Phrenic Nerve injury

My Brother-in-law age 66, just had his second CABG two weeks ago.  Every thing seemed to go ok, although he had some bleeding problems in the OR.  Came home on his 5th day.  He was extremly SOB when ever he walked from room to room.  On his 5th day home, he felt and looked great.  He was standing in a doorway, when his automatic garage opened and a great whip of COLD air hit him in the face.  He could barely walk and the SOB was so bad, he thought himself that he was going to croke at that minute.  The SOB never got any better and decided to call 911 4 hrs later.  He was re-admitted to the hospital, where there did a throcentisis (spelling) removed a minimal amount of fluid from his left lung.  He was then intubated, chest tube insterted, ng tube along with all the other tubes inserted.  They extubated him some 36 hrs later and did other diagnosic breathing tests on him the next day.  Now they have told my sister, that there is a "nick" on his diaphram, which they can't to anything for it.  So I'm thinking he has some type of phrenic nerve injury.  I know phrenic injury is somewhat common in CABG, but a "nick"?  What is the prognosis for a "nick"?  Will he ever be able to walk without SOB?  Will he need to use Oxygen continuously?  Will it ever resolve on it's own?  She's not getting any questions answered and doesn't seem to be to pushy for answers.  Can anyone give me some infomation on this?  My brother-in-law has always been very active. At this time he is Slightly and I mean slightly over weight, mostly in the gut and does have type2 diabetes and is on oral medication for this.
Thank you in advance for any insight on this condition.