Appendices

INTRODUCTION

Calculation of Oxygen Consumption

Calculation of oxygen consumption is a relatively simple process that involves subtracting the amount of oxygen exhaled from the amount of oxygen in-haled:

The volume of O₂ inspired (I) is computed by multiplying the volume of air inhaled per minute (V̇_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 F_IO₂. 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 F_EO₂. The volume of expired O₂ is the product of the volume of expired gas (V̇_E) and F_EO₂. Equation (1) can now be symbolized as:

The exercise values for F_IO₂, F_EO₂, V̇_I, and V̇_E for a subject are easily measured in most exercise physiology laboratories. In practice, F_IO₂ is not generally measured but is assumed to be a constant value of .2093 if the subject is breathing room air. F_EO₂ will be determined by a gas analyzer, and V̇_I and V̇_E can be measured by a number of different laboratory devices capable of measuring airflow. Note that it is not necessary to measure both V̇_I and V̇_E. This is true because if V̇_I is measured, V̇_E can be calculated (and vice versa). The formula used to calculate V̇_E from the measurement of V̇_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, V̇_I can be computed if V̇_E, F_IO₂, and F_EO₂ are known. For example, to solve for V̇_I:

Likewise, if V̇_I was measured, V̇_E can be computed as:

The values ...