When Bill Clinton underwent quadruple coronary bypass surgery on Labor Day, the former president, like most Americans who have similar operations, spent time (73 minutes) hooked up to a heart-lung machine while surgeons rerouted blood vessels to his heart.
With luck and his relative youth and health going for him, Clinton, 58, will likely rebound from the bypass surgery, in which doctors replace clogged heart arteries with blood vessels from elsewhere in the body.
But many who undergo the procedure, as 305,000 Americans did in 2001, the latest year for which figures are available, find that their brains don't work as well as they did before - at least for a few days, but often for weeks and sometimes years.
Doctors who acknowledge the problem - and some still pooh-pooh it - call it post-surgical "neurocognitive deficits."
Everybody else calls it "pump head," reflecting the widespread - though unproven - belief that pumping blood through a heart-lung machine while the heart is stopped for surgery causes small blood clots, air bubbles or other debris to travel to the brain, disrupting memory.
Nobody really knows how common it is because most cardiac patients aren't tested for intellectual function before and after surgery. Detecting all but the most subtle cognitive changes "depends on how hard you look," said Dr. William Cohn, director of minimally invasive surgical technology at the Texas Heart Institute in Houston.
Still, in a 2002 editorial in the Journal of the American Medical Association, Duke researchers concluded the syndrome had been "convincingly demonstrated," with an incidence of 80 percent to 90 percent.
In their study, Dr. Daniel B. Mark and Dr. Mark F. Newman found that as long as five years after surgery, 42 percent of bypass patients still showed some cognitive decline. The deficits are often small but quite real.
"It's not that you can't solve a problem," said Mark, "but that you can't solve it as quickly."
Many cardiologists, among them Dr. Christopher Cannon of Brigham and Women's Hospital in Boston, believe that "pump head" is most likely to occur in older patients who might have blocked blood vessels in the brain as well as the heart. So it might just be a symptom of generalized atherosclerosis.
At the moment, there's no cure for "pump head." Nor do doctors understand why some patients get better over time and others do not.
Though it's not clear that the heart-lung machine is the real culprit, for years, many doctors assumed it was and focused on the technology - which has continually improved.
Now, the machine's tubing is coated with material that reduces the body's inflammatory response, which can be triggered as blood cells course through the machine. Historically, scientists believed this inflammation caused some cognitive problems after surgery, said Dr. William Baumgartner, chief of cardiac surgery at Johns Hopkins Hospital.
Better yet, some doctors argue, would be to get rid of the pumps altogether and operate on still-beating hearts using devices that stabilize just one part of the heart at a time.
But off-pump surgery, as it's known, is used in only 22 percent of bypass procedures, said Dr. John Puskas, associate professor of surgery at Emory University in Atlanta.
"I think it's clear that off-pump is better, but proving it with scientific rigor is challenging," he said. In general, off-pump patients leave the hospital a day or so sooner and have less blood loss.
A study by Dutch researchers in 2002 found that off-pump patients fared better immediately after surgery, but by a year later had the same rate of cognitive decline as pump patients. Puskas' still-unpublished analysis also shows mixed results.
Other doctors question the value of off-pump surgery because "pump head" can also occur after operations that don't involve a heart-lung machine. They say it could result from the stress of surgery, the duration of anesthesia, postoperative infections or respiratory problems.
Baumgartner's team compared patients who had on-pump bypass surgery with similar coronary artery disease patients who did not have surgery. A year later, there was no difference in cognitive function.