PATHOPHYS: PFTs Flashcards
What are some indications for PFTs?
- Symptoms (dyspnea, cough)
- Pre-Operative Evaluation
- Occupational exposure
- Evaluate therapeutic response
What is the “lung age”?
way that you can “coach” patients and explain the results of PFTs
What are the common PFTs that are run together?
Spirometry MVV Lung volumes DLCO ABG
What dimesions are measured with PFTs?
Volume
Flow
Pressure
What should you do when you look at a spirometry reading?
- Check test quality
- Check vital capacity
- Look at FEV1/FVC (should be around 80%)
ON TEST
What factors impact vital capacity?
Sex
Age (negative correlation)
Height (positive correlation)
NOT WEIGHT!!!!
ON TEST
What is considered to be a positive post-bronchodilator response?
200 ccs and 12% of vital capacity
OR
15% from basal FEV1
ON TEST
What is MVV?
Maximal voluntary ventilation: gross predictor of the strength of the lung
What should your MMV be?
40 times FEV1
What makes up the vital capacity?
Tidal volume + IRV + ERV
TEST
What makes up the functional residual capacity?
Expiratory reserve volume + Residual volume
TEST
True or False: both restrictive and restrictive lung disorders have low FVCs.
TRUE
How do you define an obstructive ventilatory defect?
FEV1/FVC ratio below 70%
ON TEST
What lung volume cannot be measured by spirometry?
Residual volume
How do you measure TLC?
Spirometry + Body plethysmograph (gold standard)
ON TEST
What type of diseases decrease TLC?
Disease of thorax, inspiratory muscles, pleural diseases, and loss of functioning alveoli
What type of diseases decrease VC?
- Chest pain (too much pain to have maximum inspiratory effort)
- Fatigue
- Poor effort
What is dynamic hyperinflation?
People with obstructive airway diseases air-trap in the chest due to destruction of septi between alveoli which increases the residual volume! When a patient with COPD exercises, the hyperinflation gets worse (stacking of air with each inspiration).
ON TEST
What capacity is decreased due to static hyperinflation?
Inspiratory capacity
What is compliance?
change of volume over change in pressure
What is the compliance of a restrictive disease?
LOW (takes a lot of pressure to change a little volume)
ON TEST (know curves)
What is the compliance of an obstructive disease?
HIGH (takes a little pressure to make a large volume change)
ON TEST (know curves)
A normal slow vital capacity excludes what type of disorder?
a restrictive disorder
What is commonly seen in COPD patients?
concominant restriction
What leads to flow velocities being higher for each given instantaneous volume?
elastic recoil of the lungs
ON TEST
What are the two portions of an expiration in the flow loop?
Effort dependent AND a portion that is driven by elastic recoil of the lungs
What leads to “cut off” inspiration and expiration?
upper airway obstruction (tracheal stenosis)
How quickly does oxygen exchange occur in the capillary?
all exchange is done in the first 1/4 of the capillary transit time
What does the lung diffusion capacity measure?
Functioning capillary bed in contact with ventilated alveoli
What do things like emphysema and fibrosis do to the DLCO?
Decrease DLCO
What does blood in the lungs (ex. Goodpasture’s syndrome) do to the DLCO?
Increase DLCO
What is used to measure the DL of the lung?
carbon monoxide
What leads to a “cut off” inspiration only?
Extrathoracic upper airway obstruction (vocal cord paralysis)
What leads to a “cut off” expiration (which slightly alters inspiration)?
Intrathoracic upper airway obstruction (endobronchial mass)
True or false: Diffusion has a small role in producing gas exchange abnormalities in resting conditions.
True!
What two things alter DL?
Reduced by reductions in TLC
Altered per gram of Hb
What are the limitations of “single breath” test of DLCO?
it requires inhaled VC of > 1L and 10 seconds of breath holding (which may be difficult for some patients)
What is considered to be “normal” DLCO?
81-140%
How can you differentiate between COPD and asthma?
DLCO is decreased in emphysema
What else can the COPD help differentiate between (restrictive diseases)?
interstitial v. chest wall diseases
Does a positive bronchoprovocation test rule in asthma?
NO! negative test rules it out!
What is considered to be a positive bronchoprovocation test?
FEV1 decrease of 20% with a methacholine dose of 8 mg/dL
