CLINICAL EVALUATION (continued)

C. Ventilation/Perfusion Non-uniformity

1. Measure ventilation distribution

a. N₂ washout: switch rapidly from breathing air to breathing pure O₂ and follow gas concentration changes at mouth level during a maximum expiration

1) Single breath test: measure N₂ increase between 750 ml and 1250 ml exhaled gas; for a normal person, the increase in N2 should be less than 1.5%

Reasoning: Most of the alveolar gas exhaled early in the breath comes from the better ventilated alveoli, while the gas exhaled later comes from the underventilated alveoli

b. Tracer distribution: measure the distribution of inhaled radioactive Xenon gas

2. Measure pulmonary circulation distribution

a. intravenous injection of radio-iodinated albumin aggregates; measure distribution in pulmonary circulation