"For reasons we don't yet understand, it appears that during rewarming, an autoregulation mechanism that protects the brain from fluctuations in the body's blood pressure can malfunction," says Brijen Joshi, M.D., the study's leader and a research fellow in anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine. "This could increase the chances that the brain won't get enough blood flow and oxygen and increase the risk of brain injury."
As many as five percent of cardiac bypass patients, the study finds, wake up from surgery with significant loss of controlled movement or speech caused by an interruption of blood flow to the brain — a stroke — but physicians have been unable to explain why. In a report on the observational study, published in the journal Anesthesia & Analgesia, the scientists suggest that the culprit could be a breakdown of this blood-flow regulation mechanism.
That mechanism seems to fail, they say, as doctors work to restore body temperature to its normal 36 degrees Celsius after cooling it to protect organs and facilitate heart bypass. If the autoregulation mechanism stops working, blood flow in the brain becomes entirely dependent upon blood pressure and can allow too much or too little blood to flow into the brain — a dangerous result.
"You come in with a heart problem and now you can't move a limb or you can't speak and you have a neurological problem," says Joshi. "We have to figure out why this is happening."
As part of the study, Joshi and his colleagues monitored the blood pressure and brain blood flow of 127 patients undergoing standard, lengthy cardiac bypass surgery during which they spent two hours on a heart-lung machine that circulated their blood for them. Their bodies were cooled to below 34 degrees Celsius and then rewarmed. Eleven patients undergoing shorter bypass operations were kept at normal body temperature throughout and served as a control group.
After surgery, none of the control patients had experienced any neurological problems, while seven of the standard group had strokes and one experienced a transient ischemic attack, or TIA, a brief interruption of blood flow that's considered a harbinger for future stroke.
The study notes that while cooling and rewarming to protect organs during bypass surgery may impair autoregulation and increase the risk of stroke, there is little evidence that this practice is necessary.
Joshi and his colleagues say more research is necessary into the precise causes of the malfunction in the brain's blood-flow regulation mechanism. Currently, there is no good monitor to alert doctors in real time that blood flow in the brain is too low or too high, says Charles W. Hogue Jr., M.D., associate professor of anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine and the study's principal investigator.
"We measure the heart, blood pressure, kidney function and more during surgery," Hogue says. "But there's a huge need for a better monitor for the brain."
To that end, the team has been developing a monitoring device that, during bypass surgery, would measure blood flow to the brain using near infrared spectroscopy, along with software that tracks changes in individual patients as they happen. When the body gets to the point where it isn't properly regulating blood flow in the brain, doctors don't know it in real time. If a monitoring device could alert doctors that blood flow to the brain had declined, they could quickly adjust blood pressure, restoring adequate flow and potentially avoid a stroke.
"Once we find the point at which this mechanism fails, we might be able to keep blood pressure above that threshold and prevent brain injury," Joshi says.
The study was funded through grants from the American Heart Association, the National Institutes of Health and the Foundation for Anesthesia Education and Research Training.
Other Johns Hopkins researchers who worked on the study include Kenneth Brady, M.D.; Jennifer Lee, M.D.; Blaine Easley, M.D.; and Rabi Panigrahi, M.D.For more information: http://www.hopkinsmedicine.org/anesthesiology_critical_care_medicine/
Stephanie Desmon | EurekAlert!
Study relating to materials testing Detecting damages in non-magnetic steel through magnetism
23.07.2018 | Technische Universität Kaiserslautern
Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
15.08.2018 | Physics and Astronomy
15.08.2018 | Earth Sciences
15.08.2018 | Physics and Astronomy