To really understand the powerful interconnections between the breath, heart and brain, we must take a journey along the wandering vagus nerve and through the
Autonomic Nervous System (ANS). This BLOG will cover a lot of ground. If we seem to be heading away from the central issue of breathing, you will soon see how the vagus nerve connects with the breath in powerful life-transforming ways.
The vagus nerve (the 10th cranial nerve or CN X) has multiple branches that diverge from 2 thick stems rooted in the cerebellum or ‘little brain’ (the area at the lower back of the brain and the brain stem).
It can be found behind the artery in your neck where you feel for a pulse.
These branches travel throughout the body, influencing a wide range of functions including heart rate, digestion, and even emotional regulation. Notably, the Vagus nerve acts as a key communication highway between the body and the brain, constantly relaying information and helping to maintain internal balance, known as homeostasis.
Vagus, to wander in Latin, comes from the same root as our vagabond, vagrant and vague. The name gives some clue to just how extensively this nerve travels. During its journey through the body, the nerve supplies nerves to the heart, the respiratory system, and gastrointestinal tract, reaching the lowest viscera of the abdomen.
It is the most wide-ranging cranial nerve in the human body and is responsible for, among other things, many functions of the mouth, including speech, appetite control, and even vomiting. Ultimately, it conducts nerve impulses to every major organ in the body.
The vagus nerve is made up of 80 – 90% afferent (body to brain) nerve fibres. This means that most of the information it conveys travels from the body to the brain.
Instead of orders flowing from the brain, affecting the various physiological systems and organs, the afferent fibres take information back from the body to the brain. The heart, however, is innervated with efferent (brain to body) vagus fibres – a top-down line of communication. The resulting 2 way flow of data provides the building blocks for feedback loops in which information from the brain impacts the physical systems of the body and vice versa.
Many studies have shown the vagus nerves positive potential to influence physical health, mental health and cognition. This nerve can be stimulated to reduce anxiety, alleviate depression, and even inhibit inflammation to fight disease in the body by combating the cortisol-producing stress response we know as ‘fight or flight’.
To understand the vagus nerves importance to the heart-breath-brain connection, we need to start our journey by looking at the 2 sides of the autonomic Nervous System, beginning with the fight or flight response.
THE VAGUS NERVE AND AUTONOMIC BALANCE
The fight or flight response is the body’s instinctive survival mechanism. From simple evolutionary perspective, it allows mammals, including humans to react to situations that may be life threatening. When humans lived in constantly unsafe environments, it was useful for fighting off enemies and hunting for food. While it still has a valuable roll to play in keeping us safe in the modern world, problems arise when we have the same response to things that are probably not fatal. We might be fearful about giving a presentation, turning up for an interview, receiving unexpected bill, or even being blocked on social Media. When fight or flight is in constant overdrive, the result is chronic stress, that all too common modern day malady.
Fight or flight is controlled by the Sympathetic Nervous System (SNS) which is one half of the overall Autonomic Nervous System (ANS). The vagus nerve is the main driver of the other branch of the ANS, the Parasympathetic Nervous System (PNS). While the SNS triggers fight or flight, the vagus led PNS is responsible for rest and digestion, the state in which the body perceives no threat, the mind is relaxed and digestion is active. Crucially, as we will discover, it is through the ANS that the respiratory system, lung ventilation, and blood-gas exchange connects with the working of the heart rate and blood vessels. Ideally, the 2 responses of the ANS fight/flight and rest/digest, work in balance. The primary purpose of the ANS is to regulate the body’s main functions.
The SNS prepares the body for external challenges. It increases metabolic output, stimulates and prepares the muscles, and mobilises existing energy reserves. It also constricts the blood vessels, increasing heart rate and blood pressure. In contrast, the PNS focuses inward, supporting growth, restoration, reproduction, relaxation and conservation of energy. It maintains the balance of heart frequencies; notably it reacts much faster to external and internal changes than the SNS, responding within just 1 second, in contrast to the 5 or more seconds it takes the SNS to kick in.
These 2 opposing forces within the ANS are never static.
This dynamic interplay ensures that the body can swiftly adapt to both challenges and periods of safety. When the parasympathetic system dominates, activities such as lowering the heart rate, stimulating salivation, and enhancing digestive processes occur, promoting repair and maintenance throughout the body. By modulating these responses, the vagus nerve acts as a vital mediator, ensuring that physiological arousal does not remain unchecked, and that the body can return to a state of equilibrium once a perceived threat has passed.
The system continually fluctuates to maintain a stable internal environment that operates within healthy parameters. This constant balancing act to maintain homeostasis is key to keeping organs working properly. For example, if your body temperature is too high, the ANS adjusts to bring it back to the optimal body temperature of 37 degrees Celsius (98.6 Fahrenheit). This is not just a reactive system, that waits passively to meet the next external crisis; it works incessantly to promote stability within the body.
While the 2 branches of the ANS may seem to function in opposition, they often operate in synergy to meet metabolic demands. For example, during exercise, PNS tone decreases while SNS activity increases. There are even unique situations when both the PNS and the SNS are either inhibited or activated. For example, sexual arousal is adult humans is characterised by the excitement of both.
