The process of dying and what happens to the body and brain in the final moments before death is a fascinating area of science. When death approaches, the body undergoes various changes and processes that ultimately result in the cessation of life. Determining which organ shuts down first during death has been the subject of much research and debate. Some key questions around this topic include: Does the brain shut down before the heart stops beating or vice versa? What actually causes the brain and heart to stop functioning? And what biological changes are occurring in the body as death nears?
The Brain and Circulatory System
To understand which organ fails first in death, it is important to first consider how the brain interacts with the circulatory system. The brain requires a constant supply of oxygen and nutrients to function, which it receives through the blood flow. The heart pumps blood containing oxygen and nutrients through the vasculature system of arteries, capillaries and veins. This transports oxygen and nutrients to organs and tissues, including the brain. Any disruption to this flow of blood will quickly deprive the brain of oxygen.
The brain is extremely sensitive to decreases in oxygen. Significant brain damage can occur within minutes if oxygen supply is cut off. Without oxygen, brain cells rapidly begin dying. The cerebrum region of the brain that controls consciousness and higher order functions is especially vulnerable. Overall, the brain essentially relies on the constant circulation of oxygenated blood delivered by the heart to stay alive.
What Happens in the Body as Death Approaches
As a person is actively dying and death nears, several key processes are taking place in the body:
- Breathing becomes irregular and often slower.
- The heartbeat becomes faint and irregular as cardiac output decreases.
- Blood pressure drops significantly as circulation slows.
- Kidney function declines leading to metabolic waste buildup.
- Brain cells begin dying rapidly due to lack of oxygen.
- Bodily functions like digestion begin to shut down.
- Body temperature may drop.
- The skin may become cool to the touch and turn bluish in color.
Many of these processes stem from the circulatory system starting to fail as death nears. This reduces blood flow and oxygen delivery to vital organs like the brain and heart. But what initiates this circulatory system collapse?
The Heart Stops First
Research indicates that the heart stops beating before the brain shuts down. Doctors have reported observing that in the process of dying, the heartbeat becomes highly irregular and eventually stops before brain activity ceases. There are a few reasons the loss of a heartbeat precedes loss of brain function:
- The heart relies on electrical impulses from the brain to drive its pumping action. As oxygen levels drop, brain cell death occurs and impairs the brain’s ability to regulate the heart.
- Reduced blood circulation due to heart failure further accelerates brain cell death from lack of oxygen.
- The cells that drive heartbeat, located in the sinoatrial node, are highly sensitive to oxygen deprivation which causes them to die rapidly.
Overall, the scientific consensus based on both clinical observations and research is that the heart ceases pumping blood first, before the brain completely shuts down in the dying process. This loss of circulation then quickly causes total brain death.
Detailed Look at How the Brain Shuts Down
Although the heart stops first, the intricate processes occurring in the brain as it loses oxygen and shuts down are fascinating. Here is a more detailed look at what is taking place in the brain as death nears:
- Unconsciousness sets in – As oxygen levels fall, brain cells start dying in area like the cerebral cortex leading to unconsciousness. People are often still breathing and have a heartbeat at this stage.
- Brain stem reflexes are lost – Lower parts of the brain like the brain stem control basic functions like breathing and reflexes. These areas begin dying as blood flow drops, causing breathing to stop and reflexes to be lost.
- Coma occurs – At this stage, all brain function shuts down including the areas controlling consciousness, senses and cognition. This is a deep coma state.
- Brain cells die rapidly – With no oxygen, brain cells die at a massive scale across all regions of the brain. Cell death is so rapid that the brain shrinks visibly.
- Brain stem cells die – Finally, the oxygen starved brain stem dies which control essential involuntary functions like heartbeat and breathing, resulting in complete death.
The precise timing and sequence can vary from person to person, but this represents the general physiological processes the brain goes through before complete cell death. The areas controlling higher order functions like reasoning and personality tend to die first, while basic function centers like the brain stem survive longest as oxygen disappears.
