Pulmonary Function Measurements
The total amount of air that the lungs can accommodate is divided into four
separate volumes and four capacities. Combinations of these volumes are used
to designate lung capacities.
LUNG VOLUMES
The lung volumes are the:
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Tidal volume (VT): the volume of air that normally moves in and out of the
lungs in one quiet breath
Inspiratory reserve volume (IRV): the maximum volume of air that can be
inhaled after a normal tidal volume inhalation
Expiratory reserve volume (ERV): the maximum volume of air that can be
exhaled after a normal tidal volume exhalation
Residual volume (RV): the amount of air remaining in the lungs after
maximum exhalation; air that cannot be exhaled
Lung Capacities
The lung capacities consist of the:
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Vital capacity (VC): the maximum volume of air that can be exhaled after a
maximum inspiration; expressed as IRV + VT + ERV. Two VC
measurements are the slow vital capacity (SVC), in which exhalation is
performed slowly, and the forced vital capacity (FVC), in which exhalation
is performed rapidly with maximum effort. Obstructive disorders with small
airway collapse will cause the FVC to decrease as a result of air trapping
with forced exhalation.
Inspiratory capacity (IC): the volume of air that can be inhaled after a
normal exhalation; expressed as VT + IRV
Functional residual capacity (FRC): the volume of air remaining in the
lungs after normal exhalation; expressed as ERV + RV
Total lung capacity (TLC): the maximum amount of air that the lungs can
accommodate; expressed as IC + FRC
Residual volume/total lung capacity ratio: the percentage of the total lung
capacity occupied by the residual volume; expressed as RV/TLC  100
Lung volume and capacity vary with age, race, height, and gender. Table 4-1 in
the text shows the approximate lung volumes and capacities of average men and
women ages 20 to 30.
In obstructive lung disorders:

Residual volume (RV), functional residual capacity (FRC), and residual
volume/total lung capacity (RV/TLC) ratio are increased.

Vital capacity (VC), inspiratory capacity (IC), inspiratory reserve volume
(IRV), and expiratory reserve volume (ERV) are decreased.
Obstructive lung disorders include asthma and other COPDs, such as
emphysema and chronic bronchitis.
The figure below shows how obstructive lung disorders alter lung volumes and
capacities.
In restrictive lung disorders:

Vital capacity (VC), inspiratory capacity (IC), residual volume (RV),
functional residual capacity (FRC), tidal volume (VT), and total lung
capacity (TLC) are all decreased.
Restrictive lung disorders include pulmonary fibrosis, adult respiratory distress
syndrome, and pulmonary edema.
The figure below shows how restrictive lung disorders alter lung volumes and
capacities.
Measuring RV
Because the residual volume (RV) cannot be exhaled, the RV and the lung
capacities that contain the RV are measured indirectly by:
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Closed circuit helium dilution method: The patient rebreathes from a
spirometer that contains a known volume of gas and a known
concentration of helium.
Open circuit nitrogen washout method: The patient breathes 100 percent
oxygen through a one-way valve.
Body plethysmography: The gas volume in the lungs is measured
indirectly using Boyle’s law while the patient sits in an airtight chamber.
Pulmonary Mechanics
In addition to volumes and capacities, the rate at which gas flows into and out of
the lungs can be measured. Collectively, the tests used to measure expiratory
flow rates are referred to as pulmonary mechanic measurements. These tests
are discussed below.
FORCED VITAL CAPACITY (FVC)
The forced vital capacity (FVC) is the maximum volume of gas that can be
exhaled as forcefully and rapidly as possible after a maximal inhalation.
In normal lung function:

