The real purpose of breathing goes far beyond oxygen.
Ask most people why we breathe, and they’ll say: to get oxygen. That’s only half the story. Oxygen is abundant; we’re rarely short on it.
To test this for yourself, hold your breath as long as you can while wearing a pulse oximeter. It’s surprisingly hard to decrease your oxygen saturation.
The real reason we breathe is to regulate the chemistry and circulation of the body — maintaining balance between dissolved gases, pressure, and pH. Each breath acts as a calibration cycle, fine-tuning blood chemistry, circulating fluid, and modulating the nervous system thousands of times a day.
At rest, the body uses surprisingly little oxygen. Each minute, an average adult consumes roughly 250 milliliters of O₂ while moving six to nine liters of air through the lungs (West, 2017). Arterial blood leaves the lungs nearly saturated — about 97–99% full of oxygen.
Even if you hold your breath for a full minute, oxygen levels barely change (Nunn & Hill, 1960). What does change quickly is carbon dioxide (CO₂). The urge to inhale again isn’t triggered by falling oxygen, but by rising CO₂.
CO₂ is the main determinant of blood acidity. When it dissolves in plasma, it forms carbonic acid, lowering pH (very slightly). The brainstem’s chemoreceptors are highly sensitive to this shift. A slight increase in acidity sends the signal: breathe now.
We breathe not to take in oxygen, but to release carbon dioxide at precisely the right pace.
“Take a deep breath” is often suggested as a way to relax. Physiologically, though, depth matters less than pace.
When breathing is too fast or forceful — a common pattern under stress — it drives off CO₂ faster than the body produces it. Blood pH rises slightly (a state called respiratory alkalosis) and vessels constrict. Ironically, less oxygen reaches tissues, even though you’re breathing more (Gardner, 1996).
This is the paradox of over-breathing: more air, less oxygen delivery.
Efficient respiration isn’t about filling the lungs; it’s about maintaining equilibrium — keeping CO₂ within its narrow optimal range (around 35–45 mmHg in arterial blood). That balance ensures hemoglobin releases oxygen where it’s needed most.
We often think of the diaphragm as a passive muscle that moves air. In reality, it’s a powerful hydraulic pump influencing nearly every system below the neck.
Each inhale draws the diaphragm downward, creating negative pressure in the thoracic cavity that pulls blood into the heart and lungs. Exhalation reverses the gradient, pushing blood upward through the veins and toward the brain.
These diaphragmatic oscillations form a secondary circulation system that supports the heart in moving blood throughout the body. Research by Stephen Elliott and others has shown that rhythmic breathing at specific frequencies can synchronize with these pressure waves, improving venous return and even cerebral blood flow (Elliott & Edmonson, 2019).
A striking demonstration came from Elliott’s observation of a sedated giraffe: with each breath, blood flow to the brain rose and fell in time with respiration, not heartbeat. When the giraffe paused its breath, circulation slowed dramatically. It was the breath, not the heart, that kept blood moving to the brain.
Humans are no different, just on a smaller scale — and with the added advantage that we can consciously influence the pump itself.
Breathing is one of the few autonomic functions we can consciously control. That bridge is what makes it so powerful.
Each breath influences the vagus nerve, which carries information between the brainstem and the organs. Slow breathing enhances the body’s natural respiratory sinus arrhythmia (RSA), activating vagal pathways that lower heart rate and promote parasympathetic calm (Porges, 2007).
At the same time, baroreceptors in the arteries detect pressure changes created by each breath. These signals feed back to the brainstem, fine-tuning cardiovascular rhythm (Benarroch, 1993). Over time, deliberate slow breathing strengthens these reflexes, improving the stability of both heart rate and blood pressure.
The breath responds to the nervous system — but, practiced deliberately, it can also retrain it.
When the rhythm of breathing aligns with the natural oscillations of the cardiovascular system — typically around 0.1 Hz, or one breath cycle every 10 seconds — the body enters what physiologists call resonance (Lehrer et al., 2000).
In this state, heart rate, blood pressure, and respiration move together in a smooth sinusoidal pattern. This synchrony optimizes gas exchange, circulation, and autonomic balance. It’s the physiological signature of calm — the body’s version of coherence.
You can think of it as tuning a mechanical system: when the components move in phase, efficiency amplifies.
Breathing is the only lever that simultaneously influences every major control system — cardiovascular, neurological, and emotional. It’s both mechanical and perceptual, bridging physiology and awareness.
Each breath sends information to the brain about the state of the body. Fast and shallow signals activation, while slow, steady breathing signals safety and recovery.
That’s why practices like resonance breathing, or even a single controlled exhale, can change how we feel in seconds. The signal travels upward through the vagus nerve and downward through the body, recalibrating the entire system.
The body naturally regulates its breathing rhythm to maintain homeostasis, but we can also guide it consciously to support emotional and physiological stability.
Oxygen is the headline, but CO₂, pH, pressure, and rhythm are the story beneath it — the mechanics that shape how we function and feel.
Each time you manipulate your breath, it’s a small act of regulation — a way to engage the same systems evolution designed to keep us balanced in the first place.
Benarroch, E.E. (1993). The central autonomic network: Functional organization, dysfunction, and perspective. Mayo Clinic Proceedings.
Elliott, S. & Edmonson, S. (2019). The New Science of Breath: Exploring the Diaphragm’s Role in Circulation and Emotion. Coherence Press.
Gardner, W.N. (1996). The pathophysiology of hyperventilation disorders. Chest.
Lehrer, P.M., Vaschillo, E., & Vaschillo, B. (2000). Resonant frequency biofeedback training to increase cardiac variability. Applied Psychophysiology and Biofeedback.
Nunn, J.F. & Hill, D.W. (1960). Respiratory physiology and breath-holding. Journal of Applied Physiology.
Porges, S.W. (2007). The polyvagal perspective. Biological Psychology.
West, J.B. (2017). Respiratory Physiology: The Essentials. 10th ed.
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