Paul, Rick
We are talking about second stage scuba regulators which are triggered by the negative pressure of inhalation correct?
When this is in your mouth there is a large gradient between your inhalation trigger and the surrounding pressure and this delivers the on demand flow.
If the regulators are strictly inside the cabin with you, how do they know what's happening outside? Unless there is some sort of differential membrane trigger such as the one Chip described. As Rick had described, I am assuming this bank of regulators is just sitting there in the cabin with you, and absent a differential sensor, I don't see a trigger for the flow.
Joe