The roiling economy appears to be ripping into the ranks of upper management, as the chief executive turnover rate is at an all-time high. This year, 1,132 CEOs have left their posts, according to employment consulting firm Challenger, Gray & Christmas Inc. Challenger chief executive John A. Challenger said the rise in the turnover rate probably reflects increasing pressure on corporate leaders from their boards and shareholders. Turnover was heaviest in the healthcare sector, with 206 departures. In part, however, that stems from the large number of small healthcare businesses, Challenger said.