Installation and Settings
CardioCoach PRO User Manual | Page 82
the amount of heat produced by the body. This method is referred to as
direct calorimetry. Direct calorimetry is difficult and impractical, as it
requires a client to be placed in a special insulated room where the flow of
energy into and out of the room is measured and controlled. A more
common method of metabolic rate measurement is indirect calorimetry.
Indirect calorimetry is a measurement of the amount of oxygen consumed,
rather than the amount of heat produced. Every calorie consumed requires
a fixed amount of oxygen to be converted to energy. The rate at which
oxygen is consumed is directly proportional to the rate of caloric
expenditure. In short, measuring the rate of oxygen consumption is
equivalent to measuring the number of calories being used.
The volume of oxygen consumed per minute is commonly written as VO
2
.
Values of VO₂ are reported in milliliters per minute (ml/min). These values
are often normalized to the weight of the person being measured. The
weight-normalized VO₂ is reported in milliliters per minute per kilogram of
body weight (ml/min/kg). The maximum weight-normalized amount of
oxygen that an individual can consume in a minute is referred to as their
“VO₂ max” and is a measure of their level of fitness. Factors that affect a
person’s VO₂ max include level of cardiac and pulmonary fitness, muscle
mass, muscle perfusion, fat mass, and other variables. Exercise levels for a
given individual are often determined as a percent of their maximum VO₂.
Oxygen Consumption
The CardioCoach calculates oxygen consumption by measuring the volume
of air that is exhaled and the concentration of oxygen in that air. The
volume of air exhaled multiplied by the difference between inspired and
expired oxygen concentration is equal to the oxygen consumption. The
CardioCoach measures the concentration of exhaled oxygen 50 times each
second. The concentration of inspired (room) air oxygen is measured
during an automatic calibration cycle prior to each test. The CardioCoach
also measures the temperature, relative humidity and barometric pressure
to compensate for local variations and further improve the accuracy of the
calculations. Note that the concentration of oxygen in the inspired air
remains constant over the course of an exercise test.
To measure oxygen consumption, all of the air exhaled by the user must
pass through the CardioCoach. Two (2) one-way valves are connected in or
near a mask or mouthpiece. This ensures that fresh air is inhaled and all
exhaled gas passes through the hose and into the CardioCoach. Because of
the one-way valves, the user can never inhale gas from the hose or the
CardioCoach, thereby eliminating the possibility of cross-contamination
between users. When a mouthpiece is used, it is important to use a nose
clip so that there is no leak through the nose and the CardioCoach analyzes
all exhaled air.
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