Understanding the Basics of Breathing from a Neuroscience Perspective
Through this post let’s understand the basics of breathing. This will help the readers with future posts, where we will cover the influence of breathing in Yogasana and Pranayama techniques on high-level functions from a Neuroscience perspective.
In Yogic texts, the mind is considered the master of the body (senses), and the breath is considered the master of the mind. Neuroscience now has evidence of this link between the body, mind, and breath. Now it is known that our breath has influence beyond physical and physiological states. We covered Neuroscience evidence of the influence of the breath over the mind through Pranayama in a previous post.
Breathing influences the higher states and higher functions of the mind – emotions, cognition and consciousness (and also psyche and spirituality, which modern science is yet to acknowledge). The state of the mind influences our breathing and the breathing influences the state of the mind. Similarly, the breathing and state of mind affect our posture, and our postures affect breathing and state of mind. We covered Neuroscience Biofeedback in our post. Hence, through the proper practice of Yogasanas and Pranayama techniques, we can maintain the health of every aspect of our being – physical, physiological, psychological, emotional and consciousness.
There are four muscle groups that are involved in respiration:
1. The diaphragm is a dome-shaped muscle that separates the thoracic cavity and abdominal cavity. It is the primary muscle used in respiration. Its movement up and down changes the volume of the thoracic cavity (or chest cavity), helping the air come in and out of the lungs. During inhalation, the diaphragm contracts and creates space in the chest cavity for the lungs to expand so that the air can flow in.
2. Intercostal muscles run between the ribs and assist the diaphragm by elevating the rib cage to allow more air into your lungs. External intercostal muscles expand the rib cage during inhalation, and internal intercostal muscles pull the ribs closer during exhalation. The movement of the rib cage creates additional volume in the thoracic cavity for the inward flow of air.
3. Abdominal muscles are mainly used to help the diaphragm retract during exhalation. They are voluntarily used in forced exhalations in Abdomino-diaphragmatic breathing and to restrict the diaphragmatic movement in deep thoracic breathing (as discussed below).
4. The muscles around your neck that run from the back of the skull towards the sternum and clavicle (collarbone) assist the intercostal muscles to further expand the chest cavity. These muscles are not used in the normal course but may come to our rescue in situations when breathing becomes impaired (like asthma attack).
Hence the inhalation is driven by the active action of muscular contraction. While the exhalation is a passive activity carried out through elastic recoil of expanded lungs, rising of the diaphragm and pulling of the rib cage by internal intercostal muscles.
Four distinct breathing actions are possible through the use of the above mentioned muscles. Each of these actions has a different influence on the autonomic nervous system:
1. Abdomino-diaphragmatic breathing – The diaphragm is the main actor in this type of breathing while abdominal muscle contraction only helps in deep exhalation. There is no involvement of intercostal and neck muscles. This type of breathing is very relaxing and therapeutic. This is also known as “Deep Diaphragmatic breathing” or “Abdominal breathing” or “Belly breathing”. A pure form of diaphragmatic breathing can be observed in restorative yoga poses like Savasana and Viparita Karani, in which even the abdominal muscles are not active. Here the lower lobes of the lungs are active. It down-regulates the sympathetic nervous system (stress response) and activates the parasympathetic nervous system (relaxation response). You can read a post titled “Yoga stimulates the Vagus Nerve to induce relaxation response – a key to emotional health”.
2. Thoraco-diaphragmatic breathing – This is also known as “Shallow-thoracic breathing”. In this type of breathing, the diaphragm is not pulled down as much as it does in Abdomino-diaphragmatic breathing, but instead, the base of the chest gets lifted and expands sideways because of the expansion of rib cage through the action of external intercostal muscles. It mainly utilizes the lower and middle lobes of the lungs. In most of the active Yoga poses you will breathe like this. This is the most natural way people breathe in daily life.
3. Thoracic breathing – Also called “Chest breathing” or “Deep-thoracic breathing”, this is typically shallow and rapid, and involves mostly the intercostal and neck muscles. The role of the diaphragm is insignificant as it involves contraction of the abdominal muscles (transversus abdominis muscles as shown in the figure) that creates tension in the abdominal wall which prohibits the downward movement of the diaphragm. Hence the expansion of thoracic cavity happens only because of rib cage movement. This type of breathing is accompanied in many Yoga poses – particularly backbends like Dhanurasana, Shalabhasana and Chaturanga Dandasana – and carry certain advantages. But if such breathing is done habitually in daily life, it creates many health problems (that we will cover in future posts). It triggers the sympathetic nervous system.
