What Is Breath Retention and How Does It Affect the Body?

Breath retention is the voluntary act of holding your breath, pausing the normal cycle of inhaling and exhaling for a period that can range from a few seconds to several minutes. The moment you stop breathing, your body launches a rapid chain of physiological responses: oxygen levels in the blood begin dropping, carbon dioxide starts climbing, heart rate and blood pressure shift, blood flow to the brain increases, and the spleen contracts to squeeze extra red blood cells into circulation. These responses are not random panic signals but coordinated survival mechanisms, some of which have drawn serious research interest for their potential health applications.

What Happens to Blood Gases Within Seconds

The most immediate effect of holding your breath is a shift in the gases dissolved in your blood. In a study measuring arterial blood during breath-holds that started at normal lung volume while breathing room air, oxygen pressure in the blood dropped by an average of 50 mm Hg in just the first 35 seconds. Over the same period, carbon dioxide pressure rose by about 10 mm Hg and blood pH fell by 0.07, making the blood measurably more acidic.¹ That oxygen drop is steeper than many clinicians previously assumed, and it matters in any medical scenario where breathing is briefly interrupted.

These gas shifts are not just numbers on a monitor. They are the triggers for almost everything else that follows. Chemoreceptors in the brain and in the arteries near the heart detect the rising carbon dioxide and falling oxygen and begin firing signals that eventually produce the urge to breathe. But before you reach that breaking point, a whole cascade of cardiovascular, neurological, and hormonal changes is already underway.

The Cardiovascular Cascade

When you hold your breath, your cardiovascular system does not simply idle. Blood pressure climbs progressively. In one study of deep inspiratory breath-holds, average systolic blood pressure rose from about 133 mm Hg at the start to 175 mm Hg at the breaking point, and in two subjects it hit 200 mm Hg.² That pressure spike was not driven by how long the breath-hold lasted, and pre-oxygenating subjects beforehand did not prevent it.

If the breath-hold is combined with cold water exposure on the face or actual immersion, the response intensifies into what researchers call the diving reflex. Heart rate drops, sometimes dramatically. Blood vessels in the limbs constrict, shunting blood toward the core and brain. Mean blood pressure climbs even further during simulated diving than during breath-holding alone.³ At the same time, the compliance of central arteries increases to help buffer the stronger cardiac pulsations, a protective mechanism that cushions the heart and large vessels against the pressure surge.

How strongly your heart rate drops during this reflex depends heavily on your baseline autonomic nervous system activity. Research using heart rate variability measurements at rest found that people with stronger parasympathetic (vagal) tone at baseline showed greater heart-rate reductions during simulated diving.⁴ In practical terms, the diving reflex is not one-size-fits-all. Your resting nervous system state shapes how your body responds.

How the Spleen Gets Involved

One of the more surprising responses to breath retention involves the spleen, a fist-sized organ tucked behind the stomach. The human spleen stores a reservoir of red blood cells in concentrated, viscous blood. During breath-holding, the spleen contracts and squeezes those cells into the general circulation, raising hemoglobin concentration and effectively increasing the blood’s oxygen-carrying capacity on short notice.

The degree of contraction scales with the intensity and type of breath-hold. Simple breath-holding for 30 seconds produces roughly a 10% reduction in spleen volume, while simulated breath-hold diving or maximal-duration holds can shrink it by 30 to 40%.⁵ This contraction bumps up hemoglobin concentration modestly but measurably, on the order of 0.1 to 0.3 mmol/l during the strongest interventions.

Importantly, it is the act of stopping breathing itself, not just the resulting low oxygen or high carbon dioxide, that drives much of this response. When researchers compared breath-holding to a rebreathing task that produced similar blood-gas changes without actually pausing respiration, the spleen shrank about 21% after breath-holding but only about 12% after rebreathing, and hemoglobin rose about 2.4% with breath-holding versus no significant change with rebreathing.⁶ Respiratory arrest itself acts as a distinct trigger.

