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
