Propped up in a hospital bed, a 75-year-old man with amyotrophic lateral sclerosis, or Lou Gehrig's disease, must make an agonizing decision. Should he keep struggling until the illness inevitably kills him, dependent on a ventilator, unable to walk or eat or move? Or should he choose a day and a time to have the ventilator disconnected, and die? The man, who asked not to be identified to protect his privacy, was a patient at the Hospital for Special Care here, one of 400 long-term acute care hospitals in the United States. These are no ordinary hospitals: Critically ill patients, sometimes unresponsive or in comas, may live here for months, even years, sustained by respirators and feeding tubes.