4. Static and dynamic lung volumes, flow-volume loops, evaluation of lung function tests, pharmacodynamic test Flashcards
What static lung volume is high in Obstructive lung diseases?
Functional Residual Capacity, aka Expiratory Reserve Volume + Residual volume
This is because in obstructive diseases, air trapping makes the lungs hyperinflated and even on full forced expiration, a lot of air stays back in the lungs
Total Lung Capacity is INCREASED
What trend do we see in Inspiratory and Tidal volumes in Obstructive Lung Diseases?
Inspiratory Reserve Volume and Tidal Volume are usually lower than normal
This is because these patients already have residual air present on full expiration from air trapping. This makes it harder for patients to breath in fresh air on top of already inflated lungs
What trends do we see with static lung volumes in Restrictive Lung Diseases?
In restrictive lung diseases, the lungs are not compliant and tend to collapse due to increased fibrosis and ‘stiffness’ in lungs. This makes it harder for patients to breath in fresh air AND store air after full expiration
Thus, Functional Residual Volume, Tidal volume, Inspiratory Reserve Volume are ALL LOWER than normal
Total Lung Capacity is DECREASED
What shift we observe in Flow-Volume loops for Obstructive Lung Disease?
‘Left’ shift occurs from normal
FVC is reduced
RV is increased
TLC is increased
What shift we observe in Flow-Volume loops for Restrictive Lung Disease?
‘Right’ shift occurs from normal
FVC is reduced significantly
RV is reduced
TLC is reduced
What trends we observe in Forced Spirometry regarding Lung diseases?
Obstructive Lung Diseases:
- FEV1 is significantly reduced
- FVC is reduced
- FEV1/FVC ratio < 0,7
Restrictive Lung Diseases:
- FEV1 is slightly reduced
- FVC is significantly reduced
- FEV1/FVC ratio > 0,7 or equal to 0,7
How do we differentiate between COPD and Asthma when it comes to Obstructive Lung Disease dx?
Bronchodilator and Bronchoconstriction Tests
In Asthma SABA will improve FEV1 > 12% [considered reactive, reversible]
In Asthma Methacholine will decrease FEV1 by 20% [considered inducible]
In COPD SABA will improve FEV1 < 12% [considered non-reactive, irreversible]
Thus a pharmacodynamic test involving SABA and Methacholine that increases FEV1 more than 12% post SABA and decreases FEV1 by 20% post Methacholine is suggestive of Asthma more than COPD [consider patient history to make clinical diagnosis]
