Dying is not the only danger of choking
I strongly recommend not to practice choking. This article is part of a series intended to show that choking is unsafe, may cause brain damage, and is potentially lethal.
What happens when the brain lacks oxygen?
To stay conscious and alive, our brain needs a continuous supply of oxygen and glucose from the blood.
Neurons are the most finicky cells of the body. If they don’t get their oxygen, they throw a tantrum and die. Tantrum is quite an appropriate metaphor, because a neuron that is starving for oxygen begins firing a lot of action potentials and releasing its neurotransmitters.
The main excitatory neurotransmitter in the brain is the amino acid glutamate, which is also an abundant metabolite. When a neuron dies, all of its glutamate is released into its surrounding medium, activating glutamate receptors in its nearby neurons. Too much activation of glutamate receptors kills those neurons, too, setting off a chain reaction that produces a wave of cell death spreading through the brain.
This glutamate release is what produces brain damage during a stroke. A stroke happens when a capillary inside the brain is blocked by a blood clot. Neurons that were supplied with oxygen by that capillary die, releasing glutamate and starting this wave of death. So, why doesn’t it end up killing the whole brain? Because there are cells in the brain, the glia, that are in charge of preventing damage by absorbing glutamate and other neurotoxic substances. Still, considerable harm can be done before these cells manage to bring the situation under control.
Once neurons die, the body cannot replace them.
The carotid arteries detect blood pressure
Oxygenated blood is supplied to the brain through the carotid arteries, situated on the sides of the neck, towards the front. Just above the thyroid cartilage, or Adam’s apple, the carotid arteries split into the external carotid, which supplies blood to the face, and the internal carotid, which supplies blood to the brain.
This bifurcation of the carotid artery is very important because it forms the carotid sinus, a swelling of the internal carotid artery. The carotid sinus is one of the two places in the circulatory system where there are baroreceptors. The other place is the aortic arch, situated in the aorta artery just above the heart.
Baroreceptors are sensory neurons is charge of detecting blood pressure. They send this information to the brain so it can adjust the beating of the heart and the dilation of the capillaries. The carotid sinus sends blood pressure information to the brain through the glossopharyngeal nerve, while the aortic arch sends it through the vagus nerve. Both nerves end in the same place: the nucleus of the solitary tract or solitary nucleus, in the medulla oblongata. The solitary nucleus modulates the activity of the sympathetic and parasympathetic systems through the hypothalamus. Among other things, this modulates the heartbeat and the dilation of the capillaries, forming a feedback loop that controls blood pressure.
Problems with the blood choke
In a previous article, I explained that an air choke is blocking the entrance of air into the lungs, while a blood choke is blocking the carotid arteries and the jugular veins to interrupt the blood supply of the brain. The information above is crucial to understand the problems with the blood choke.
In an air choke, a person can survive for several minutes without breathing. The air that remains in the lungs and the oxygen stored in the blood's hemoglobin and the muscles’ myoglobin can supply the organs, including the brain, for some time. Free-divers can hold their breath and remain conscious for several minutes, even while swimming vigorously in cold water (Scott et al., 2021).
Interrupting the oxygen supply to the brain is an entirely different matter. Unconsciousness takes place in 10 to 20 seconds, irreversible neurological damage before one minute, and death soon afterwards. Therefore, a blood choke has to be timed precisely to avoid brain damage and death.
But even if a blood choke is done for a time short enough for survival, there are other problems involved. It compresses or blocks the carotid arteries, which supply blood to the brain, and the jugular veins, which are the exit route of blood from the brain. This decreases blood flow (cerebral ischemia) and therefore the supply of glucose and oxygen (cerebral hypoxia). This represents a big problem for the brain, as shown by the damage caused by stroke. Except that, with a blood choke, we are altering the blood supply to the entire brain and not just a small part of it. Some neurons may be more sensitive to hypoxia than others, resulting in localized trauma that is hard to detect.
