What this means is the manifold pressure sensor is not tracking the paw (airway) pressure and it should be. Both pressure sensor are in the cVIB – or Vent Interface Board.
As an example, when the bellows is all the way at the bottom of the housing during ventilation and the next breath occurs, we drive the bellows further down, but the bellows cannot go down any more.
This generates bellows collapsed (or unable to drive bellows) alarm condition.
And as mentioned by Geoff, it is one example that is typically caused by a leak.