Impending death and your autonomic nervous system

What happens just before you die? Some cancer researchers addressed this question by studying 350 advanced-stage cancer patients who had approximately three days to live. They attempted to identify physical signs that correlated with a person entering the last days/hours/minutes of life (link).

They compiled the following list of 8 signs of impending death (at least for a cancer patient):

1. Inability to close the eyelids
2. Diminished ability to react to visual stimulation
3. Reduced ability to react to sounds and words
4. Facial drooping
5. Non-reactive pupils
6. Hyperextension of the neck (this causes the head to tilt further back when lying down)
7. Vocal cord grunting
8. Bleeding in the upper digestive tract

Taken together these signs indicate a loss of basic reflexes, and point to a dysfunction in the autonomic nervous system (ANS). What is the autonomic nervous system? According to Wikipedia:

"The autonomic nervous system is a control system that acts largely unconsciously and regulates the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response and its role is mediated by two different components. Within the brain, the autonomic nervous system is regulated by the hypothalamus. Autonomic functions include control of respiration, cardiac regulation (the cardiac control center), vasomotor activity (the vasomotor center), and certain reflex actions such as coughing, sneezing, swallowing and vomiting. Those are then subdivided into other areas and are also linked to ANS subsystems and nervous systems external to the brain. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving ANS regulatory input from the limbic system to do so."

The key fact of the ANS is that it is part of the peripheral nervous system, which consists of the nerves and ganglia outside of the Central Nervous System (CNS) i.e. outside of the brain and spinal cord. Ganglia are collections of motor neurons situated in the head, neck, thorax, abdomen, and pelvis. Certain parts of the brain like the hypothalamus and brain stem help to regulate the functioning of the ANS.

Thus, the autonomic nervous system (ANS) is responsible for unconscious, involuntary actions and responses that largely operate in the background to keep us alive (e.g. heartbeat). By contrast, the somatic nervous system is associated with conscious, voluntary movements and actions i.e. "is the part of the peripheral nervous system associated with skeletal muscle voluntary control of body movements" (Wikipedia, e.g. lifting your hand). Together the autonomic and somatic nervous systems encompass the neural pathways (both voluntary and involuntary) by which the brain communicates with the body.

As the above study shows, signs your autonomic nervous system is failing make a good predictor of impending death. Although none of the 8 signs are lethal in themselves, they indicate the imminent dysfunction of more essential functions like regulation of heart rate, breathing, blood pressure, etc. In other words, the control of fundamental bodily processes is starting to breakdown.

The autonomic nervous system is often under-appreciated because it is not under conscious control; however, one should never take involuntary but essential physiologic function for granted.

Figure 1. The breakdown of your autonomic nervous system portends impending death. (Photo : Getty Images / Andrew Burton)