Three of the major issues affectung health care today are global in nature: poverty, violence and the aging of the American population. In the absence of a concerted national effort to deal with them, communities across the country are experimenting with their own local solutions. The Valencia County Coalition in New Mexico, for instance, is breaking down the barriers between low-income residents and the state's Medicaid managed care program. Another example: The DeKalb Medical Center in Decatur, Ga., opened a unit to treat elderly patients' acute medical problems and keep them functional so they can go straight home from the hospital rather than to subacute or skilled nursing care.