When my brother has an asthma attack, he can breathe in perfectly well, but can't breathe out properly. Surely, if the airway's constricted it's constricted in both directions. What's going on?

it's called air-trapping and it's typical of spastic airway disease. Part of the explanation has to do with negative (when you breathe in) versus positive (when you exhale) pressure in the chest cavity. The airways tend to open with inspiration because of that negative pressure, and close down on expiration and the effect is much exaggerated in spastic or narrowed airways

Thank you for explaining that way because that's exactly whats happens! When I have an asthma attact, I can breath fine, although its more shallow breathing rather than the deeper breaths one takes normally. It's the breathing out that makes me wheeze and hurts sometimes, too. The Albuterol helps open the air way, right away so that I can breath more deeply and exhale without struggling While the Atrovent is a longer lasting med to keep the air way open. There are quite a few asthma meds out there, these days. Yet, it's still can be a life threatening condition.