Reperfusion injury
Another problem is reperfusion injury, the harm produced when blood suddenly enters a tissue that has been deprived of it. Reperfusion increases the production of reactive oxygen molecules from the sudden increase in oxygen, as well as cytokines and chemokines, which are pro-inflammatory molecules produced by immune cells and microglia (Kalogeris et al., 2012).
All this is extremely damaging to nervous tissue.
The vasovagal response
Yet another problem arises from the fact that the carotid sinus contains the baroreceptors that control blood pressure in the entire body. A blood choke changes the pressure detected by these baroreceptors.
Pressure on the neck above the trachea would be exerted directly on the carotid sinuses, stimulating the baroreceptors. Pressure lower on the neck would decrease the blood reaching the carotid sinus, making it detect a lower blood pressure. The error signal thus produced in the carotid sinus would affect the beating of the heart, usually decreasing it.
A highly controversial issue among pathologists is whether this could stop the heart altogether. This could explain why some deaths by strangulation occurred even though the choke did not last long enough to produce brain damage.
The vasovagal response or reflex syncope “is a brief loss of consciousness due to a neurologically induced drop in blood pressure. Before the person passes out there may be sweating, a decreased ability to see, or ringing in the ears. […] Carotid sinus syncope is due to pressure on the carotid sinus in the neck. The underlying mechanism involves the nervous system slowing the heart rate and dilating blood vessels resulting in low blood pressure and therefore not enough blood flow to the brain.” Wikipedia.
Other problems with the blood choke
Messing with the blood pressure sensing by the baroreceptors in the carotid sinuses also affects the sympathetic and parasympathetic nervous systems, explaining why choking can produce reactions like nausea and vomiting. The whole body is thrown out of balance.
There may be other complications of carotid occlusion, like cholesterol plaques being released from inside the carotids to cause strokes in the brain.
Carotid occlusion is much more dangerous than other forms of asphyxiation. The key fact is that when you hold your breath, or when somebody blocks your breathing, there is a big reservoir of oxygen that your body can use to stay alive. However, your brain cannot store oxygen. When you block the carotids, your brain starts to run out of oxygen right away.
Is there a risk of cumulative brain damage?
Even if it does not cause death, repeated choking to the point of unconsciousness may have cumulative effects, leading to brain damage. Neuronal death may happen without any symptoms because the brain is very good at compensating for loss of function. You don’t know what is going on in your brain when you drive it close to unconsciousness, just because it’s so much fun! Your neurons could be dying while you party.
This is what happened with traumatic brain injury (TBI), which is now called a “silent epidemic” (Alkhaibary et al., 2021). Sports like boxing and football cause repeated concussions that have an additive effect. When TBI finally manifests itself, it is too late to do anything about it. TBI is different from one person to another because different brain regions are affected. It produces sensory hypersensitivity, chronic pain, motor problems, memory loss and cognitive decline.
While TBI and brain anoxia may seem different, they both involve neuronal death, so they may produce similar symptoms.
Recreational choking may lead to another silent epidemic that would remain unknown for many years because the symptoms take a long time to appear and their cause may not be apparent at first.
But, is there any evidence of this? Or is it just speculation and fearmongering? In the next article of this series, I will present evidence that repetitive choking leads to cognitive deficits and psychological problems.
References
Alkhaibary A, Alshalawi A, Althaqafi RMM, Alghuraybi AA, Basalamah A, Shammaa AM, Altalhy AA, Abdelrahman TM (2021) Traumatic Brain Injury: A Perspective on the Silent Epidemic. Cureus 13:e15318.
Kalogeris T, Baines CP, Krenz M, Korthuis RJ (2012) Cell biology of ischemia/reperfusion injury. Int Rev Cell Mol Biol 298:229-317.
Scott T, van Waart H, Vrijdag XCE, Mullins D, Mesley P, Mitchell SJ (2021) Arterial blood gas measurements during deep open-water breath-hold dives. J Appl Physiol (1985) 130:1490-1495.
Copyright 2023 Hermes Solenzol.