PORTLAND, Ore. (AP) — Low-income Oregon residents were supposed to be big winners after the state expanded Medicaid under the federal health care overhaul and created a new system to improve the care they received.

But an Associated Press review shows that an unexpected rush of enrollees has strained the capacity of the revamped network that was endorsed as a potential national model, locking out some patients, forcing others to wait months for medical appointments and prompting a spike in emergency room visits, which state officials had been actively seeking to avoid.