Bohr effect (medical or scientific explanation is down below)
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
What is Bohr effect in simple terms (for dummies)?
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
Bohr effect summary. More oxygen is released in those
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.
Note that advanced stages of some conditions (e.g., asthma and CF) can lead to lung destruction,
ventilation-perfusion mismatch and arterial hypercapnia causing further reduction in body oxygen levels.
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 & Ttreault, 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
affinity to hemoglobin”). Hence, CO2 deficiency (hypocapnia)
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)
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.
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
It is however known that dozens of these studies that measured the Bohr effect were done in vitro. It is still not clear if hyperventilaiton and arterial hypocapnia (low CO2) indeed cause reduced oxygen transport due to one tricky effect that I explain in the bonus content right below here.
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