## 4 Discussion
In designing the CoroQuant flow sensor, emphasis was placed on ensuring that the resulting design would not cause an excessive increase in dead space. The final flow sensor's dead space is comparable to that of flow sensors used in respiratory care, such as the D-Lite (GE Healthcare, Chicago, IL, USA). The CoroVent ventilator uses CoroQuant to measure flow based on the commonly used differential pressure measurement. However, the internal resistance element of the CoroQuant sensor has a unique shape, resulting in distinct pressure-flow characteristics. To ensure future compatibility with commercial flow sensors, such as the D-Lite (GE Healthcare, Chicago, IL, USA), the ventilator's software allows modification of the \"slope\" and \"exp\" coefficients via the service menu. These parameters define the bidirectional pressure-flow characteristics and enable adjustment of the flow calculation algorithm based on the measured pressure difference. The simplicity of the ventilator design is underlined by the unique solution of generating inspiratory flow and gas mixing by two fast electronically controlled ON/OFF valves. Standard ICU ventilators typically use proportional valves with mixing chambers or turbines with feedback control to generate inspiratory flow. However, the testing and design of such ventilators is time consuming and often requires specially designed medical components which were not commercially available during the COVID-19 pandemic situation. An important advantage of this unique solution is also its easily adaptable scalability. The fast ON/OFF valves are controlled by a digital (PWM) signal, providing a simple yet highly flexible control method. This design allows the ventilator to easily adapt to different patient populations, ranging from neonates to adults and large animals in veterinary care, by simply replacing the ON/OFF valves with models suited to the required flow rates. The core control algorithm does not need to be changed. Sterilization and biocompatibility were also considered, particularly for components directly exposed to the gas mixture entering the patient's airways. The expiratory valve and CoroQuant were sterilized before use, and all relevant components were manufactured using biocompatible materials, ensuring patient safety. The simple design required the omission of certain standard features available in advanced ICU ventilators, such as patient-triggered ventilation, real-time oxygen concentration monitoring, sophisticated ventilation modes, or integrated waveform analysis. However, in line with the initial design plan, CoroVent was only intended to increase the potential capacity of ventilator-dependent patients, not to fully replace standard ICU ventilators. Once the patient's condition improved to the point where they could breathe spontaneously, they were transitioned to another ventilator to allow for weaning. In the case of \(FiO_{2}\) monitoring, the inspiratory branch design assured precisely controlled gas mixing, making additional measurement unnecessary. If there was a risk of incorrect oxygen delivery in the ventilation mixture, the alarm was triggered by a malfunction of one of the ON/OFF valves. In addition, the device relied on a hospital air and oxygen supply, which was not always readily available in all settings, particularly low-resource settings or field hospitals. Future iterations could explore the implementation of additional functionalities; however, some of these would highly complicate the possible rapid mass production. Despite these limitations, the CoroVent ventilator provided an effective and reliable solution for emergency scenarios. The successful use of CoroVent ventilators in Czech hospitals during the COVID-19 pandemic demonstrated the practical utility of such devices in mitigating ventilator shortages. In addition, the results of this study support the potential for simple yet effective ventilator designs to play a critical role in crisis response.