Spirometry

Question 1

Key

Answer 1

FEV1 = forced expiratory volume in 1 second
FEV = forced expiratory volume
FVC = forced vital capacity
TlCO = transfer capacity of lung for CO
KCO = transfer coefficient i.e. diffusing capacity of the lung per unit volume (KCO - korrected)

Question 2

Obstructive vs restrictive

Answer 2

Obstructive e.g. asthma and COPD - airway resistance to expiratory flow so decreased FEV1. This results in a smaller FEV1/FVC ratio

Restrictive e.g. pulmonary fibrosis, interstitial lung disease, obestity, neuromuscular and chest / spine deformities restrict lung expansion, reducing the amount of air the lungs can hold - lower FVC, also lower FEV1. FEV1/FVC ratio remains near normal

Question 3

Advanced interpretation - TLC

Answer 3

TLC = total volume of air inside the lungs including the VC (maximal volume that can be breathed in and out) and the residual volume

TLC low in restrictive disorders
TLC may be high in emphysema

Question 4

Advanced lung intepretation - TlCO and KCO

Answer 4

TlCO = total diffusing capacity of the lung. Pt inspires fixed amount of CO and quantity expired is then calculated to determine how much went into blood

KCO = TlCO/alveolar volume = diffusing capacity of lung per unit volume

Reduced TlCO may be due to:
Pulmonary vascular bed abnormalities i.e. PE / PHTN - KCO is also low
Alveolar destruction e.g. ILD, emphysema - KCO is also low
Reduced alveolar volume e.g. pneumonectomy - KCO normal
Incomplete alveolar expansion i.e. restrictive disorders - KCO normal