By ultrasound are you referring to an echocardiogram and i assume you are. An echo can measure intra chamber pressures. The pulmonary artery would have higher than normal if there is pulmonary embolism (clots) in the lungs and occlusions within the vessel (thrombosis). Sensitivity is 80 to 100%.
If you have known respiratory problems, I agree a cardiopulmonary exercise testing provides better information than traditional treadmill stress tests. The test will diagnose exercise induced reductions in blood slow to the heart. The test also provides doctor data on gas exchanges in the lungs at rest and during exercise and yields breath-by-breath measures of oxygen uptake. Combining these findings with data traditionally obtained by cardiologists from treadmill would be more appropriate it seems to me.
Thanks for the question, and I wish you well going forward. Take care,
Ken