Physiology - Volume and Flow, Pulmonary Function Tests Flashcards
How do we assess ventilation?
Blood gases - PaO2 (hypoxia) PaCO2 (hypercapnia)
Lung Volumes/Flows - spirometry, peak flow rates (PEFR)
Exhaled nitrous oxide (eNO)
Remember: PCO2 is only influenced by ventilation!!!
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What does spirometry measure?
Measures how much and how fast
Common simple test
Mechanical/digital
Test response to therapy before vs after
What is the tidal volume?
500ml, VT
Volume of air that moves in and out during normal quiet ventilation
What is the inspiratory reserve volume?
3L
An extra 3L can be inspired if the external intercostal muscles are contracted too
What is expiratory reserve volume?
1.5L
An extra 1.5L can be expelled if the internal intercostal and abdominal muscles are contracted for maximal active expiration
Which intercostal muscles are used for inspiration and expiration?
External = inspiration Internal = expiration
What is the Residual Volume
About 1 L
Even after maximal expiration, our lungs are still partially inflated.
What is the vital capacity?
5L
Maximal breath in to maximal breath out
(ERV + VT + IRV)
What is the total lung capacity?
About 6L
If you breathe all the way in.
VC + RV
What is the inspiratory capacity?
Tidal volume (VT) + IRV
What is the Functional Residual Capacity?
2.5L
Volume in the lungs at the end of tidal expiration
(RV + ERV)
What does the functional residual capacity represent?
Equilibrium point
Which capacities or volumes cannot be measured with a spirometer?
Residual volume
How do we measure Residual Volume?
Use Helium dilution
Breathe on spirometer, add known amount of He
How do we determine how fast we breathe?
Forced measurements give information about flow.
Forced Vital Capacity is used.
What is FEV1?
Forced expiratory volume in the first one second
What reduces FEV1?
Diseases causing resistance to airflow (airways obstruction) Small lungs (scarred or fibrotic lungs)
What should the FEV1/FVC ratio be?
Value <0.70 defines obstructive dysfunction
What are normal/predicted values based on?
Age
Height
Sex
What are normal values for forced volumes?
FVC >/= 80% of predicted
FEV1 >/= 80% of predicted
FEV1/FVC ratio >/= 0.70
How do we control the quality of spirometry?
Technician dependent/subject dependent
Need acceptable effort
3 acceptable attempts within 5% of each other
What is PEFR?
Peak Expiratory Flow Rates can be obtained from spirometry or portable devices
PEFR measure RATES, not volumes
How do we interpret PEFR?
Determine normal values for each individual - absolute value not that useful
Can be used to change/assess therapy
What does a decrease in PEFR suggest?
Decreased flow e.g. worsening asthma
What is obstructive lung diseases?
Resistant to AIRFLOW
e.g. COPD (chronic bronchitis and emphysema), Asthma
Think O FOR FLOW
What are restrictive lung diseases?
Decrease in lung volume/stiff lungs
E.g. lung compliance related disease (pulmonary fibrosis/oedema), chest wall compliance (kyphoscoliosis), pleural and respiratory muscle disease
What happens in restrictive lung disease?
FVC decreased
FEV1 often decreased proportionate to FVC
FEV1/FVC normal or increased
May need lung volume measurements (RV, FRC, TLC) to confirm
What happens to lung values in obstructive lung disease?
FEV1/FVC ratio <0.70
FEV1 usually decreased
FVC may be decreased e.g. if expiration incomplete due to air trapping
Note - there can be simultaneous obstructive and restrictive diseases
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