Respiratory Investigation — DCE Clinical Case

The read — deliver this to the examiner in order

Quality first. "The manoeuvres are acceptable and reproducible, so these numbers can be trusted" — always open with test quality, because it tells the examiner you read like a physiologist, not a pattern-matcher [1].

Ratio. "The FEV1/FVC ratio of 0.83 is comfortably above the LLN of 0.66 — there is no obstruction. Note that I am reading the ratio against the lower limit of normal, not a fixed 0.70, because the ratio falls with age and fixed cut-offs misclassify older patients" [1].

Volumes. "The TLC of 63% predicted is below the LLN — this is true restriction, confirmed by volumes. Spirometry alone could only suggest it; the TLC is the defining measurement. The reduced RV fits a small lung rather than air trapping" [1] [3].

Gas transfer. "The DLCO is 48% predicted against a normal haemoglobin, with a KCO of 60% and an alveolar volume of 82% — a genuine, disproportionate impairment of gas transfer that localises the disease to the alveolar-capillary membrane. This is not an artefact of small lungs, and not an anaemia artefact" [2].

Synthesis. "In one sentence: Mr Ngata has a confirmed restrictive ventilatory defect with a severe membrane-level gas-transfer impairment — the physiological signature of a fibrotic interstitial lung disease — and my next investigation is an HRCT chest to define the pattern, because pattern determines treatment" [1] [2].