What You Need to Know About Carbon Dioxide (CO2)

The Role of CO2 in the Respiratory System

The primary function of the respiratory system is to exchange oxygen and carbon dioxide. Inhaled oxygen enters the lungs and reaches the alveoli. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other. This barrier between air and blood averages about 1 micron (1/10,000 of a centimeter) in thickness. Oxygen passes quickly through this air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled.

Oxygenated blood travels from the lungs through the pulmonary veins and into the left side of the heart, which pumps the blood to the rest of the body (see Biology of the Heart and Blood Vessels: Function of the Heart). Oxygen-deficient, carbon dioxide-rich blood returns to the right side of the heart through two large veins, the superior vena cava and the inferior vena cava. Then the blood is pumped through the pulmonary artery to the lungs, where it picks up oxygen and releases carbon dioxide (see Biology of the Heart and Blood Vessels: Function of the Heart).

To support the exchange of oxygen and carbon dioxide, about 6 to 10 liters of air per minute are brought in and out of the lungs, and about three-tenths of a liter of oxygen is transferred from the alveoli to the blood each minute, even when the person is at rest. At the same time, a similar volume of carbon dioxide moves from the blood to the alveoli and is exhaled. During exercise, it is possible to breathe in and out more than 100 liters of air per minute and extract 3 liters of oxygen from this air per minute. The rate at which oxygen is used by the body is one measure of the rate of energy expended by the body. Breathing in and out is accomplished by respiratory muscles (see Biology of the Lungs and Airways: Diaphragm's Role in Breathing).

The function of the respiratory system is to exchange two gases: oxygen and carbon dioxide. The exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.

Three processes are essential for the transfer of oxygen from the outside air to the blood flowing through the lungs: ventilation, diffusion, and perfusion. Ventilation is the process by which air moves in and out of the lungs. Diffusion is the spontaneous movement of gases, without the use of any energy or effort by the body, between the gas in the alveoli and the blood in the capillaries in the lungs. Perfusion is the process by which the cardiovascular system pumps blood throughout the lungs. The body's circulation is an essential link between the atmosphere, which contains oxygen, and the cells of the body, which consume oxygen. For example, the delivery of oxygen to the muscle cells throughout the body depends not only on the lungs but also on the ability of the blood to carry oxygen and on the ability of the circulation to transport blood to muscle.

The effects of aging on the respiratory system are similar to those that occur in other organs: maximum function gradually declines. Age-related changes in the lungs include decreases in the peak airflow, gas exchange, and vital capacity (the maximum amount of air that can be breathed out following a maximum inhalation); weakening of the respiratory muscles; and a decline in the effectiveness of lung defense mechanisms. In healthy people, these age-related changes seldom lead to symptoms, but they can contribute to an older person's reduced ability to perform vigorous exercise, especially intense aerobic exercise, such as running, biking, and mountain climbing.

Obesity also reduces pulmonary function. Additionally, older people are at higher risk of developing pneumonia after bacterial or viral infections. Importantly, age-related changes in the lungs compound the effects of heart and lung diseases the person may have, especially those caused by the destructive effects of smoking.


Carbon dioxide affects brain function by controlling brain blood flow and oxygen delivery. Carbon dioxide also directly controls the threshold required for a neuron to fire with insufficient carbon dioxide leading to excessive neuronal firing. Low carbon dioxide therefore causes the brain to become oxygen and blood deficient and hyperactive at the same time. This can be experienced as anxiety. Increasing carbon dioxide to optimal levels normalizes brain blood flow, oxygen levels, and neuronal firing leading to a calmer and healthier mind.


Carbon dioxide is the body's natural bronchodilator. As a person's carbon dioxide level decreases, breathing becomes more difficult and conditions such as asthma, sleep apnea, and snoring can develop. Carbon dioxide is also the body's natural antihistamine. Low carbon dioxide makes allergic reactions more intense. Increasing carbon dioxide levels to their optimum levels can help make breathing easier and limit allergic responses.


Carbon dioxide plays two important roles in circulation. First, carbon dioxide helps relax and dilate the arteries and capillaries so blood can reach the tissues. Second, carbon dioxide displaces oxygen from the red blood cell allowing it to reach the tissues. Without enough carbon dioxide, the oxygen in your blood will never be released into the tissues where it is needed.


Low levels of carbon dioxide are associated with increased sensitivities to pain. As pain tends to decrease carbon dioxide levels further, a viscous cycle ensues with pain lowering carbon dioxide, and low carbon dioxide causing more pain, and so on. Increasing carbon dioxide to optimum levels can help stop the pain feedback cycle.


Sleep disorders such as apnea, snoring, and insomnia can all be linked to low carbon dioxide levels. Carbon dioxide taken just before going to sleep can help increase ease of breathing, decrease inflamed tissues leading to snoring, and normalize excessive brain activity allowing one to drift off to sleep rather than lie in bed incessantly thinking.


The body naturally uses carbon dioxide to help detoxify itself from toxic metals. When toxic metals in solution interact with carbon dioxide in the form of carbonates and bicarbonates in the bloodstream, they come together to form complex ions. These complex ions are now less toxic to the body and easier to remove due to increased solubility. Even more important, optimal levels of carbon dioxide are vital to the proper detoxification of toxic metals.


Low carbon dioxide can cause excessive activity of the nerves leading to the muscles which can result in tremor activity. In addition, low carbon dioxide can result in a buildup of brain ammonia levels which can also cause tremors. Increasing carbon dioxide to optimal levels can help with tremors by normalizing nerve function and converting toxic ammonia into urea which is then harmlessly excreted from the body via the kidneys.

Prepared by: Dr. Marian Porter
The Oxygen Spa
14346 Cape May Road
Silver Spring, MD 20904
(301) 879-0212

Disclaimer: All information in this handout is provided by Dr. Porter and The Oxygen Spa for educational purposes. It does not, and should not, replace the advice of your personal health practitioner.

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