Systematic Interpretation of Pulmonary Function Testing
I.
Calculate the percent of predicted values for each parameter measured except for the
FEV1.0/FVC%.
a. Percent Predicted (% pred.) = measured / predicted
b. Example:
i. measured FVC = 3.5L, predicted FVC = 4.0L
ii. % predicted = 3.5 / 4.0 = 0.88 = 88% predicted
II.
Interpret the results
a. Forced Vital Capacity (FVC)
i. Normal > 79% predicted
ii. Mild restriction = 60-79% predicted
iii. Moderate restriction = 40-59% predicted
iv. Severe restriction < 40% predicted
v. Note: Use this parameter to determine overall degree of severity for
restrictive diseases
b. Forced Expiratory Volume 1.0 (FEV 1.0)
i. Normal > 79% predicted
ii. Mild decrease = 60-79% predicted
iii. Moderate decrease = 40-59% predicted
iv. Severe decrease < 40% predicted
v. Decreased in both obstructive and restrictive diseases
c. FEV1.0/FVC%
i. Evaluate the actual reported value, do not calculate percent of predicted
ii. Normal >70%
iii. Mild obstruction = 61-69%
iv. Moderate obstruction = 45-60%
v. Severe obstruction < 45%
vi. Note: Use this parameter to determine overall degree of severity for
obstructive diseases
d. Forced Expiratory Flow 25%-75% (FEF 25-75%)
i. Normal > 79% predicted
ii. Mild obstruction = 60-79% predicted
iii. Moderate obstruction = 40-59% predicted
iv. Severe obstruction < 40% predicted
v. Indicates integrity of small and medium sized airways
e. Forced Expiratory Flow 200-1200mL (FEF 200-1200)
i. Normal > 79% predicted
ii. Mild obstruction = 60-79% predicted
iii. Moderate obstruction = 40-59% predicted
iv. Severe obstruction < 40% predicted
v. Indicates integrity of large airways (bronchi)
f. If FEV1/FVC% < 70% and FVC normal, repeat spirometry after bronchodilator
i. If FEV1.0 or FVC increases by > or = 12% (200 mL) or FEF 25-75 increases
by > 30% = asthma
ii. No significant improvement = COPD (emphysema)
g. If FEV1.0/FVC% is < 70% and FVC < 80% predicted, check lung volumes
i. Total Lung Capacity (TLC) < 80% predicted = obstructive and restrictive
disease
ii. TLC normal with increased residual volume (RV) = air trapping,
obstructive disease
iii. TLC > 120% predicted = hyperinflation
h. Lung Volumes: Functional Residual Capacity, Residual Volume, Total Lung
Capacity
i. Normal = 80 – 120% predicted
ii. Obstruction > 120% predicted
iii. Restriction < 80 % predicted
iv. RV/TLC%: normal = 20 – 35%
i. Diffusing Capacity (DLCO)
i. Measures the ability of the lungs to transfer gases across the alveolarcapillary membrane
ii. Normal = 25 mLCO/min/mm Hg (STPD)
iii. Obstruction with hyperinflation and decreased DLCO = emphysema
iv. Obstruction with hyperinflation and normal DLCO = asthma
v. Restriction with decreased DLCO = pulmonary fibrotic diseases,
pneumonia, atelectasis, pulmonary edema
vi. Restriction with normal DLCO = neuromuscular diseases, kyphosis,
scoliosis
vii. Isolated decreased DLCO = anemia, pulmonary embolism
j. Maximum Voluntary Ventilation (MVV)
i. The largest volume of gas that can be moved in and out of the lungs in one
minute
ii. Evaluates respiratory muscle strength, compliance, airway resistance, and
neural control mechanisms
iii. Normal > 80% predicted, (150 to 200 L/min) only large reductions are
significant
iv. MVV decreases in COPD
v. MVV decreases with age
vi. MVV relatively normal in restrictive diseases
vii. Estimate the MVV
1. FEV1.0 x 35 = minimum expected MVV
2. The patient may not achieve the minimum expected MVV for the
following reasons
a. poor effort
b. fatigue
viii. Calculate the MVV
1. The MVV is measured for 12 seconds or 15 seconds and then
extrapolated out to 1 minute’s time (if we were to have the patient
breathe like that for a whole minute they would probably collapse).
a. For 12 second volume collection
i. if measured for 12 seconds, then 60 sec./12 sec. = 5
ii. multiply the volume measured in 12 seconds by 5
iii. 25 L x 5 = 125 L/min.
b. For 15 second volume collection
i. if measured for 15 seconds, then 60 sec./15 sec. = 4
ii. multiply the volume measured in 15 seconds by 4
iii. 25 L x 4 = 100 L/min.
k. Peak Expiratory Flow Rate (PEFR)
i. The maximum flow rate that can be achieved during an FVC maneuver
ii. Reflects flow from the large airways (effort-dependant portion of the
FVC)
iii. Normal > 80% predicted
iv. Decreases in obstructive disease and with age
v. Inexpensive and effective measurement used both in the hospital and at
home to monitor airway integrity in patients with reactive airways disease
III.
Summary of Interpretation of Spirometry
Interpretation:
FVC
FEV1.0
FEV1.0/FVC%
Normal
Normal
Normal
Normal
Obstructive
Normal
Decreased
Decreased
Restrictive
Decreased
Decreased
Normal
Mixed
Decreased
Decreased
Decreased