Pulmonary Function Tests Flashcards
Volume vs. capacity
- volume is the smallest subunit
- capacity has at least two volumes (ex: all volumes and capacities together make up total lung capacity TLC)
Tidal Volume (TV)
the amount of air inspired during normal, relaxed breathing
Inspiratory reserve volume (IRV)
additional air that can be forcibly inhaled after the inspiration of a normal tidal volume.
expiratory reserve volume (ERV)
additional air that can be forcibly exhaled after the expiration of a normal tidal volume.
Residual volume (RV)
volume of air still remaining in the lungs after the expiratory reserve volume is exhaled.
total lung capacity (TLC)
maximum amount of air that can fill the lungs (TLC = TV + IRV + ERV + RV).
vital capacity (VC)
total amount of air that can be expired after fully inhaling (VC = TV + IRV + ERV)
inspiratory capacity (IC)
maximum amount of air that can be inspired (IC = TV + IRV).
functional residual capacity (FRC)
amount of air remaining in the lungs after a normal expiration (FRC = RV + ERV)
Why FRC is so frequently used in pulmonary testing
- most reproducible of all lung volumes and capacities
- tends to be the most accurate
Two opposing forces that determine changes in FRC
- two opposing elastic recoils are:
- the chest wall pulling out and the lung pulling in
- when these two forces equalize you stop at that volume
Diseases like emphysema that reduce lung elastic recoil results in a ____ in the FRC
-rise (FRC increases)
In diseases that increase the lung elastic recoil (interstitial lung diseases) the FRC will
-Fall
In emphysema, which force is predominant–the lung or the chest wall? Consequences for FRC?
-Because elastic recoil is lost in emphysema and there is no change in chest wall recoil, the forces of the chest wall outweigh the lung forces and “pull” the FRC higher into the lung volume
In infiltrative diseases which force is predominant?
-since elastic recoil increases, FRC “falls”
Volume-pressure curve–x and y axis
- x axis: Translung pressure (cm H2O)
- y axis: Vital capacity (L)
When lungs go from a normal size to a smaller size (bucket to cup) it is called obstructive or restrictive lung disease?
-Restrictive
When lungs go from a bucket to a bottle, it is called?
-Obstructive
Main problem in obstructive lung diseases
- Volume is NOT the issue
- it is the ability to empty the lung–determined by the degree of obstruction as measured by flow
Hallmarks of obstructive and restrictive lung diseases
- Obstructive: reduced FLOW
- Restrictive: reduced VOLUME
Examples of obstructive diseases vs restrictive lung diseases
Obstructive: COPD, Asthma, Bronchiectasis
Restrictive: Everything else (interstitial lung disease, pleural disease like effusions or pneumothorax, neuromuscular diseases and chest wall deformities, central brain problems, etc)
More use of PFTs for obstructive or restrictive disease?
Obstructive
How to measure whether there is obstruction or restriction?
- Spirometry–ask pt to blow as hard and as fast and as long as they can into a spirometer–measures how much air can be forcibly exhaled.
- called Forced Vital Capacity (FVC)
- Another calculation made of how much of the FVC is able to be exhaled in first second–called FEV in 1 sec
Obstructive vs. restrictive disease in spirometry
- Obstructive–low FEV1 aka low FEV1/FVC ratio
- Restrictive–looks like a normal one but with less volume (shorter curve)