Factors that Influence How Long the Brain Survives
Exactly how long the brain can survive after the heart stops depends on several key factors:
- Cause of cardiac arrest – Trauma or damage to the heart muscle can result in a sudden and complete loss of heart function. For example cardiac arrest from heart attack. Other causes like respiratory arrest lead to a more gradual loss of circulation.
- Preexisting brain damage or disease – Already having brain abnormalities restricts how long the brain can go without oxygen.
- Age – Younger people’s brains tend to withstand oxygen deprivation better than older individuals.
- Body temperature – Colder temperatures help preserve brain cells and extend the time the brain survives.
- Brain oxygen levels before heart stopped – If the brain was already hypoxic before complete cardiac arrest, brain cells die more rapidly.
In optimal conditions such as a healthy young person at cool temperatures, the brain may persist for 5-10 minutes without oxygen after the heart has stopped. But the brain can shut down in as little as 30 seconds in less ideal circumstances. After no blood flow for 10 minutes, the chances of resuscitation drop dramatically as brain damage is almost always severe.
Restarting the Heart May Not Restore Brain Function
If cardiac arrest occurs and the heart stops pumping blood, restarting the heart through CPR, defibrillation or medication is critical. But even with cardiac activity restored, the person may have already experienced extensive brain injury during the time the brain went without oxygen.
The brain is so sensitive that just a few minutes of no blood flow can cause irreversible damage. Patients who achieve return of spontaneous circulation after the heart stops often remain in a coma or vegetative state due to brain damage. The extent of brain function loss depends on factors like how long the brain went without oxygen and the health of the brain prior to cardiac arrest.
In essence, the heart can be restarted while the brain function has been permanently lost. So while initially the heart stops beating before the brain shuts down, if blood flow is restored the heart may continue working while the brain remains permanently damaged or shut off.
Balancing Blood Flow in Brain and Heart
An interesting phenomenon during the dying process is that the body tries to balance declining blood flow and oxygen between the heart and brain. The body uses various mechanisms to maintain circulation and oxygen to the heart and brain for as long as possible when overall circulation is failing:
- Blood vessels in less critical organs constrict to maintain central circulation.
- Certain areas of the heart and brain get preferential blood flow.
- The body extracts more oxygen from the blood as levels drop.
This allows the heart and brain, the two most vital organs for life, to function for a longer duration even as the body is dying and blood flow decreases. However, eventually these compensatory mechanisms fail and both the brain and heart cease receiving adequate oxygen leading to death.
Clinical Death Versus Brain Death
A person is declared clinically dead when their heart and breathing stop. But due to modern resuscitation techniques, clinical death does not always mean the brain is irreversibly damaged. The concept of brain death means the brain has died completely with no chance of recovery even if the heart is restarted.
Criteria for brain death include:
- No response to stimuli
- No cranial nerve reflexes
- No spontaneous breathing
- No brain activity on EEG
All brain function has permanently ceased. So while the heart may be able to be restarted after stopping clinically, brain death means even with cardiac resuscitation the person will never regain brain function. When brain death occurs, the person is declared legally dead even if cardiopulmonary resuscitation is continued.
Conclusion
In summary, the physiological events leading to death involve an intricate interplay between the heart and brain as oxygen supply declines. Current evidence indicates the heart stops pumping blood before the brain completely shuts down. However, the loss of blood circulation then rapidly leads to brain death. Restarting the heart may not be able to bring back brain function if oxygen loss has already caused permanent damage. Balancing declining resources between these two critical organs to maintain life for as long as possible represents the body’s last act of homeostasis before death.
| Organ | Cause of Failure | Effects |
|---|---|---|
| Heart | Loss of electrical impulses from brain, oxygen deprivation killing heart muscle cells | Loss of circulation leads to catastrophic brain cell death |
| Brain | Hypoxia from heart stopping, higher areas controlling consciousness dying first | Loss of reflexes, coma state, complete cell death |
This summarizes the key points around the brain and heart shutting down during the dying process. Understanding these physiological processes sheds light on a highly complex set of events and interactions that ultimately result in the cessation of life functions.