Trained breath-hold divers show a more exaggerated version of this effect. In one comparison, trained divers saw their red blood cell volume rise by about 5% and white blood cell counts by about 15% after repeated breath-holds, while untrained subjects with intact spleens showed smaller increases. People who had their spleens removed showed no red blood cell volume change at all, confirming the spleen as the source.⁷

What Happens in the Brain

As carbon dioxide builds up in the blood during a breath-hold, cerebral blood vessels dilate. The result is a substantial increase in blood flow to the brain. Using flow-sensitive MRI, researchers found that breath-holding produced a regional cerebral blood flow increase of roughly 47% to 87% in gray matter.⁸ White matter saw little change. In elite breath-hold divers pushing maximal durations, blood flow through the internal carotid artery roughly doubled from baseline to the end of the hold.⁹

This surge in blood flow is the brain’s built-in safety valve. As oxygen in the blood falls, increased flow compensates by delivering more total oxygen per minute. It is also why breath-holding has become a standard tool in brain-imaging research: even a three-second pause in breathing can generate detectable changes in brain blood-oxygenation signals on an MRI scanner.¹⁰

Beyond blood flow, holding your breath lights up a specific network of brain regions. Functional MRI work has identified activity in the insula, basal ganglia, frontal cortex, parietal cortex, thalamus, and pons during voluntary breath-holds.¹¹ Many of these regions overlap with networks involved in impulse control and response inhibition. The pons, a structure in the brainstem, appears to integrate signals from higher brain areas and then suppress the automatic respiratory neurons that would otherwise force you to inhale.

Why You Eventually Have to Breathe

No matter how determined you are, your body will eventually override your will and force you to take a breath. This moment, called the breaking point, is governed by a surprisingly complex mix of factors. Rising carbon dioxide is the dominant chemical driver, but falling oxygen contributes too. Peripheral chemoreceptors in the neck and central chemoreceptors in the brainstem both detect these shifts and ramp up the drive to breathe.¹²

But the breaking point is not purely chemical. Lung stretch receptors, psychological factors, and prior practice all play a role.¹³ Taking a larger breath before holding extends the time because the lungs are more stretched, which sends inhibitory signals that suppress the breathing urge. People with training can learn to tolerate higher levels of carbon dioxide and the discomfort of involuntary diaphragm contractions, pushing their breaking point further without any change in their underlying blood chemistry. This is why elite breath-hold divers can hold for over five minutes while most untrained people give up well before two.

Hormonal and Cellular Responses

Repeated breath-holds stimulate the production of erythropoietin, or EPO, the hormone that tells the bone marrow to produce more red blood cells. After a series of breath-holds, circulating EPO rose by an average of 24% compared to baseline, an effect that was confirmed by the absence of any EPO change on a control day without breath-holding.¹⁴

The magnitude of this EPO response depends on training status and the type of breath-hold performed. In a study comparing elite breath-hold divers to non-divers, EPO rose by about 60% within 30 minutes of a dynamic (swimming) breath-hold protocol in the elite group, but showed no significant change in non-divers performing the same protocol.¹⁵ The EPO spike correlated with how low blood oxygen saturation dropped, suggesting the deeper the oxygen dip, the stronger the hormonal signal. This is a training adaptation: experienced divers tolerate lower oxygen levels, which in turn triggers a larger EPO release.

Metabolically, breath-holding during intense exercise also leads to higher lactate accumulation compared to normal breathing.¹⁶ And in elite divers performing maximal-duration pool breath-holds, where oxygen saturation can plummet to around 58%, blood glucose actually tended to rise slightly rather than fall, suggesting the body mobilizes stored sugar to feed the brain during extreme oxygen deprivation.¹⁷

Breath Retention in Yoga and Modern Breathwork

Breath retention is not a modern discovery. In yogic practice, it has been formalized for centuries under the name kumbhaka. The two main forms are holding after a full inhale (antar-kumbhaka) and holding after a full exhale (bahir-kumbhaka), and they produce meaningfully different physiological states. Holding after an inhale tends to raise carbon dioxide and dilate blood vessels, increasing cerebral blood flow. Holding after an exhale shifts autonomic balance more toward the parasympathetic (calming) side.¹⁸

A pilot study on bahir-kumbhaka (external breath retention) found that systolic blood pressure and the heart’s rate-pressure product rose during the practice but returned to normal afterward, while diastolic and mean arterial pressure remained somewhat elevated even after the session ended.¹⁹ This lingering elevation is something people with high blood pressure should be aware of.

