There is another possible explanation - damage in the lungs from bronchiectasis and repeated infections is cumulative - so over time you can lose some lung function, elasticity and healthy tissue. This can result in lower oxygen-carrying capacity, especially during/after exertion. The body tries to compensate - thus the heart beats faster trying to supply more oxygen...
I have had asthma for near 40 years, bronchiectasis for at least 6 years but more likely 10, and have had MAC and pseudomonas infections as well as pneumonia. As it is now the allergy and bad air season (much wind, dust & pollen), my O2 sats dropped from 97-98 at rest to 95-96. On exertion, they will fall to 91-92. At the same time my resting heart rate increases from 72-75 to 80-86. This is with all meds taken on schedule and daily yoga and airway clearance. When I exercise vigorously or do light weight training, it leaps well up over 105. The longer I have asthma and bronchiectasis, the longer recovery to resting rate takes. This morning, just casual walking on level ground put my heart rate at 99, and it took 30 minutes to fall into the 70's - as a runner in my 40's recovery to base rate took only 5-6 minutes after an extended run.

So, Ling, you may or may not have asthma, but you do have damaged lungs, which in turn taxes your heart to work harder. Since the Wixela is not helping much, maybe you can talk to your pulmonologist about alternatives. For example, I find the mist inhaler Symbicort more effective than the dry powder. Symbicort uses formoterol, a long-acting beta-agonist (LABA) instead of salmeterol, a short-acting beta-agonist (SABA) so it keeps the airways dilated longer.
Another thing to consider - your doctor or your pharmacist should double-check to make sure no other medication is interacting with your inhaler. It often happens that beta-blockers such as blood pressure or heart medications like metroprolol and beta-agonists like salmeterol "fight" with each other, reducing the effectiveness of both.
Sue