Abstract

This prototype is of a low-cost portable substitute for ventilator to be used in mass casualty cases until a proper state of the art ventilator is available. This will help in supplying breathable air into and out of the lungs with prescribed parameters, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. The device delivers breaths by compressing a conventional bag-valve mask (BVM) known by the proprietary name Ambu Bag. The proposed system eliminate the need for a human operator for the Ambu bag . It is achieved using a stepper motor and pivot arrangement. The main features include adjustable tidal volume, flow, breath per minute (BPM), Inspiratory Expiratory ratio (IE), FiO2 and PEEP . All parameters are set via digital interface and an LCD screen will display the status. When an Ambu bag is controlled manually it cannot be used for longer time as a ventilator. As the proposed system is automated and have a control over many necessary parameters, it can be used for a longer duration. It is completely portable and can be operated with a built in battery provided. The prototype also features an alarm to indicate various system failures and other such situations. Through this prototype, the strategy of compressing a conventional bag-valve mask (BVM) is proven to be a viable option to achieve low-cost, low-power portable ventilator technology that provides some of the essential ventilator features at a fraction of the cost of existing technology.

Presentation (PDF) link

Design

The initial design setup was made by utilising stepper motor and CNC kit. It suffered from various drastic drawbacks. Even though it allowed control of various parameters it was not efficient and the controls were limited.

Switching to the current design that used the same stepper motor and a different pivot and lever mechanism with a ratio of 2:5 utilised the motor’s ability to deliver torque more efficiently without sacrificing its control. Since the design process had to meet medical application, at most care was taken so as to ensure minimum fail condition of the device and for achieving the same very basic mechanical assemblies that are totally reliable were used. And this design is light weighted and has high portability.

Working

The prototype is designed in such a way that the settings for operation (Flow, Tidal Volume, RR, I/E ratio, FiO2 and PEEP) is input by the user. These inputs are processed in a microcontroller that controls the operation of a stepper motor. The stepper motor drives a lever arrangement that compress and expands an ambu bag placed on the device. The advantage of using a stepper motor in this scenario is that it gives precise movement and controlled speed set according to the input settings by the user. Depending on the user defined values, control over flow rate is achieved by defining the delay between each step of the motor. One step is 1.8 degrees i.e. 200 steps give one complete rotation. And the number rotation is proportional to amount of volume given out by the ambu bag. So, the control over tidal volume is achieved by varying the number of steps. I:E is achieved by the combined manipulation of delay between step and delay between every inhalation and exhalation. The device cross checks all these values including BPM with ideal conditions already programmed into the device and yields the exact user defined values as result making it user friendly and more reliable. The below figure illustrates the block diagram of the prototype developed.

The prototype developed is very simple to use. Once the power button is turned on, initialisation process begins. When the initialisation is completed, the lever is set to its initial position and “Initialising: OK” is displayed in the LCD screen. The user is provided with two switches for up down commands and a selection switch. The user is now prompted to select the flow rate as high or low by clicking the UP or DOWN button. Clicking OK will select the flow rate set by user and is now prompted to select the Tidal volume in ml RR . Using the UP and DOWN button select the TV required and clicking the OK button will set the corresponding value. Now the user is prompted to select the RR in bpm. Clicking the OK button will set the RR value and now the user can enter the I/E ratio. When all the settings has been input by the user, the screen displays the current settings and the device starts working.

Circuit Diagram

Dimension

Team