- Updated on September 10, 2020
CO2 Breath Control (Regulation of Respiration): O2 vs. CO2
Proofread by Thijs Oosting Proofreader on Aug 31, 2019
CO2 and O2 chemoreceptors are the primary regulators that control our breath (control of respiration). Whether CO2 or O2 is the most important (CO2 or O2), depends on a person’s state of health since the chemical regulation of breathing is different in healthy and sick people.
CO2 Breath Control in healthy people
Any medical or physiological textbook that discusses CO2 breath control in the human body states that respiration in healthy people is mainly controlled by CO2 concentrations in the brain and arterial blood.
Modern research focuses on specifics and details of the chemistry in breath control (Binet & Dejours P, 1962; Chernick et al., 1975; Dejours, 1963; Gautier, 2003; Forster & Pan LG, 1994; Heymans C, 1951; Honda Y, 1985; Kiwull-Schune et al., 1994; Lahiri et al., 1978; Lahiri et al., 2003; Murai et al., 1987; Nattie, 1999; Nye et al., 1983; O’Regan & Majcherczyk, 1982; Richerson et al., 2005; Wennergren & Wennergren, 1983).
The main physiological ideas related to the regulation of breathing can be found in Chapter 2. The chemical and physiological mechanisms of immediate regulation of breathing (pages 50-59) of my eBook “Normal breathing: the key to vital health.” An extract that includes these pages can be found here: Breath Control.
If carbon dioxide would indeed be poisonous, it would be logical to find lower amounts of CO2 in healthy people. However, the opposite is true. Healthy people have higher CO2 concentrations. The so-called “poison” actually controls our breathing (or outer respiration), which of course is a fundamental function of the human body.
The breathing center located near the rear of the brain (medulla oblongata) regulates our way of breathing. This breathing center (also called the master center of the body) uses special chemoreceptors to measure CO2 concentrations in the brain and arterial blood. The central chemoreceptors detect changes in the pH of the cerebrospinal
fluid and hereby have the ability to regulate breathing in the long run. Since CO2 dissolves in the blood and can penetrate through the blood-brain barrier, the primary reason for pH variations in the brain are changes in CO2 concentrations. Peripheral chemoreceptors monitor immediate changes in CO2, O2, and pH concentrations of the blood, and control our breathing in the short run.
It is agreed that peripheral chemoreceptors include the carotid and aortic bodies. The carotid bodies,
which can sense hypocapnia (low CO2), hypercapnia (high CO2) and hypoxia (low O2), play a more prominent role (in humans) compared to the Aortic Bodies. However, immediate changes in CO2 have a far larger effect on involuntary breathing patterns than anything else.
The breathing of healthy people during typical daily activities (rest, work, light and moderate exercise, sleeping, etc.) is mainly regulated by pre-set (or their usual) chemical CO2 concentrations (CO2 breath control).
For example, when a healthy person takes several deep and fast breaths, CO2 in the lungs and blood decreases. The breathing center detects this drop and reduces or even stops the activity of the respiratory muscles.
In such cases, the person naturally holds their breath until the CO2 level reaches the initially pre-set value. Conversely, when a person decides to hold his breath, carbon dioxide will accumulate in the body.
The breathing center senses this increase and intensifies breathing. This overbreathing is going to continue until extra CO2 is removed and the pre-set value is reached again.
We breathe more heavily during physical exercise when our bodies produce more carbon dioxide. However, the rate of CO2 production matches the rate of CO2 removal in such a fashion that CO2 and O2 values in the arterial blood only changes slightly during exercise.
Do you know by how many times CO2 is more influential than O2 (if we are speaking about breath control in healthy subjects)? The answer (a number) is provided right below here as your bonus content.
CO2 changes in the blood are about 200 times more significant for breath control than changes in blood O2.
Breath control in the sick: increased role of O2
Control of the breath, for sick people, is a bit different than for healthy individuals. Of course, CO2 still plays a huge role, but the sicker a person becomes, the more critical blood O2 concentrations become. The urge for oxygen gets stronger with the advance of many diseases.
For sick people, the control of the automatic breath is accomplished by blood and brain CO2 concentrations and O2 drive, which becomes stronger with the progression of chronic diseases and increasing cell hypoxia due to increased respiration (elevated minute ventilation).
In severely sick people, O2 can become the main factor in the regulation of respiration.
The change in air composition during human evolution and the evolution of animals on Earth was the key factor that led to the appearance of chronic diseases. Hyperventilation, 1-2 million years ago, used to be beneficial for creatures living in the primitive air that contained very low amounts of O2 and high amounts of CO2.
However, since this ratio has changed significantly, overbreathing has become destructive to health.
This YouTube video “Evolution of Air” features Dr. Artour Rakhimov. He explains the key cause of bronchospasm, spasm of blood vessels, reduced Bohr effects and other effects caused by changes in the air, and low CO2 in the modern air.