Hypoxic Training???

Anyone tried it?

Most recently I've been riding my bike to work and back home.  I use a camel back for water and a backpack to store my work/bike stuff.  The backpack has a strap that goes across my chest.  I've had it strapped down pretty tight but didn't think much about it.  As a side note, I've never felt lightheaded or under any duress, just not able to take a huge breathes after a hill or a hard push.  I think I have been self-inducing hypoxic training by limiting the amount my lungs can expand.  Now when I go running it's awkward to take deep/fast breaths.  Also as a result it's now incredibly hard to get my max HR up and my AVG overall HR has been dropping like a rock compared to past history training. 

Would you all consider constricting lung/chest expansion as being a form of hypoxic training?