Normal TLC = 94%
Normal DLCO = 86%
Obstructive Lung Diseases=COPD, Bronchiectasis, Asthma
Total Lung Capacity [TLC] & Residual Volume [RV] are increased in all the above three.
FEV1/FVC ratio is reduced in obstructive diseases.
DLCO is reduced in COPD and Bronchiectasis. But, DLCO is normal in Asthma.
Restrictive Lung diseases=2 Types
Total Lung Capacity [TLC] is decreased in below both the types of restrictive diseases.
FEV1/FEV Ratio is Normal [>80%] in Restrictive lung disease.
- Restrictive Intrathoracic=Fibrosis, Sarcoidosis, Pneumoconiosis, Asbestosis
As fibrosis is inside the lung, TLC is decreased, DLCO is decreased, RV is decreased.
2. Restrictive Extrathoracic=Kyphosis, Obesity, Spondylitis, Myasthenia gravis, Muscular Dystrophy, Guillian Barre Syndrome
As there is external pressure on thorax, TLC is decreased, DLCO is normal as lung tissue is normal, RV is increased as air gets trapped due to poor respiratory effort.
If you are given lung volumes,
- First look at TLC, if high, then its one of the Obstructive type of lung disease. If low, then its restrictive type of lung disease.
- Then look at DLCO to further differentiate.
- Finally, look at RV.
Tip to Remember- TDR. [Tender Lung Volumes. lol. ]
Let’s practice now.
Question 1. TLC is high. DLCO is low. RV is increased. What could be the lung condition?
TLC is high means it should be Obstructive lung disease. COPD, Bronchiectasis or Asthma.
DLCO is low. It could be COPD or Bronchiectasis.
RV is increased. It could be COPD or Bronchiectasis. Then probably, history will differentiate these two conditions at this point.
Question 2: TLC low, DLCO is normal. RV is high.
TLC low means it should be restrictive lung disease.
DLCO is normal means Restrictive Extrathoracic like Kyphosis, Obesity etc.
RV is high in both obstructive and some Restrictive lung diseases. RV is increased. It could be COPD or Bronchiectasis. Then probably, history will differentiate further.
What lung volumes do you expect in COPD?
TLC is high as its obstructive lung disease.
DLCO is low in COPD.
RV is high due to trapped air.
Instead of telling you high or low lung volumes, they will give numbers. You can tell if high or low if you remember the numbers I gave on the top of this page.
DLCO can be high in conditions when there is more blood in the lung alveoli and DLCO can be low in conditions when there is less blood in the alveoli.
I hope you are an expert now.