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Interpreting pulmonary function tests
Selim Krim, MD
Assistant Professor
Texas Tech University Health Sciences Center
Be familiar with the indications for pulmonary function tests (PFT’s)
Use a stepwise approach when interpreting PFT’s
Know how to differentiate obstructive from restrictive pattern
Be familiar with common etiologies of obstructive and restrictive
Know how to distinguish a mixed pattern from air trapping
Know how to distinguish parenchymal from extra parenchymal
causes of restrictive diseases
Indications for PFT’s
To evaluate symptoms and signs of lung disease (eg, cough,
dyspnea, cyanosis, wheezing, hyperinflation, hypoxemia,
To assess the progression of lung disease
To monitor the effectiveness of therapy
To evaluate preoperative patients in selected situations
To screen people at risk of pulmonary disease such as smokers or
people with occupational exposure to toxic substances in
occupational surveys.
To monitor for the potentially toxic effects of certain drugs or
chemicals (eg, amiodarone, beryllium)
Lung volumes and capacities
Flow-volume and flow-time loops
Obstructive disease
Decreased FEV1/FVC ratio (usually<70%)
COPD ( Chronic bronchitis, emphysema)
Response to bronchodilator therapy is defined by an increase
of >12% in FEV1
Staging of obstruction
I: Mild
FEV1≥ 80% predicted
II: Moderate
50%≤FEV1<80% predicted
III: Severe
30%≤FEV1<50% predicted
IV: Very severe
FEV1 <30% predicted or
FEV1 <50% predicted plus
chronic respiratory failure
Restrictive disease
FEV1/FVC normal, FEV1 is decreased or normal, FVC is decreased,
TLC decreased
Intrinsic lung diseases, which cause inflammation or scarring of the
lung tissue (interstitial lung disease) or fill the airspaces with
exudates or debris (acute pneumonitis).
Extrinsic disorders, such as disorders of the chest wall or the pleura,
which mechanically compress the lungs or limit their expansion.
Neuromuscular disorders, which decrease the ability of the
respiratory muscles to inflate and deflate the lungs.
Parenchymal vs. extra parenchymal
causes of restriction
Mixed pattern vs. air trapping
Mixed pattern
Air trapping
Normal or
Pseudorestriction or air trapping
Obstructive vs. restrictive
Stepwise Approach to PFT’s
Case 1
A 51-year-old woman presents for evaluation of shortness of breath,
cough, and wheezing especially in the summer. Her symptoms are
relieved with albuterol, salmeterol, and fluticasone inhalers. She does
not smoke. Her PFT’s are as follow; FVC=83%, FEV1=63%,
FEV1/FVC=58.2%. After bronchodilator therapy her FVC increases
by 12%, FEV1 by 34%, and FEV1/FVC ratio by 29%. Which of the
following patterns is present?
A- Obstructive pattern without response to bronchodilators
B- Restrictive pattern
C- Obstructive pattern with response to bronchodilators
What is the severity of this patient’s defect?
1- Mild
2- Moderate
3- Severe
Case 2
A 68-year-old woman presents for evaluation of shortness of breath
without cough or wheezing. She has systemic lupus erythematosus
(for which she takes prednisone and methotrexate) and hypertension
(for which she takes metoprolol and hydrochlorothiazide). Her
oxygen saturation is 94% by pulse oximetry while breathing room air.
Her hemoglobin concentration is 12.3 g/dL. FVC=60%, FEV1=70%,
FEV1/FVC=88.6%, RV=38%, TLC=53%, DLCO=38%. Which of the
following best describes the pattern seen on this patient’s pulmonary
function tests?
A- Obstructive pattern with suspicion of emphysema
B- Restrictive pattern
C- Obstructive pattern without emphysema
D- Normal spirometry
Case 3
A 68-year-old woman presents for evaluation of progressive
shortness of breath. She describes 18 months of gradually increasing
dyspnea on exertion. She has not noted any prominent cough,
wheezing, chest pain, lightheadedness, or edema. Her review of
systems is positive only for cold fingers and mild joint pains. She has
never smoked and has no other medical history. Her only medication
is hormone replacement therapy. Her FVC=96%, FEV1=101%,
FEV1/FVC=81.7%, TLC=83%, DLCO=43%, Adjusted DLCO=59%.
Which of the following are potential causes of this pattern?
A- Anemia
B- Pulmonary arterial hypertension
C- Chronic thromboembolic disease
D- Obesity
E- All of the above
Case 4
A 45-year-old man is evaluated for mild dyspnea on exertion. He has
smoked 1.5 packs of cigarettes a day for 30 years. His personal and
family medical history is unremarkable. On physical examination, the
chest is clear; cardiac examination and chest radiograph are normal.
