A lot more is riding on HCA's return to being a public company than raising a bunch of money to chip away at its hefty corporate debt as the hospital chain's stock starts trading on Wall Street again this week. The expected stock sale — probably the largest private equity-backed initial public offering in U.S. history — could have broader implications for the local and national health-care industries as it sparks the flow of tens of millions of dollars into the hands of corporate insiders and other investors cashing out a portion of their HCA holdings. As executives turn private ownership stakes into stock that trades readily on the New York Stock Exchange, that wealth could help finance new startup health-care companies or even fuel the sale of some high-end homes if investors reap large enough profits.