Measurements
|
|
Restrictive Lung Disease |
Obstructive Lung Disease |
|---|---|---|
|
FVC |
↓ |
↓/Normal |
|
FEV1 |
↓ |
↓/Normal |
|
FEV1/FVC |
Normal/↑ |
↓ |
|
TLC |
↓ |
↑/Normal |
|
VC |
↓ |
Slightly ↓ |
- DLCO: diffusing capacity for carbon monoxide. Reduced in PCP, interstitial lung disease, emphysema, pulmonary hypertension or any other process that causes pulmonary capillary bed obliteration.
- MIF: maximum inspiratory force. Decreased in progressive neuromuscular dysfunction (e.g., spinal cord injury) and can help predict which patients need mechanical ventilation.
Diagnostic Approach
- Obstructive defect: FEV1/FVC <70% or flow volume loop is curvilinear.
- Asthma: improvement in FEV1 of 12% and >200ml following albuterol; obstruction is responsive to bronchodilators.
- COPD: no improvement in FEV1 following albuterol; check DLCO, lung volume measurements.
- Emphysema: DLCO is low.
- Air trapping: TLC is high.
- Restrictive defect: TLC low.
- DLCO low: interstitial process.
- DLCO normal: chest wall process such as anatomic defect, pleural pathology, or diaphragmatic weakness.
- Isolated low DLCO: consider anemia, early ILD, pulmonary vascular disease.
Evans SE, Scanlon PD. Current practice in pulmonary function testing. Mayo Clin Proc 2003;78:758-763.
Pellegrino R, Viegi G, Brusasco V, et al. ATS/ERS Standardization of Lung Function Testing: Interpretative strategies for lung function tests. Eur Respir J 2005;26:948-968.