Did the imaging show what is compressing the subclavian artery?
Or maybe causing it to be compressed in certain positions?
Knowing those details will give a better idea on what needs to be addressed.

Many of us have to explore & experiment to find what will work best for each of us. There isn't a specific amount of exercises or reps, just try what you can and see if it is feeling better or worse and adjust from there.
There is a good TOS program put out by Sharon Butler, that I have used and still do.
You can find the details on her website - www.selfcare4rsi.com
TOS pgm info- http://www.selfcare4rsi.com/thoracic...-syndrome.html
We just had some good bodywork style stretches posted lately -
http://neurotalk.psychcentral.com/thread149529.html


and these should be good for nearly anyone that has forward head /shoulders postures



foam roll or large towels rolled up tightly - pillow if needed for neck comfort - then just relax with arms at a comfortable position