Pulmonary Function Flashcards
What are the three main components of PFTs?
spirometry (how air exits and enters) lung volume diffusion capacity
What are three ways of determining lung volumes?
- helium dilution 2. nitrogen washout 3. body plethysmography
How does helium dilution lung volume testing work?
Helium is inhaled and allowed to equilibrate. decrease in concentration is compared to previous concentration and volume, to calculate for new volume (of the lung)
What equation is used to determine lung volume during body plethysmography?
boyles law P1 V1 = P2V2
What would be characteristic of lung volumes in obstructive diseases?
hyperinflation
Why does emphysema increase lung volumes?
loss of elastic recoil elevates RV, while airway collapse traps gas on exhalation
Why does chronic bronchitis and asthma cause increased lung volumes?
Increased airway resistance traps air and causes hyperinflation
What is responsible for the decrease in lung volumes in restrictive diseases?
INcreased elastic recoil (decreased compliance) decreases lung volume
What is true of lung volumes in restrictive diseases?
they are decreased
What is the volume that patients are asked to inhale on spirometry?
total lung capacity
What is the volume that patients are asked to exhale to during spirometry?
RV
What value is generated from the difference between inhaled volumes and exhaled volumes in spirometry?
the forced vital capacity = TLC - RV
In normal individuals, how long does it take to reach FVC in spirometry?
~ 4 seconds
What is a normal FEV1?
~75%
In health, what is the ratio of FEV1 to FVC?
75% or 0.75
As you age, what happens to FEV1/FVC?
the ratio drops
When there is expiratory obstruction, what happens to FEV 1 and FVC?
FEV1 drops more than FVC, lowering FEV1/FVC
Why does FEV1 drop in obstructive lung disease?
FEV1 drops because of decreased lung elastic recoil pressure or increased airflow resistance
What accounts for the fact that FEV1 tends to drop more than FVC in obstructive disease?
patients compensate by exhaling longer to reach the same FVC
What do restrictive defects do to FEV1 and FVC?
drop both of them
Although FEV1 and FVC drop in restrictive disease, what happens to flow?
Flow at any given point will be higher (isovolume flow)
Why is isovolume flow higher than normal in restrictive defects?
they may be higher than normal because elastic recoil pressure is higher and airway resistance is lower than normal i.e. exhalation is shorter than normal and FEV1/FVC may increase
Although FEV1 and FVC both drop in restrictive diseases, FEV1/FVC can increase. Why?
exhalation is shorter and isovolume flow is higher, so the ratio of FEV1 to FVC is higher
Can you tell asthma and COPD apart on spirometry alone?
no, unless you compare pre and post bronchodilator and see improvements in FEV1 and/or FVC
What type of conditions elevate DLCO?
DLCO is elevated in disorders resulting in increased hemoglobin in areas of intact ventilation (e.g.: alveolar hemorrhage and polycythemia)
What effect does alveolar hemorrhage have on DLCO?
increases it
What effect does polycythemia (from chronic hypoxemia, for example) have on DLCO?
increases it
What type of conditions decrease DLCO?
decreased when ventilation does not match perfusion (i.e. low V/Q) or when there is loss of blood (anemia) or functional blood vessels (pulmonary embolism, emphysema, interstitial lung disease)
What does a low V/Q do to DLCO?
Decreases it
What does anemia do to DLCO?
decreases it
What does pulmonary embolism do to DLCO?
Decreases it
What does emphysema do to DLCO?
decreases it
What does ILD do to DLCO?
decreases it
How do you calculate inspiratory capacity?
TLC - FRC
How do you calculate the expiratory reserve volume?
FRC - RV
how do you calculate theinspiratory reserve volume?
IC-TV
Where is TLC found on the flow volume curve?
on the X axis, where you shift from inspiration to expiration
What does the width of the flow volume curve correspond to?
the FVC
What is suggested by a flattened inspiratory loop on the flow volume curve?
Flattening of the inspiratory loop suggests inadequate strength, effort or technique during the forced inhalation maneuver, or upper airway obstruction (eg, vocal cord dysfunction, epiglottitis, laryngeal edema, and laryngeal malignancy).
Which side of the flow volume loop is asymmetric: expiratory or inspiratory?
expiratory
Why is the expiratory part of the flow volume loop asymmetric?
The normal expiratory loop is asymmetric because higher expiratory flows are generated at larger lung volumes. This is because at higher lung volumes lung elastic recoil pressure (Pel) is greater (like stretching a sponge or rubber band) and airway resistance is lower as the inflated lung “pulls” airways open via the tethering effects of alveoli.
What are the two determinants of maximal expiratory flow?
flow = Pel/Rus
Where Pel: elastic recoil pressure
Rus: resistance distal to the equal pressure point
Why is Ppl (pleural pressure) not part of the equation for maximum flow in the flow volume loop?
Ppl, which is related to effort, is not a part of this equation; thus the concept of effort independence of maximal airflow: expiratory flow is independent of effort
How are expiratory flow rates related to lung volume?
at higher lung volumes, expiratory flow rates are higher
what does the obstructive defect look like on the time volume curve?
A ramp
What does restrictive disease look like on the volume time curve?
a rectangle
Expiratory airflow is decreased most by what combination of pathophysiologic conditions?
a) low Pel and high Raw
b) high Pel and high Raw
c) low Pel and low Raw
d) high Pel and low Raw
a) low Pel and high Raw
b) high Pel and high Raw
c) low Pel and low Raw
d) high Pel and low Raw
Emphysema is best characterized by:
a) high FEV1/FVC
b) hyperinflation with low DLCO
c) high Pel and low Raw
d) fixed inspiratory and expiratory airflow obstruction
a) high FEV1/FVC
b) hyperinflation with low DLCO
c) high Pel and low Raw
d) fixed inspiratory and expiratory airflow obstruction
. Isovolume airflow is high in:
a) asthma
b) vocal cord paralysis
c) pulmonary fibrosis
d) pulmonary embolism
a) asthma
b) vocal cord paralysis
c) pulmonary fibrosis - restrictive disease
d) pulmonary embolism
Which of the following test results suggests asthma?
- Low FEV1/FVC that normalizes after albuterol
- Low FEV1/FVC with low diffusing capacity
- Normal FEV1/FVC after an irritant challenge
- Normal FEV1/FVC with low diffusing capacity
- Low FEV1/FVC that normalizes after albuterol
- Low FEV1/FVC with low diffusing capacity
- Normal FEV1/FVC after an irritant challenge
- Normal FEV1/FVC with low diffusing capacity
Flattening of the inspiratory loop suggests:
a) asthma
b) vocal cord paralysis
c) pulmonary fibrosis
d) pulmonary embolism
a) asthma
b) vocal cord paralysis
c) pulmonary fibrosis
d) pulmonary embolism
