Pulmonary function testing Flashcards
Reference values for Pulmonary function tests
GLI reference equations currently used for adults
Height, Age and Sex
Ethnic origin (12% correction for volumes only)
What are the contra-indications for pulmonary lung function tests?
Recent MI
Recent abdominal, thoracic or eye surgery
Pulmonary embolism
Haemoptysis of unknown origin
Pneumothorax
Thoracic, abdominal or cerebral aneurysms
Acute disorders affecting performance (e.g nausea)
Pregnancy
What is spirometry?
Method of assessing lung function by measuring the volume of air that the patient can expel from the lungs after a maximal inspiration’
Basis of all pulmonary function tests
FEV1, FVC, FEV1/FVC % and PEF
What are the features of spirometry?
Relatively simple, quick test
Must be performed correctly or the results are misleading
Used in diagnosis, monitoring, measurement of an intervention and pre-operatively to evaluate risk
Measures dynamic volumes
What is FEV1, FVC, FEV1/FVC ratio, PEF?
FEV1 = Forced expiratory volume in one second
FVC = Forced vital capacity
FEV1/FVC Ratio = Expressed as a percentage (< 70% = Obstruction – Caution older population!)
PEF = Peak Expiratory Volume
How do we carry out spirometry?
Explain test procedure and gain consent
Performed sitting
(values differ in different positions – Supine!)
Patient instructed to inhale fully and then exhale as hard as they can for as long as they can
Encourage maximum effort, verbally encouraging patient to continue to exhale (plateau on the volume/time graph)
How do we get the results for spirometry?
At least 3 technically acceptable results
Best 2 have to be reproducible! – 5% or 100mL whichever is greater
Maximum of 8 attempts
Report should note poor technique or any other relevant comments
How do we take lung volumes? (Not the same as spirometry)
Simple technique but requires good seal around mouthpiece
Determine / Confirm presence/extent of restriction
Useful to assess extent of hyperinflation in obstructive patients
RV and TLC cannot be measured directly
3 Methods: Body Plethysmography, Helium Dilution, Nitrogen Washout
What is the TLC, RV, FRC, VC?
TLC = Volume of gas in the lungs and airways at the position of full inspiration
RV = Volume of gas that remains in the lungs after a full expiration. Helps prevent lungs from collapsing.
FRC = Volume of gas in the lungs and airways at the end of a normal expiration.
Measured during lung volumes and used to calculate other subcomponents (TLC!).
VC = Total volume of gas that can be mobilized
IVC / EVC
What is the gas transfer test?
Relatively simple technique but also requires good seal around mouthpiece
Estimates the overall oxygen diffusing capacity
Helps differentiate between thoracic and extra-thoracic lung restriction
Obtain baseline measurement when prescribing certain drugs that can cause lung fibrosis (Amiodarone and Methotrexate)
What can gas transfer be referred to as as well what its useful for?
Transfer Factor and Diffusing Capacity
It is a useful tests as it estimates the oxygen diffusing capacity of the lungs using a small amount of carbon monoxide.
What is TLco, Kco, and Va?
TLco = Total diffusion capacity for the lung
Kco = Permeability of the alveolar-capillary membrane
Va = Alveolar volume. Gives an estimate o the amount of alveoli available for the gas transfer
Spirometry interpretation
Slide 20 in lung function talk slides
Normal FEV1 N FVC N FEV1/FC% N(>70%)
Obstruction Low N/ Low (<70%)
Restriction Low Low N
Mixed pattern Low Low (<70%)
Degree of severity for spirometry
Mild 1 >80
Moderate 2 50-79
Severe 3 30-49
Very severe 4 <30
What are the lung volume interpretations for an obstructed lung?
IRV Dec
VT Inc
ERV Dec
RV Inc
VC Dec
IC Dec
FRC Inc
TLC inc
Lung volume interpretation for restricted lung?
IRV Dec
VT Dec
ERV Dec
RV dec
VC dec
IC dec
FRC dec
TLC dec
What are other pulmonary function tests can be used?
FeNO (Fractional exhaled nitric oxide)
Eosinophilic airway inflammation
Useful in steroid/inhaler trial
Normal <25ppb; high >50ppb
Mouth pressures
MIP/MEP
Neuromuscular/diaphragmatic weakness
Normal values ≥ 80cmH2O
Supine spirometry
Diaphragmatic weakness
FEV1 and FVC
What exercise tests can be done?
Incremental Shuttle Walk Test (ISWT)
Externally paced bleep test
Maximal effort – May have to run
Measures exertion breathlessness (BORG)
6 Minute Walking Test (6MWT)
Self paced and allows stops
Better for less mobile
It reflects the impact that the disease has on the everyday activity
SpO2 and HR response recorded on both test
What is the CPET? Cardiopulmonary Exercise Test)
Assess if respiratory, cardiac or both are the cause of symptoms
Cycle test as standard
Indications:
Major surgery
? SOB
Heart Failure
Exercise induced Asthma
Measures:
VO2 max, ventilation, CO2 output, anaerobic threshold, ventilatory equivalents, oxygen pulse, ECG, workload, SpO2, HR and BP
How and why do we use capillary blood gases?
Diagnosis of respiratory failure and monitoring of treatment
Ear lobe sample
Comparable to ABGs but less painful
PO2, PCO2 and acid base status
Type I vs Type II respiratory failure
What is ambulatory oxygen is used?
6MWT - Standard
ISWT – Pulmonary Rehab
If significant desaturation then patient retested on Oxygen
Demonstrable improvement in SpO2 and distance and/or breathlessness on exertion with oxygen
Must be clinically stable
Flight assessment
It is not a fitness to fly test!
Simulates pressurised plane breathing at 15% O2 for 20min
If SpO2 <92% in-flight oxygen is needed
If on LTOT:
The supplemental O2 given in flight should be double the flow at ground level
If not on LTOT:
And SpO2 92-95% (with risk factors), pre CBGs are necessary (monitor SpO2)
If PaO2 <6.6kPa in-flight oxygen at 2L/min O2
What is CPAP Continuous Positive Airway Pressure ?
First line of treatment for moderate and severe OSA
Uses positive airway pressure to maintain the airways during sleep
Good compliance is >4hrs/night for greater than 80% of the time
Implications for DVLA and insurance (ESS!)
What is BiPAP non invasive ventilation?
Nocturnal bi-level ventilation – uses positive pressure to provide inspiratory (IPAP) & expiratory (EPAP) support
