[Equipment] How is leakage measured?

[multicast]

In a general sense, leakage is the difference between the volume of inhaled and exhaled air.  Now I presume that the inhaled volumed may be calculated by the pressure the machine delivers. (I may be wrong.)  

But how exactly does the machine determine the exhaled volume?

Mike

[unidee]

Good question!

[Gideon]

Our machines have 3 types of sensors, pressure, flow, and time.  These measurements allow the machine to determine the volume of air that is being delivered, allowing for the intentional leaks from the mask. it records the ebb and flow in detail.  Without this intentional vent the inhale and exhale is easily seen, it is just offset by the intentional leak.  Additioal leaks are seen as a higher baseline.  Obviously we do need the mask vent.

[multicast]

Thanks a lot for your response, but I still don't know *how* the leakage is measured.  Here's what I know.  (Of course we habe a timer ...)

The air flows first through a flow sensors (which might be a sensor that measures differences of pressures, but that doesn't matter that much, goes through the vent, then through a pressure sensor to the hose, finally to the mask.  A teardown in our German forum, see https://forum-schlafapnoe.de/viewtopic.p...15#p113857, shows in the third picture the pressure sensor (those two blue thingies), while the fourth picture shows the vent's chamber.  On these two orange nozzles  the flow sensor (or a sensor that measure the difference of pressures) is located; it measures the flow between the inside and outside of the chamber.

So there're a lot of number recorded, but how actually is leakage detected?  The amount of air, from the machine's point of view, is represented by the area of the flow curve above (as a positive amount of volume) and below the zero line; the latter counts negative.  Now if that difference is zero (modulo the intended leak) we have indeed zero leakage -- from the machine's point of view.

How the amount of delivered air is calculated seems plausible to me: you integrate the flow sensor's date on inhalation over the time.  But how is the volume of an expiration measured?

I'm asking because I'm wondering about the different shape of waveforms associated with mouth leakes (which are significantly flat on the zero line) and mask leaks, which cross the zero line with a positive gradient.  

A flattened crossing on the zero line means that the machine *detects* no flow, despite there is one, namely through the opened mouth. 

OTOH, regarding a mask leak, assume that there is just little hole in the mask where the air escapes.  In that case not all of the delivered air is inhaled but escapes through that hole. Hence measuring the exhaled volume (in which way ever) and comparing is to the delivered amount -- which is not the inhaled one -- must lead to erroneous result.

Can someone lighten me up, please?

Mike

[Gideon]

There is a big difference between a mouth leak and a mask leak. A mask leak is a leak from the "closed system", an expiratory mouth leak is shunting the air before it returns to the mask.

[multicast]

You're definitely right, I know about the different reasons for these leaks. But how are they measured? Explicitely: how is the amount of exported air measured?

Mike

NB: Even in case there's a mask leak the system isn't "closed" ...

[srlevine1]

Thanks a lot for your response, but I still don't know *how* the leakage is measured.  Here's what I know.  (Of course we habe a timer ...)

The air flows first through a flow sensors (which might be a sensor that measures differences of pressures, but that doesn't matter that much, goes through the vent, then through a pressure sensor to the hose, finally to the mask.  A teardown in our German forum, see https://forum-schlafapnoe.de/viewtopic.p...15#p113857, shows in the third picture the pressure sensor (those two blue thingies), while the fourth picture shows the vent's chamber.  On these two orange nozzles  the flow sensor (or a sensor that measure the difference of pressures) is located; it measures the flow between the inside and outside of the chamber.

Thank you for the link to the German site. Interesting photos of breakdown of a CPAP.