This video gives a good explanation to those engineers specifically mechanical engineers to understand the basic design and concept for lost cost ventilators. Keeping in mind that most of the medical experts are busy in tackling this pandemic, so by sharing this short insight it might help engineers in their research and development for innovative ideas in designing such ventilators.
A further explanation by a medical physicist on ventilators :
I’m a medical physicist and we're basically responsible for bridging the gap between technology & doctors in hospitals. Most of what we do is with radiation but ventilators were a really big part of the non-ionizing equipment so i had to study ventilators a lot. Here's my explanation :
Ventilators can deliver anything from normal air to 100% oxygen, or any ratio in between, and they operate on the 4 basic variables of flow, volume, pressure, and # breaths per minute. Technology is getting more & complex and every manufacturer throws in more sensors & software features every day to get a competitive edge but everything ultimately stems from those 4 variables. The reason those 4 variables are so fundamental to ventilators is because:
- Volume determines the amount of air that gets into your lungs. the ventilator needs to pump enough air in to sustain you and it needs to know when to stop before it damages the lungs. if the lungs are screwed you can increase the oxygen but that maxes out at 100%, and if it’s still not enough then your in real trouble.
- Pressure is important because the alveoli are very thin to allow gas exchange and too much pressure will rupture them, but too little pressure will cause the alveoli to collapse and the gas exchange stops. it then requires much higher pressures to re-open them which can be damaging too. a sick lung may also be too stiff to allow enough air in and then you’re goosed (this is called low compliance).
- Flow rate is important because ventilators cannot suck air out, they can only push air in, the air must leave the lungs passively. but a sick lung may be too floppy to expel the air fast enough, this another area where you reach a wall (called high compliance) - breathing rate is closely related to the flow and if you want to increase the efficiency of the lungs flow is where you can make up time in the breathing cycle to get more breaths per minute, but an asthmatic lung may be too restrictive to accept air very fast (called high resistance).
- If you’re good at maths/physics you might know that flow is heavily related to volume as well breathing rate so you can see how changing 1 thing affects a bunch of other parameters which each have their own limits.
- The oxygen/air ratio is generally only boosted when the other variables are maxed out and still not hitting it. breathing enhanced is ok but not ideal, the body isn’t designed for it and the patient will have come back to normal air before they leave.
As for the gases dissolved in the blood :
- Ventilators usually only measure the CO2 as that changes from ~0 to 4% between inspiration & expiration.
- Oxygen is harder to measure since its present in appreciable amount at both stages so a more sensitive test would be necessary. a fancy ventilator may have a dedicated sensor for oxygen but it’s generally ok to just assumed that the difference in CO2 = difference in O2. these readings are only used for the ventilators to run on auto mode. when measuring blood oxygen levels doctors & nurses use a dedicated device called a pulse oximeter instead (clip on your finger with a red light).
- Nitrogen is not measured because it’s an inert gas. the only situation when there’s nitrogen being absorbed or released from the blood is when there’s an environmental pressure change. this is only an issue for the hyperbaric chamber which has dedicated ventilators that are totally different & specially designed for it. all the pumps & sensors are different, and even the electronics since air is far more flammable under pressure.
- Other inert gases such as helium which are similar to nitrogen.
Hope this deep-dive is explains things, also NUI Galway is the only place in Ireland that teaches a medical physics masters. so that's another area of expertise found in galway!
@Ace of Spades