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.

The problems come amid nationwide growing pains associated with the unprecedented restructuring of the U.S. health care system, and they show the effects of a widespread physician shortage on a state that has embraced Medicaid expansion.

It's too early to tell whether there will be lasting troubles associated with these immediate challenges. Overhaul supporters say they anticipated the need for more doctors and are already implementing solutions to improve access to care. They also point to the crush of new Medicaid enrollees as proof that their efforts are necessary and working.

Still, early indications show clear challenges associated with expanding Medicaid and establishing coordinated care networks, the centerpiece of Gov. John Kitzhaber's plan to reduce costs and improve care by focusing on primary care and keeping patients out of emergency rooms.

"As soon as people got insured, they all showed up at once, wanting to deal with the problems they couldn't deal with for years," said John Guerreiro, a primary care doctor in northwestern Oregon.

Under the federal overhaul, the state this year added nearly 360,000 people to the Oregon Health Plan, its version of Medicaid. It was more than twice the number projected and swelled the state Medicaid rolls to nearly 1 million people, about a quarter of the state's population.

Timothy McDaniel, a self-employed computer programmer from Springfield, gained Medicaid coverage in January and said it took him six months to find a doctor. He even went to an urgent care clinic seeking a wellness exam but was turned away, because the facility didn't provide such evaluations.

"It was rather frustrating because I'm getting older, I'm in my late 50s," McDaniel said. "I thought I had this health insurance. I wanted to use it. I wanted to get checked out, and I couldn't."

The flood of new enrollees like McDaniel has hit hardest in rural parts of the state, where the physician shortage is most severe. But problems have been reported from every corner, the AP has learned after contacting each of 15 regional coordinated care organizations, regional networks of doctors and nurses intended to see patients more often for treatment of small and chronic problems.

The coordinated care model has been championed by the state's Democratic governor, an early supporter of President Barack Obama's Affordable Care Act, and is unique to Oregon.

Five of the 15 regional coordinated care organizations declined to comment. The others reported a list of complications.

— Two regions have stopped accepting new patients, locking out more than 16,000 new enrollees in western and southern Oregon, state data shows. The new patients are still insured, but without a coordinated care network, they're on their own to find a doctor.

— Eight regions saw some practices, clinics and individual doctors close to new Medicaid enrollees.

— In five regions, thousands of enrollees haven't been assigned to a doctor or been in for their first medical appointment.

— Seven regions report that new patients are facing long waits for primary care visits, delays that can last months.

— Seven regions report an increase in ER visits, up to 30 percent, in a statistic that has been particularly troubling for supporters of Oregon's efforts.

Officials say the jump in ER use is likely fueled by newly covered patients who are unable to access primary care. "Medicaid expansion has exposed how serious the provider shortage is, that we definitely need more doctors," said David Cole, CFO of the Eugene-based coordinated care organization Trillium, one of the two that's turning away Oregon Health Plan patients. Trillium also has more than 9,000 enrollees for whom it's yet to find a doctor.

For critics, these problems are the latest in a series of Oregon woes that include the state's decision to spend a quarter of a billion dollars on an online marketplace that failed under a litany of embarrassing problems and prompted a switch to a federal site.

But many state officials consider such issues as bumps in the road, far from anything that would threaten the overhaul. They say they're working on bringing in all enrollees into the coordinated care system by year's end.

"I would consider it a rare success story for Oregon to absorb all these new patients," said Leslie Clement, chief policy director at the Oregon Health Authority, a state medical regulating agency. "The primary care shortage is a national problem; it's not an Oregon issue."

Solutions include starting a new residency program in Eugene and using more nurse practitioners, physician assistants, pharmacists and a system of team-based care.

Coordinated care organizations are also opening new clinics and offering grants to physicians who'll accept more Oregon Health Plan members, offsetting low federal reimbursements that had prompted many doctors to turn Medicaid patients away. Two coordinated care regions have even increased Medicaid reimbursement rates for doctors to run even with commercial rates.

The Virginia Garcia Memorial Health Center, which comprises nine clinics in northwestern Oregon, serves 36,000 patients in Washington and Yamhill counties. The center has been working through a backlog to link thousands of people to doctors, using innovations such as group visits and telemedicine.

About 2,600 new patients are yet to be assigned at the Beaverton clinic where Guerreiro practices alongside seven other doctors. "It's a little intimidating," Guerreiro said, "but we need to bring all these new patients in."

It's widely agreed that Kitzhaber's coordinated care organizations have provided examples of success, most notably the 2-year-old system led to a decrease in ER visits before the massive influx of new patients. And supporters say the approach will save billions once it's operating properly.

It's not clear, however, when that will be.

"From 2007 to 2014, we're going to triple our enrollment," said Bill Guest, executive director of southern Oregon's Cascade Health Alliance, the other coordinated care organization that has closed its doors to new patients.

"Unfortunately," he added, "the primary care supply has not tripled over that period."