Respiratory Physiology

The Gas You're
Wasting.

Carbon Dioxide Is Not Just a Waste Product

Most people try to breathe more to get more oxygen. The science says the opposite: breathing less — and tolerating more CO₂ — is the key to better oxygen delivery, improved blood flow, and greater endurance.

Explore the Science
CO₂ Required for hemoglobin to release oxygen to your tissues
↑ Blood Flow Increased CO₂ in blood improves circulation to the brain
22% Reduction in ventilation volume with nasal breathing (Dallam, 2018)
01

The Bohr Effect

Hemoglobin carries oxygen through your bloodstream. But here's the paradox: hemoglobin won't readily release that oxygen to your tissues without sufficient carbon dioxide present. This is the Bohr effect — and it's why over-breathing actually reduces oxygen delivery to the muscles and brain.

  • CO₂ facilitates the release of oxygen from hemoglobin to working tissues
  • Over-breathing (hyperventilation) blows off too much CO₂
  • Less CO₂ = hemoglobin holds onto oxygen = tissues get less
  • More CO₂ tolerance = more efficient oxygen delivery
References
  1. Bohr, Hasselbalch & Krogh, Skandinavisches Archiv Für Physiologie, 1904
  2. Jensen, Acta Physiologica Scandinavica, 2004 (PMID: 15491402)
  3. Lumb, Nunn's Applied Respiratory Physiology, 8th ed., 2017
O₂ ↓ Hemoglobin ↓ Tissues oxygen delivery pathway
CO₂ = The Key
catalyst for O₂ release
02

CO₂ and Blood Flow to the Brain

Carbon dioxide is a potent vasodilator. Increased CO₂ in your blood causes blood vessels to widen, directly increasing blood flow to the brain. This is why slow, reduced breathing improves focus, cognitive clarity, and mental calm.

  • CO₂ dilates cerebral blood vessels
  • Over-breathing constricts blood flow to the brain
  • This is why hyperventilation causes dizziness and lightheadedness
  • Controlled, reduced breathing enhances cognitive performance
References
  1. Willie et al., Journal of Physiology, 2012 (PMID: 22495584)
  2. Ito et al., Journal of Cerebral Blood Flow & Metabolism, 2003 (PMID: 12796714)
↑ CO₂ ↓ ↑ Blood Flow ↓ ↑ Brain O₂
03

The Paradox: Breathe Less, Get More

The counterintuitive truth of respiratory physiology: reducing your breathing volume increases oxygen delivery. When you breathe less per breath (reducing tidal volume), you retain more CO₂, which triggers the Bohr effect, releasing more oxygen to your tissues.

  • Tidal volume — reducing the amount of air per breath increases efficiency
  • Body adapts to a higher tolerance to the accumulation of carbon dioxide
  • This in turn leads to a reduction in ventilation, leading to reduced breathlessness and greater economy
  • Ventilation (volume of breathing) was reduced by 22% in nasal breathing (Dallam, 2018)
The goal isn't to breathe more — it's to breathe better. Light, slow, deep breathing maximizes oxygen delivery while minimizing wasted effort.
References
  1. Dallam et al., International Journal of Kinesiology & Sports Science, 2018
  2. Courtney, Greenwood & Cohen, Journal of Bodywork and Movement Therapies, 2011 (PMID: 21147415)
  3. Russo et al., Breathe, 2017 (PMID: 29209423)
Breathe Less ↓ Retain CO₂ ↓ Bohr Effect ↓ More O₂ Delivered
04a

Building Tolerance

Your body can adapt to higher levels of CO₂ through consistent practice. Nasal breathing during rest and exercise naturally builds this tolerance. Over time, breathlessness decreases and breathing economy improves.

References
  1. McKeown, The Oxygen Advantage, 2015
  2. Dallam et al., Int J Kinesiol & Sports Sci, 2018
04b

The Training Effect

As CO₂ tolerance increases, ventilation decreases. Less air moved per minute means less energy spent breathing, less water lost, and more oxygen delivered to working muscles. This is why elite athletes who train with nasal breathing often see performance gains despite breathing less.

References
  1. Morton, King & Papalia, Australian Journal of Science and Medicine in Sport, 1995
  2. Dallam et al., Int J Kinesiol & Sports Sci, 2018

Over-Breathing vs. Efficient Breathing

How breathing volume affects your physiology

MetricOver-BreathingEfficient Breathing
CO₂ levelsDepletedMaintained
O₂ delivery to tissuesReducedEnhanced
Brain blood flowConstrictedDilated
Ventilation volumeExcessiveEconomical
BreathlessnessIncreasedReduced
Energy costHigherLower
HydrationMore lossConserved
PerformanceImpairedOptimized