I suspect Dr. Shen is swamped. With appointments, phone calls and emails. The bigger of a "star" a doctor becomes, the more demands there are of his time. This is why he has assistants and other staff. If you don't get a reply in a few days, don't get mad, but send a new one. It is easy for messages to fall to the bottom of a long list. Only so many hours in a day.
My GI isn't even anyone renown, but he's a very busy guy. His office has a nurse practitioner just for follow up calls and another for medication management issues. It's a real team approach. One thing for sure, my docs never give long winded replies to my emails. Just a line or two.
Jan