Crisis Stress: Part 2 – Acute Stress Response (ASR)
In the second installment of this four-part essay series I want to briefly overview some of the typical human physiological reactions to crisis situations including the Acute Stress Response (ASR).
Crises are stressful events. Humans respond to crises with several physiological changes including the Acute Stress Response (ASR) which normally enables us to focus on one singular task (perceptual narrowing or “tunnel vision”), be attentive in order to concentrate on that core task (to the lack of focus on other tasks or stimuli) and physically excel (that is the fighting or fleeing aspect of the ancient “fight or flight” response). The heightened focus and perceptual narrowing can be advantageous for some circumstances. However, beyond certain optimal threshold levels, too much or too prolonged stress of emergency contexts can crate dysfunctional physical and mental impacts.
Acute Stress Response (ASR)
The ASR crisis stress physical response begins in the human brain. When someone perceives and recognizes a danger, threat, crisis or emergency, this sensory threat-fear information is first transmitted to the amygdala, an area of the brain that contributes to emotional processing. The amygdala interprets the images and sounds. When it perceives danger, it instantly sends a distress signal to the hypothalamus.
The hypothalamus is a bit like a crisis command center within each of us. According to the Health Harvard summary of the physical response to crisis, this area of the brain communicates with the rest of the body through the autonomic nervous system, which controls such involuntary body functions as breathing, blood pressure, heartbeat, and the dilation or constriction of key blood vessels and small airways in the lungs called bronchioles. The autonomic nervous system has two components, the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system triggers the involuntary “fight-or-flight” response, providing the body with a burst of energy so that it can respond to perceived dangers. The parasympathetic nervous system acts as a counter measure. It promotes the “rest and digest” response that calms the body down after the danger has passed.
After the amygdala sends a distress signal, the hypothalamus activates the sympathetic nervous system by sending signals through the autonomic nerves to the adrenal glands. These glands respond by pumping the hormone epinephrine (adrenaline) into the bloodstream. As adrenaline circulates through the body, it brings on several changes. The heart beats faster than normal, pushing blood to the muscles, heart, and other vital organs. Pulse rate and blood pressure go up. The person undergoing these changes also starts to breathe more rapidly. Small airways in the lungs open wide. This way, the lungs can take in as much oxygen as possible with each breath. Extra oxygen is sent to the brain, increasing short term alertness. Sight, hearing, and other senses become sharper but more narrowly focused. Meanwhile, adrenaline triggers the release of blood sugar (glucose) and fats from temporary storage sites in the body. These nutrients flood into the bloodstream, supplying energy to all parts of the body which are then quickly consumed (if one stays at these heightened alert levels for long the issue of fatigue is a significant factor).
All these involuntary physical changes happen so fast that people are not aware of them. In fact, the evolved physiological process is so efficient that the amygdala and hypothalamus appear to start this cascade even before the brain’s visual centers have had a chance to fully process what is happening. Humans can physiologically respond to crisis events even before they fully understand what exactly is happening. Like a hiker on a trail who “sees” a “snake” (but perhaps only a branch or vine that looks “snake-ish”) whose brain instantly goes into ASR mode and subsequently their body with elevated heart rate, hormone fueled rush jumps back before they even are able to process what it was that they saw in the corner of their eye that made them jump.
According to the Health Harvard summary of the ASR process, as the initial surge of adrenaline subsides, the hypothalamus activates the second component of the stress response system — known as the HPA axis.
This network consists of the hypothalamus, the pituitary gland, and the adrenal glands. The HPA axis relies on a series of hormonal signals to keep the sympathetic nervous system hyperactive. If the brain continues to perceive something as dangerous or threatening, the hypothalamus releases corticotropin-releasing hormone (CRH), which travels to the pituitary gland, triggering the release of adrenocorticotropic hormone (ACTH). This hormone travels to the adrenal glands, prompting them to release cortisol. The body, flooded with these hormones, thus stays revved up and on high alert for an extended period. When the threat passes, cortisol levels fall. The parasympathetic nervous system then dampens the stress response which should calm the body.
Negative Physical Effects of Crisis Stress
In summary, there are involuntary physical effects of crisis stress on our bodies. Typically, there is a flood of hormones released (for example adrenaline, nonadrenaline and cortisol), accompanied by an elevated heart/pulse rate, elevated blood pressure, increased muscle tension, and faster and shallower breathing. At one point in human history, these automatic reactions served us quite well. In many contemporary circumstances, given the complexities of tasks and managing situations in a modern environment, these can be dysfunctional obstacles to performing necessary and critical behaviors. The hormones released provide prompt readiness for unusual physical demands and the energy needed for ancient and fundamental dangers and risks. These appear to help prepare the body for the “fight or flight” in response to the threatening danger. In addition, nervous system response also goes into response mode (which can also do the work of adrenaline / non-adrenaline hormones) and excite the adrenal medulla which in turn sends messages to the heart, lungs, and other vital organs to boost their functions.
While these physical changes can be beneficial (in the short term) we know that there are serious health and well-being implications of these physical responses to both acute and chronic stress. Many people are unable to find a way to destress during or even after a crisis. Chronic (even low-level) stress may keep the HPA axis activated on a prolonged basis. This influences the body in ways that contributes to the health problems associated with chronic stress. Further persistent epinephrine surges or sustained high levels can damage blood vessels and arteries, increase blood pressure, and raise the risk of heart attacks or strokes. Elevated cortisol levels create physiological changes that help to replenish the body’s energy stores that are depleted during the stress response can likewise cause harm at high or prolonged levels. In such cases they may inadvertently contribute to the buildup of fat tissue and perhaps even to weight gain. (*For example, cortisol increases appetite, so that people will want to eat more to obtain extra energy. It also increases storage of unused nutrients as fat.) Sustained, prolonged or high levels of ASR may be very unhealthy and perhaps dangerous.
Although not everyone reacts to specific stressors in the same way, nor to the same degree, and not at the precise same trigger levels, the most common progression of effects of stress are usually similar in most people. In part 3 of this essay series I will cover some of the psychological and cognitive reactions to crises.
About the author: Dr. Robert C. Chandler
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