Sunday, April 15, 2007

Manometer Operation Details

I have been away for the last 10 days and so have not been posting. Now that the control system is built and the software is running. I will be working on getting the pressure monitoring installed.

The system so far accomplishes about as much as if you had an automated ambu-bag running. It could provide repeated breaths of a controllable volume, and a fairly consistent rate but there is no pressure monitoring or fail-safe should something go wrong. What we want to have is to be able to determine if an overpressure situation arises and so be able to stop the ventilator to prevent lung injury. We should also have some sort of backup failsafe that does not depend on the PLC or exhale valve functioning properly, in case the source of the problem is in fact one of these components. We should also have some sort of visual indication of the pressure at any time in order to aid the clinician that is monitoring the device.

The design for this is very basic. It is a manometer with a float, magnet and sensors. The floating magnet and sensors provide a signal to the PLC if the positive over pressure or lower pressure limits are exceeded. The lower pressure sensor can also be used to operate the ventilator in a demand mode or to implement PEEP. A third or fourth sensor could also be added later to provide redundant alarm points for tubing disconnect or blockage.


In the following diagrams you can see the function of the manometer.
  • In Figure 1, the manometer is at its neutral state and both sides are at the same level.
  • In Figure 2, the manometer is under negative pressure and the lower sensor is activated.
  • In Figure 3, the manometer is under a positive pressure and the maximum sensor is activated.
  • In Figure 4, the manometer has gone past the positive control point and it is acting as a safety overpressure. The air will leak past the bottom of the U portion of the curve and bubble up through the top.

Figure 1 Manometer Zero Pressure


Figure 2 Manometer Minimum Pressure

Figure 3 Manometer Maximum Pressure


Figure 4 Manometer Over Pressure

Figure 1 Manometer Zero Pressure

Figure 2 Manometer Minimum Pressure

Figure 3 Manometer Maximum Pressure

Figure 4 Manometer Over Pressure

Sunday, April 1, 2007

Control Box and Lung Simulator

Here is a picture of the control box and the PLC unit for the Pandemic Ventilator. In the back you can see the original bellows I built. I am using it as a lung simulator to test the operation of the system. You can see the ventilator in operation in the following video.

Valves Picture

Here is a picture of the valves. The valve on the left is the exhale valve, the center one is the inhale valve and the one on the right is the bellows fill valve. The manometer is not yet constructed. You can see the clamp for the bellows unit at the bottom of the picture.

New Bellows Design and Magnetic Sensors

Here is the new bellows design. It is open at the ends and sides to prevent wear on the bag. I also taped the seams of the bag for extra strength. It is clamped into place, and the clamp provides strain relief for the tape seal along the open end of the bag. The upright section on the left has the two magnetic sensors duct taped to it.

Video of the Ventilator Running

Here is a video of the Pandemic Ventilator on its first test run. This is just the control system, we have no alarms in place yet. The new style bellows is on the main board with the valves, control box and the PLC. The original bellows unit I built a week before is being used as the patient lung simulator. The wrenches on the bellows and the simulator provide weight to empty the bellows and simulator.