On the old forums we had a long thread on this topic started by a nice lass from the USA who had wandered on to the RWUK site by mistake - it turned out that she had an interesting mix of longstanding asthma, anxiety, and possible sensitivity to allergens in the air.
Amazed there aren't more responses to your question, Helen, since lots of people here, including some of the near-elites, have asthma and use Ventolin or similar.
I don't have asthma, but I agree with Eamonn that if you don't wheeze, Ventolin (used correctly - many people can't use inhalers very well) doesn't make a difference, and your peak flow is stable (out of curiosity, what number does it read?), your symptoms are unlikely to be due to asthma, and a funny feeling or tightness in the windpipe area is often stress-related. This is, of course, a significant health problem in its own right and merits hands-on medical attention if you can't resolve it by dealing with whatever is hanging over your head.
Best wishes - hope it works out well!
Cheers, V-rap.