Interpretation of Lung Function Flashcards
What are the values of lung function dependent on
- Age
- height
- sex
- BMI
- ethinic origin
What are the 4 main lung function tests
- Spirometry
- PEF
- Lung volume
- Gas exchange
What does spirometry measure
Spirometry measures the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled
What are the two measurements that spirometry measures
- forced vital capacity (FVC)
- Forced expiratory volume in one second (FEV1)
what is forced expiratory volume in one second
This is the amount of air you can blow out within one second.
- With normal lungs and airways you can normally blow out most of the air from your lungs within one second.
What is forced vital capacity
The total amount of air that you blow out in one breath.
what is the ratio in spriometry
FEV1 divided by FVC (FEV1/FVC).
- Of the total amount of air that you can blow out in one breath, this is the proportion that you can blow out in one second.
spirometry is more
reproducible than PEF
What airways does spirometry mostly detect changes in
- Mostly detects changes in the smaller airways
What is PEF
- Maximal rate that a person can exhale during a short maximal expiratory effort after a full inspriation
What is PEF useful for detecting
- detecting changes or trends in a patients asthama control
What type of airways does PEF detect changes in
- detects changes mostly in the larger airways
PEF has significant
testing variability
what is the differences in spirometry in obstructive and restrictive lung disorders
Obestructive
- FEV1 is lowered by a greater proprotion than the FVC
- FVC is lowered
- FEV1/FVC is lowered
restrictive
- FEV1 is lowered
- FVC is lowered
- FEV1/FVC is raised or normal
What is the normal FEV1/FVC ratio
when the ratio is 0.7 or 70% or above
If the FEV1/FVC falls below 0.7 what type of lung disease is this
Obstructive
Name some obstructive disorders
- asthma
- COPD
- endobronchial tumour
- foreign body
Name some restrictive disorders
PAINT P- pleural A - alveolar I - interstitial N - neuromuscular T - thoracic cage
define tidal volume
- volume of air breathed in and out in each breath at rest
How do you wokr out inspriatory capaicty
IRV + TV
How do you work out vital capacity
IRV + TV + ERV
How do you work out total lung capacity
IRV + TV + ERV + RV
How do you work out functional residual capacity
ERV + RV
Why can you not measure residual volume on spirometry
- RV cannot be expired
- Since RV is the volume left in the lungs after a maximal expiration, it cannot be measured by simple spirometry. Similarly, the capacities containing RV (i.e. FRC & TLC) cannot be measured directly with a spirometer
How do you measure residual volume
- use a tracer gas (helium) which mixed with the air in the lung but does not diffuse out the lung
- the volume is then determined by the amount that this tracer gas is diluted as it mixes with the air in the lungs
How do you measure oxygen transfer
O2 transfer is measured indirectly using CO
- CO has a higher affinity than oxygen
What happens to the flow volume loop in obstruction
- loop moves to the left
What happens to the flow volume loop in restrictive
- loop moves to the right
What happens to the flow volume loop in extrathroacic tracheal obstruction
- inspriatory loop is flattend but the expriatory loop is normal
What happens to the flow volume loop in intrathroacic large airway obstruction
- expiratory loop is flattend but the inspiratory loop is normal
anything between
80-120% is given as normal in lung function tests
- excpet the FEV1/FVC ratio in which the normal value is 0.7
Why do you measure alveolar volume
- measures CO transfer or KCO
