Is Pressure Bad in Air Ds?

The rapid cycling between high pressures and low pressures, the sheer stress that you develop there is thought to be injurious. A p r v tries to avoid that by keeping all of the airway, all thalvili open all the time,. So you don't get that sheer stress of repeated opening, closing, open and closing. The short amount of time at a lower pressure doesn't give time for the alvili to closethat's what smmix does.