On April 18th, 2019, the British magazine Nature published a cover article entitled “Let Time Back”, which was developed by the neuroscientist Nenad Sestein research team at Yale University School of Medicine. BrainEx’s in vitro perfusion system restores brain circulation and partial brain cell function to pig brains after death for a minimum of 6 hours.
Successfully “resurrected” the dead pig brain
The Sebastian team obtained the dead pig from the food processing plant, and took the complete pig brain from the head of the pig, and then passed the carotid artery and the extracorporeal perfusion system, namely the BrainEx system (which can simulate the blood flow pulsation at a normal temperature of 37 degrees Celsius). The in vitro perfusion is linked to a hemoglobin-free cell-free perfusate supplied to the pig brain.
These pigs have died more than 4 hours, and during the 6-hour perfusion of the BrainEx system, 32 pig brains recovered the circulation of major arteries, small blood vessels, and capillaries. Moreover, after applying a drug for increasing blood flow to the human brain in the perfusate, the blood vessels of these pig brains expand and accelerate the flow rate of the perfusate. This shows that the dead pig brain also responded to the drug.
More importantly, the BrainEx system repairs the brain’s nervous system. With the support of the BrainEx system, neuronal death in the cerebral cortex of pigs is reduced, the morphology and density of nerve cells are maintained, and the function of some nerve cells is restored. The evidence is that using electrodes to detect biocurrent activity in a single neuron can reveal that neurons produce spontaneous synaptic activity. This suggests that the brain’s brain cell recovery function may be better than previously thought.
The recovery of neuronal function is considered to be an important basis for the maintenance and recovery of brain function. In the past, the brains of humans and other advanced mammals were very fragile. Once the blood supply stopped for 4 minutes to 6 minutes, the neurons could be irreversibly damaged and died due to lack of oxygen and lack of nutritional support. First aid is generally required to be as early as possible, preferably within 6 minutes.
The results of this study suggest that degeneration of brain cells after interruption of blood supply is more likely to be a slow process. Due to limited resources, the study interrupted perfusion after 6 hours of maintenance. If not interrupted, it is unclear whether the BrainEx system can maintain the pig brain for a longer period of time and whether it can restore all normal brain function. It should be noted that the current results are not certain that dead pigs have recovered brain consciousness, sensation, or other whole brain electrical activity associated with advanced brain function. Therefore, Sebastian also cautioned that the recovery of brain neurophysiological activity cannot be compared with the recovery of overall function.
However, only the recovery of some physiological activities of the brain after death is enough to have a huge impact on the current standards of brain death and the resulting organ transplant policies, systems and procedures. Therefore, the comments published in the same period of Nature indicate “BrainEx research opens up possibilities that were previously unimaginable.”
“Death” is redefined
The BrainEx system makes the partial recovery of the dead brain a social impact. It is now conceivable that the first is the standard of brain death, and the subsequent organ transplant. Now, more than 100 countries in the world have implemented brain death standards. In 2017, more than 5,000 patients with heart and brain deaths in China made organ donations. At least one third of them were brain deaths. According to the results of the Sebastian team, if the brain death is still possible, it will actually prevent the implementation of the brain death standard. As a result, it is difficult to extract the organ of the brain death donor for organ transplantation.
For death, human society has been following the criteria of cardiopulmonary death (breathing heartbeat). In 1959, French scholars Morare and Gurung at the 23rd International Neurological Society reported that 23 patients with severe brain injury were seriously injured. zero. As a result, they first proposed the concept of “excessive coma” and used the term “brain death”. This concept was gradually accepted and accepted by the medical community, but it was not implemented in clinical death judgment.
In 1966, the American medical community proposed that brain death should be regarded as a sign of clinical death. At the 22nd World Medical Congress in 1968, the Special Committee on the Definition of Brain Death in Harvard Medical School of the United States proposed “unreversible loss of brain function” as a new The standard of death and the development of the world’s first diagnostic criteria for brain death. The criteria include: irreversible deep coma; no spontaneous breathing; brainstem reflexes disappear; brain electrical activity disappears (electrical rest). Those who meet these criteria and repeat the test within 24 hours – 72 hours, the results will be unchanged, you can declare death.
In the same year, the World Medical Organization (WHO) International Medical Science Organizing Committee also established brain death standards, which are based on the standards of Harvard Medical School, but there are certain differences, including five: coma, the response to the entire environment disappears; The various reflections disappeared, the pupils were not reflected by the light, and they were in an expanded state; the spontaneous breathing disappeared, including no spontaneous breathing after stopping artificial respiration for 3 minutes; if not maintained manually, the blood pressure dropped sharply; even if the stimulation was given, the EEG was straight. . Patients with low body temperature (less than 23 ° C) and drug abusers should be removed from the above. Repeat the above test for 24 hours and the results will not be confirmed.
Controversy over brain death
Brain death itself is also controversial. For example, brain death is divided into whole brain death and brain stem death. In 1976, the Royal Society of Medicine proposed brainstem death as the standard for brain death. In 1998, the British Ministry of Health formally proposed the guidelines for brain stem death diagnosis: including guidelines for identifying and managing potential organ and tissue donors. In addition, in 1980, Chinese scholar Li Dexiang proposed that whole brain death should be the standard of brain death, which can avoid brain death, brain stem death and other brain deaths equivalent to brain death defects.
At present, medical experts from all over the world have proposed about 30 kinds of diagnostic criteria for brain death. The brain death standards implemented in more than 100 countries around the world are all standards of brain death. Mainly divided into 4 categories.
The first category is that the law clearly states that brain death is the basis for the declaration of death. Such countries include the United States, Finland, Germany, etc. The second category is that although there is no formal law, clinical and actual recognition of brain death, such countries include Belgium, The United Kingdom, New Zealand, etc.; the third category is the simultaneous recognition of cardiopulmonary death and brain death, such countries include Japan, Austria, etc.; the fourth category is the legal recognition of brain death is the basis for the declaration of death, but medically recognize brain death, such as China.
China has also established medical brain death criteria “brain death criteria and technical specifications (adult quality control version)” and “brain death judgment standards and technical specifications (children’s quality control version)”, using comprehensive criteria to judge death. In essence, the comprehensive standard is the standard of cardiopulmonary death. It has been widely accepted and recognized by the Chinese legal scholars and the public. It has been the legal standard for determining death until now. However, the standard of brain death is only recognized by the medical profession and has not been adopted by the legal profession, society and the public. Therefore, organ transplantation in China mainly relies on the cardiopulmonary death standard to extract the donor’s organs.
The findings of Sestein et al. may have the greatest impact on China’s brain death legislation and challenge other 100 countries that have recognized and implemented brain death.