PASCO PS-2152 Spirometer - Manual (Page 6)

Spirometer Interpretation of PFT Data
6 ®
Lung Volume vs. Time
Lung Volume is the constantly-changing amount of air in the lungs. A
spirometer can measure how it changes, but cannot directly measure its
absolute value. Lung volume can be calculated if one of two specific
absolute volumes, residual volume (RV) or functional residual capacity
(FRC), is known or estimated.
Residual volume (RV) is the amount of air remaining in the lungs at the
end of a forced expiration. A typical RV is 1.2 L.
Functional Residual Capacity (FRC) is the amount of air left in the lungs
after a normal expiration (FRC = RV + ERV). A typical FRC is 2.5 liters.
The formula for Lung Volume is:
Lung Volume = V
0
- TotalFlow
V
0
is the lung volume when the subject first starts to breath through the
Spirometer. Set V
0
equal to the subject's FRC, or 2.5 L. Once you have
acquired data, you may need to adjust V
0
so that the graph reflects the
subject's known or estimated FRC or RV.*
TV
ERV
IRV
FEV
1.0
IC
VC
1 sec.
RV
FRC
TLC
*See DataStudio
Online Help, or the
Xplorer GLX manual
for instructions on
entering and
graphing this
calculation.