Homeostasis (balance or equilibrium) is a fundamental goal of all biological systems. In humans, it operates at the level of the whole body, within tissues and even individual cells. Where homeostasis can be described as a healthy, dynamic feedback And regulation system, stress can simply as an autonomic state that reflects a disturbance of that balance. Stress is a state where a psychological, environmental, or physical situation, whether a single event or a long term issue, disrupts the body’s ability to self-regulate. Modern life presents us with a world where it can be difficult to maintain that balance. Think about some of the terms used to describe an emotional upset. You’re ‘out of whack’ , you feel ‘all over the place’ or you literally ‘off balance’.
Stress can manifest itself in each of the 3 dimensions of dysfunctional breathing. It can show up biomechanically, as imbalances in the respiratory muscles. This can lead to neck and back pain, upper chest breathing and poor diaphragm control. Biochemically, chronic hyperventilation can impact the body’s delicate Ph balance. Psychologically, anxiety, depression and anger can destroy your equilibrium.
Living in a constant state of fight or flight poses the danger of cortisol overload. Cortisol is the primary stress hormone. When released into the blood stream it enhances the brains use of glucose (blood sugar) and makes substances that repair tissues more available. In essence, it prepares the body to escape from the sabre tooth tiger and not to bleed too much if that doesn’t work out. Aligned with that purpose, cortisol also curbs bodily functions that are not immediately essential to the fight or flight situation. It alters immune system responses and supresses digestive, reproductive, and growth processes. As you might expect, it communicates with the parts of the brain that control mood, motivation and fear.
Ideally the body’s stress response is self-limiting. Hormones go back to normal levels after the perceived threat has passed, and the body returns to homeostasis. However, when stressors are constantly present or stress is chronic (which is like signing up for a long-term fight-or-flight subscription), a cortisol imbalance occurs. Considering how many of the body’s processes cortisol can supress, it is hardly surprising that people who suffer from high levels of stress display a plethora of physical and mental conditions, including anxiety, heart disease, weight gain, digestive problems, depression, headaches, sleep disorders, poor memory and decreased ability to concentrate.
On the other (balancing) side of the ANS, we find the well-studied connection between the vagus nerve and the PNS, the rest and digest side of the ANS. The vagus nerve, which sends impulses to all the major organs and is particularly connected to the heart and respiratory system, secretes a brilliantly useful substance called acetylcholine or ACh.
ACh, the first neurotransmitter ever to be identified was discovered in 1913 by English chemist Arthur Ewins. Later, in 1921, the Nobel Prize winning physiologist Otto Loewi determined its functional significance. Loewi found that activating the vagus nerve reduced heart rate. He did this by isolating the heart of a frog and stimulating the vagus nerve to release something he called ‘Vagusstuff’. This substance, later identified as acetylcholine, caused the frogs heart to slow, replicating relaxation, the reaction to a non-threatening environment – or the rest and digest state. The implications of this are huge. It means that stimulating the vagus nerve can activate the PNS, subduing or balancing out the fight or flight reaction of the SNS.
This ‘Vagusstuff’ (ACh) released by the vagus nerve is a neurotransmitter – a chemical messenger released by nerve cells to send messages to other cells. This neurotransmitter is found in all motor neurons, where it stimulates smooth muscles to contract, slows the heart rate, and dilates the blood vessels. It is also present in many brain neurons where it has a roll in vital mental processes such as cognition and memory. Sever depletion of ACh has been associated with conditions such as Alzheimer’s.
STRESS, INFLAMMATION, AND WELLNESS
From a health perspective, if we define stress as a disruption of homeostasis, inflammation often begins as the body’s natural response to stress.
What’s more, chronic, low grade inflammation has been proven to indicate an overactive fight or flight response. It makes sense therefore to deduce that inhibiting the fight or flight response (as the ACh released by the vagus nerve does) could reduce inflammation.
Inflammation is a defence mechanism triggered by injury or infection. It is at the extreme end of the spectrum that ranges from homeostasis to stress response to inflammatory response. It combines different immune mechanisms that work to neutralise invading pathogens such as bacteria and viruses, repair injured tissues, and heal wounds. However, when out of balance, inflammation plays a key role in the development and persistence of many diseases. It can be triggered by extreme internal imbalances or by external challenges that disturb homeostasis. After a stressor occurs, the inflammatory response kicks in.
While modern life has its benefits such as longer life span, advanced technology, and home delivered groceries, the nature of stress has changed dramatically. When stress is severe and prolonged, it causes the body to compensate, physiologically, and behaviourally, to maintain homeostasis. Long term, this can put an unsustainable load on the body’s systems.
There is increasing evidence that chronic stress increases the risk of both physical and mental health disorders. It can play a critical role in the onset and progression of stress related illness including disease of the heart, digestive system, brain and many forms of cancer. Chronic stressors are known to suppress immune function. In fact, while not yet fully understood, studies show that stress is a common risk factor in 75 – 90% of human diseases.
That’s nearly all of them.
AN EXCERPT FROM THE BREATHING CURE BY PATRICK MCKEOWN
