Two calligraphic "A"s combine to form an abstract butterfly. As an asthma/allergy sufferer myself, my thoughts went to what is so precious to me: clean, clear breathing -- and the lightness of a butterfly came to mind. Soft blues reinforce the message.
An alternate, more "realistic" butterfly (the shape of which also gently made me think of the two lungs). A soft, gentle, light image that could especially appeal to your younger patients.