measuring lung function

Question 1

what is the FVC or Tiffeneau manouvre?

Answer 1

• take a deep breath in
• don’t hold your breath
• put your lips around the outside of the tube and breathe out as hard as you can for as long as you can

Question 2

how do you interpret FEV1/FVC?

Answer 2

ratio of FEV1 and FVC values

Question 3

what is counted as an abnormal spirometry result?

Answer 3

any result <80% of the predicted value
or
any results < lower limit of normal

Question 4

where is the lower limit of normal taken?

Answer 4

taken to new equal to the 5th percentile of a healthy, non-smoking population

Question 5

how do you interpret spirometry?

Answer 5

a patients PFT values are compared to the predicted values which are derived from a healthy population of people of the same gender and of similar ages and height

Question 6

what are flow volume loops used for?

Answer 6

indicate where obstructions are located in the tracheobronchial tree

Question 7

what is the peak flow rate useful for?

Answer 7

• diagnosis: asthma
• monitoring day to day variation
• picking up exacerbations
• assessing response to treatment

Question 8

when is a peak flow mandatory?

Answer 8

for patients on nebulised Rx

Question 9

what is the equation for recall flow?

Answer 9

pressure gradient / raw

Question 10

what could cause a decrease in the radius of an airway?

Answer 10

mucous or other obstructions, bronchoconstriction, compression (from a mass)

Question 11

what happens with low lung volume?

Answer 11

• reduced TLC, FRC and RV
• preserved total volume
• reduced IRV/inspiratory capacity
• reduced vital capacity

Question 12

what are causes of lower lung volume?

Answer 12

• alveolar filling process
• lung tissue disease
• pleural disease
• chest wall disease
• weakness

Question 13

how is emphysema spotted using graphs?

Answer 13

loss of elastic recoil leads to CL curve plateau occurring at larger volumes increasing TLC

Question 14

what happens in gas exchange?

Answer 14

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

Question 15

what causes abnormal gas exchange?

Answer 15

• airway disorders
• alveolar destruction
• fibrotic lung disease
• abnormal ventilatory control
• abnormal environment
• measured as CO transfer factor

Question 16

how do you measure gas transfer?

Answer 16

• inhale known volume of gas with low concentrations of CO and helium
• hold breath for known time
• measure CO and He in expired air
• He dilution gives alveolar volume

Question 17

what PFTs are in place in routine clinical practice?

Answer 17

• assessment of airway reversibility
• assessment of ventilation
• fitness to fly
• respiratory muscle assessment