Pulmonary Function Testing

Question 1

Types of pulmonary function tests?

Answer 1

Effort dependent tests - involve breathing out maximally, with effort

Effort independent tests - breathing out with no effort

Gas diffusion tests - information obtained about gaseous diffusion across alveolar bed

Question 2

Examples of effort dependent tests?

Answer 2

Measuring Forced Expiratory Volumes (FEV) - spirometry

Measuring flow rates - volume exhaled in given time (purest measure of airflow obstruction)

Question 3

Limitation of effort dependent tests?

Answer 3

Not a physiological maneuvre; essentially involves forced expiratory volume (FEV) - an artificial maneuvre

Question 4

Examples of effort independent tests?

Answer 4

Relaxed vital capacity (VC) - spirometry

Helium/N2 washout - for STATIC LUNG VOLUMES, with N2 being used more than helium

Whole body plethysmography - for static lung volume

Impulse oscillometry

Exhaled breath nitric oxide

Question 5

Examples of gas diffusion tests?

Answer 5

CO transfer factor

Arterial blood gases (resting)

SaO2 during exercise

Question 6

Dynamic lung volumes?

Answer 6

Forced expiratory volume in 1 second (FEV) - proportion of FVC expired in 1st second

Forced vital capacity - FVC

Forced expiratory ratio (FER) - FEV1 / FVC

Relaxed vital capacity - RVC

Question 7

Difference between normal and asthmatic airways?

Answer 7

During FEV, no small airway closure normally so FEV1/FVC > 75%

During FEV in asthmatic patient, small airways start closing so it takes longer to reach FVC in asthma that normal

Question 8

Difference between FVC of asthma and COPD

Answer 8

ASTHMA - normally, FVC is PRESERVED (takes longer to reach); exception is when airway remodelling has occured

COPD - lots of small airway closure and scarring, so FVC is NEVER REACHED

Question 9

FEV1/FVC ratio in obstructive lung diseases?

Answer 9

FEV1 is DISPROPORTIONATELY decreased, compared to FVC

Question 10

FEV1/FVC ratio in restrictive lung disease?

Answer 10

FEV1 has PROPORTIONATELY decreased, compared to FVC, so ratio will be >75%

Essentially, reduced lung volume but there is no issue with exhalation

FUNDAMENTAL difference between obstructive and restrictive lung disease

Question 11

What does a peak flow meter measure?

Answer 11

Peak expiratory flow rate - maximum speed that can be attained during expiration

Question 12

Peak expiratory flow rate in asthma?

Answer 12

Peak flow rate becomes blunted/concave as there is dynamic small airway closure

Question 13

When does volume dependent expiratory airway closure occur?

Answer 13

Asthma

Chronic bronchitis

Peak expiratory flow rate decreases and curve becomes concave

Question 14

When does pressure dependent expiratory airway closure occur?

Answer 14

Emphysema

Peak expiratory flow rate is even lower than in asthma & chronic bronchitis

Question 15

Briefly explain what the forced expiratory flow rate is?

Answer 15

FEFR at a % of FVC - Forced expiratory flow 50%, FEF25-75% Flow (or speed) of air coming out of the lung during the middle portion of a forced expiration

Question 16

Describe bronchial challenge testing?

Answer 16

Used to assess bronchospasm/twitchiness Induced in different ways:

Exercise

Metacholine/histamine/mannitol (MARKER OF AIRWAY HYPER-RESPONSIVENESS ) - conc. chosen to produce a 20% decrease in FEV1

Allergens/chemicals are used to check if there is an early/late response and can be used to diagnose occupational asthma

Question 17

How does bronchial challenge testing using metacholine work?

Answer 17

Using metacholine, post-ganglionic M3 receptors are stimulated with muscarinic agonists, so bronchoconstriction occurs

Question 18

Bronchial challenge testing using metacholine/histamine/mannitol in normal vs asthma?

Answer 18

FEV1 decrease to 80% of full value (20% decrease)

Even if not asthmatic, FEV1 would still fall but, with ASTHMA, a LOWER DOSE of inducer is required

Question 19

How does FEV1 vary in exercise?

Answer 19

Increases during exercise but, after exercise has stopped, FEV1 decreases in asthma due to rebound worsening

Question 20

Describe exercise testing and where it can be used

Answer 20

FEV1 or peak expiratory flow (PEF)

DECREASES in ASTHMA

Decreased SaO2, during exercise, in insterstitial lung disease (used to monitor treatment response)

CPET (full cardiopulmonary exercise test) - differentiates between cardiac and respiratory dyspnoea (breathlessness), by comparing heart rate, oxygen uptake and ventilatory rate

Question 21

Static lung volume tests?

Answer 21

Via effort INDEPENDENT tests

Can be measured using helium dilution/N2 washout to find functional residual capacity

Question 22

Changes in static lung volumes and when they occur?

Answer 22

Total lung capacity increased in hyper-inflation (emphysema) - elasticity decreases

Total lung capacity decreases in restrictive lung disease

In COPD, GAS TRAPPING occurs (due to small airway closure) and hyper-inflation of static lung volume occurs

Question 23

Abbreviation of transfer factor?

Answer 23

AKA TLCO or DLCO (Transfer factor of Lung for Carbon Monoxide or Diffusing capacity of Lung for Carbon Monoxide)

Question 24

What does transfer factor measure?

Answer 24

CO diffusion across alveolar-capillary barrier (extent to which oxygen passes from the air sacs of the lungs into the blood)

KCO is corrected for alveolar volume

Question 25

When does TLCO decrease?

Answer 25

Anaemia

Emphysema

Interstitial lung disease

Pulmonary oedema

Pulmonary embolus

Bronchiectesis

Question 26

Example of what is TLCO used for?

Answer 26

To monitor treatment response in interstitial lung disease

Question 27

How is airway resistance measured?

Answer 27

Whole body plethysmography

More common/easier is IMPULSE OSCILLOMETRY (IOS)

Question 28

How does impulse oscillometry work?

Answer 28

Measures airway resistance during quiet tidal breathing (at different resonant frequencies to give total resistance (@5Hz) and central resistance (20Hz) - peripheral airway resistance by subtraction of R5 - R20

So, smaller frequency reflects distal airways and higher frequencies reflect promximal airways

Question 29

When is impulse oscillometry useful?

Answer 29

Useful in patients, like kids, where it is easier to breathe at tidal volume than doing a forced expiratory maneuvre

Question 30

Describe exhaled breath condensate measurement and when it is used

Answer 30

Exhaled breath nitric oxide is measured at flow of 50 ml/s (FeNO)

Non-invasive marker of EOSINOPHILIC AIRWAY INFLAMMATION in ASTHMA - high level of exhaled NO reflect uncontrolled asthmatic inflammation

Not useful in COPD (NO suppressed by smoking)

Used as an adjunct to bronchial challenge to assess asthmatic inflammation (esp. when spirometry is normal)

Question 31

Compare obstructive and restrictive lung disease?

Answer 31

PEFR:

Obstructive - decreases

Restrictive - normal

FEV1:

Obstructive - decreases

Restrictive - decreases

FVC:

Obstructive - normal in asthma and reduced in COPD

FEV1/FVC:

Obstructive 75%

Gas transfer (TLCO):

Obstructive - decreased in emphysema and normal in asthma

Restrictive - decreased

FEV1 response to β2-agonist:

Obstructive - >15% in asthma and