The underlying electrophysiological indicators of subarachnoid hemorrhage have been analyzed by a group of researchers in Germany. Subarachnoid hemorrhage is the second most common type of brain hemorrhage, and can lead to ischemic stroke within a matter of days.
This type of hemorrhage occurs in the area between the membranes surrounding the brain. Patients with subarachnoid hemorrhage can develop complications within approximately one week. Between one in three and one in four patients will develop symptoms of ischemic stroke, a type of stroke caused by an inadequate blood supply.
This phenomenon occurs as the result of mechanisms triggered by the molecular breakdown products of the patient’s earlier hemorrhagic stroke. It sets off a wave of electrochemical depolarization, or “spreading depolarization,” within the brain tissue.
Affected areas of the brain require large amounts of energy in order to restore normal conditions.
Negative Ultraslow Potential
In healthy brains, this depolarization of nerve cells is linked to blood supply, meaning blood vessels widen in areas of the brain that are active. However, a subarachnoid hemorrhage may disrupt the signaling cascades between nerve cells and blood vessels, so that the depolarization of nerve cells causes extreme constriction of the blood vessels, which leads to spreading ischemia.
Deprived of energy, the nerve cells are incapable of restoring normal electrochemical gradients. If depolarization persists for too long, affected nerve cells will begin to die off.
SD inducing NUP and spreading ischaemia. (A) The NUP of Patient 6, a 44-year-old previously healthy female, was recorded on Day 9 (onset: 218 h 4 min) after the initial haemorrhage. (B) The NUP of Patient 2, a 50-year-old previously healthy female, was recorded on Day 1 (onset: 39 h 37 min) after the initial haemorrhage. Credit: Janos Lückl, et al. CC-BY
Measurements of the electrical brain potential will then show an extreme and very gradual change, a process known as “negative ultraslow potential,” which is indicative of terminal spreading depolarization.
“Two months ago, we were able to show for the first time that terminal spreading polarization occurs in humans—namely in patients who had suffered cardiac arrest. Now we have been able to show that it also occurs in patients with cerebral infarctions after subarachnoid hemorrhage,”
explained Prof. Dr. Jens Dreier of Charité – Universitätsmedizin Berlin’s Center for Stroke Research Berlin (CSB). Prof. Dreier and his team analyzed data from 11 patients, comparing their findings with results obtained from experiments on male laboratory rats.
Potentially Important Tool
The waves of depolarization observed indicate disturbances of energy metabolism. The ‘negative ultraslow potential’ constitutes the electrophysiological correlate of infarction, and of tissue death due to an inadequate supply of blood.
“Measurements of spreading depolarization may prove as important to the development of interventions for patients with stroke, global ischemia and traumatic brain injury, as similar electrophysiological tools have proved in the past, in the areas of epilepsy or cardiology — because they make the underlying causes visible,”
Prof. Dreier said.
The work was supported by the Bundesministerium für Bildung und Forschung (BMBF) Center for Stroke Research Berlin, and Deutsche Forschungsgemeinschaft.