Chronic Stress, Adrenal Fatigue and Hyperbaric Oxygen Therapy

Scientists have explored the human stress response across time, from the era of cavemen to modern society. Interestingly, the brain’s physiological reaction remains identical regardless of the nature of the perceived threat: whether it is being chased by a tiger, grieving the death of a loved one, or grappling with a pile of unpaid bills.

When a person detects a sensory threat—whether through sight, sound, touch, or another sense—the amygdala (a small, almond-shaped structure in the brain) acts as the first responder. It processes the danger and sends a distress signal to the hypothalamus, often described as the brain’s “command center.” The hypothalamus communicates with the rest of the body via the Autonomic Nervous System (ANS), sending signals to major organs to either release or halt the release of specific hormones.

The ANS regulates involuntary bodily functions, such as breathing, heart rate, digestion, and respiration. Under normal circumstances, the ANS maintains a balanced state known as the parasympathetic response. During this state, all bodily functions operate smoothly and calmly—far from the “stress or survival mode.” It is frequently called the “rest and digest” response because the body prioritizes essential restorative functions: resting, digesting food, reproducing, and healing.

When the hypothalamus sends out distress signals, a rapid sequence of events unfolds via the ANS. To prepare the body to face an impending threat, the adrenal glands (located near the kidneys) release a surge of “response hormones,” including cortisol and adrenaline. These hormones trigger the sympathetic response in the ANS—more commonly known as “fight-or-flight” mode.

In the sympathetic response state, the body undergoes targeted changes to prioritize survival: it increases respiration (to take in more oxygen), raises heart rate, and redirects blood flow to the brain and muscles (to enhance focus and physical strength). At the same time, it suppresses “non-essential” functions such as digestion, sleep, healing, immune response, and reproduction. This state allows a person to concentrate fully on surviving the stressful situation—whether that means fleeing a dangerous animal or pushing through a terrifying public speaking engagement.

Once the danger or stressful event ends, the body signals the adrenal glands to stop releasing stress hormones. Instead, the glands release calming hormones (such as acetylcholine) that slow the heart rate and return the body to the parasympathetic “rest and digest” state, allowing it to recover.

Unfortunately, modern society places significant strain on the Autonomic Nervous System. Unlike our ancestors, who faced occasional acute, life-threatening dangers (like tiger attacks), modern humans often contend with constant micro-stressors—small, ongoing pressures that add up over time. In this state of persistent stress, the body can become “stuck” in fight-or-flight mode.

People trapped in this sympathetic dominance include combat veterans and survivors of abuse (well-documented cases), as well as less recognized groups: single parents juggling multiple responsibilities, individuals struggling financially, students under academic pressure, and those in high-stress jobs.

Chronic fight-or-flight mode takes a severe toll on health: it can lead to insomnia, digestive problems, autoimmune diseases, frequent illnesses, slow wound healing, heart disease, and even cancer. When the body prioritizes basic survival functions for too long, other critical processes slow down or stop entirely. Over time, the adrenal glands may struggle to produce the hormones the body needs to function—resulting in a condition called Adrenal Fatigue.

Stress also harms the body at the cellular level. Mitochondria (the “powerhouses” of cells) rely on oxygen to function, but stress can deplete oxygen levels or redirect oxygen to other parts of the body. Without enough oxygen, mitochondria cannot produce sufficient ATP (adenosine triphosphate)—the molecule that provides energy for all cellular processes. This energy deficit leads to widespread cell death, inflammation, and further damage throughout the body.

Fortunately, Hyperbaric Oxygen Therapy (HBOT) has emerged as a promising solution for individuals trapped in sympathetic dominance. Researchers have studied HBOT using heart rate variability (HRV) monitoring—a tool that tracks the balance between the sympathetic and parasympathetic nervous systems. The findings show that HBOT can calm the ANS, prompting the hypothalamus to shift its signals from a sympathetic (fight-or-flight) response to a parasympathetic (rest-and-digest) response. In fact, researchers can observe this shift in real time as patients undergo HBOT.

On a broader scale, HBOT has been studied in patients with Post-Traumatic Stress Disorder (PTSD)—a condition closely linked to chronic sympathetic dominance. Many of these studies confirmed positive outcomes, with some patients even achieving full recovery.

HBOT also addresses the cellular damage caused by stress: by increasing oxygen levels in the body, it provides mitochondria with the “fuel” they need to produce adequate ATP. This energy allows cells to repair or replace damaged tissues. Once the brain no longer perceives a constant threat, the body can initiate healing across all systems—even in areas patients may not expect, such as resolving persistent fatigue, easing muscle or joint pain, and restoring a dysfunctional immune system.