I am a very fit ironman triathlete. I am 50 years old. I have a resting heart rate of 44. BP is 118 over 70. I have had a problem for 2 years now where I can't take full breaths. It feels like I'm breathing through a straw. This happens when I'm driving, or not sitting up perfectly straight. It also happens if I exert myself harder than a slower aerobic pace. I used to be able to run 10mph for many many miles. Now running 7mph is a challenge. I've been to a pulmonologist. Also my family doctor. No one has answers. Any suggestions?