Pulmonary Function Tests Flashcards
what is demonstrated with the maximal effort flow volume loop?
the maximal flow that can be attained at each lung volume
when is maximal flow greater? why?
at greater lung volume because airways are distended and have less resistance to flow`
why is the maximal expiratory flow volume curve often used as a diagnostic tool?
because it does not require the use of an esophageal balloon and the test does not require as much patient cooperation because it is effort independent
what types of diseases can be recognized with the MEFV curve?
obstructive and restrictive diseases
how is the MEFV curve recorded?
with a spirometer that measures air flow and expired volume during a breathing cycle. the patient inspires fully and expires with maximal force to residual volume
how can an IVPF curve be converted to a MEFV curve?
by taking points off the flow pressure plateaus at each lung volume and replotting maximal flow vs volume expired
what happens to the MEFV curve when lung elastic recoil pressure is low or if the airway dimensions are restricted?
the maximal expiratory flow rate will be low
what is responsible for the MEFV curve?
dynamic compression
in the flow volume loop, why are the inspiratory and expiratory curves not symmetric?
because dynamic compression is only a factor during expiration
what does a concave down portion of the expiratory curve in the flow volume loop indicate?
increased compliance resulting in increased dynamic compression
what is the FEV1?
the portion of the vital capacity that can be expired in 1 second (usually 80%)
why could looking at the inspiratory portion of the maximal effort flow-volume loop be helpful?
because greater assymmetry of the two portions may point you in the direction of certain diseases
what is normal vital capacity?
4.75 L
when does peak expiratory flow occur in the maximal effort flow-volume loop?
at about 75% of vital capacity
what is FVC?
forced vital capacity
what are two examples of obstructive diseases and how do they impact the MEFV loop?
emphysema and bronchitis.
may cause the expiration part of the loop to become concave (moreso with emphysema) but keep vital capacity the same
what is an example of restrictive disease and how does it impact the MEFV loop?
fibrosis of the lung and it decreases vital capacity and narrows the loop without having much impact on the shape otherwise
what would a change in overall size of the MEFV loop indicate?
a smaller lung
what does a plateau of the MEFV with a decrease in maximum flow indicate?
a respiratory muscle disease or a lack of effort on the part of the patient
which lab finding on the MEFV curve is independent of effort?
concavity in the expiratory portion of the loop.
