Pulmonary Function Tests Flashcards
What is the main test used to identify obstruction?
Spirometry
What is the main test used to identify restriction?
Lung Volume Determination
What is the main test used to identify diffusion defects?
Diffusion Capacity Measurement
What is the normal range of PFT values determined by?
Within 80-120% of the predicted values
What do pre- and post- values refer to in the PFT?
Pre and post bronchodilator treatment
What happens to the spirometry measurements in obstruction?
In Obstruction, less air is exhaled per unit time than expected for any given lung volume.
How is spirometry conducted?
After a full inspiration, patient blows out as forcefully as possible until all air has been exhaled.
What is the main value that identifies obstruction?
Reduced FEV1/FVC Ratio below 0.7
What will happen to the flow volume loop in cases of obstruction?
Scooping will occur
When is airflow on expiration the highest?
At High Lung Volumes. Both elastic recoil and airway diameter are maximal and thus flow is highest.
What is the normal range of FEV1?
At least 70%. Younger people should have an FEV1 closer to 80%.
What is reversibility of obstruction with a bronchodilator indicative of?
Response to a bronchodilator is indicative of asthma
What is a methacholine challenge?
Used to determine hyper reactivity in cases of asthma
What defines hyper reactivity?
FEV1 decreases by 20% in response to methacholine
What are the common obstructive diseases?
Asthma
COPD
Bronchiectasis
Where does the obstruction occur the majority of the time?
99% of the time it will be found in the lower airways
What is seen in small airway obstruction (lower)?
- obstruction worsens as lung volume decreases
due to decreased “tethering” of bronchioles
- gradually decreasing airflow
What is seen in large airway obstruction (upper)?
Obstruction even at high lung volumes since large airways don’t depend upon “tethering” to remain open
What will be the flow in upper airway obstruction at high lung volumes?
Flow is STILL reduced - in contrast to lower airway which will still have higher airflow at high lung volumes
What are the features of Fixed upper airway obstruction?
- Intra-thoracic pressure changes do NOT affect the
degree of obstruction - Both Inspiratory and Expiratory limbs of the FVL are affected
- Obstruction may be located either intra- or extra-thoracic
What are the features of Variable upper airway obstruction?
There are two types:
- Inspiratory limb affected = Extra-thoracic obstruction
- Expiratory limb affected = Intra-thoracic obstruction
How does inspiratory variable upper airway obstruction occur?
Caused by extra thoracic obstruction as expiration is unaffected. Inspiration could be obstructed by trachea narrowing.
How does expiratory variable upper airway obstruction occur?
Caused by intrathoracic obstruction as inspiration is unaffected. Expiration is obstructed due to the pressure increase in the lung upon exhalation
What can cause an intrathoracic UAO?
Tracheomalacia
What can cause an extra thoracic UAO?
Vocal Cord Dysfunction
What are some techniques that can be used to measure lung volumes?
- Helium Dilution
- Body Box Plethysmography
What happens to lung volume with increased elastic recoil?
It will decrease
What is RV?
The volume of gas trapped due to airway closure
What is FRC determined by?
The balance between Elastic Recoil of the Lung (in) vs Chest Wall (out)
What is the main value that identifies restriction?
Reduced Total Lung Capacity below 80% of predicted value
What are the 3 categories of diseases that can cause restriction?
- Interstitial Lung Disease
- Chest Wall Disease
- Neuromuscular Disease
How does interstitial lung disease cause restriction?
Increases the elastic recoil of the lungs
How does chest wall disease cause restriction?
Decreases the elastic recoil of the chest wall
How does neuromuscular disease cause restriction?
Decreases TLC and Increases RV
What are examples of interstitial lung diseases?
- Sarcoid
- Hypersensitivity Pneumonitis
- Idiopathic Pulmonary
- Tuberculosis
What are examples of chest wall diseases?
- Obesity
- Kyphoscoliosis
What are examples of neuromuscular diseases?
- ALS
- Muscular Dystrophy
How is neuromuscular disease proven in relation to PFTs?
- Negative Inspiratory Force (NIF)
- Positive Expiratory Force (PEF)
What is the most likely cause of restrictive lung disease?
Interstitial lung diseases
What is the diffusion capacity?
Alveolar-Capillary Surface Area available for gas exchange
How is the diffusion capacity determined?
Using CO to test. Carbon Monoxide easily diffuses across alveolar and capillary membranes.
DLCO = [CO]inhaled - [CO]exhaled
DLCO is used as a measure of the diffusion capacity - normal is 25
What is the corrected DLCO?
It is corrected using the patient’s Hb
DLCO x (15/Pt Hb) = Corrected DLCO
What is the DL/VA?
It corrects for the patient’s lung volume
DL/VA = DLCO corrected / Alveolar Volume
What is a reduced DLCO indicative of?
- Loss of alveoli - Both Emphysema and ILD
- Loss of capillaries - Pulmonary Hypertension
- Anemia
What is an increased DLCO indicative of?
- Alveolar Hemorrhage
- CHF
- Polycythemia
When is the DLCO expected to be low?
Expected DLCO to be low in any disease with loss of either alveoli or capillaries. Both obstruction (emphysema) and restriction (pulmonary fibrosis) will have a low DLCO.
When is pulmonary HTN suspected?
Suspect Pulmonary Hypertension when DLCO is low but spirometry and lung volumes are normal
Reduced FEV1/FVC Indicates
Asthma
COPD
Bronchiectasis
Reduced TLC Indicates
Interstitial Disease
Chest Wall Disease
Neuromuscular Disease
Decreased DLCO Indicates
Associated with COPD and/or ILD
Isolated indicates Primary Pulmonary HTN
