There's a lot that yoga can offer, actually.
But not just general everyday yoga, you need to understand that for a condition like asthma, you will need something more; something which is somewhat directly suited and related to the betterment of the condition; which in this case is Pranayama.
Pranayama even before becoming popular has been practiced by millions of individuals in India for thousands of years.
It is only now that this method has been gaining more and more attention due to the vast number of benefits for asthmatics and non asthmatics alike.
Pranayama is composed of two parts, prana which means energy and ayama which means to stretch, expand, lengthen, regulate, prolong, restrain and control which somewhat describes the actions involved in the practice.
By no means should it be considered a singular solution of course.
Pranayama should only be treated as a complimentary alternative to your conventional medication and treatment.
With regular practice and mastery though, Pranayama may be able to reduce the frequency and intensity of your flare-ups and attacks as well as decrease your dependence on medication, which in turn can greatly improve your quality of living.
Regular practice of Pranayama can increase the lung's airflow, air capacity, stamina as well as efficiency.
Not only effective as a form of preventive exercise, Pranayama also involves techniques that can help you alleviate and put your condition under control during flare-ups and attacks.
Simple stretches like back bends and forward bends for example have been known to have beneficial effects for asthmatics depending on the situation.
Aside from helping you control and prevent your condition from coming about, Pranayama has also been known to reduce stress, physical tension, muscle tightness and increase general wellbeing by stimulating the parasympathetic nervous system.
If you are interested in using Pranayama for your condition though, it would be best to research a bit as it is further broken down into different specific exercises which cater to different needs.
If you want more accurate advise it would be best to get expert and experienced help in the form of a yogi as they will be able to asses your condition further and give you ideas as to what you might want to go with.
Ask your doctor as well, they might be able to give you further information about your condition and whether yoga might be right for you or not.
Asthma and yoga actually have had a long history together, and it's about time you start learning the benefits that Pranayama can give to you.