Lymphangioleiomyomatosis Sirolimus Therapy

A 34-year-old non-smoking premenopausal woman presents with progressive exertional dyspnea, two prior episodes of spontaneous pneumothorax, and chylous pleural effusions. High-resolution CT chest shows innumerable thin-walled round cysts distributed diffusely throughout both lungs with intervening normal parenchyma. Serum VEGF-D is markedly elevated at 1450 pg/mL. Spirometry reveals FEV1 55% predicted, FVC 88% predicted, and FEV1/FVC ratio 0.52 with minimal bronchodilator reversibility. Total lung capacity is at the upper limit of normal. The flow-volume loop obtained is shown in the diagram. Which of the labeled flow-volume loop patterns (marked **B**) best represents this patient's spirometric findings?