Manometer
Described here is a display manometer with a settable alarm. The purpose is to allow clinicians to observe the patient's breathing cycle at a glance, from a distance. Also to be able to make measurements of the pressure cycle (the PEEP and PIP pressures) and see if these change over time. Also to set an alarm for over-pressure, which is of particular concern.
Simplest possible manometer
A manometer can be as simple as a loop of 1/4" ID plastic tubing, taped around a support strip. It's filled with dyed water. At the top, the tubing on one side goes to the pressure source to be measured. The tubing on the other side is open.
VID_20200506_161217twoman.mp4Our still simple manometer
This is a slightly fancier version made with hard-walled tubes (still 1/4" ID) and snapped into a convenient clear plastic extrusion. The dyed water is lightly salted which makes it electrically conductive, and this is used to build a very simple over-pressure alarm which can be set to any desired alarm pressure level.
<<video (or, same video on youtube)
The turn-around at the bottom includes a damper which helps the water column settle smoothly without bouncing, when the pressure changes. It also includes a section of copper tubing to facilitate electrical contact with the water column as part of the alarm. And a fill-port.
These are the parts that go into construction of the manometer. The manometer can be built at minimal cost out of materials that are widely available in hardware stores. The alarm unit is simple and can be reproduced quickly.
VID_20200403_132253.mp4This video shows an early version, in which an alarm sounds every time the pressure reaches a predetermined alarm level (or, same video on youtube)
The alarm is implemented by inserting a wire down the open leg of the tubing at the top of the manometer. The end of the wire is positioned at the desired alarm pressure level, typically ~50 (cm-water). If the water level in the manometer reaches the wire, a low voltage circuit through the slightly conductive water is completed causing the alarm to sound.