Pulmonary Function Testing

Question 1

appreciate the difference between effort dependant and independent tests of pulmonary function

Answer 1

effort dependant tests;
forced expiratory volume (FEV)
flow rates - spirometry

effort indépendant tests;
relaxed vital capacity - spirometry 
He/N2 washout static lung volumes
while body plethysmograph 
impulse Oscillometry
exhaled breath nitric oxide 

gas diffusion tests;
CO transfer factor
arterial blood gases (Resting)
sats during exercise

Question 2

explain the measurement of forced expiratory volumes and flow using spirometry in assessment of asthma and COPD

Answer 2

from flow volume curve;
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 between 25 and 75% of FVC - FEF25-75%

obstructive lung disease;
decrease in PEFR and FEV1
FVC is normal is asthma but decreased in COPD
FEV1/FVC ratio <75%
FEV1 response to beta2-agonist - asthma (>15%), (COPD <15%)

restrictive lung disease;
normal PEFR
decrease in FEV1 and FVC
FEV1/FVC ratio >75%
no FEV1 response to beta2-agonist

Question 3

explain static lung volume and single breath diffusion measurements

Answer 3

static lung volumes - effort independent test
N2 washout : functional residual capacity (FRC)
RV = FRC - ERV
TLC = VC + RV

increase in TLC in hyperinflation (emphysema)
decrease in TLC in restrictive lung disease
gas trapping in COPD - RV/TLC%

Question 4

explain bronchial challenge testing

Answer 4

assists in diagnosis os asthma
patient breathes in metacholine/histamine/mannitol - marker of airway hyper-responsiveness, contraption to produce 20% decrease in FEV1
the different allergens and chemicals induce early and late responses

nitrogen washout test measures functional residual capacity

Question 5

describe exercise testing

Answer 5

decrease in FEV1 and PEF post exercise is an indication of asthma
decrease in sats during exercise in interstitial lung disease monitors treatment response
full cardiopulmonary exercise test (CPET) - differentiates cardiac vs respiratory dyspnoea, heart rate vs oxygen uptake vs ventilatory rate

Question 6

describe diffusing capacity

Answer 6

CO diffusion across alveolar-capillary barrier - aka single breath capacity
DLCO - total lung transfer for CO (or diffusing capacity) : corrected for alveolar volume (KCO)
decrease in DLCO: anaemia, emphysema, Int lung disease, pulmonary oedema, Po emboli
to monitor treatment response in Int lung disease

Question 7

describe airway resistance

Answer 7

measured by either whole body plethysmography or more commonly/easily with impulse oscillomtry 
impulse oscillometry (IOS) measures airway resistance during quiet tidal breathing - at different resonant frequencies to give total resistance at 5Hz (R5) and central resistance at 20Hz (R20) - and hence peripheral airway resistance by subtraction R5-20
useful in patinets (e.g. kids) where easier to breathe at tidal volume than forced expiratory manoeuvre

Question 8

explain exhaled breath condensate

Answer 8

exhaled breath nitric oxide measured at flow f 50ml/s (FeNO) - non invasive marker of eosinophilic airway inflammation in asthma - mediated by IL13
not useful in COPD as nitric oxide suppressed by smoking
high levels of exhaled NO (>35ppb) reflect uncontrolled asthmatic inflammation
used as an adjunct to bronchial challenge to assess asthmatic inflammation - especially when spirometry is normal