Breathing… a universal function of living organisms and yet, we rarely think about it during our day.
From a biological perspective, all living organisms breathe; from cellular respiration to plants and animals, a respiratory cycle is a constant exchange of molecules (input/output), indispensable for energy production in the organism. In animals, oxygen is taken through each inhale and carbon dioxide is eliminated with each exhale. Such a fundamental function as it is, life ceases to exist without respiration. Similarly, poor respiration results in poor functioning of organs that can trigger different chronic pathological states, such as inflammation and indigestion.
Interestingly, breath is also related with the function of the heart and its control through the autonomous nervous system (ANS). As most of our organs, the heart is innervated by both branches of the ANS, the sympathetic (accelarator) and the parasympathetic (brake) systems. On every inhale the heart is governed by the sympathetic branch and thus the heartbeat is accelerated. On every exhale, the vagus nerve, part of the parasympathetic nervous system, is activated and takes over the control of the heart slowing down the heartbeat. This is the normal function of the heart that results in a variable rate of the heartbeat in every respiratory cycle, known as heart rate variability (HRV). We can easily calculate this HRV through an electrocardiogram and use it as an index of the activity of the vagus nerve. HRV can vary according to the context or situation we are into, but at rest each individual has his proper intrinsic level of HRV (= vagus nerve activity), called resting vagus nerve activity. This index is quite robust and does not change within short time unless after a specific intervention. However, HRV decreases gradually with age.
Given the relation of the breath and the vagus nerve, when we consciously increase the length of our exhalation we momentarily activate the vagus nerve. A commonly used breath ratio to induce relaxation is the 1:2 (inhale: exhale), meaning you inhale counting 4 and exhale counting 8. Usually done for 1-5min this type of breath instantly creates a feeling of peace (= vagus nerve is activated). In yogic practices, control of the breathing cycle is one of the main tools that aims at calming the mind and aligning a person to thyself. Numerous breathing techniques exist, called pranayamas, with different control points and manipulations of the autonomous nervous system.