PORTLAND — For thousands of Oregonians, the path to a medical marijuana card starts at a clinic in Southeast Portland staffed by Dr. Thomas Orvald, an 80-year-old retired heart surgeon from Yakima.

The Oregon Health Authority says a typical doctor is unlikely to see more than 450 medical marijuana patients at a time.

In the past year, Orvald has signed off on 4,180.

And he is not alone. The health authority says 37 doctors have exceeded the 450-patient threshold since 2005. These doctors signed statements asserting “primary responsibility for the care and treatment” of as many as 5,400 medical marijuana patients each.

The Oregonian’s examination of high-volume marijuana doctors — including interviews with physicians and clinic operators as well as a review of state documents, medical licensing reports, court records and caseload data — paints a picture of a highly specialized industry.