Lung Function Testing Flashcards
List 3 spirometry tests/graphs.
List 8 other lung function tests.
SPIROMETRY:
Lung volumes
Time/volume plots
Flow/volume plots
OTHER LUNG FUNCTION TESTS: Peak flow (PEF) Reversibility tests Bronchial provocation Transfer factor Residual lung volumes Pulse oximetry Alveolar oxygen equation Arterial blood gases
How would you define a spirometry test?
What would you tell the patient when doing one? (3)
Forced expiratory manoeuvre from total lung capacity, followed by a full inspiration; measured as the best of 3 acceptable attempts (within 5% of each other)
METHOD:
- Take a big breath in as far as you can
- Blow out as hard as you can for as long as possible
- Then take a deep breath in
List 4 disadvantages of spirometry.
Needs appropriately trained technician
Effort and technique dependent
Affected by patient frailty
Can’t be done if patient is too unwell
List 5 lung volumes which can be directly measured by spirometry.
Inspiratory reserve volume Inspiratory capacity Expiratory reserve volume Tidal volume (VT) Vital capacity (VC)
List 3 volumes which can be calculated from spirometry tests.
Total lung capacity
Residual volume
Functional residual capacity (FRC)
What is the difference between inspiratory reserve volume (IRV) and inspiratory capacity (IC)?
INSPIRATORY RESERVE VOLUME (IRV):
Volume between PEAK tidal volume and volume after full inspiration
INSPIRATORY CAPACITY (IC): Volume between END tidal volume and volume after full inspiration
What is the vital capacity (VC)?
Maximum amount of air a person can expel from the lungs after maximum inhalation
What is the expiratory reserve volume?
Volume between end tidal volume and the volume after full expiration
How do you calculate the total lung capacity (TLC)?
TLC = vital capacity (VC) + residual volume (RV)
What is the functional residual capacity (FRC)?
Amount of air left in the lungs after a normal breath (i.e. at the end tidal volume)
Which 2 graphs can be plotted with spirometry results?
Time/volume plot
Flow/volume loops
Draw a time/volume plot.
See poster
Draw a flow/volume loop.
See poster
Which 4 measurements can be taken from a time/volume plot?
How?
Peak expiratory flow (PEF)
-Extrapolate a line from beginning of plot; calculate gradient
Forced expiratory volume in 1 second (FEV1)
-Find volume at 1 second on the graph
Forced vital capacity (FVC)
-Plateau level of graph
FEV1/FVC ratio
Which measurement can be taken from a flow/volume loop?
Vital capacity
-Distance between the two x-axis intercepts
On a flow/volume loop, what are the 2 parts of the expiratory limb?
Briefly explain the physiology behind each.
Effort dependent part
- Initial expiration requires effort to forcefully exhale
- This creates the maximum rate of flow in the flow/volume loop
Effort independent part
- After maximum expiratory flow is reached, the rest of the lung volume is exhaled automatically (due to pressure differences)
- Flow is highest in the terminal bronchioles, so by the time air reaches the central airways, flow decreases
- Therefore flow decreases on the loop
What is predicted FEV1 adjusted for? (5)
Age Gender Race Height Atmospheric values
What is a normal % predicted FEV1?
Depends on individual - because predicted FEV1 is just an estimate, therefore doesn’t reflect true lung function
As long as % predicted FEV1 remains the same as it’s always been, it’s normal
What is a normal FEV1/FVC ratio?
70+%
How do you do reversibility testing on the lungs?
What do the
results indicate?
METHOD:
- Measure spirometry
- Give nebulised/inhaled salbutamol
- Measure spirometry 15 minutes after
RESULTS:
Reversible if:
-More than 15% improvement in FEV1
-More than 400ml improvement in FEV1
When doing serial peak flow tests (PEFR), what do you look for? (3)
Diurnal variation
Variation over time
PEFR response to steroids
How do you measure transfer factor? (Also called: TLCO, KCO, DLCO)
- Patient is given a single breath of CO (very low concentration)
- CO has a high affinity for Hb, so it will easily diffuse into the blood
- Measure the amount of CO breathed out
a. Then calculate the amount of CO absorbed (this is the transfer factor)
List 4 features which affect the transfer factor.
Alveolar surface area
Pulmonary capillary blood volume
Haemoglobin concentration
V/Q mismatch
List 4 possible causes of a decreased transfer factor.
List 1 possible cause of an increased transfer factor.
DECREASED TRANSFER FACTOR: Emphysema Interstitial lung disease Pulmonary vascular disease Anaemia
INCREASED TRANSFER FACTOR:
Polycytaemia
What are the 2 methods of measuring residual lung volume?
Helium dilution
Body plethysmography
How do you carry out helium dilution, to find out residual volume? (2)
- Ask patient to inspire a known quantity of inert gas (which is NOT absorbed)
- Measure the amount breathed out
a. The difference is equal to the residual volume
How do you carry out body plethysmography, to find out residual volume? (3)
- Ask patient to carry out respiratory manoeuvres in a sealed box
- This causes changes in air pressure
- Using the Archimedes principle, you can then derive lung volumes
Describe the disadvantages of pulse oximetry. (2)
Give examples of when each might affect measurement of O2 sats.
Depends on adequate perfusion; inaccurate in:
- Shock
- Heart failure
Does not measure CO2 levels, therefore does not measure ventilation; inaccurate in:
- Acute asthma
- COPD
- Hypoventilation
What is the normal saturation of haemoglobin in the body?
66%
What is the alveolar oxygen equation?
Alveolar oxygen = (inspired oxygen concentration) - (1.25 x pCO2)
What is a normal alveolar-arterial (A-a) oxygen gradient?
What can cause a high alveolar arterial oxygen gradient? (1)
Normal: <2-4 kPa
High gradient: V/Q mismatch
Briefly describe a systematic approach to arterial blood gas analysis. (3)
- Look at pO2 (normal: 8 kPa)
- Look at pCO2
a. If low: type 1 respiratory failure
b. If high: type 2 respiratory failure - Look at H+ levels
a. If high: acidosis
b. If low: alkalosis - Look at HCO3- levels
a. Consider compensation of acid/base balance
Describe an obstructive pattern on lung function tests. (3)
FEV1/FVC: <70%
Flow/volume loop:
- “Church and steeple”
- Lower PEF
Time/volume plot:
- Slow-rising plot
- Lower FEV1
- Lower FVC
Describe a restrictive pattern on lung function tests. (3)
FEV1/FVC: normal
Flow/volume loop:
- Normal shape
- Smaller size/area
- Reduced FVC
Time/volume plot:
- Normal shape
- Smaller/shorter plot
- Reduced FEV1
List 6 causes of a restrictive pattern on lung function tests.
Interstitial lung disease Kyphoscoliosis Previous pneumonectomy Neuromuscular disease Obesity Poor effort/technique
