Lung Volumes and Function Testing Flashcards
When is lung compliance higher? When is it lower?
. Compliance higher at lower pressure (more pliable)
. Compliance lower at high pressures (stiffer)
Define compliance.
The ease with which the lungs can expand under pressure.
When is lung compliance highest?
At moderate lung volumes (very high or low volumes give lower compliance)
What does surfactant do?
Reduces surface tension of alveoli to make them more stable and less likely to collapse. Means that alveoli inflate to equal sizes with same pressure (e.g. smaller volume alveoli have more surfactant so inflate faster than larger volume alveoli so they ultimately inflate to the same size)
Define tidal volume. What is a normal value for this?
Volume of air entering and leaving the lungs when breathing normally (normal is around 0.5l)
Define inspiratory reserve volume (IRV)
The additional volume of air that can be forcibly inhaled after a normal tidal volume is inhaled
Define expiratory reserve volume (ERV)
The additional volume of air that can be exhaled after a normal tidal volume is exhaled
Define vital capacity
The greatest volume of air that can be expired from the lungs after taking the deepest possible breath in
Define residual volume
The volume of air remaining in the lungs after the ERV is exhaled
Define functional residual capacity
Volume of air in the lungs after passive expiration (at equilibrium with no exertion by diaphragm or respiratory muscles)
Define total lung capacity
Maximum volume of air that the lungs can hold
Define forced vital capacity (FVC)
Total volume of air forcibly exhaled after taking in the deepest breath possible
Compare the similarities and difference of vital capacity (VC) and forced vital capacity (FVC).
. With both, the person (using spirometer) needs to take in the deepest possible breath and a volume plateau should eventually be reached
. With vital capacity, the person breathes out in a relaxed slow way. In forced vital capacity, the person breathes out hard and fast
How can total lung capacity/residual volume be measured?
Can’t be measured using spirometer because can’t expire the residual air, so can use helium dilution or nitrogen washout
How do you work out forced residual capacity from helium dilution?
FRC= Reservoir vol x [(initial conc helium - final conc helium)/ final conc helium)
How does helium dilution work?
. Closed system with set amount of helium in reservoir
. Helium can’t cross alveoli barrier, so closed system
. Patient breathes in helium from reservoir until equilibrium is reached
. Volume of helium in reservoir shows volume of helium in lungs, so can determine lung capacity/volume
How does nitrogen washout work?
. Patient breathes in 100% oxygen and expires into spirometry system
. Procedure repeated until nitrogen in lungs is replaced with oxygen
. FRC calculated from exhaled nitrogen and estimated alveolar nitrogen
What are vitalographs used for?
Measure volume of air expired in a given time, so can work out FEV1 and FVC
What does the flow-volume curve show?
Expiratory flow rate and expiratory volume
What does the initial steep rise of the curve represent?
FVC
What does the maximum volume of the flow-volume curve show?
Total lung capacity
What does the minimum volume of the flow-volume curve show?
Residual volume
What are on the axis of a flow-volume curve?
Volume on the x-axis, flow expiration on the y-axis
At what point are the airways the widest?
When the lungs are fully expanded (max flow)
Which parts of the curve are effort-dependent?
From TLC to PEF because as effort increases, flow rate increases
Which parts of the curve are effort-independent?
From PEF to RV because increase in effort doesn’t decrease flow rate
Draw a flow-volume curve.
(Check notes in purple folder!)
What does gas transfer-diffusion conductance measure?
Used to measure how easily carbon monoxide crosses from alveoli into blood
How is gas transfer-diffusion conductance carried out?
. Patient inhales single breath of dilute CO and holds breath for 10 secs
. Use lung vols and % CO in alveoli at start and end of the 10 sec breath hold to measure gas diffusion
. E.g. with fibrosis gas exchange across the alveoli would be a lot slower due to the thickened alveolar walls
What is the normal value for forced vital capacity?
5 litres
Name 4 factors that would decrease gas exchange in the lungs.
. Decreased alveolar surface area (e.g. emphysema)
. Decreased blood flow (e.g. due to clot- decreases concentration grad for gas exchange)
. Fibrosis (thickens diffusion pathway)
. Decreased surfactant means alveoli have higher surface tension (causes infant respiratory distress syndrome)
Which alveolar cells secrete surfactant?
Type II (small, round, secretory)
