Barry is sounds to me like you have too much time on your hands or something and should not be tempting fate in trying to alter your heart rate of agressively try to trigger an arrythmia or palp. You have to remember w. what you are doing is not how you normally would breathe or force a rhythm to stay in limbo for any length of time. I do not think that it would be good for you because you could really endanger yourself by doing this in forcing the blood to back up and possibly coagulate and form a clot that could be thrown somewhere into your body where it shouldn;t. You are actually putting stress and work onto your heart. You should be so glad that the holters came back neg. and you say that the BB are doing their job so why attempt to trigger this? If you feel that the lungs are pressing on your heart i would not be surprised when you are inhaling beyond the norm and building up air....again endangering yourself. Sounds to me like in a nutshell that you need to just simply accept the fact that you are okay and stop looking for trouble where there is none my friend and just be so thankful that this isn;t something more serious which alot of people on this site unfortunately cannot say....good luck and personally i would buy a slinky or something LOL !!!!!!!!!!!!!!!!!!!
It is normal for the heart rate to increase on the intake of a breath... the body knows that is when the fresh oxygen is available and time to get it into the blood.
It may be that you are just paying too much attention to your HR. For me, with AFib, I hardly ever feel my irregular pulse (lucky me) and have to work hard to find it.. so I can't say my HR increases on an intake of breath, but I bet it does.