Death can be described as asynchronous—not all of the parts of the human body die at the same time after the heart stops functioning. For example, after the human brain ceases to function, with the assistance of a ventilator (respirator) for blood flow and oxygenation, many body organs, such as the heart, lungs, cornea, liver, pancreas, small bowel, skin, tendons, kidney, and bone, may be kept viable long enough for the purposes of donation to save the life of another person.  A human limb can survive if kept cool immediately after amputation. An arm can be reattached successfully within three to four hours, and a finger up to eight hours after severance from the human body. But when does the brain actually stop functioning after the heart stops pumping oxygenated blood?
In the United States, all 50 states have legally defined death with neurological criteria, according to The Journal of Medicine and Philosophy.  Now scientists have observed that the human brain, like many other body parts, does not stop working immediately after the heart stops beating and may still function for up to five minutes afterward, according to their study published in 2018 in the Annals of Neurology titled “Terminal spreading depolarization and electrical silence in death of human cerebral cortex.”
A research team, led by professors Jens Dreier of Charité’s Center for Stroke Research and Jed Hartings of the Department of Neurosurgery at the University of Cincinnati, discovered that humans, like animals, undergo an event known as “terminal spreading depolarization,” beginning within minutes of circulatory arrest. This discovery has “important implications for survivable cerebral ischemic insults.” 
Following cardiac arrest, irreversible human brain damage occurs within an estimated 10 minutes due to the lack of oxygen.  Within 20-40 seconds of oxygen deprivation, the brain becomes electrically inactive, and interneuronal activity stops. In a healthy, oxygenated human brain, ion gradients, the uneven distribution of ions between the inside and outside of nerve cells, are maintained. Within minutes, the brain’s ion gradient starts to deteriorate, and depolarization spreads as a “massive wave of electrochemical energy release in the form of heat,” called a “brain tsunami.”
As the energy loss is distributed through the cortex to other areas of the brain, pathophysiological cascades occur which “gradually poison the nerve cells.” According to the research study, “this wave remains reversible up to a certain point in time: nerve cells will recover fully if circulation is restored before this point is reached.”
According to Dreier, “Knowledge of the processes involved in spreading depolarization is fundamental to the development of additional treatment strategies aimed at prolonging the survival of nerve cells when brain perfusion is disrupted.” For cardiac arrest, medical professionals may try to resuscitate patients using various techniques, such as cardiopulmonary resuscitation (CPR), and defibrillation. This research may help in developing future medical technology and treatment to reverse the impact that the disrupted circulation of oxygen has on the nerve cells of the human brain.
Copyright © 2018 Cami Rosso All rights reserved.
1. NHS. “What can I donate? NHS Organization. Retrieved on 22 October 2018 from https://www.organdonation.nhs.uk/about-donation/what-can-i-donate/.
2. Nikas, Nikolas T.; Bordlee, Dorinda C.; Moreira, Madeline. “Determination of Death and the Dead Donor Rule: A Survey of the Current Law on Brain Death.” The Journal of Medicine and Philosophy. 2016 June.
3. Dreier, Jens P.; Marjor, Sebastian; Foreman, Brandon; Winkler, Maren K.L.; Kang, Eun-Jeung; Milakara, Denny; Lemale, Coline L.; DiNapoli, Vince; Hinzman, Jason M.; Woitzik, Johannes; Andaluz, Norberto; Carlson, Andrew; Hartings, Jed A. “Terminal spreading depolarization and electrical silence in death of human cerebral cortex.” Annals of Neurology. 13 January 2018.
4. Charité – Universitätsmedizin Berlin. (22.02.2018). “The giant wave that marks the beginning of the end – the neurobiology of dying [Press release].” Retrieved from https://www.charite.de/en/service/press_reports/artikel/detail/die_ries…