Flashcards in Pulmonary Function Tests Deck (28):
What is a "volume" in terms of pulmonary function?
something you can measure
What is a "capacity" in terms of pulmonary function?
a combination of 2 or more volumes
Since having a patient exhale as much air as they can and then holding it, in order to measure residual volume, what do we do instead?
use the functional residual capacity (FRC) minus the expiratory reserve volume (ERV).
Does residual volume tend to be large if FRC is large?
What does a pulmonary function test (PFT) demand?
reproducible maximal effort (about 3 times). Take the highest sum of FVC + FEV1.
How do we measure the FRC?
using a body plethysmograph and the application of Boyle's law= the pressure and volume of a gas have an inverse relationship when temperature is held constant.
What does an increased FRC represent?
HYPERINFLATION (NOT necessarily emphysema)!
Where is hyperinflation seen?
- structural changes as with emphysema
- compensatory overinflation as in post operative pneumonectomy.
- deformity of chest wall
- partial obstruction of the airway as with asthma.
What do we need to explain to pts with COPD whom complain that they can't get a breath in?
that it is because they weren't able to get their last breath all the way out!
What is forced vital capacity (FVC)?
maximum amount of air that can be exhaled after a maximal inhalation. It measures the expansion of the chest wall and lung, and the ability to forcefully exhale.
What is slow vital capacity (SVC)?
same as FVC only this is blown out slowly rather than forcefully.
*Should be the same as FVC in healthy individuals.
When will FVC be reduced?
RESTRICTIVE lung disease and in severe obstruction
What is FEV1?
the forced vital capacity blown out in the FIRST second (should be greater than 70% of FVC). This measures the diameter/patency of the airway.
When will FEV1 be reduced?
OBSTRUCTIVE lung disease, because as the diameter NARROWS, less volume can go through the airways.
What is the main purpose of PFTs?
to narrow your differential diagnosis to:
- combined obstruction and restriction
What is obstruction defined as using PFTs?
FEV1/FVC that is less than 70%
What are some causes of obstructive patterns?
- chronic bronchitis
- retained secretions
- foreign body
- enlarged lymph nodes
- peribronchial edema
What is important to remember regarding errors when grading past FEV1/FVC ratios with current FEV1/FVC ratios?
look at BOTH numbers and not just the ratio, because if both numbers are decreasing, the ratio may look fine, when really the pt is getting worse.
**** What is a RESTRICTION?
an inability to get the air INTO the lungs (decrease in ALL lung volumes; or you can say the VC and RV are down because this encompasses them all). If less than 80% in all volumes, then you have a restriction.
What can cause a RESTRICTION?
problems of lung parenchyma, pleura, chest wall, or neuromuscular disease:
- myasthenia gravis
- lung fibrosis- sarcoidosis
- fibrocalcific changes to the pleura
What is used for a SPECIFIC PFT?
diffusion of lung using carbon monoxide (VERY LITTLE so not harmful). This measures the rate at which O2 and CO2 can diffuse across the alveolar/capillary membrane (because it doesn't build up).
What will decrease the diffusion of carbon monoxide in a specific PFT?
lung fibrosis and excessive lung fluid
*** What is the equation for diffusion capacity of the lung?
(he said not to memorize but it makes sense logically)
area x (P1 - P2)/ thickness
*aka as the area decreases or the thickness (scaring) of alveolar-capillary interface increases, the diffusion decreases.
What happens to the alveoli in emphysema?
instead of having nice nooks and crannies (like an english muffin), they are large and flat (like flat bread), and because you lost the nooks and crannies, you lose the extra surface area created by them.
As a RBC passes through the lung capillary bed (in 0.75 sec), how long should it take to pick up all of the O2 that it needs?
Why do emphysema pts (or any diffusion abnormality) feel short of breath when the get up and move around or have a high fever, but relieved when they rest?
it already takes them longer to pick up all the O2 that they need (increased diffusion time) and because the cardiac output increases with exertion, this decreases the transit time of the RBC and thus the available time for diffusion, leading to less RBCs carrying their maximum O2 :(
If the FEV1/FVC is 49% and the FVC is 59%, what is the diagnosis?
obstructed and possibly restricted, but you can't comment on that because you don't have the RV (even though you have the FVC, which covers all volumes except RV). So you would have to do an FRC to determine if the RV is also down, to diagnose a restriction.