Executives at smaller records companies say the legislation cemented the established companies’ leading positions in the field, making it difficult for others to break into the business and innovate. Until the 2009 legislation, growth at the leading records firms was steady; since then, it has been explosive. Annual sales growth at Cerner, for instance, has doubled to 20 percent from 10 percent.

“We called it the Sunny von Bülow bill. These companies that should have been dead were being put on machines and kept alive for another few years,” said Jonathan Bush, co-founder of the cloud-based firm Athenahealth and a first cousin to former President George W. Bush. “The biggest players drew this incredible huddle around the rule-makers and the rules are ridiculously favorable to these companies and ridiculously unfavorable to society.”

This industry, which was pioneered in the late 1970s, first gained widespread attention in 2004 when President Bush in his State of the Union speech called for digitizing national health records.

“After that, every technology C.E.O. wanting a piece of health care would have visited me every day if I had let them,” said David Brailer, whom President Bush appointed as the nation’s first health information czar. Over the next few years, Cerner and many of the other health care data companies increased their presence on Capitol Hill.

The records systems sold by the biggest vendors have their fans, who argue that, among other things, the systems ease prescribing medications electronically. But these systems also have many critics, who contend that they can be difficult to use, cannot share patient information with other systems and are sometimes adding hours to the time physicians spend documenting patient care.

“On a really good day, you might be able to call the system mediocre, but most of the time, it’s lousy,” said Michael Callaham, the chairman of the department of emergency medicine at the University of California, San Francisco Medical Center, which eight months ago turned on its $160 million digital records system from Epic. Michael Blum, the hospital’s chief medical information officer, said a majority of doctors there like the Epic system.

Whatever the case, the legislation has been a windfall to top executives at the leading health records companies. Neal L. Patterson, who grew up on a farm near Manchester, Okla., population 100, co-founded Cerner in 1979. As Cerner’s sales have soared in recent years, so have Mr. Patterson’s fortunes. From 2007 to 2011, he received more than $21 million in total compensation, according to the executive compensation research firm Equilar, and his stake in the company is worth $1 billion.