On May 25, 2020 an African-American man named George Floyd was apprehended by four police officers in Minneapolis, Minnesota. During the apprehension, a police officer named Derek Chauvin placed the handcuffed Floyd prone on the street, then knelt over him, placing his left knee on top of Mr. Floyd’s neck. From the image circulated in the media, it appears that Chauvin exerted his full weight over his bent knee. He kept his knee in position for 8 minutes and 46 seconds despite please from Floyd that he could not breathe. Tragically, Mr. Floyd died at the scene. Two autopsies on Mr. Floyd ruled the death a homicide. The county version “revealed no physical findings that support a diagnosis of traumatic asphyxia or strangulation” while a private autopsy ruled he died of “asphyxiation due to neck and back compression.” Asphyxiation is the deprivation of oxgyen to the body, resulting in death. Chauvin was fired and arrested shortly after the incident, and charged with 3rd degree murder and second degree manslaughter.
This tragic and awful case spurred protests and civil disobedience throughout major cities in the U.S., against systemic police brutality and racism towards African-American men, which continues as I write this. It is also a case that has drawn interest in the medical and forensics community, as to how exactly George Floyd died. This is important to investigate, as it has consequences for the trial and also provides information to police forces to help them determine which types of restraints should and should not be used.
Before discussing the medical aspects of Mr. Floyd’s death, I want to emphasize that the most important thing about this incident is that a man unnecessarily lost his life to a trusted law enforcement officer, in a most inhumane way. It is especially bad because of the systemic racism element to it, and the fact that Chauvin had several opportunities to get off of him in time after being warned by another officer at the scene and multiple witnesses, but failed to do so. This was a textbook lesson on how not to subdue a person, and the price of this lesson is going to play out for weeks to months and will be costly to society in more ways than one.
That being said, I will discuss the anatomical and physiological factors involved in Mr. Floyd’s death. There is some controversy over how he died, which will determine what sentence, if any, Derek Chauvin will receive.
As you will see, the neck contains several structures directly tied to sustaining life, which is why the neck is a logical target when it comes to martial arts/ self-defense, and yes, murder.
Mr. Floyd was lying prone (stomach down) with his hands handcuffed behind his back and neck turned to his right. So when Chauvin placed his knee over his neck it contacted the lateral (side) aspect of his neck and some of the anterior portion. The critical structures found at the side of the neck include the vertebral arteries, cervical nerve roots, carotid arteries, jugular veins and lymphatic vessels. Attached to the carotid artery is the carotid body, a cluster of special cells that detect oxygen saturation levels in the blood leaving the heart, and passes the information to the brain, which the brain uses to regulate heart and breathing rates accordingly.
Inside the cervical spine (the neck bones) there is the spinal cord which is comprised of the neuron axon bundles that control body movement and sensation; and lying just outside and against the cervical spine is the sympathetic chain ganglia, which play a role in innervating the heart, lungs, adrenal glands (adrenaline secretion) and other organs during “fight or flight” moments of stress.
The critical structures found in the anterior neck are the esophagus, trachea (wind pipe), larynx and thyroid gland. Also present but not critical to life are the vocal cords.
The contact area on Mr, Floyd’s neck, based on the typical size of a bent knee, was about 4 square inches. Chauvin weighs about 170 pounds, so I estimate that the force placed on Mr. Floyd’s lateral-anterior neck was (.9)(170 lbs)/4 in sq. =153 lbs/ 4 in sq. = 38.25 lbs./in sq. So imagine four, 40 pound dumbells stacked and resting on the side of your neck for nearly 9 minutes.
What I believed happened is blood flow to the brain was cut off, making Mr. Floyd unconscious after a few minutes, as would happen in a martial arts choke hold. We can assume the loss of consciousness due to restricted blood flow to the brain occured the moment he stopped talking. Chauvin kept his knee in place for nearly 3 minutes after Floyd stopped moving. If there was any chance of resuscitation, that chance ended with this additional time of compression.
The pressure also activated Mr. Floyd’s sympathetic chain ganglion, which caused a surge of adrenalin– a neurotransmitter secreted by the adrenal glands of the kidneys that prepares the body’s response to stress. This increased his heart rate, increased blood pressure by vasoconstricting his arteries; dilated his pupils, and attempted to increase breathing rate. However, with Chauvin’s knee on Floyd’s neck, the increased respiratory rate did not result in more oxygen getting to the body and the diaphragm, the sheet of muscle that pulls down and expands the lungs for breathing may have spasmed as it fought against the air blockage.
Most of Chauvin’s knee was over the side of the neck, but the front (anterior) was subject to some compression. This likely partially collapsed the trachea, restricting air flow. Mr. Floyd was initially able to express his inabilty to breathe, suggesting that his trachea was still patent, but his words became less and less as the seconds ticked. Perhaps Chauvin’s knee shifted forward with his weight, slowly closing off the trachea. This makes sense, as the neck has a curved contour which would promote such slipping.
As the knee hold persisted cutting blood flow to his brain, Mr. Floyd’s blood rapidly turned acidic as all oxygen was used up (the brain has a high metabolic rate and therefore a high rate of oxygen consumption) and CO2 levels were rapidly rising (CO2 is a byproduct of cell respiration). This may have affected his speech center, which is supported by the fact he stopped talking a few minutes after the knee hold. The apneustic (breathing) center in his brainstem was starting to break down as well from the hypoxia (insufficient oxygen), hampering his breathing further.
It’s not clear at what point Mr. Floyd expired. Coroners define time of death at the point when brain activity ceases. But the nature of Mr. Floyd’s death was so prolonged, it is likely he experienced irreversible brain damage and would have been in a vegetative state even if Chauvin had gotten off of him a little earlier and Mr. Floyd was given immediate medical attention.
One of the tell-tale signs of asphyxia by strangulation is ruptured blood vessels in the conjunctiva (whites of eyes) and face, called petechial hemmorhaging. This information, as far as I know, is not available to the public. If there was no evidence of this, I can see why the county autopsy reached the conclusion that he did not die of asphyxia. In this case, it would suggest that Mr. Floyd’s primary cause of death was something else; perhaps sudden stoppage of the heart due to a breakdown in the cardioregulatory system. But, it is not clear if you can die from asphyxia from “gradual” strangulation and not have petechial hemmorhaging. It could also be that death was from a combination of both asphyxia and heart stoppage.
The autopsy did not mention fractured cervical vertebrae, which I could see happening if it were a smaller-framed person. The force Chauvin exerted on the neck appears enough to break one or several neck bones, especially if the person had osteopenia (bone thinning). Fractured neck vertebrae often result in spinal cord damage and paralysis.
Conclusion
George Floyd’s tragic death is a wake-up call for police forces across the country. Knees to the neck to restrain someone must be prohibited. There are too many ways for this to go wrong, given the high concentration of structures critical to maintaining life that reside in the neck. I understand that safety to police officers is important and fully support it, but it must not be accomplished by jeopardizing the safety of the person being restrained.
