter adjustment and ventilator operation. The respiratory phases are hard-controlled. Ventilation is managed without sensor feedback. This means that all phases are rigidly timed according to the current CoroVent settings, as determined by the respiratory therapist. Any adjustment to the respiratory settings initiates a recalculation of timings of all valves. Sensor data are currently limited to providing ventilation information to the respiratory therapist and managing alarms as the ventilator does not support synchronized ventilation modes. During ventilation, inspiratory and expiratory tidal volumes (_VTi_ and _VTe_), _PEEP_, peak inspiratory pressure reached during inspiratory phase (_P_max), plateau pressure (_P_plat), the ratio of inspiratory phase duration to the total time of the respiratory cycle (_Ti_/_T_), and _RR_ are displayed. Ventilation parameters are set using a touchscreen (glove compatible) and two rotary knobs on the front panel: one for _PEEP_ and the other for _P_lim. All parameters shown in green in Figure 6A are parameters set by the user. All parameters marked in white on the touchscreen are parameters measured by a specially designed pneumotachograph flow sensor CoroQuant [26]. The volume and pressure measured by CoroQuant at the airway opening are sensed by a differential pressure sensor (MPXV7002, NXP, Einthoven, The Netherlands) and an absolute pressure sensor (MPXV4006 DP, NXP, Einthoven, The Netherlands). The ventilator includes a basic alarm system per ISO 80601-2-12 [22] and EN ISO 60601-1-8 [23], with audible and visual signals. A single alarm level is implemented. In addition, the ventilator, its touchscreen, labels, and software use established respiratory care terminology. Distinct from many emergency ventilators developed during the COVID-19 pandemic, the CoroVent incorporates the full suite of safety features and functionalities expected of a standard Intensive Care Unit (ICU) ventilator. These features have been independently verified by the Electrotechnical Testing Institute in the Czech Republic (test report no. 020857-01/01, issued 21 April 2020), confirming its compliance with essential performance standards. Testing included assessments of mechanical resistance and safety, electromagnetic compatibility, and protection from water, all within the requirements for medical device use and within scope of ingress protection of IP21. Four key safety principles protect against excessive airway pressure. These protective measures are arranged in order of detection and the severity of any unwanted pressure increase in the patient's circuit. Software-based features include a user-adjustable maximum pressure alarm threshold that can be set up to 45 cmH\({}_{2}\)O and an automatic response that initiates expiration and triggers an alarm if pressure exceeds 55 cmH\({}_{2}\)O for 150 ms or longer. The hardware protections provide an extra layer of safety.