Bohr Effect: Healthy vs. Sick People

Bohr effect (medical or scientific explanation is below)

“All chronic pain, suffering and diseases are caused
from a lack of oxygen at the cell level."
Prof. A.C. Guyton, MD, The Textbook of Medical Physiology*

* World’s most widely used medical textbook of any kind
* World's best-selling physiology book

The Bohr effect explains cells oxygen release or why red blood cells unload oxygen in tissues, while carbon dioxide (CO2) is the key player in O2 transport due to vasodilation and the Bohr effect (or Bohr law).  The Bohr effect was first described in 1904 by the Danish physiologist Christian Bohr (father of famous physicist Niels Bohr).

What is Bohr effect in simple terms?

Bohr effect in healthy people

The Bohr effect is a normal process in healthy people since healthy people have normal breathing at rest and normal arterial CO2 levels. How does the Bohr effect work? As we know, oxygen is transported in blood by hemoglobin cells. How do these red blood cells know where to release more oxygen and where less? Or why do they unload more oxygen at all? Why is O2 released in tissues? The hemoglobin cells sense higher concentrations of CO2 in tissues and release oxygen in such places.

 

Bohr effect summary. More oxygen is released in those tissues that have higher absolute and/or relative CO2 values. Note that this is true for healthy people who have normal breathing pattern.

Suppressed Bohr effect in people with chronic diseases

Can people with chronic diseases enjoy the normal Bohr effect and normal oxygen delivery to the brain, heart and all other vital organs? Consider these medical studies.

Minute ventilation rates (chronic diseases)

Condition	Minute ventilation	Number of people	All references or click below for abstracts
Normal breathing	6 L/min	-	Medical textbooks
Healthy Subjects	6-7 L/min	>400	Results of 14 studies
Heart disease	15 (±4) L/min	22	Dimopoulou et al, 2001
Heart disease	16 (±2) L/min	11	Johnson et al, 2000
Heart disease	12 (±3) L/min	132	Fanfulla et al, 1998
Heart disease	15 (±4) L/min	55	Clark et al, 1997
Heart disease	13 (±4) L/min	15	Banning et al, 1995
Heart disease	15 (±4) L/min	88	Clark et al, 1995
Heart disease	14 (±2) L/min	30	Buller et al, 1990
Heart disease	16 (±6) L/min	20	Elborn et al, 1990
Pulm hypertension	12 (±2) L/min	11	D'Alonzo et al, 1987
Cancer	12 (±2) L/min	40	Travers et al, 2008
Diabetes	12-17 L/min	26	Bottini et al, 2003
Diabetes	15 (±2) L/min	45	Tantucci et al, 2001
Diabetes	12 (±2) L/min	8	Mancini et al, 1999
Diabetes	10-20 L/min	28	Tantucci et al, 1997
Diabetes	13 (±2) L/min	20	Tantucci et al, 1996
Sleep apnea	15 (±3) L/min	20	Radwan et al, 2001
Liver cirrhosis	11-18 L/min	24	Epstein et al, 1998
Hyperthyroidism	15 (±1) L/min	42	Kahaly, 1998
Epilepsy	13 L/min	12	Esquivel et al, 1991
CHV	13 (±2) L/min	134	Han et al, 1997
Panic disorder	12 (±5) L/min	12	Pain et al, 1991
Bipolar disorder	11 (±2) L/min	16	MacKinnon et al, 2007
Dystrophia myotonica	16 (±4) L/min	12	Clague et al, 1994

Overbreathing or hyperventilation in the sick causes hypocapnia or reduced CO2 tension in the lungs and arterial blood (since ventilation-perfusion mismatch is not a common finding in the sick). This leads to hampered oxygen release and reduced cells oxygen tension due to the suppressed Bohr effect (Aarnoudse et al, 1981; Monday & Tétreault, 1980; Gottstein et al, 1976).

Hence, for the suppressed Bohr effect, the absolute CO2 concentration is low (see the picture of the right side), and O2 molecules are stuck with red blood cells. (Scientists call this effect “increased oxygen affinity to hemoglobin”). Hence, CO2 deficiency (hypocapnia) leads to hypoxia or decreased cell-oxygen levels (the suppressed Bohr effect). The more we breathe at rest, the less the amount of available oxygen in the cells of vital organs, like the brain, heart, liver, kidneys, etc.

Many people believe that breathing more air increases oxygen content in cells. This is not true. Generally, breathing more even reduces oxygen content even in the arterial blood. Indeed, hemoglobin cells in normal blood for very small normal breathing are about 98% saturated with O2. When we hyperventilate this number is about the same (in real life it gets less since most people make a transition to automatic costal or chest breathing that reduces arterial blood O2 levels), but without CO2 and the Bohr effect, this oxygen is tightly bound with red blood cells and cannot get into the tissues in required amounts. Hence, now we know one of the causes why heavy breathing reduces the cell-oxygen level of all vital organs.

The Bohr effect is crucial for our survival. Why? During each moment of our lives, some organs and tissues work harder and produce more CO2. These additional CO2 concentrations are sensed by the hemoglobin cells and cause them to release more O2 in those places where it is most required. This is a smart self-regulating mechanism for efficient cells oxygen transport.