Spirometry shows the FEV1 of 70%, FVC of 75%, FEV1/FVC of
68%. After administration of a bronchodilator, the FEV1 rises to 80%
and the FVC to 85%; the FEV1/FVC ratio is 75%. The serum IgE
concentration is normal, and there are no eosinophils on the
peripheral blood smear. Which of the following is the most likely
A- Chronic obstructive pulmonary disease, stage 0
B- Chronic obstructive pulmonary disease, stage 1
C- Chronic obstructive pulmonary disease, stage 2
D- Moderate persistent asthma
E- Restrictive lung disease
Case 5
A 64-year-old woman is evaluated for a 9-month history of progressive
exertional dyspnea and nonproductive cough. She is an ex-smoker with a 30pack-year history. She has no constitutional symptoms or environmental
exposures. There is no history of cardiovascular disease. She was recently
treated with several courses of oral antibiotics for “bronchitis.” On physical
examination, no exanthem or joint abnormalities are apparent. Cardiac
examination is normal. Bibasilar, coarse mid to end-inspiratory crackles are
noted. Chest radiograph shows increased bibasilar reticular markings in the
periphery that were not evident 3 years ago. Pulmonary physiology shows a
decreased total lung capacity (TLC), force vital capacity (FVC), and forced
expiratory volume in 1 sec (FEV1), an increased FEV1/FVC ratio, and a
decreased diffusing capacity for carbon monoxide (DLCO). Which of the
following tests is most likely to provide specific diagnostic and prognostic
A- Measurement of antinuclear antibodies and rheumatoid factor
B- Timed walk test with oximetry (6-minute walk test)
C- High-resolution computed tomographic scan (HRCT)
D- Gallium scan
E- Cardiopulmonary exercise test
Case 6
A 53-year-old man is evaluated for a 6-month history of progressive dyspnea,
mild cough, and fatigue. He had been previously healthy and has never
smoked. His medical history includes systemic hypertension diagnosed 18
months ago, which is controlled with an ACE inhibitor. Results of his physical
examination are normal. Chest radiograph and high-resolution computed
tomography show increased basal and peripheral predominant reticular lines
and moderate basal ground-glass opacity without honeycombing. Pulmonary
function studies show a forced vital capacity (FVC) of 73% of predicted and a
carbon monoxide diffusing capacity (DLCO) of 56% of predicted. Oximetry is
normal at rest, but desaturation to 84% is noted with brisk walking. What is
your diagnosis?
A- Non specific pneumonitis
B- Asthma
D- Emphysema
E- Idiopathic pulmonary fibrosis
Case 7
An 18-year-old male high school football player is evaluated for recurrent
episodes of dyspnea, chest tightness, and cough that have occurred during a
game and limited his ability to participate. The symptoms resolve
spontaneously in 20 to 30 minutes. The patient's father has known allergies
but no known lung disease. On physical examination, the patient is a healthy
young man; the lungs are clear on auscultation. Office spirometry shows an
FEV1 of 90% predicted and FEV1/FVC 80%. Which of the following is the
most appropriate next step in the evaluation of this patient?
A Measure lung volumes and diffusion capacity
B Perform an exercise challenge test
C Perform allergy skin testing
D Prescribe a physical conditioning program
Case 8
A 44-year-old woman is hospitalized because of respiratory failure. She has
had flu-like symptoms with arthralgias, low-grade fever, cough, and rare
hemoptysis for 2 months. Respiratory failure developed during the past 48
hours. Three days ago a chest radiograph revealed bibasilar alveolar
infiltrates. Physiology revealed an FVC 85% of predicted, FEV1 88% of
predicted, and a DLCO of 120%. On physical examination there is no
exanthem. Loud end-inspiratory bilateral crackles are heard. Mild anemia is
present. The PaO2 is 48 mm Hg, and the PaCO2 is 29 mm Hg. The current
chest radiograph shows extensive bilateral infiltrative lesions. Intravenous
therapy with appropriate antibiotics for overwhelming community-acquired
pneumonia is begun; 24 hours later respiratory failure continues. Which of the
following is the best management option for this patient?
A- Surgical lung biopsy
B- Corticosteroids
C- Bronchoscopy with bronchoalveolar lavage
D- High-resolution computed tomography of the chest
Key points
Along with PFT’s a good history and physical exam usually help
getting the right diagnosis
First look at the ratio FEV1/FVC, if low think obstructive disease the
next step in that case is to assess for the severity of the obstruction
by looking at the FEV1
If FEV1/FVC is normal, think either restrictive disease or normal
pattern. The next step is to check for the FVC, if FVC is low the
diagnosis is restrictive disease. A normal FVC indicates a normal
Finally when dealing with a restrictive pattern, a decreased corrected
DLCO indicates parenchymal disease were as a normal corrected
DLCO indicates extra parenchymal disease.