Pulmonary Function Tests + Respiratory Mechanics Flashcards
What do predicted pulmonary test values depend on?
age, height, and sex
What is FVC?
forced vital capacity (amount you can forcefully exhale after forceful inhalation)
If an FEV1/FVC ratio is normal, but FVC is low, what is indicated?
What else is needed to confirm this diagnosis?
restrictive pattern
low total lung capacity would confirm restrictive disease
What measurement will air trapping increase?
In what diseases does this happen?
residual volume
in severe obstructive disease
What happens in obstructive disease w/ pseudorestriction?
air trapping occurs –> RV increases so much it encroaches on the amount of air you can exhale –> FVC is lowered
will see low FEV1/FVC ration w/ low FVC, but NORMAL TLC
What is FEV1?
forced expiratory volume in 1 second
What are the indications for pulmonary function testing?
evaluate symptoms and signs of lung disease assess progression of a disease monitor effectiveness of therapy evaluate preoperative pts screen ppl at risk (smokers, etc) monitor for side effects of other drugs
What is diffusing capacity decreased by?
anemia/conditions that min ability of blood to accept O2
decrease in surface area of alveolar-capillary membrane
conditions that increase membrane thickness
What is measurement of residual volume and TLC useful for?
for pts with obstructive disease - can demonstrate air trapping and hyperinflation
What is diffusing capacity?
measure of the ability of the lungs to transfer gas
What does a low FEV1/FVC ratio indicate?
obstructive pattern
When are pulmonary function tests NOT indicated?
pts without symptoms
results can be confusing w/ heart disease
If FEV1/FVC ratio is low, but FVC is normal, what is indicated?
pure obstructive disease
Is asthma considered an obstructive or restrictive disease?
obstructive
If FEV1/FVC ratio is low and FVC is low, what is indicated?
mixed obstructive and restrictive disase
must have low TLC to confirm
What does a normal FEV1/FVC ratio indicate?
normal or restrictive pattern
What can spirometry NOT measure?
residual volume or total lung capacity
What generally characterizes restrictive lung disease?
can’t fully expand lungs w/ inspiration
What generally characterizes obstructive disease?
can’t fully exhale
What is compliance?
slope of the volume - pressure curve = stretchability of lungs
(deltaV/deltaP)
Where is compliance of lungs the highest?
in the normal breathing range
What is compliance of the lungs the lowest?
at very low volumes and very high volumes
What is hysteresis?
What do we think its due to?
the difference between inspiration and expiration curves
We think it’s because surfactant is in little droplets –> grow during inspiration and blob back up in expiration but in a different pattern
What is the difference in the saline and air volume-pressure curves due to?
presence of surfactant = surface tension exists
remember that saline curve is steeper bc no surface tension
What is the slight hysteresis from saline-filled curve due to?
resistance of the tissue sliding over one another
What is minimal volume?
What the lungs will shrink down to without the ribcage
Why is RV > minimal volume?
because of rib cage - pulls lungs out more than they would like to be alone
If you have a pneumothorax, what happens to the lungs and ribcage?
lungs will shrink down to mv
ribs will pop out without pleural pressure holding them in
At what point do the elastic recoil of the lungs and the rib cage exactly counter each other?
FRC = functional residual capacity
What changes the radius of the airway?
When might this happen?
bronchial smooth muscle –> decreasing radius increases Resistance of airway
would see this in alveolar dead space
In a normal person, how much of the FVC is exhaled in the first second of forced expiration?
70-80%
What is interdepence?
shared walls of alveoli and airways prevent their collapse because the recoils oppose each other
What could reduce interdependence?
emphesema/COPD –> lose some walls –> lose interdependence and other alveoli also collapse
In the work of breathing, what is the largest amount of work/ largest shaded area on graph?
work done to stretch the lungs - opposing compliance
What is the smaller amount of work done/smaller shaded area on the work of breathing graph?
work done to overcome airway resistance
When does expiration have to become active?
when passive recoil isn’t enough –> work done to deflate overcomes the work put into stretching the lungs
