Lung Function Tests Flashcards
What causes variations in lung function?
Age, ethnicity, sex and height.
Tall, young adults will have peak lung function.
How do you measure peak expiratory flow (PEF)?
The patient takes a full breath and exhales as rapidly as possible into a Wright’s Peak Flow Meter or a spirometer.
What are some advantages and disadvantages of measuring PEF?
Portable and suitable for home monitoring.
Not very precise.
Describe the shape of a graph of flow rate against lung volume.
Flow rate rises rapidly to reach the peak value relatively early in exhalation.
Flow rate declines slowly until exhalation is complete.
What are typical values for PEF?
620 (+/-60) litres/min.
A reduced PEF value suggests airflow obstruction (at any level from the small airways up to the larynx).
How do you measure dynamic lung volumes?
During a forced expiration, the forced expiratory volume in one second (FEV1) and the total volume exhaled (FVC) are measured by a spirometer.
FEV1, FVC and FEV1/FVC give an indication of lung volume and the calibre of the airways.
How can dynamic lung volumes be extrapolated from a graph?
Expired volume is plotted against time.
FEV1 can be read off a graph.
FVC = the total volume exhaled.
What are some advantages and disadvantages of measuring dynamic lung volumes?
More reproducible than PEF measurements.
Less portable and effort dependent.
What are typical values for dynamic lung volumes?
FEV1 = 4.5 (+/-0.5) litres.
FVC = 5.6 (+/-0.6) litres.
FEV1/FVC = 80 (+/-5)%.
How do certain lung pathologies affect dynamic lung volumes?
Reduction of FEV1 and FEV1/FVC - obstructive lung lesion.
Reduction of FEV1 - restrictive ventilatory problem (due to intrinsic lung disease or problems with the chest wall).
What is the inert gas dilution technique?
Measures static lung volumes.
The subject breathes in a closed circuit from a bag containing air with helium, until the gas in their lungs is fully mixed with the bag.
A sample of gas is taken, and [helium] is measured.
How can static lung volumes be calculated by the inert gas dilution technique?
FRC is known before inert gas dilution.
Using the original bag volume and [helium], as well as the final [helium], lung volume can be calculated.
From FRC, RV and other lung volumes can be calculated by spirometry.
What are the different classes of spirometry measurements?
Static - only considers volume exhaled.
Dynamic - the time for a certain volume to be exhaled is considered.
What are typical values for static lung volumes?
FRC = 3.7 (+/-0.7) litres.
RV = 1.9 (+/-0.4) litres.
VC = 5.6 (+/-0.6) litres.
TLC = 7.3 (+/-0.8) litres.
RV/TLC = 25 (+/-0.4)%.
What is obstructive lung disease?
Gas is trapped in the chest, causing SOB and difficulty exhaling.
The rate at which air is exhaled is slower.
What is restrictive lung disease?
Small or stiff lungs cause a restriction in lung expansion.
The absolute rate of airflow and TV is reduced.
What lung volumes are affected by obstructive lung disease?
Increased TLC, RV and FRC.
Decreased FEV1 and FEV1/FVC.
What lung volumes are affected by restrictive lung disease?
Reduced FEV1, TLC, RV, FRC and VC.
How can static lung volumes be calculated by carbon monoxide transfer?
The subject exhaled to RV and then inhales a known amount of CO and helium.
A breath hold allows CO to be absorbed.
A sample of exhaled gas is collected.
[CO] is measured.
What calculations are made in CO transfer?
The rate of assumed transfer in the blood is calculated using initial [CO] and final [CO].
Exhaled [helium] is used to calculate the volume into which the CO was distributed.
How is CO transfer (Tco) expressed?
As a rate, in mmol/min/kPa.
What is the typical value of Tco?
11.6 (+/-1.7) mmol/min/kPa.
What factors directly influence Tco?
Pulmonary blood flow and volume.
Hb concentration.
Background levels of COHb in the blood.
When does Tco increase?
Where pulmonary blood flow and volume increases.
Shunts, pregnancies, alveolar haemorrhages.
When does Tco decrease?
Many types of lung disease.
Anaemia.
Smoking.
