Late last year, Biosensors International, a medical device company, shut down its operation in Southern California, which had once housed 90 people, including the company's top executives and researchers. he reason, executives say, was that it would take too long to get its new cardiac stent approved by the Food and Drug Administration. "It's available all over the world, including Mexico and Canada, but not in the United States," said the chief executive, Jeffrey B. Jump, an American who runs the company from Switzerland. "We decided, let's spend our money in China, Brazil, India, Europe." Medical device industry executives and investors are complaining vociferously these days that the industry's competitive edge in the United States and overseas is being jeopardized by a heightened regulatory scrutiny.