How the Lung-Brain connection works
Step 1.
Stress is perceived through our brain after one or more of our sensory systems (e.g., our eyesight) is triggered.
Step 2.
The excitation of our brain engages our Autonomic Nervous System (ANS). ANS is divided into two parts, the Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). SNS causes us to go into “fight-or-flight” mode by engaging all the mechanisms required for movement, preservation, and fast reaction. PNS, on the other hand, causes feelings of relaxation and enables us to recover, digest, and heal. Experiencing psychological stress will almost immediately engage SNS and partially deactivate PNS.
Step 3.
Our brain is connected to our lungs and other critical organs through the vagus nerve, a principal conduit responsible for many of the psychosomatic processes in our body or the interaction between emotions and physical symptoms. The vagus nerve helps form the brain-lung axis. Specifically, SNS is connected to the upper part, whereas PNS is connected to the lower lungs. Due to the anatomy of the connection among lungs, SNS, and PNS, when psychological stress occurs, thus engaging SNS and partially deactivating PNS, we breath faster and shallower. On the contrary, when we deliberately breathe deeper and slower, we can activate PNS thanks to its connection to the lower part of our lungs and thus enable feelings of relaxation.
Step 4.
Due to the rise in breathing rate, the amount of air exhaled increases along with the amount of carbon dioxide (CO2) expelled through the body. As more CO2 leaves the body, CO2 circulating in the blood declines, causing a cascade of adverse effects as it is responsible for two critical biological functions. First, CO2 enables oxygen molecules to detach from hemoglobin (the substance in our blood responsible for transporting oxygen from our lungs across the body) and enter the cells that need them in order to produce energy. Second, CO2 regulates how narrow or wide our arteries are and the amount of blood delivered across the body. As a result, a reduction of CO2 levels in the blood will cause a tighter connection between oxygen molecules and hemoglobin, making it harder for oxygen to enter cells and narrowing the arteries, diminishing blood delivery to the brain and across the body.
Step 5.
Our brain understands the critical nature of CO2 for our physiology and will try to compensate for its changes. To achieve this, our brain is equipped with a sensory system that detects variations in CO2 concentrations and sends signals to our lungs to change the breathing rate accordingly.
Step 6.
When stress becomes constant, steps 1-5 become almost permanent, thus causing breathing to be faster and CO2 levels to be lower constantly. After years of exposure to this state, our brain’s CO2 sensory system becomes accustomed to lower blood CO2 levels and faster breathing, a condition also known as Chronic Hyperventilation Syndrome (CHS). As described above, lower blood CO2 levels reduce oxygen delivery to every cell and the brain. Insufficient brain oxygenation reduces cognitive capacity and mental clarity and increases the likelihood of mental disorders.
Step 7.
A constant state of rapid and shallow breathing (i.e., chest breathing) will engage SNS, the “fight-or-flight” part of our nervous system because SNS is connected to the upper part of our lungs.
The infographic below provides a visual representation of these steps.
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