Yoga breathing with intermittent breath retention has also been linked to improved response inhibition, the ability to stop yourself from acting on an impulse. The researchers speculated this might work through activation of the same cortical and subcortical brain areas engaged during voluntary breath-holding, combined with enhanced vagal tone from the slow-breathing portions of the practice.²⁰

More recently, protocols that pair cyclic hyperventilation with breath retention, such as the Wim Hof Method, have drawn attention for their effects on the immune system. In a controlled trial, subjects trained in this method showed sharply increased epinephrine levels during practice, which in turn boosted levels of the anti-inflammatory cytokine IL-10 and reduced levels of several pro-inflammatory markers after injection with a bacterial endotoxin. They also reported fewer flu-like symptoms.²¹ A systematic review concluded that the method may reduce inflammation in both healthy and non-healthy participants through this epinephrine-driven pathway.²²

Structured breathing practices more broadly, including those involving breath retention, have been shown to improve markers of oxidative stress. A systematic review and meta-analysis found that breathing exercises increased the activity of protective antioxidant enzymes while decreasing a marker of oxidative damage.²³ A separate trial comparing daily breathwork to mindfulness meditation found that both reduced anxiety and negative mood over 28 days while increasing positive mood.²⁴

Long-Term Adaptations in Trained Breath-Hold Divers

People who practice breath-holding regularly develop measurable physiological changes over time. Trained breath-hold divers exhibit a more pronounced diving reflex than non-divers, and elite divers show adaptations in both their blood composition and skeletal muscle that appear to be driven primarily by training rather than genetic selection.²⁵ These divers can tolerate cerebrovascular and neurological strains that would cause blackout or injury in untrained individuals.

The adaptive picture is consistent across reviews: training enhances the bradycardia response, sharpens splenic contraction, and improves the efficiency of oxygen management, prioritizing delivery to the brain and heart through peripheral vasoconstriction and blood centralization.²⁶ However, real uncertainty remains about the long-term health consequences. Repeated exposure to extreme hypoxia and the associated pressure swings may carry risks to the lungs, brain, and cardiovascular system that are not yet fully understood.²⁷

The Risks of Pushing Too Far

The cardiovascular and neurological demands of breath retention are not trivial, particularly at longer durations or combined with water immersion. In a study of 16 breath-hold divers performing maximal static holds while immersed, cardiac arrhythmias appeared in 77% of subjects. These included premature heartbeats from multiple sites in the heart and conduction abnormalities, and their frequency increased with breath-hold duration and declining oxygen saturation.²⁸ These were elite, experienced divers, not novices pushing beyond their limits carelessly.

Diving medicine reviews emphasize that even seemingly shallow breath-hold dives place considerable stress on the cardiovascular system, ears, and lungs, and that unexpected events, reduced functional reserve, or pre-existing conditions raise the risk of an accident.²⁹ The most feared acute risk is hypoxic blackout, where oxygen drops so low the brain loses consciousness, which in water can lead to drowning in seconds. Deep dives add risks including lung compression injuries, pulmonary edema, and decompression problems.

For people practicing breath retention on dry land in controlled settings, the risks are much lower but not zero. The blood pressure spikes described earlier are real, and anyone with uncontrolled hypertension, a history of stroke, or heart disease should approach breath-holding exercises with caution and medical guidance. The hyperventilation-plus-retention protocols used in some modern breathwork methods can cause very low carbon dioxide levels (respiratory alkalosis) that produce tingling, lightheadedness, and in rare cases fainting.

An Evolutionary Footnote

Perhaps the most striking evidence that breath retention has shaped human biology comes from the Bajau people of Southeast Asia, traditionally known as sea nomads for their centuries of subsistence diving. Genetic analysis revealed that the Bajau carry variants in the PDE10A gene that give them significantly larger spleens compared to neighboring non-diving populations, providing a bigger reservoir of oxygen-rich red blood cells available for release during dives. Researchers also found signs of strong natural selection on BDKRB2, a gene involved in the human diving reflex itself.³⁰ The same splenic contraction mechanism that modern breath-holders trigger voluntarily has, in at least one human population, been genetically amplified by generations of selection pressure. It is a vivid reminder that the body’s response to breath retention is not an accident or a quirk but a deep physiological program rooted in our mammalian biology.