The Respiratory System and Yoga

Breathing is the one physiological function that operates both automatically and voluntarily. The heart beats without conscious direction, digestion proceeds without awareness, but breathing — though it continues during sleep — can be consciously controlled in ways that no other autonomic function can. This is the doorway that pranayama enters through: by taking voluntary control of the breath, the yogi gains indirect access to the autonomic nervous system and ultimately to states of consciousness that are otherwise inaccessible.

The Mechanics of Breathing

Inhalation is an active process. The primary muscle of inhalation is the diaphragm — a large dome-shaped muscle that spans the base of the rib cage. When the diaphragm contracts, it flattens and descends, increasing the volume of the thoracic cavity. By Boyle’s Law (pressure and volume are inversely proportional in a fixed container), increasing volume decreases pressure, and air flows in from outside to equalise.

Exhalation at rest is largely passive. When the diaphragm relaxes, it returns to its dome shape, reducing thoracic volume and increasing pressure, which pushes air out. Forced exhalation uses the abdominal muscles (particularly the transverse abdominis and internal obliques) and the internal intercostal muscles to actively reduce thoracic volume beyond the resting level.

The Diaphragm in Yoga

Most people breathe with approximately 20–30% of their diaphragm’s capacity. The habit of thoracic breathing — using primarily the chest muscles rather than the diaphragm — is extremely common in people who spend long hours sitting under stress. This pattern keeps the body in a mild state of sympathetic activation because shallow chest breathing is associated with the stress response.

Teaching full diaphragmatic breathing is therefore one of the most beneficial things a yoga teacher can offer. When the diaphragm descends fully on inhalation, the belly rises. This movement — often described as “belly breathing” — is the first foundational pranayama practice taught at Medhya Laya. Most students arrive having never breathed this way consciously.

The Three-Part Breath (Dirga Pranayama)

The classical three-part breath teaches students to fill the lungs in three successive stages: lower (belly/diaphragm), middle (mid-chest/ribcage expansion), and upper (clavicle/upper chest). This ensures full use of lung capacity and systematically releases tension from all three sections of the respiratory musculature. The exhalation reverses the order: upper, middle, lower. At Medhya Laya, this is the first formal pranayama taught in every program.

Lung Volumes and Pranayama

The total lung capacity of an average adult male is approximately 6 litres. Of this, approximately 2.5 litres is the resting tidal volume (the air moved in and out in normal breathing). The remaining capacity — expiratory reserve volume and inspiratory reserve volume — is accessed through deep pranayama. Kapalabhati, by producing complete exhalation with each stroke, systematically exercises the expiratory reserve volume. Kumbhaka (breath retention after full inhalation) works with the inspiratory capacity. Over time, pranayama practice measurably increases both tidal volume and the practitioner’s comfort with breath holding.

The Vagus Nerve and Slow Breathing

The vagus nerve is the primary nerve of the parasympathetic nervous system, and it passes through the diaphragm. Research has established that slow, deep diaphragmatic breathing — particularly with extended exhalation — stimulates the vagus nerve and activates the parasympathetic (rest-and-digest) response. Heart rate slows, blood pressure decreases, cortisol levels drop, and the digestive system activates. This is the physiological basis for the well-documented calming effects of pranayama. At Medhya Laya, teaching the anatomy and physiology of the vagus nerve response gives students a clear scientific understanding of why pranayama works.

Oxygen and Carbon Dioxide

A common misunderstanding is that the urge to breathe is driven by low oxygen levels. It is actually driven primarily by rising carbon dioxide levels in the blood. Carbon dioxide, when dissolved in blood plasma, forms carbonic acid, which lowers blood pH. The chemoreceptors in the brain stem respond to this pH drop by triggering the breathing reflex. Understanding this explains why hyperventilation — breathing very rapidly — reduces carbon dioxide and suppresses the breathing reflex, creating the temporary breath suspension sometimes experienced. It also explains why Kumbhaka becomes easier when the practitioner learns to remain relaxed and metabolically calm, producing less carbon dioxide per unit time.