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Approach to the Respiratory Patient : Pulmonary Function Tests (PFTs)

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  • useful in differentiating the pattern of lung disease (obstructive vs. restrictive
  • assess lung volumes, flow rates, and diffusion capacity (Figures 4a and 4b below)
  • normal values for FEV1 are approximately ±20% of the predicted values (for age, sex and height); race may affect predicted values

Subcompartments of Lung Volumes

 

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FEV1  Forced Expiratory Volume in one second
MMFR Maximal Mid-expiratory Flow Rate
FVC  Forced Vital Capacity
FEF Forced Expiratory Flow Rate
FRC Functional Residual  Capacity
TLC  Total Lung Capacity
VC Vital Capacity
RV Residual Volume
Dco Diffusion Capacity of Carbon Monoxide

Expiratory Flow Volume Curves

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Obstructive Lung Disease

  • characterized by obstructed airflow, decreased flow rates (most marked during expiration), air trapping (increased RV/TLC), and hyperinflation (increased FRC, TLC)
  • differential diagnosis includes asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), and bronchiectasis

Restrictive Lung Disease

  • characterized by decreased lung compliance and lung volumes
  • differential diagnosis includes interstitial lung disease, neuromuscular disease, chest wall disease, pleural disease, and parenchymal disease (pulmonary fibrosis)

Comparison of Lung Flow and Volume Parameters in Obstructive vs. Restrictive Lung Disease

Flow Rates

 

Obstructive

Restrictive

FEV1
FVC   
FEV1/FVC
FEF25-75

decreased
decreased
decreased
decreased

decreased or N
decreased
increased or N
increased or N

Lung Volumes

Obstructive

Restrictive

TLC   
FRC
VC   
RV   
RV/TLC

increased or N
increased or N
decreased or N
extremely increased
increased

decreased
decreased
decreased
decreased
N

Diffusion Capacity

 

Obstructive

Restrictive

DCO

decreased or N

decreased or N

 

 

Interpreting PFTs

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Dco decreases with:

 

1. Decreased surface area (i.e. emphysema)
2. Decreased hemoglobin (i.e. anemia)
3. Interstitial lung disease
4. Pulmonary vascular disease

Approach to the Respiratory Patient : Pulmonary Function Tests (PFTs) Approach to the Respiratory Patient : Pulmonary Function Tests (PFTs) Reviewed by Radiology Madeeasy on November 06, 2010 Rating: 5
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