I would add that poor posture and a collapsing chest inhibit the flow of air for both, what Greg refers to as passive and active, and thus invites choking. The diaphragm wants to come up. A relaxed chest helps with this. My experience is that a collapsing chest most often goes together with tight arms and shoulders moving to the front and inwards instead of floating. If this tension is removed however by not collapsing the chest, then inhalation also becomes more easy and is more full as Ronald mentioned.