When interpreting Lung Function, what values are important to consider before doing so?
Patient’s
- Age
- Sex
- Height
- BMI
- Ethnicity
What different types of Lung Function tests exist?
- Spirometry (Lung Volume)
- Total Lung Capacity (Helium)
- Peak Flow Measurement (Airflow using Vitalograph)
- V/Q Test Matching (Isotopes)
- Measuring Gas Transfer (Comparing PO2 at different sites)
- Exercise Testing (Challenge)
CR1 (L26)
What does a spirometer measure? And what values are often obtained?
Volume and Flow of Air that can be Inhaled and Exhaled.
FEV1 (Forced Expiratory Volume in a second)
FVC (Forced Vital Capacity, total amount you can blow in a breath)
Of the two, which lung function method is more reproduceable?
PEF is less reproduceable than Spirometry
What is PEF?
What do we use it to test?
How do we test it?
Maximum rate/HOW FAST a person can exhale during a Short Maximal Expiratory Effort after Full Inspiratory
Assesses for Airway resistance
COPD/Asthma control at home/GP
Full inspiration + Sharp blow
- Average of Three attempts
With regards to Spirometry, how would the values change in an individual with Obstructive Lung Disease?
Decrease in All Three --------------------------------- FEV1 FVC FEV1/FVC
With regards to Spirometry, how would the values change in an individual with Restrictive Lung Disease?
FEV1
FVC
Increase in FEV1/FVC Ratio
What conditions could lead to Obstructive Lung Diseases?
Foreign Bodies
Asthma
COPD
Endobronchial Tumour
What conditions could lead to Restrictive Lung Diseases?
Pleural Alveolar Interstitial Neuromuscular Thoracic Cage
Though usually, it is more due to
- Intrinsic (Parenchyma Inflammation/Scarring ILD)
- Extrapulmonary Causes (Chest Wall/NMA Pleura, Myasthenia Gravis)
How do we measure TLC/Lung Function?
TLC cannot be measured directly with Spirometry
- Measured by inspiring a FIXED VOLUME of gas (with Helium)
- You then rebreathe it until the Helium is evenly distributed in lung gases
- Helium does not get absorbed into the blood, thus the sample has a lower [Helium] since it is now part of the RESIDUAL VOLUME
- Volume is determined by amount of Tracer Gas is diluted
TLC = V2 = (C1xV1)/C2
- C1 = Helium Inspired
- V1 = Inspired Gas
- C2 = [Rebreathed Gas]
- V2 = Volume
How do we test for Restrictive Lung Disorders?
DLCO (Diffusing capacity of the lungs for CO)
- Quantity of CO transferred per minute from Alveolar Gas to RBCs
- Lung SA available for GE (Va) x Rate of Capillary Blood CO Uptake
- 80-140% is generally a good score
- Below 40% is not
For a Flow Volume Loop, what would we see in Obstructive Lung Diseases?
There would be a reduction in area and a steeper slope
