Pulmonary Function Testing Flashcards
Indications for pulmonary function testing
Evaluate signs/symptoms of lung disease
Assess progression of lung disease
Monitor effectiveness of therapy
Evaluate pre-op patients in selected situations
Screen those at risk of pulmonary disease (smokers, occupational exposures)
Monitor for potentially toxic effects of certain drugs or chemicals (e.g., amiodarone, beryllium)
Contraindications to pulmonary function testing
Not generally indicated in pts without symptoms
May be confusing when non-pulmonary diseases that affect pulmonary system are active (e.g., CHF)
Component of pulmonary function testing that results in measurement of air movement into and out of the lungs using respiratory maneuvers, determining how much air can be inhaled and exhaled, and how fast
Spirometry
3 most important measures of spirometry
Forced vital capacity (FVC)
Forced expiratory volume in 1 second (FEV1)
FEV1/FVC ratio
Describe respiratory maneuvers used for spirometry
Pt inhales as deeply as possible, then exhales as long and as forcefully as possible — the amount exhaled is the FVC. The amount of air exhaled during the first second of the FVC maneuver is the FEV1
What effect might asthma or emphysema have on the FEV1?
Decrease it (these are obstructive diseases)
Why might spirometry be repeated?
To check for reproducibility (usually performed 3x)
After giving bronchodilator to check for significant response
Diffusing capacity is another component of PFTs. It is the measure of the ability of the lungs to transfer gas and is most efficient when surface area for gas transfer is high and blood is readily available to accept gas being transferred. What compound is typically used to measure diffusing capacity?
Carbon monoxide, because it is more soluble in blood than lung tissue, and the amount entering the blood is limited by the lungs ability to transfer it (i.e., it binds avidly to Hb)
In what conditions might diffusing capacity be decreased?
Conditions that minimize ability of blood to accept and bind diffusing gas (e.g., anemia)
Conditions that decrease the surface area of alveolar-capillary membrane (e.g., emphysema, PE)
Conditions that alter membrane’s permeability or increase its thickness (e.g., pulmonary fibrosis)
What 2 measurements in pulmonary function testing cannot be determined by spirometry?
Residual volume (RV) Total lung capacity (TLC)
What are 2 ways in which to measure RV and thus TLC? [TLC = RV + FVC]
Pt breathes in inert gas like helium, then concentration of helium is measured in expired air. This measurement is used to calculate RV
Pt sits in airtight booth in which pressure is measured as pt breathes
RV and TLC measurements can be used to add information gained from spirometry. How are these measurements useful in obstructive vs. restrictive disease?
Obstructive: measurement of RV and TLC can demonstrate air trapping and hyperinflation
Restrictive: the TLC is needed to confirm true restriction and better quantitate the degree of restriction
Describe changes (or lack thereof) in FVC, FEV1, FEV1/FVC ratio, and TLC in pt with obstructive disease
FVC decreased or normal
FEV1 decreased
FEV1/FVC decreased
TLC normal or increased
[note that diffusing capacity is typically decreased d/t decreased surface area needed for gas exchange]
To quantify the degree of obstruction, the clinician needs to note the pt’s _____ as a percentage of predicted value
FEV1
Describe changes (or lack thereof) in FVC, FEV1, FEV1/FVC ratio, and TLC in pt with restrictive disease
FVC decreased
FEV1 decreased or normal
FEV1/FVC normal
TLC decreased
[note that diffusing capacity is often decreased d/t altered membrane permeability]
To quantify degree of restriction, one should note either the pt’s _____ or ____ as a percentage of the respective predicted value
FVC; TLC
Once you have identified that a pt has an obstructive pattern on PFTs, if you note that they also have a low FVC, 2 possibilities exist — what are they?
- Mixed pattern with both obstructive and restrictive components (this is the case if TLC is also decreased)
- Obstruction is very severe and has lead to significant air trapping (this is the case if TLC is normal or increased, and RV is increased)
Restrictive patterns seen on PFT may be due to causes inside or outside the lung parenchyma. What is an example of a pulmonary parenchymal cause of a restrictive pattern?
Pulmonary fibrosis
Restrictive patterns seen on PFT may be due to causes inside or outside the lung parenchyma. What are some extraparenchymal causes of a restrictive pattern?
Obesity
Neuromuscular diseases
Chest wall deformities
Large pleural effusions
Restrictive patterns seen on PFT may be due to causes inside or outside the lung parenchyma. How can you distinguish between pulmonary parenchymal causes and extraparenchymal causes?
Distinguish based on diffusing capacity of the lung (DLCO)
If DLCO is still below normal after being adjusted for lung volume, Hb level, or both, then parenchymal disease is likely.
If DLCO is normal after adjustment, it suggests that the cause is extraparenchymal
Bronchoconstricting agent that is administered to confirm the diagnosis of suspected asthma when PFTs have failed to establish diagnosis
Methacholine
[i.e., methacholine challenge test; also usefuly in evaluating occupational asthma]
Is hypersensitivity pneumonitis typically characterized as an obstructive or restrictive pattern on PFTs?
Restrictive
Is alpha 1 antitrypsin deficiency typically characterized as an obstructive or restrictive pattern on PFTs?
Obstructive
In a patient with alpha-1 antitrypsin deficiency, why would you expect their DLCO to be markedly decreased on PFTs?
Neutrophil elastase is an enzyme that breaks down tissue/alveoli in the lung, when unopposed due to deficiency in alpha-1 antitrypsin, there is excessive destruction resulting in decreased surface area for gas exchange
[DLCO = diffusing capacity of the lung]
A patient presents c/o dyspnea on exertion. Pulmonary function testing reveals that the FVC, FEV1/FVC ratio, and total lung capacity are all normal. However, the DLVA (DLCO adjusted for volume) is significantly reduced. What conditions might present this way?
Anemia
Pulmonary HTN
Chronic thromboembolic disease
