Lung Function and Spirometry

Question 1

What is Peak Expiratory flow?

Answer 1

The patient takes a full breath in (ie, to total lung capacity) and then exhales as rapidly as possible into a suitable measuring instrument.

The expiratory flow rate rises rapidly to reach the peak value relatively early in the exhalation and then declines slowly until exhalation is complete at which point the lungs contain only the residual volume.

Question 2

How is a PEFR measurement interpreted?

Answer 2

Flow rate for height and age based on chart

Question 3

What are the dynamic lung volumes?

Answer 3

FVC and FEV1

Question 4

How are FEV1 and FVC measured?

Answer 4

As with peak expiratory flow measurement, the patient takes a full breath in to total lung capacity, and then exhales as rapidly as possible into a suitable measuring instrument.

Expired volume can be plotted against time, allowing the volume expired in one second (FEV1) to be read off from the tracing. The forced exhalation is continued to residual volume, and the total volume exhaled is the forced vital capacity (FVC)

Question 5

What Dynamic lung volume results indicate obstructive pathology?

Answer 5

• FEV1 reduced - < 80% predicted
• FVC reduced - not to same extent as FEV1
• FEV1/FVC <75%

Question 6

What dynamic lung volumes indicate a restrictive pattern of lung disease?

Answer 6

• FEV1 reduced - <80% predicted
• FVC reduced
• FEV1/FVC > 75%

Question 7

What are the static lung volumes?

Answer 7

• FRC
• RV
• VC
• TLC
• RV/TLC%

Question 8

What happens to static lung volumes in obstructive lung disease?

Answer 8

Obstructive lung diseases may lead to gas trapping in the chest, leading to increased TLC, increased RV and FRC and increased RV/TLC ratio

Question 9

What happens to static lung volumes in restrictive lung disease?

Answer 9

Restrictive lung disease will lead to reductions in all parameters with preservation or reduction of RV/TLC ratio.

Question 10

What do Carbon Monoxide tranfer tests look at?

Answer 10

Ideally like to measure oxygen transfer across the lungs directly, but this is not possible for technical reasons. A useful substitute is to measure the transfer of carbon monoxide. The gas is toxic in high concentrations, but is useful in low concentrations since it rapidly crosses the alveolar/blood barrier and is then firmly bound to haemoglobin, to be carried away into the circulation as carboxyhaemoglobin (COHb).

Question 11

What are the units of measure of carbon monoxide gas transfer?

Answer 11

• CO transfer (Tco or DLco) - rate in units of mmol/min/kPa.
• Transfer coefficient (Kco) - Tco expressed per unit lung volume

Question 12

When would Tco be increased?

Answer 12

Where pulmonary blood flow or volume increases:

• Shunts
• Polycythemia
• Pregnancy
• Haemorrhage occurs into the alveoli

Question 13

When would Tco be decreased?

Answer 13

Tco is reduced by many types of lung disease, by anaemia, smoking (due to high background COHb + smoking related lung disease).

Question 14

What is the difference in terms of gas trasnfer between COPD and asthma?

Answer 14

Tco is normal in asthma, but reduced in COPD