Impact on the front of the chest has potentially put some ribs out of position (according to some lines of thought) As a result potentially some muscle reaction which maintains the problem. You use either MET techniques to sort it out or Strain-Counterstrain. the latter I find far more effective. As you can understand elevated or depressed ribs will affect the breathing and definitely when breathing heavily. You should look 1st in the spinal mobility: rotation (left=right?) flexion and extension of the thoracic spine. All directions of the neck. The reason is that you will not solve the problem with focusing on the ribs because most of the time it is a combination of (mobility)problems. Look into the mobility of the ribs on inhaling exhaling. Look for tenderpoints in the area and definitely the ones which seem to cause a feeling of thightness of the chest (sternum, ribs anterior/lateral/dorsal, Vertebraes). I can recommend you to buy the MET DVD's by Tom Ockler which you can obtain on this website (I feel they promote a good understanding of the function of the musculoskeletal issues you mention and beyond). By the way I have no financial interest in these dvd's
Hope this will help.