AMA Open Source Ventilator

Having been inspired to assist in the battle with COVID-19 and the lack of ventilators, AMA has developed a working, open-source, portable ventilator system. 

A ventilator is a machine designed to mechanically move air in and out of the lungs to intermittently or continuously assist or control pulmonary ventilation. This device is primarily used in intensive therapy to help improve the patients breathing by regulating the flow of gas in the lungs.

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If you are interested in assisting to develop or improving the AMA Ventilator, contact us at info@ama-inc.com

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Features

3.5 inch color display screen displays the configurable parameters and waveforms.

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Powered by 115VAC  or a 12-volt DC source.

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Driven by an Arduino-Mega microcontroller processor

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Operations

The AMA ventilator uses a reusable single limb patient circuit with an exhalation valve and a reusable D-Lite spirometer pipe.

Air and oxygen are supplied to the ventilator by two separate connections, one for the hospital air supply another for the hospital oxygen supply. The air and oxygen are connected to an internal chamber were the air and oxygen are mixed to provide a precise oxygen concentration and air flow to the patient.

 

The ventilator uses hospital air and oxygen from a wall plate with hose fittings and a cutoff valve with a pressure of around 50 to 60 PSI.

The hospital air connects to an adjustable pressure regulator in the ventilator. This regulator has a mechanical gauge and a knob to adjust the pressure.

The ventilator connect to the hospital oxygen supply oxygen flow regulator.

A cast aluminum mixing chamber enclosure combines the air and oxygen before being delivered to the patient.

The pressure in the mixing chamber determines the air flow and lung pressure being delivered to the patient. A pressure of around 5 PSI in the chamber will deliver a lung pressure of around 20 cmH2O. The volume of the mixing chamber is 322 milliliters.

Lung pressure is set by adjusting the air pressure in the mixing chamber. This is done by turning the knob on the pressure regulator and reading the mechanical gauge on the regulator. The chamber pressure is also shown on the color display.

The percent of oxygen is set by adjusting an oxygen flow regulator at the oxygen source. The percent of oxygen is shown on the color display. The percent of oxygen going to the patient is only read during ventilation because the oxygen sensor samples the air going to the patient.

A temperature and barometric pressure sensors are installed on the main printed circuit board for oxygen sensor accuracy.

During inhalation, the air flow solenoid valve opens releasing the air pressure in the mixing chamber to the patient. When the air flow solenoid valve opens, the atmosphere solenoid valve closes, and the FESTO 2-Way solenoid valve opens applying a pressure from the mixing chamber to close the exhalation valve pressure diaphragm on the patient circuit.

During exhalation, the air flow solenoid closes shutting off chamber air pressure to the patient. When the air flow solenoid closes, the FESTO 2-Way valve vents the exhalation valve on the patient circuit and the atmosphere solenoid valve opens sending the exhaled gas to the atmosphere. Exhaled gas has two ways to expel to the atmosphere. If the exhalation port on the patient circuit is capped, the exhalation gas will go through the atmosphere solenoid valve in the ventilator, through the PEEP fan, and through a HEPA filter to the atmosphere. If the exhalation port on the patient circuit is uncapped, exhalation gas will exit through the port opening to the atmosphere. If a mechanical PEEP valve is connected to the exhalation port, exhaled gas will go through the PEEP valve.

Lung pressure is measured through a tube from the ventilator to the patient circuit. This tube connects to an electronic pressure sensor on the main printed circuit board inside the ventilator. The lung pressure is converted to cmH2O and displayed in a graph on the color display on the ventilator. Air flow is measured by a reusable medical Venture pipe, called a D-Lite sensor. The D-Lite sensor connects to the patient circuit just before going to the patient.

During inspiration, the air/oxygen from the mixing chamber flows from the ventilator to the patient through the D-Lite sensor. Two ports on the D-Lite sensor measure the total pressure and the static pressure. The difference between the two gives a dynamic pressure, which is proportional to the velocity of air flow.

During expiration, the process is reversed. Two tubes from the D-Lite connect to an electronic differential pressure sensor on the main printed circuit board inside the ventilator. From this sensor, measurements such as volume to the lungs and if assisted breaths are needed.

When Assisted Breaths or AC is turned on, the differential pressure sensor in the ventilator connected to the D-Lite sensor can detect if the patient tries to take a breath. If the patient tries to take a breath, the ventilator will supply the breath in sync with the patient’s breathing. If the patient does not try to take a breath, the ventilator will supply the breath at the rate (breaths per minute) and lung pressure (cmH2O) set by the operator.