measuring lung function

Question 1

what is spirometry? 3

Answer 1

• can be done slowly of forced
• most often done as forced expiration
• FVC of tiffeneau manoeuvre: deep breath, don’t hold your breath, put lips around outside of the tube and blow out for as long and hard as you can

Question 2

how do we interpret spirometry? 4

Answer 2

• FE1/FVC: ratio of FEV1 and FVC values
• for all other results, compare to actual predicted values
• predicted values may vary by gender, height and age
• abnormal result: any result <80% of the predicted value or any results less than the lower limit of normal

Question 3

how much of FVC should be exhaled in the first second?

Answer 3

• 70%

- if FEV1.FVC is <0.7 then an obstruction is present

Question 4

what do expiratory flow- volume loops show? 3

Answer 4

• early airflow obstruction
• mid expiratory flow rates are usually more affected
• PEFR (peak expiratory flow rate) may be normal
• where an obstruction is located in the tracheobronchial tree

Question 5

when is peak flow used normally? 2

Answer 5

• for people with asthma

- it can show extrathoracic obstructions including tracheal, stenosis

Question 6

explain a peak flow rate? 7

Answer 6

• easy to perform
• easy to maintain device
• diagnosis of asthma
• monitoring day-day variation
• picking up exacerbations
• assessing response to treatment
• mandatory for patients on nebulised Rx

Question 7

how can we measure lung function?

Answer 7

• helium dilution

- plethysmography

Question 8

name some causes for lung restriction? 5

Answer 8

• alveolar filling process (pneumonia)
• lung tissue disease: fibrotic lung disease
• pleural disease: pneumothorax, large pleural effusion, fibrosis of pleural tissue
• chest wall disease
• weakness due to nerve or muscle disease

Question 9

where does gas exchange take place? 5

Answer 9

• takes place at the alveoli
• depends on adequate ventilation of alveoli
• influenced by alveolar surface area and thickness of alveolar membrane
• delivers oxygen to where is combines with Hb
• gets rid of carbon dioxide to exhaled air

Question 10

how do we measure gas transfer? 6

Answer 10

• CO diffuses like O2
• CO binds to Hb and is carried away
• inhale known volume of gas with low concentration of CO and helium
• hold breath for the known time
• measure CO and He in expired air
• He dilution give alveolar volume