The volume of air displaced between normal inspiration and expiration when extra effort is not applied. It is normally around 500 ml in a young healthy adult.
This is the partial pressure of CO2 in the arteries. It can be obtained and measured with an arterial blood gas (ABG).
The partial pressure of CO2 in the expired air is an important piece of information for calculating the physiologic dead space. This can be obtained from capnometry clinically.
Physiologic dead space can be calculated by multiplying the tidal volume (TV) with the difference between the arterial partial pressure of CO2 (PaCO2) and the partial pressure of CO2 in the expired air (PECO2) and divided by the arterial partial pressure of CO2 (PaCO2). In other words, it is the volume of air that is proportional to the percentage of CO2 that entered the lungs but did not get exchanged.
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