In the first part, we examined how the respiratory system is structured fr om the nasal cavity to the alveoli, studied the role of the diaphragm and intercostal muscles, and understood the mechanics of inhalation and exhalation. Now we move to the next level: from mechanics to chemistry and bioenergetics. The functions of the respiratory system are not limited to lung ventilation; they include pH regulation, thermoregulation, and voice production. Breathing is not just the movement of air. It is a highly complex biochemical process that begins in the lungs, continues in the blood, and ends in the mitochondria of every cell. The physiology of respiration encompasses this entire path — from gas exchange to cellular energy exchange. Our well-being, endurance, and even the rate of aging depend on how harmoniously all stages of this process function.
The goal of this article is to show how breathing works at the chemical and cellular levels, and how knowledge of these processes helps make the practice of pranayama conscious and maximally effective.
The respiratory center in the brainstem does not work alone. Its activity is constantly adjusted by signals from chemoreceptors — specialized cells sensitive to the composition of the blood and cerebrospinal fluid.
Key stimulus: CO₂, O₂ and pH
The main regulator of breathing at rest is carbon dioxide. When CO₂ levels rise, the blood becomes more acidic (pH drops), which is immediately detected by central chemoreceptors. Located in the medulla oblongata, in the region of the retrotrapezoid nucleus, they instruct the respiratory center to increase the rate and depth of breaths1. Modern research shows that a unique vascular response in this area enhances chemoreception, preventing the "washing out" of CO₂2.
Peripheral chemoreceptors — the carotid bodies — kick in when oxygen levels drop. They send an alarm signal, forcing faster and deeper breathing, but their contribution under normal conditions is smaller — approximately 20—40%13.
Mechanisms of homeostasis maintenance
The respiratory center continuously processes signals from chemoreceptors and adjusts the work of the respiratory muscles. If CO₂ increases, the center speeds up and deepens breathing — this helps remove excess gas and restore pH. If CO₂ drops (for example, during hyperventilation), breathing automatically slows down to retain the necessary level of carbon dioxide for acid-base balance.
The self-regulation system is designed so that any deviation from the norm instantly triggers mechanisms that bring the parameters back to the proper range—this is the principle of negative feedback
This process operates on the principle of negative feedback: any deviation from the norm triggers a correction that returns values to optimal levels. Central chemoreceptors provide the main portion of regulation (60—80% of the response to hypercapnia — a condition in which the level of carbon dioxide in the blood increases), while peripheral ones complement it, especially during oxygen deficiency1.
Such an automatic loop allows for maintaining a stable blood gas composition and pH across a wide range — from a state of rest to intense exertion. It is this system that makes breathing resilient and reliable.
The brain's sensitivity to CO₂ is a complex, distributed system that connects breathing with blood circulation, sleep, and metabolism. It is precisely this system that you influence when practicing breath retentions (kumbhakas) in pranayama.
An interesting fact: CO₂ acts faster and stronger than O₂. That is why hyperventilation (frequent deep breaths) lowers CO₂ levels and can cause dizziness — this is the brain's reaction to a sudden shift in pH.
To understand how pranayama affects the body, it is important to distinguish between two levels of breathing.
External respiration: gas exchange in the lungs
This is the exchange of gases between the atmosphere and the blood. In the alveoli, oxygen passes through the ultra-thin air-blood barrier and binds to erythrocyte hemoglobin. Simultaneously, carbon dioxide leaves the blood and is eliminated with exhalation.
Deep diaphragmatic breathing increases the contact area of blood with the alveoli, enhancing the efficiency of gas exchange. This is especially important for the lower lobes of the lungs, which are ventilated less effectively during shallow breathing.
Internal (cellular) respiration
This is already the level of the mitochondria. Oxygen delivered by hemoglobin enters the cells, wh ere it participates in the oxidation of nutrients. As a result, ATP is synthesized — the universal fuel for all processes in the body.
Without oxygen, cells switch to an anaerobic pathway: only two ATP molecules are formed from one glucose molecule, instead of 36 during aerobic oxidation, and toxic metabolic products accumulate. Therefore, full tissue oxygenation is the foundation of health and endurance.
Modern biochemistry describes cellular respiration through Peter Mitchell's mitochondrial theory (1961, Nature) of converting nutrients into ATP
The mitochondrial theory of respiration is a modern biochemical concept explaining how cells convert food energy into universal fuel — ATP molecules. Its founder was British biochemist Peter Mitchell, who published his revolutionary article in the journal Nature in 1961.
An interesting fact: Mitchell received the Nobel Prize in Chemistry in 1978 for this theory.
Mitchell's key idea is that ATP synthesis directly depends not on chemical reactions, but on a physical proton gradient — the difference in hydrogen ion concentration across the inner mitochondrial membrane. The process looks like this: the inner membrane contains a respiratory chain of four protein complexes that, like an assembly line, transfer electrons from nutrients to oxygen. The energy released during this process is used to pump protons from the matrix into the intermembrane space. As a result, an electrochemical potential arises — a difference in concentration and electrical charges on both sides of the membrane. Protons tend to return back, and their only pathway is through the enzyme ATP synthase, which uses this flow to synthesize ATP from ADP and phosphate.
