Biomedical Engineering Reference
In-Depth Information
FEV
t
will be the portion of the FVC that can be expelled within a given period,
typically 0.5 or 1 s.
The MVV is the volume of air moved in 1 minute with the subject breathing as deeply
and rapidly as possible. The test is generally performed over 20 s to minimize the effects
of hyperventilation.
PF is the maximum flow velocity attainable during the FEV maneuer and represents
the maximum slope of the expired volume-time curve.
9.5.1.3 Oxygen Uptake Test
This is the measurement of oxygen use per unit time, called the O
2
uptake test. A spirometer
with input and output check valves passes the exhaled breath through soda-lime. This is a
mixture of calcium hydroxide, sodium hydroxide, and silicates of sodium and calcium and
it absorbs CO
2
. Starting with a spirometer full of oxygen, normal respiration causes the bell
to move up and down in a cyclical fashion in the normal way, but as oxygen is absorbed the
baseline of the recording rises. By measuring the slope of the baseline on the spirogram,
as shown in Figure 9-19, the volume of oxygen consumed per minute can be determined.
To determine the true volume of oxygen consumed, a correction factor,
F
, must
be applied to compensate for the temperature difference and the pressure. Starting with
Boyle's law
P
1
V
1
T
1
P
2
V
2
T
2
=
(9.8)
the final volume,
V
2
, can be determined as a function of all of the other parameters as
T
2
T
1
V
1
=
FV
1
P
1
P
2
V
2
=
(9.9)
FIGURE 9-19
Oxygen
consumption
measurement.
