Restrictive Spirometry in Severe Kyphoscoliosis (Chest-Wall Restriction)

A 32-year-old woman with severe idiopathic thoracolumbar kyphoscoliosis (Cobb angle 92°) presents with progressive exertional dyspnea (NYHA III), morning headaches, and resting oxygen saturation of 92% on room air. Spirometry shows the pattern marked **A** in the diagram: FVC 1.42 L (44% predicted), FEV₁ 1.28 L (46% predicted), and FEV₁/FVC ratio 0.90. Body plethysmography confirms TLC 2.8 L (48% predicted). DLCO is 78% predicted but DLCO/VA is elevated at 112% predicted. Which of the following best explains the physiological mechanism underlying this spirometric pattern?