4. Clavicular breathing – This is an extreme form of breathing, mostly happens as an extension to thoracic breathing, when you engage the neck muscles to draw some more air in the upper lobes of the lungs. Contraction of neck muscles (the sternocleidomastoid and scalenus) and upper back, can help to lift the rib cage up, thereby increasing the depth of inhalation. Such breathing is seen during extreme physical exertion, hyperventilation and in the patients of Asthma. It may trigger an extreme sympathetic response. It has some therapeutic benefits when done is some specific yoga poses like in Kapotasana.
In Yogic breathing, also known as Pranayamic breathing, the lungs are used to their maximum capacity by combining all four breathing actions wherein the whole breathing process is a continuous movement – each phase of breathing prepares the ground for (and merges into) the next without any obvious transition point.
Breathing that involves diaphragm is physiologically the most efficient. There are three primary reasons. First, when upright, a major portion of the blood circulating in the lungs goes to the lower portions because of gravity. When breathing involves diaphragm, expansion occurs in these lower portions and the exchange of air with the blood is efficient. Second, as diaphragmatic breathing is slow and steady, the exchange of oxygen and carbon-dioxide (called oxygenation in inhalation and decarbonization in exhalation respectively) in the blood are efficient because of sufficient time spent in such exchange. And third, because the air flow in diaphragmatic breathing is smooth, slow and deep, more fresh air is inhaled. Hence the ratio of the volume of fresh air received by the lungs vs total inhaled air is more. The difference between these two is called ‘anatomic dead space’, which is the volume of the air passage between the tip of the nose and lungs. We will cover this in-depth in future posts correlating the breath with the nervous system and circulatory system. These are the reasons why Abdomino-diaphragmatic breathing is the most efficient form of breathing followed by Thoraco-diaphragmatic, and then Thoracic/Chest.
Also, it is to be noted that Chest breathing fills the middle and upper portion of the lungs with air. But when you are upright, most of the blood is in the lower portions of the lungs. This means air is not mixed as efficiently with blood if breathing is done by expanding the ribs alone. This type of breathing also requires more work to accomplish the same amount of mixing of blood and air than Diaphragmatic breathing. Because more work is required, more energy (i.e. oxygen) is needed, requiring more frequent breaths. And, more blood is required to be circulated through the lungs, requiring more work (heartbeats) by the heart.
A little deeper understanding of muscular action for breathing. Refer to the figure. If you look at the phases in a complete yogic breath, there are three sets of muscle groups that produce the action. On the upper chest part (clavicular region), there are several muscles attached to clavicles – one group acts to elevate the clavicular area and upper chest, while the other acts in the opposite direction. In the thoracic region, you have external and internal intercostal muscles attached to the rib cage – each group opposing the action of the other to expand and contract the rib cage (referred to as agonist and antagonist pair). But there is no such agonist/antagonist pairing for the diaphragm. That means there is no muscle that is paired with the diaphragm to produce contraction in the opposite direction. But four layers of muscles that crisscross each other in the front and side walls of the abdomen (abdominal muscles) produce some form of the antagonist effect. During inhalation, the diaphragm pushes organs in the abdominal cavity downward and forward. Due to this, the abdomen bulges forward. While exhaling the abdomen contracts and pushed the organs upwards, which in turn help the diaphragm push up. This compresses the lungs to push the air out. As a side effect of diaphragmatic movement, the abdominal organs get a gentle massage that helps circulation to keep the organs healthy. People who are habitual to Chest breathing do not benefit from such a massage.
Normally infants and young children breathe Abdomino-diaphragmatically (1). Adult men have a mix of (1) and (2), while Women breathe a mix of (2) and (3).
We plan to have our future posts focused on how different breathing actions influence different functions – nervous system, cardiovascular function, circulatory system, metabolism, and endocrine activities – and how different Yoga poses and Pranayama techniques incorporate these actions.