Bohr effect (medical or scientific explanation)

Christian Bohr stated that at lower pH (more acidic environment, e.g., in tissues), hemoglobin would bind to oxygen with less affinity. Since carbon dioxide is in direct equilibrium with the concentration of protons in the blood, increasing blood carbon dioxide content, according to the Bohr effect, causes a decrease in pH, which leads to a decrease in affinity for oxygen by hemoglobin (and easier oxygen release in capillaries or tissues).

The description of the Bohr effect, which is a physiological law, can be found in nearly all physiological textbooks. Modern studies related to the Bohr effect are devoted to more advanced topics (see the titles of studies for modern research below). It is the central proposition of the Bohr effect that oxygen affinity to hemoglobin depends on absolute CO2 concentrations and reduced CO2 values decrease oxygen delivery to body cells.

Bohr effect and physical exercise

For example, without the Bohr effect, we could not walk or run for even 3-5 minutes. Why? In normal conditions, due to the Bohr effect, more O2 is released in those muscles, which generate more CO2. Hence, these muscles can continue to work with the same high rate.

However, sick people have reduced CO2 blood values. Hence, they are likely to experience symptoms of chronic fatigue, and poor results for physical fitness tests due to tissue hypoxia (low cell-oxygen levels).

Professor Henderson about Bohr effect

This is what Professor Henderson from the Yale University wrote about the Bohr effect,

"But even as early as 1885, Miescher (Swiss physiologist) inspired by the insight of genius wrote: "Over the O2 supply of the body, CO2 spreads its protecting wings" Yandell Henderson (1873-1944), in Henderson Y, Carbon dioxide, in Cyclopedia of Medicine, ed. by H.H. Young, Philadelphia, FA Davis, 1940.

Here is YouTube video that considers the Bohr effect and explains the mechanism why overbreathing decreases cell-oxygen level.

Another web page related to oxygen transport and cell oxygenation: Vasodilation (expansion of arteries and arterioles due to higher CO2 values) or why breathing less improves perfusion or blood flow to all vital organs.

You can read medical research abstract devoted to the Bohr effect and role of CO2 in cells O2 delivery.

Click here for references used on this page.

Back to Effects of carbon dioxide on human health

* Illustrations by Victor Lunn-Rockliffe

Reference pages: Breathing norms and medical facts:
- Breathing norms: Parameters, graph, and description of the normal breathing pattern
- 6 breathing myths: Myths and superstitions about breathing and body oxygenation (prevalence: over 90%)
- Hyperventilation: Definitions of hyperventilation: their advantages and weak points
- Hyperventilation syndrome: Western scientific evidence about prevalence of chronic hyperventilation in patients with chronic conditions (37 medical studies)
- Normal minute ventilation: Small and slow breathing at rest is enjoyed by healthy subjects (14 studies)
- Hyperventilation prevalence: Present in over 90% of normal people (24 medical studies)
- HV and hypoxia: How and why deep breathing reduces oxygenation of cells and tissues of all vital organs
- Body-oxygen test (CP test) : How to measure your own breathing and body oxygenation (two in one) using a simple DIY test
- Body oxygen in healthy: Results for the body-oxygen test for healthy people (27 medical studies)
- Body oxygen in sick : Results for the body-oxygen test for sick people (14 medical studies)
- Buteyko Table of Health Zones: Clinical description and ranges for breathing zones: from the critically ill (severely sick) up to super healthy people with maximum possible body oxygenation
- Morning hyperventilation: Why people feel worse and critically ill people are most likely to die during early morning hours

References: pages about CO2 effect:
- Vasodilation: CO2 expands arteries and arterioles facilitating perfusion (or blood supply) to all vital organs
- The Bohr effect: How and why oxygen is released by red blood cells in tissues
- Cell oxygen levels: How alveolar CO2 influences oxygen transport
- Oxygen transport: O2 transport is controlled by vasoconstriction-vasodilation and the Bohr effects, both of which rely on CO2
- Free radical generation: Reactive oxygen species are produced within cells due to anaerobic cell respiration caused by cell hypoxia
- Inflammatory response: Chronic inflammation in fueled by the hypoxia-inducible factor 1, while normal breathing reduces and eliminates inflammation
- Nerve stabilization: People remain calm due to calmative or sedative effects of carbon dioxide in neurons or nerve cells
- Muscle relaxation: Relaxation of muscle cells is normal at high CO2, while hypocapnia causes muscular tension, poor posture and, sometimes, aggression and violence
- Bronchodilation: Dilation of airways (bronchi and bronchioles) is caused by carbon dioxide, and their constriction by hypocapnia (low CO2)
- Blood pH: Regulation of blood pH due to breathing and regulation of other bodily fluids
- CO2: lung damage: Elevated carbon dioxide prevents lung injury and promotes healing of lung tissues
- CO2: Topical carbon dioxide can heal skin and tissues
- Synthesis of glutamine in the brain, CO2 fixation, and other chemical reactions
- Deep breathing myth: Ignorant and naive people promote the idea that deep breathing and breathing more air at rest is beneficial for health
- Breathing control: How is our breathing regulated? Why hypocapnia makes breathing uneven, irregular and erratic.

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