In the context of Covid 19 pandemic, the Romanian InSpace Engineering proposes a low cost, rapid development mechanical ventilator made out of widely available 3D printer parts.
From the beginning, a set of high level requirements have been defined in order to ensure that the ventilator can be manufactured in large numbers with locally available parts and materials. In this context, and based on existing experience inside our team with Arduino, Raspberry Pi and stepper motors we decided to base our design on those components.
At system level, we proceeded with an extensive research on the mechanical ventilation in order to assess the system requirements. Moreover, we contacted experienced doctors in order to better understand the functionality of the existing ventilators. Also, doctors helped us with defining the human interface that shall be very intuitive for the operator and similar with the ones already in use. Some critical system requirements are presented below.
- Tidal volume: 100 – 800 mL
- Max operating pressure: 40 cmH2O
- Respirations per minute: 8 – 35
- Inspiration/Expiration ratio: 1/4 to 4/1 with 0.1 increment
- Safety valve: set to 60 cmH2O
- PEEP valve: 5-20 cmH2O
- HEPA filtration on pump inlet and outlet in order to avoid contamination of the system
System design Overview
The system consists of 3 blocks:
- Mechanical pump
- Onboard computer (OBC)
- Human interface unit
The mechanical pump is made out of a water PPR pipe as the main body material. The piston and other plastic parts are made of POM (Acetal). The pump driving mechanism uses typical 3D printer Z-axes components with minor modifications. A standard NEMA 17 stepper motor controlled by an Arduino board is used and a dedicated software was developed in order to implement the operational modes imposed by medical personnel through a set of requirements.
A standard PEEP valve is used as a unidirectional valve for the intake path while the exhaust flow is regulated by an ambu-bag expiatory valve which integrates a PEEP valve, a unidirectional flow valve and an expiratory valve. The ventilator integrates 2 HEPA 16 filters for the intake and exhaust airflow.
The OBC controls the pump as a function of the input parameters: tidal volume, air pressure, flow rate, breaths per minute, inspiration/expiration ratio, FiO2 (fraction of inspired oxygen). The OBC also acts as a connection between the human interface unit and the mechanical pump, reading the air pressure and flow sensors output and sending them to the human interface module. The input parameters for the OBC are set by the medical staff using six rotary encoders.
Human interface unit
This block consists of a Raspberry-Pi computer with a 7 inch display. A custom application has been developed for a graphical display of both the input parameters and sensors readings. We’ve continuously received requirements and feedback from doctors and medical staff in order to develop an intuitive interface.
A system functional diagram is presented in the image below.
A dedicated application has been designed in close collaboration with doctors and medical staff in order to develop an interface similar to the ones that are already installed in the hospitals. A functional scheme of the interface is presented in the image below:
The VentilaThor can be operated in three distinct modes: Tidal Volume control, Pressure mode and Assisted mode. The tidal volume control mode has two sub modes which involves constant flow or decelerated flow.
The operational modes are selected by the user via the “mode” rotary encoder. The functionality of the bottom side encoders depends on the selected mode.
The real time graph shows the pressure, flow and tidal volume. The values for those parameters are read from the integrated sensors. For instance, in Pressure mode, the operator can read in real-time the tidal volume delivered at a set pressure.
Currently the interface is under development and the system sensors are under a calibration process.
A final version of the mechanical pump is currently under construction and will be ready by the end of April. In parallel, final tunings of the application are to be implemented in a couple of days. A case for the entire system has been designed and is to be manufactured.
We already started the discussion with the local authorities in order to register the product for approval at national level. In parallel, the components and material supply chain will be put in place for rapid integration of multiple units.