Pulmonary Function Tests

 

Types

PFT comprises peak expiratory flow (PEF), spirometry, and diffusing capacity:

• PEF is a simple test, which can be self-administered, measuring expiratory flow in L/min.
• Spirometry allows calculation of a broader range of lung physiology parameters. Small electronic devices mean that it can be done at the bedside.
• Diffusing capacity (DL) – aka transfer factor (TL) – measures gas transfer in the lung. Most commonly involves diffusing capacity of carbon monoxide (DLCO, TLCO). Raised in pulmonary haemorrhage, polycythaemia, and non-acute asthma (or normal). Reduced in most lung diseases, including acute asthma.

Predicted values:

• Based on age, gender, and height.
• Uses data from the whole population – including the unhealthy – so most healthy people should be a little above predicted.

Procedure

• PEF: you reset marker, patient breaths out, takes deep breath in, then breaths as hard and fast as possible into the tube, without covering it any way. Take the best result of 3.
• Spirometry: same instruction but keep breathing out all in one breath until all gone.

Interpretation

• Obstructive lung disease: ↓FEV1/FVC, normal TLC.
• Restrictive lung disease: ↓TLC, normal FEV1/FVC.