A 58-year-old man presents with a two-month history of fatigue, weight loss, myalgias, and mononeuritis multiplex (foot drop). He develops acute hemoptysis and oliguria. Laboratory findings show creatinine 3.8 mg/dL, hematuria with RBC casts, and hemoglobin 8.1 g/dL. Chest X-ray reveals bilateral patchy infiltrates. Spirometry demonstrates a restrictive pattern (TLC 70% predicted). The pattern marked **B** in the diagram shows elevated DLCO (148% predicted). p-ANCA with MPO specificity is positive at high titer; PR3-ANCA is negative. Renal biopsy confirms pauci-immune necrotizing crescentic glomerulonephritis without granulomas. Which of the following best explains the elevated DLCO finding in pattern **B**?
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