Nav: Home

Slower rate of rewarming reduces cognitive declines after major heart surgery

May 08, 2000

For years, surgeons have been performing successful open heart surgeries on their patients only to find that many of them suffer cognitive deficits afterwards in such areas as memory, concentration and attention, some for as long as five years after surgery.

While researchers believe that more than one factor is involved in this decline, a new study by Duke University Medical Center anesthesiologists suggests that the rate in which patients are rewarmed after surgery is a major factor. In order to protect the brain and other organs from damage while the heart is stopped during surgery, physicians cool a patient's blood as it passes through a heart-lung machine.

The Duke researchers found that patients who were allowed an additional five to 10 minutes to return to normal body temperature scored better on standard tests of cognition six weeks after surgery. Furthermore, the researchers found that the effect was magnified in diabetic patients -- those rewarmed at the slower rate scored more than twice as high.

The researchers hypothesize that quicker rewarming may produce an imbalance between the brain's sudden need for oxygen that cannot readily be provided, resulting in the cognitive detriments.

"This is the first well-controlled prospective study to determine whether or not the rate in which patients are rewarmed has any effect on such abilities as memory, concentration and attention," said Dr. Alina M. Grigore, Duke anesthesiologist and lead researcher of the study. "While the results seem to indicate a slower rewarming would be beneficial for all heart patients, it seems especially true for the sickest heart patients, as well as those with diabetes."

A better understanding of this phenomenon is important, the researchers say, because previous studies performed at Duke have shown that up to one-third of heart patients suffer from significant declines in cognitive abilities after undergoing major open heart surgery. It is not known, however, how many and what factors are responsible for this decline.

In a typical coronary artery bypass graft procedure, a heart-lung machine takes over from the heart and pumps blood throughout the body, allowing surgeons to operate on a temporarily stopped heart. Additionally, the heart-lung machine cools the circulating blood in order the reduce the metabolic needs of the brain and other vital organs.

The Duke study compared two groups of patients undergoing the same heart procedure -- 100 were allowed to be rewarmed at the typical rate (an average of 0.56 degrees Celsius per minute), while 65 patients were brought back to normal temperature at the much slower rate (average 0.49 C per minute). Typically, it takes 15-20 minutes for patients to be rewarmed.

During surgery, all patients were cooled to temperatures between 30 and 32 C; normal body temperature is 36 C.

While it is not known exactly why temperature plays a role, Grigore believes that a slower rewarming allows for less discrepancy between the brain's growing demand for oxygen as it warms up and the supply of oxygen.

"When patients are rewarmed quickly, brain's need for oxygen and its supply is most out of balance -- the higher demands for oxygen are not matched by increased blood flow," she said. "This period of time with inadequate oxygen supply could explain the cognitive deficits."

During the standard, faster rewarming process, the temperature of the brain may temporarily rise above 36 C, as the temperature at the core of the brain comes into equilibrium with the temperatures of the brain's outer shell.

"A slower rewarming allows the temperature to be transferred from the core to the shell and prevents overheating," Grigore said. "We know from other studies that brain temperatures approaching 37 C are definitely detrimental to the brain.

"So it may be that the slower rewarming of these patients ensures that fewer of them reached temperatures above 36 C," she said.

Before surgery, each of the patients in the study was given a battery of nine standard tests that measure cognitive functions in four broad categories: attention and concentration; verbal memory; abstraction and visual orientation; and figure (numbers) memory. The same tests were then administered six weeks later.

Interestingly, Grigore said, the attention and concentration portion of the tests seemed the most sensitive to rates of rewarming. However, she said the reasons for this are not well understood.

These patients will continue to be followed to determine if the cognitive deficits persist.
-end-
The results of Grigore's study were prepared for presentation Tuesday (May 9) at the annual meeting of the Society of Cardiovascular Anesthesiologists. The study was supported by numerous grants from the National Institutes of Health.

Joining Grigore in the study were Duke colleagues Dr. Barbara Phillips-Bute, Dr. Hilary Grocott, Aimee Butler, Dr. Tom Stanley, Dr. Jerry Reves and Dr. Mark Newman.

Duke University Medical Center

Related Memory Articles:

Memory of the Venus flytrap
In a study to be published in Nature Plants, a graduate student Mr.
Memory protein
When UC Santa Barbara materials scientist Omar Saleh and graduate student Ian Morgan sought to understand the mechanical behaviors of disordered proteins in the lab, they expected that after being stretched, one particular model protein would snap back instantaneously, like a rubber band.
Previously claimed memory boosting font 'Sans Forgetica' does not actually boost memory
It was previously claimed that the font Sans Forgetica could enhance people's memory for information, however researchers from the University of Warwick and the University of Waikato, New Zealand, have found after carrying out numerous experiments that the font does not enhance memory.
Memory boost with just one look
HRL Laboratories, LLC, researchers have published results showing that targeted transcranial electrical stimulation during slow-wave sleep can improve metamemories of specific episodes by 20% after only one viewing of the episode, compared to controls.
VR is not suited to visual memory?!
Toyohashi university of technology researcher and a research team at Tokyo Denki University have found that virtual reality (VR) may interfere with visual memory.
The genetic signature of memory
Despite their importance in memory, the human cortex and subcortex display a distinct collection of 'gene signatures.' The work recently published in eNeuro increases our understanding of how the brain creates memories and identifies potential genes for further investigation.
How long does memory last? For shape memory alloys, the longer the better
Scientists captured live action details of the phase transitions of shape memory alloys, giving them a better idea how to improve their properties for applications.
A NEAT discovery about memory
UAB researchers say over expression of NEAT1, an noncoding RNA, appears to diminish the ability of older brains to form memories.
Molecular memory can be used to increase the memory capacity of hard disks
Researchers at the University of Jyväskylä have taken part in an international British-Finnish-Chinese collaboration where the first molecule capable of remembering the direction of a magnetic above liquid nitrogen temperatures has been prepared and characterized.
Memory transferred between snails
Memories can be transferred between organisms by extracting ribonucleic acid (RNA) from a trained animal and injecting it into an untrained animal, as demonstrated in a study of sea snails published in eNeuro.
More Memory News and Memory Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.