Defined Pressure Wave System
An alternative approach to the mechanically compressed volume system is a defined pressure system. In this type of approach, an ultra-sensitive dome-loaded back pressure regulator (BPR) is used to provide highly controlled inhalation and exhalation pressure waveforms. Dome-loaded means that gas or air is fed into the top (dome) of the regulator to provide the pressure waveform setpoint. This waveform setpoint can be supplied either from an electro-pneumatic pressure regulator (EPR), or through simpler mechanical means.
*** UPDATE April 7, 2020
THIS ORIGINAL SIMPLE PRESSURE WAVE SYSTEM SCHEMATIC THAT WE TESTED WAS SHOWN TO HAVE ISSUES WITH THE TIDAL VOLUME CONTROL. WE HAVE MODIFIED THE DESIGN AND THE NEW SCHEMATIC CAN BE SEEN HERE.
Simple Pressure Wave System
This design uses commonly available solenoid valves along with simple pressure control components we believe can be mass produced. A waveform signal working in combination with some solenoid valves provides a simple automated approach to generating a defined pressure wave system.
It starts with an on-off waveform signal sent to two simple solenoid valves. One controls flow from the oxygen enriched air supply to the patient and the other controls flow to the dome of the sensitive dome-loaded back pressure regulator (BPR). See schematic below.
Also controlling the air flow to the dome of the BPR is a bleed valve. As the solenoid valve opens and closes, the dome setpoint pressure alternates back and forth between the lo pressure mbar pilot regulator (open) and the hi pressure mbar pilot regulator (closed). This alternating pressure rhythm on the dome of the BPR provides the setpoint for the air going to the patient. The result is a controlled pressure rhythm from the enriched air supply to the patient. The solenoid to the patient opens in a reverse pattern from the pilot solenoid. The patient solenoid opens during hi pressure to allow air to fill the lungs, and closes during lo pressure to allow lungs to exhale
Because the sensitive dome-loaded BPR technology provides nearly instantaneous response to pressure setpoint changes, it works well for waveform pressure control.
Below is a video from the lab demonstration with Equilibar President, Jeff Jennings.
Please contact us at email@example.com with questions or feedback.
Update April 7, 2020: The following related pages also used the original schematic that we tested and WAS SHOWN TO HAVE ISSUES WITH THE TIDAL VOLUME CONTROL. We have modified the original design and the NEW SCHEMATIC CAN BE SEEN HERE.
Fully Automated Pressure Wave System
In an earlier version, a fully-automated pressure wave system was created using a programmable logic controller (PLC) in combination with an electro-pneumatic pressure regulator (EPR). It starts with a configurable waveform signal output from a PLC that includes pressure and rate (in breaths per minute) to mimic inspiratory and expiratory rhythm. These components may not be as readily available to some people, but if interested, read about it on this page.
Manual Pressure Wave System
In another version, a manual pressure wave system was created using a hand pump and a mechanical pilot regulator constructed in the Equilibar lab. With a simple hand pump and good rhythm, a manual pressure wave system can be built.