Tight Chest After Weightlifting - Low Oxygen Saturation

[Tiridatian]

Hello,

I am about 6 weeks out of recovery from bronchitis, seemingly from pollutants and/or possibly second hand smoke. The case of bronchitis was fairly severe, and while being tested was also discovered I have a stiff heart (diastolic dysfunction stage II).

My doctors have instructed me to keep exercising, however I have found something peculiar and alarming. I can do boxing/kickboxing for 1-2 hours at a time, and I feel great. However, if I lift weights for 40 mins or so, I feel OK during the workout, but get a really tight pressure in my chest later in the day and my oxygen saturation seems to drop in the evening.

Interestingly, my heart rate is much higher when boxing (170-180bpm) as opposed to weight lifting (120-140 bpm). I am also extremely focused on proper breathing when weightlifting to avoid really high blood pressure.

My doctors keep telling me it's just me getting over the bronchitis, but it's odd to me that running/boxing doesn't seem to bring on the chest tightness. I am confused, and anxious, and just want to be able to exercise regularly to deal with my heart stiffness.

I am 6'0, 186 lbs, 34 years old. Any insight whatsoever would be greatly appreciated.