Physiology - Volume and Flow, Pulmonary Function Tests

Question 1

How do we assess ventilation?

Answer 1

Blood gases - PaO2 (hypoxia) PaCO2 (hypercapnia)
Lung Volumes/Flows - spirometry, peak flow rates (PEFR)
Exhaled nitrous oxide (eNO)

Question 2

Remember: PCO2 is only influenced by ventilation!!!

Answer 2

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Question 3

What does spirometry measure?

Answer 3

Measures how much and how fast
Common simple test
Mechanical/digital
Test response to therapy before vs after

Question 4

What is the tidal volume?

Answer 4

500ml, VT

Volume of air that moves in and out during normal quiet ventilation

Question 5

What is the inspiratory reserve volume?

Answer 5

3L

An extra 3L can be inspired if the external intercostal muscles are contracted too

Question 6

What is expiratory reserve volume?

Answer 6

1.5L
An extra 1.5L can be expelled if the internal intercostal and abdominal muscles are contracted for maximal active expiration

Question 7

Which intercostal muscles are used for inspiration and expiration?

Answer 7

External = inspiration 
Internal = expiration

Question 8

What is the Residual Volume

Answer 8

About 1 L

Even after maximal expiration, our lungs are still partially inflated.

Question 9

What is the vital capacity?

Answer 9

5L
Maximal breath in to maximal breath out
(ERV + VT + IRV)

Question 10

What is the total lung capacity?

Answer 10

About 6L
If you breathe all the way in.
VC + RV

Question 11

What is the inspiratory capacity?

Answer 11

Tidal volume (VT) + IRV

Question 12

What is the Functional Residual Capacity?

Answer 12

2.5L
Volume in the lungs at the end of tidal expiration
(RV + ERV)

Question 13

What does the functional residual capacity represent?

Answer 13

Equilibrium point

Question 14

Which capacities or volumes cannot be measured with a spirometer?

Answer 14

Residual volume

Question 15

How do we measure Residual Volume?

Answer 15

Use Helium dilution

Breathe on spirometer, add known amount of He

Question 16

How do we determine how fast we breathe?

Answer 16

Forced measurements give information about flow.

Forced Vital Capacity is used.

Question 17

What is FEV1?

Answer 17

Forced expiratory volume in the first one second

Question 18

What reduces FEV1?

Answer 18

Diseases causing resistance to airflow (airways obstruction) 
Small lungs (scarred or fibrotic lungs)

Question 19

What should the FEV1/FVC ratio be?

Answer 19

Value <0.70 defines obstructive dysfunction

Question 20

What are normal/predicted values based on?

Answer 20

Age
Height
Sex

Question 21

What are normal values for forced volumes?

Answer 21

FVC >/= 80% of predicted
FEV1 >/= 80% of predicted
FEV1/FVC ratio >/= 0.70

Question 22

How do we control the quality of spirometry?

Answer 22

Technician dependent/subject dependent
Need acceptable effort
3 acceptable attempts within 5% of each other

Question 23

What is PEFR?

Answer 23

Peak Expiratory Flow Rates can be obtained from spirometry or portable devices
PEFR measure RATES, not volumes

Question 24

How do we interpret PEFR?

Answer 24

Determine normal values for each individual - absolute value not that useful
Can be used to change/assess therapy

Question 25

What does a decrease in PEFR suggest?

Answer 25

Decreased flow e.g. worsening asthma

Question 26

What is obstructive lung diseases?

Answer 26

Resistant to AIRFLOW
e.g. COPD (chronic bronchitis and emphysema), Asthma
Think O FOR FLOW

Question 27

What are restrictive lung diseases?

Answer 27

Decrease in lung volume/stiff lungs
E.g. lung compliance related disease (pulmonary fibrosis/oedema), chest wall compliance (kyphoscoliosis), pleural and respiratory muscle disease

Question 28

What happens in restrictive lung disease?

Answer 28

FVC decreased
FEV1 often decreased proportionate to FVC
FEV1/FVC normal or increased
May need lung volume measurements (RV, FRC, TLC) to confirm

Question 29

What happens to lung values in obstructive lung disease?

Answer 29

FEV1/FVC ratio <0.70
FEV1 usually decreased
FVC may be decreased e.g. if expiration incomplete due to air trapping

Question 30

Note - there can be simultaneous obstructive and restrictive diseases

Answer 30

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