Americans could soon be able to see a doctor without getting out of bed, in a modern-day version of the house call that takes place over the Web. OptumHealth, a division of UnitedHealth Group, the nation's largest health insurer, plans to offer NowClinic, a service that connects patients and doctors using video chat, nationwide next year. It is introducing it state by state, starting with Texas, but not without resistance from state medical associations. OptumHealth believes NowClinic will improve healthcare by ameliorating some of the stresses on the system today, like wasted time dealing with appointments and insurance claims, a shortage of primary care physicians, and limited access to care for many patients. But some doctors worry that the quality of care that patients receive will suffer if physicians neglect one of the most basic elements of health care: a physical exam.