Overview of Pulmonary Function Tests

Question 1

Give examples of pulmonary function tests

Answer 1

Spirometry
-Can be an effort dependent/independent test
-Effort dependent = forced expiratory volumes/flow rates
-Effort independent = relaxed vital capacity

Exhaled Breath Nitric oxide
-Effort independent

Arterial Blood gases
-Gas diffusion test

Question 2

Give examples of dyanmic lung volumes measured in spirometry

Answer 2

Forced expiratory manoeuvre: from TLC to RV
-inhales fully to total lung capacity and exhales as hard and fast as possible residual volume
-produces the curve

FEV1 (L) = Forced expiratory volume in 1 s

FVC (L) = Forced vital capacity
-total volume of air exhaled during a forced expiration
-measures overall lung capacity available for expiration
-reduced in restrictive diseases

FER (FEV1/FVC ratio) = Forced expiratory ratio
-percentage of the FVC exhaled in the first second; should be more than 75%/0.75
-decreased in obstructive disease.
-normal or high in restrictive disease.

RVC (L) = Relaxed vital capacity
-maximum volume exhaled slowly and gently (not forced)

Of a volume (L) vs time (s) curve with time on X axis

Question 3

Which is which ?

Answer 3

Question 4

How do obstructive lung diseases affect a spirometry graph ?

Answer 4

PEFR = Decreased
FEV1 = Decreased (<80% of predicted normal)
FVC = reduced, but to a lesser extent than FEV1
FEV1/FVC ratio = Reduced (<0.7)
DLCO = Decreased in emphysema, normal in asthma
FEV1 response to β2-antagonist = Decreased in emphysema, normal in asthma
RV = Greater in COPD/Emphysema than asthma

e.g. asthma

Question 5

How do restrictive lung diseases affect a spirometry graph ?

Answer 5

PEFR = Normal
FEV1 = Decreased (<80% of predicted normal)
FVC = Decreased (<80% of predicted normal)
FEV1/FVC ratio = Normal (>0.7)
DLCO = Decreased
FEV1 response to β2-antagonist = No response

Question 6

How does COPD affect relaxed and forced vital capacities ?

Answer 6

Relaxed vital capacity is greater than forced vital capacity in COPD
-if this is found think air trappign

Question 7

How is total lung capacity worked out ?

Answer 7

Total lung capacity = vital capacity + residual volume
-essentially constant in a health individual

Question 8

How does COPD affect total lung capacity ?

Answer 8

RV ↑↑ (air trapping) so VC ↓ so TLC ↑ (hyperinflation)

Total lung capacity = vital capacity + residual volume

Question 9

Compare forced vital capacities in different obstructive diseases

Answer 9

Asthama tend to haver a preserved forced vital capacity (FVC) whereas COPD does not
-severe asthma with airway remodelling behaves more like copd and loooses preserved forced vital capacity (collagen deposition in airways and not in alveoli)

Question 10

Compare obstructive and resitrictive lung disease

Answer 10

Restrictive lung disease
-affects ability of lungs to fully expand
-lungs become stiff due to problem in alvoeli
-e.g. diffuse pulmonary fibrosis causing collagen in alveoli or inflammatory intrate in alveloli (like in alveolitis)

Obstructive lung disease
-difficult to exhale all air from lungs

Question 11

How do different lung disease affect FEV1/FVC ratio ?

Answer 11

Restrictive
-FVC curve is normal shape but shruken down so FEV1/FVC ratio is preserved due to proportionate reductions
-Ratio still greater than 0.75

Obstructive (conducting airways)
-FEV₁ is reduced disproportionately more than FVC so FEV1/FVC decreases
-Ratio < 0.75 depending on criteria

Question 12

What is a sympathmemtic

Answer 12

Mimics the effects of the sympathetic nervous system
-e.g. salbutamol (B2 selective)

Question 13

How would salbutamol affect obstructive and restrictive lung diseases ?

Answer 13

Obstructive e.g. asthma
-Salbutamol should shift curve back to normal at that point due to bronchodilatory reversibility
-Can measure sucess of response to bronchodilator; perecentage improvement should be equal to or
greater than 12% reversibility but less than this in COPD

Restrcitve
-has no reversibility withsalbotamal as problem not in conducting airways

Question 14

What is a flow volume graph ?

Answer 14

Flow rate (L/s) plotted against forced expiratory volume (L) -from TLC to RV

Question 15

What are different kinds of airway closure and how do these affect the shape of expiratory flow-volume curves ?

Answer 15

Volume dependent expiratory airway closure
-asthma, chronic bronchitis

Pressure dependent expiratory airway closure
-emphysema

Question 16

Which expiratory flow rates can be taken from a flow-volume curve ?

Answer 16

Peak expiratory flow rate (PEF)
-expressed in L/min (L/s x 60)
-also measurable with simple linear peak flow meter

Forced expiratory flow rate (FEFR) at a % of FVC
-FEF 50, FEF25-75%

Question 17

How do obstructive and restrictive lung diseases affect different test values ?

Answer 17

Question 18

What is bronchial challenge testing ?

Answer 18

An effort independent test
Evaluates how ‘reactive’ a patient’s lungs are to certain things in the environment e.g.
-exercise
-methacholine/histamine/mannitol (for bronchial hyper-responsiveness)
-allergens/chemicals (for occupational asthma)

Question 19

How do different substances used for bronchial channenge testing to assess hyper-responsivness work ?

Answer 19

Histamine also indirect

Question 20

What is exercise testing ?

Answer 20

An effort dependent test so uses spirometry
-Decreased FEV1 or PEF post exercise → asthma (Adrenaline increases FEV1 but we measure the dip after)
-Decreased SaO2 during exercise → interstitial lung disease, fibrosis, advanced COPD esp emphysema; used to monitor treatment responses

Full cardiopulmonary exercise test (CPET)
-Differentiate cardiac vs respiratory dyspnoea
-Heart rate vs oxygen uptake vs ventilatory rate

Question 21

How are RVC and TLC calculated ?

Answer 21

(RV = FRC - ERV) (TLC = VC + RV)

Question 22

How can different diseases affect TLC ?

Answer 22

Increased TLC in hyperinflation (Emphysema)

Decreased TLC in restrictive lung disease

Question 23

What is CO transfer factor ?

Answer 23

This is a type of gas diffusion test

Measures gas diffusion across alveolar-arteriolar barrier (single breath diffusing capacity)
-TLCO (or DLCO) - total lung transfer for CO ( or Diffusing capacity ) : corrected for alveolar volume (KCO)
-Decreased DCLO indicates anaemia, emphysema, interstitial lung disease, pulmonary oedema, pulmonary embolism

Aka CO TRANSFER FACTOR (DIFFUSING CAPACITY)

KCO tells you diffusion efficiency per unit lung volume.

Question 24

What is exhaled breath condensate ?

Answer 24

Fractional exhaled breath nitric oxide (FeNO)
–Point of care non-invasive marker of T2 airway inflammation (IL-13) in asthma
-High levels of exhaled NO (>50ppb) reflct uncontrolled asthmatic eosinophilic airway inflammation
-Used with bronchial challenge to assess asthmatic inflammation especially when spirometry is normal
-Not useful in COPD – NO suppressed by smoking

Effort independent test