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Calculation of Oxygen Consumption

Calculation of oxygen consumption is a straightforward process that involves subtracting the amount of oxygen exhaled from the amount of oxygen inhaled:

(1)Oxygen consumption(V˙O2)=[volume ofO2inspired][volume ofO2expired]

The volume of O2 inspired (I) is computed by multiplying the volume of air inhaled per minute (V˙I) by the fraction (F) of air that is made up of oxygen. Room air is 20.93% O2. Expressed as a fraction, 20.93% becomes .2093 and is symbolized as FIO2. When we exhale, the fraction of O2 is lowered (i.e., O2 diffuses from the lung to the blood) and the fraction of O2 in the expired (E) gas is represented by FEO2. The volume of expired O2 is the product of the volume of expired gas (V˙E) and FEO2. Equation (1) can now be symbolized as:


The exercise values for FIO2, FEO2, V˙I, and V˙E for a subject are easily measured in most exercise physiology laboratories. In practice, FIO2 is not generally measured but is assumed to be a constant value of .2093 if the subject is breathing room air. FEO2 will be determined by a gas analyzer, and V˙I and V˙E can be measured by a number of different laboratory devices capable of measuring airflow. Note that it is not necessary to measure both V˙I and V˙E. This is true because if V˙I is measured, V˙E can be calculated (and vice versa). The formula used to calculate V˙E from the measurement of V˙I is called the “Haldane transformation” and is based on the fact that nitrogen (N2) is neither used nor produced in the body. Therefore, the volume of N2 inhaled must equal the volume of N2 exhaled:


Therefore, V˙I can be computed if V˙E, FIO2, and FEO2 are known. For example, to solve for V˙I:



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