How actively mitochondria produce ATP depends on the state of the cell. Chance and Williams (1955—1956) identified five metabolic states of mitochondria4. At rest, tissue is in "State 4" — background respiration when ATP is barely consumed. Under exertion, when the demand for energy grows, the system transitions to "State 3": oxygen consumption and ATP synthesis accelerate sharply. It is this mechanism — respiratory control — that ensures fine-tuning of energy production to the body's current demands.
Understanding this theory helps pranayama practitioners realize that breathing is not just gas exchange in the lungs, but a profound cellular process. Oxygen serves as the ultimate electron acceptor in the respiratory chain — without it, the assembly line stops and ATP synthesis drops. Regular pranayama practice improves tissue oxygenation and can stimulate the formation of new mitochondria (biogenesis), increasing overall endurance. According to a meta-analysis by Gerbarg and Brown (2019), conscious breathing optimizes cellular bioenergetics5. Meanwhile, Lenaz et al. (2006) link mitochondrial efficiency with lifespan.
The Stange test (breath hold on inhalation, norm 40–60 seconds) shows the level of resistance to hypoxia and the efficiency of the respiratory muscles—the higher the reading, the better these parameters
To track progress, several tools are available to pranayama practitioners.
Objective indicators:
- Saturation (SpO₂) — blood oxygen saturation level, normal range 95—98%.
- Heart Rate (HR) — at rest 60—80 bpm. A decrease in resting HR indicates parasympathetic activation.
- Respiratory Rate (RR) — at rest 12—18 breaths per minute.
- Exhaled CO₂ Level (Capnography) — allows evaluating ventilation efficiency and the sensitivity of the respiratory center to carbon dioxide. Normal EtCO₂ range is 35—45 mmHg.
- Spirometry — measurement of vital capacity (VC). Regular practice can increase VC by 10—20%. Benchmarks: 3.5—5.0 L for men, 2.5—4.0 L for women (depending on age and height).
- Peak Flow Metering — exhalation speed, useful for monitoring bronchial patency.
Simple tests for home:
- Stange Test — breath retention after inhalation. Normal value: 40—60 seconds. An increase in this indicator indicates improved tolerance to hypoxia and enhanced efficiency of the respiratory muscles.
- Genchi Test — breath retention after exhalation. Normal value: 20—40 seconds. This is a more sensitive marker of adaptation to hypercapnia, as CO₂ accumulates faster during exhalation, and the result directly depends on the excitation threshold of central chemoreceptors.
The provided values are for reference purposes. For accurate interpretation of results, consultation with a specialist is required, taking individual characteristics into account.
An increase in retention time is an objective criterion of progress. By regularly logging results, you can adjust the load and observe real changes.
Applying knowledge in pranayama practice
An extended exhalation lowers HR and activates the parasympathetic system through vagus nerve stimulation.
Breath retentions (kumbhaka) train chemoreceptors, increasing resistance to hypoxia.
Keeping a practice diary (pulse, saturation, Stange and Genchi tests) helps objectively evaluate progress and avoid overexertion.
Regular pranayama serves as effective prevention against lung diseases by training respiratory muscles and improving ventilation.
Chemical regulation, stages of gas exchange, and mitochondrial function are the three pillars upon which breathing efficiency rests. Understanding these processes elevates pranayama beyond mechanical exercises: you begin to see how every respiratory movement resonates in cells, blood, and the nervous system.
Use this knowledge to practice mindfully, track your progress, and gradually expand your body's capabilities. Proper breathing is not just comfort; it is the foundation of health and longevity.
1. Why does hyperventilation cause dizziness?
Hyperventilation lowers CO₂ levels in the blood, leading to constriction of cerebral blood vessels and temporary hypoxia. This causes dizziness — a protective reaction of the body to a sudden shift in pH.
2. Is it possible to overtrain chemoreceptors?
Yes, regular breath-holds increase their sensitivity and resistance to CO₂. However, a sharp increase in load can cause discomfort, so retention times should be increased gradually.
3. How often should Stange and Genchi tests be performed?
To track progress, 1—2 times a week at the same time of day on an empty stomach is sufficient. Important: do not perform the tests at peak fatigue or immediately after meals.
4. Does pranayama directly affect blood pH?
Yes. Breathing regulates the level of CO₂, which is an acidic oxide. Deepened breathing lowers CO₂ and increases pH (respiratory alkalosis), while retentions, conversely, increase CO₂ and lower pH (respiratory acidosis). Pranayama trains the body's buffer systems.
5. Is there scientific evidence of pranayama's effect on mitochondria?
Yes. A meta-analysis by Gerbarg and Brown (2019) shows that conscious breathing practices improve cellular bioenergetics, while studies by Lenaz (2006) confirm the connection between mitochondrial function and longevity.