useful in differentiating the pattern of lung disease ( obstructive vs. restrictive ) assess lung volumes, flow rates, and diffusi...
- 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
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
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 | decreased | decreased or N |
Lung Volumes
| Obstructive | Restrictive | |
| TLC | increased or N | decreased |
Diffusion Capacity
| Obstructive | Restrictive | |
| DCO | decreased or N | decreased or N |
Interpreting PFTs
Dco decreases with:
1. Decreased surface area (i.e. emphysema)
2. Decreased hemoglobin (i.e. anemia)
3. Interstitial lung disease
4. Pulmonary vascular disease
