Biomedical Engineering Reference
In-Depth Information
MAXIMUM
INSPIRATION
6,000
5,000
4,000
3,000
2,000
EXPIRATORY
RESERVE
VOLUME
FUNCTIONAL
RESIDUAL
CAPACITY
1,000
RESIDUAL
VOLUME
0
MAXIMUM EXPIRATION
TIME
FIGURE 3.25
Lung volumes and capacities, except for residual volume, functional residual capacity, and total
lung capacity, can be measured using spirometry.
floating drum drops. When the patient exhales, the level of the floating drum rises. These
changes in floating drum position can be recorded and used to measure lung volumes.
EXAMPLE PROBLEM 3.9
The total lung capacity of a patient is 5.9 liters. If the patient's inspiratory capacity was found
to be 3.3 liters using spirometry, what would be the patient's functional residual capacity? What
would you need to measure in order to determine the patient's residual volume?
Solution
From Figure 3.25, total lung capacity (TLC) is equal to the sum of inspiratory capacity (IC) and
functional residual capacity (FRC).
TLC
¼
IC
þ
FRC
5
:
9
l
¼
3
:
3
l
þ
FRC
FRC
¼
2
:
6
l
TLC, which cannot be determined by means of spirometry, and vital capacity (VC), which can
be measured using spirometry, must be known in order to determine residual volume (RV), since
TLC
VC
¼
RV
