Smooth muscle activity when breathing rate increases?

I'm just studying for my exams and I have become confused with one aspect of the effects of the sympathetic nervous system. Is it that when the heart rate increases and thus the breathing rate, that the smooth muscle in the airways (e.g bronchi) contract or dilate? I'm guessing that if they dilate that more air can be breathed in .. but doesn't this contradict increased muscular activity in exercise? Or is it that the constant contraction and relaxation of smooth muscle forces more air into and out of the airways? I can't find the answer on the internet so I would appreciate any help (10 points for best answer)