In the months after he had surgery to fix his defective heart valve, Bruce Stutz didn't feel quite the same. It wasn't his physical fitness that was subpar, although that did require some post-op retraining, but rather his mental capacity. "I couldn't muster the concentration to deal with the problem," he wrote in a 2003 article for Scientific American.

During surgery, Stutz had been hooked up to a heart–lung machine, also called a cardiopulmonary-bypass pump, for the two-hours of a procedure to keep his blood oxygenated and flowing while his heart was stopped. He found that he was not the only one who, after time on the pump, had felt their brains bogged down by simple tasks.

A 2001 study in The New England Journal of Medicine found that of 261 heart disease patients who had been kept alive during surgery with the pump, 42 percent showed cognitive decline five years after the surgery, even after adjusting for age. "Interventions to prevent or reduce short- and long-term cognitive decline after cardiac surgery are warranted," the authors, led by Mark Newman of the Duke University Medical Center, concluded. And a study published earlier this year in The Annals of Thoracic Surgery, led by James Slater, a cardiothoracic surgeon at the Mid-Atlantic Surgical Associates in Morristown, N.J., supported the previous findings, showing that lowered levels of oxygen in blood flowing to the brain during surgery did correlate to increased risk of suffering from the mental impairment dubbed "pump head".

But some noticed a flaw in these studies. Most that supported the pump head condition had focused only on patients who underwent pump support during surgery for coronary artery bypass grafting (CABG) but had not controlled for those with the disease who had different types of procedures, such as off-pump surgery or no surgery at all. Could there be something missing in the data?

That's what Ola Selnes, a professor of neurology at The Johns Hopkins Hospital in Baltimore, and his colleagues set out to find. Their six-year study—published this month in The Annals of Thoracic Surgery—examined 326 people who had coronary disease and 69 who didn't. Of those who did had the disease: 152 had undergone the CABG procedure using the pump; 75 had off-pump surgery; and 99 had nonsurgical treatment. After testing subjects at several intervals starting before surgery and ending six years later, they found that those with healthy hearts retained their levels of cognitive functioning after the operation, whereas the patients with coronary disease experienced about the same amount of cognitive decline—regardless of the sort of treatment they had. The results call into question years of assumptions about the long-term safety of the pump.

But the findings did not surprise Selnes and his team, whose study was funded by the National Institute of Neurological Disorders and Stroke and The Dana Foundation, along with a grant from The Johns Hopkins Medical Institutions. They were aware that patients who have trouble with their heart arteries also have trouble with their brains' vasculatures. Other studies had even shown that 20 to 40 percent of patients set to undergo CABG already showed some degree of cognitive decline before the operation. "It's there and it's detectable through standard psychological assessments," Selnes says. The degree, however, is usually slight, he adds, which means it "is probably so common that it's probably thought of as being normal aging."

What did surprise Selnes, however, was that "it takes this long to turn around a scientific opinion," he says. That a 2001 study "done without a control group" had so thoroughly driven medical thinking, he says, was indeed "kind of surprising." He does concede that he sees how researchers could have been drawn in by the idea of individuals' symptoms and tried to rely on baseline cognitive readings as a control. But do that, Selnes, says and "you end up having to attribute all of the change to the procedure, and you miss out on the opportunity to see other factors that could be accounting for that change."

Selnes hastens to caution that after six years his team found the same rate of decline in patients with coronary artery disease as the 2001 work by Mark Newman and his colleagues. But, Selnes says, "I think that the really important message is…it's very important to have a comparison group."

Even to those who have examined cognitive decline in on-pump surgery patients, the long-term results didn't come as much of a surprise. "Patients with coronary disease actually have vascular disease all over their body," Mid-Atlantic's Slater says.

Although his work looked only at patients who had surgery while on the heart–lung machine, Slater notes that there are a lot of aspects of even off-pump surgery that could have generate the pump head phenomenon. In most bypass surgeries, regardless of technique, the heart must be moved from its natural position, opening possibilities for kinking that can cause blood pressure changes in the head.

He believes that the short-term symptoms—rather than those years out—may relay more information about the true cognitive impacts of the various cardiac treatments.

Certainly bypass operations are not the only ones with documented pump head in post-op patients—at least for a little while after surgery. The new findings don't, for example, help explain what happened to Stutz, who didn't have the same kind of coronary disease as most patients in these studies did. Stutz did find that his fuzziness eventually lifted. "Whatever it is, it does take awhile," he says. But now, years after the procedure, "The problems have gone away."