The total expiratory time needed to completely exhale the FVC is 4 to 6
seconds, and the FVC and slow vital capacity (SVC) are equal.
In abnormal lung function:
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
FVC decreases with obstructive lung disorders due to small airway
collapse resulting in air trapping.
FVC decreases with restrictive lung disorders due to the low vital capacity
that result from the inability to expand the lungs to accept more air.
Figure 4-4 in the text illustrates forced vital capacity.
FORCED EXPIRATORY VOLUME TIMED (FEVT)
The forced expiratory volume timed (FEVT) is the maximum volume of gas that
can be exhaled within a specific time (usually 1 second, but also 0.5, 2, and 3
seconds). The measurement is obtained from the FVC.
In normal lung function, the percentage of total FVC exhaled is:
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FEV0.5 = 60 percent
FEV1 = 83 percent
FEV2 = 94 percent
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FEV3 = 97 percent
In abnormal lung function, the FEVT:
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Decreases with obstructive pulmonary disease
Decreases with restrictive lung disease due to the low vital capacity
associated with the disease
Because timed FEV is decreased in both restrictive and obstructive diseases, the
ratio to FVC is important to distinguish the type of disorder.
Figure 4-5 in the text illustrates FEVT.
FORCED EXPIRATORY VOLUME1 sec/FORCED VITAL CAPACITY RATIO
(FEV1/FVC)
The forced expiratory volume1 sec/forced vital capacity ratio compares the amount
of air exhaled in 1 second to the total amount exhaled during a forced vital
capacity (FVC) maneuver. This value is also called forced expiratory volume in 1
second percentage (FEV1%).
FEV, FEV1, and FEV1% are most often used to:
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Determine the severity of an obstructive lung disorder
Distinguish between obstructive and restrictive pulmonary disorders
In normal lung function, FEV1% is 83 percent or more. (Sixty-five percent may be
acceptable for older adults.)
In abnormal lung function:
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FEV1 and FEV1% decrease with obstructive lung disorders
FEV1 decreases and FEV1% increases or is normal with restrictive lung
disorders
FORCED EXPIRATORY FLOW25%-75% (FEF25%-75%)
The forced expiratory flow25%-75% is the average flow rate that occurs during the
middle 50 percent of a forced vital capacity (FVC) measurement. The average
measurement indicates the condition of medium to small airways.
In normal lung function, FEF25%-75%:
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Is about 4.5 L/sec (270 L/min) for men ages 20 to 30
Is about 3.5 L/sec (210 L/min) for women ages 20 to 30
In abnormal lung function, FEF25%-75%:
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Decreases with age
Decreases with obstructive lung disease (flow rates as low as 0.3 L/sec)
Decreases with restrictive lung disorders, due to the low vital capacity
associated with these disorders
Figure 4-6 in the text illustrates FEF25%-75%.
Note: FEF25%-75% cannot distinguish between obstructive and restrictive lung
disease but it is helpful in further confirming or ruling out obstructive lung disease
in patients with a borderline low FEV1%. Since it is the mid-range of exhalation, it
is less effort-dependent than some other measurements.
FORCED EXPIRATORY FLOW200-1200 (FEF200-1200)
The forced expiratory flow200-1200 is the average flow rate that occurs between
200 and 1200 mL of the FVC. It is a good indicator of large airway function since
it measures expiratory flows at high lung volumes. The greater the patient effort,
the higher the FEF200-1200 value will be.
In normal lung function, the average FEF200-1200 is:
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About 8 L/sec (480 L/min) for men ages 20 to 30
About 5.5 L/sec (330 L/min) for women ages 20 to 30
In abnormal lung function, the FEF200-1200:
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Decreases with obstructive lung disorders (flow rates as low as 1 L/sec)
Decreases with restrictive lung disorders, due to low vital capacity
associated with those disorders
Figure 4-8 in the text illustrates FEF200–1200.
PEAK EXPIRATORY FLOW RATE (PEFR)
The peak expiratory flow rate is the maximum flow rate that can be achieved
during a forced vital capacity (FVC) maneuver. It is measured using a peak flow
meter. PEFR reflects initial flows from large airways.
In normal lung function, the average PEFR is:
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About 10 L/sec (600 L/min) for men ages 20 to 30
About 7.5 L/sec (450 L/min) for women ages 20 to 30
In abnormal lung function, the average PEFR:
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Decreases due to obstructive lung disease
Figure 4-10 in the text illustrates peak expiratory flow rate.
MAXIMUM VOLUNTARY VENTILATION (MVV)
The maximum voluntary ventilation is the largest volume of gas that can be
breathed voluntarily into or out of the lungs in 1 minute; it is also known as the
maximum breathing capacity. Maximum ventilation is actually measured for 12 to
15 seconds, then calculated. The test is used as a general indicator of respiratory
muscle strength, lung and thorax compliance, airway resistance, and neural
control mechanisms.
In normal lung function, the average MVV is:
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170 L/min for men ages 20 to 30
110 L/min for women ages 20 to 30
In abnormal lung function, the MVV:
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Decreases with chronic obstructive pulmonary disease
Is relatively normal with restrictive pulmonary disease
MVV also decreases with age.
Figure 4-11 in the text illustrates maximum voluntary ventilation.
Flow-Volume Loop
The flow-volume loop is a graphic presentation of a forced vital capacity (FVC)
followed by a forced inspiratory volume (FIV) maneuver. The flow-volume loop
compares both the flow rates and the volume changes produced at different
points of the FVC and FIV maneuver.
A number of measurements can be obtained from the flow-volume loop,
including:
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Peak expiratory flow rate (PEFR)
Peak inspiratory flow rate (PIFR)
Forced vital capacity (FVC)
Forced expiratory volume timed (FEVT)
Forced expiratory volume1 sec/forced vital capacity ratio (FEV1/FVC ratio)
Forced expiratory flow (FEF25%, FEF50%, and FEF75%.)
The figure below illustrates a normal flow-volume loop.
Figures 4-13 and 4-14 in the text illustrate abnormal flow-volume loops resulting
from obstructive and restrictive lung disorders.
EFFECTS OF DYNAMIC COMPRESSION ON EXPIRATORY FLOW RATES
During the first 30 percent of forced vital capacity (FVC), the maximum peak flow
rate depends on the amount of effort exerted by the individual. Originating from
the large airways, this part of FVC is called effort-dependent. The more effort the
patient exerts, the higher the FEF200-1200 and PEFR values.
The flow rate of the last 70 percent of FVC is effort-independent: Once the
maximum flow rate is obtained, further muscular effort will not increase the flow
rate. This limitation of flow rate during the last 70 percent of FVC is due to the
dynamic compression of the airway walls.
Inspiratory and Expiratory Pressures
An individual’s maximum inspiratory pressure (MIP) and maximum expiratory
pressure (MEP) are directly related to muscle strength. These measurements
can help evaluate a patient’s ability to maintain spontaneous, unassisted
ventilation. MIP should be measured at the patient’s residual volume, and MEP
should be measured at the patient’s total lung capacity.