Arterial blood gasesEmphysema is a disease of alveolar wall destruction. The loss of the alveolar capillaries creates areas of high ventilation relative to perfusion. Typically, patients with emphysema will adapt to high / ratios by increasing their minute ventilation. They may maintain nearly normal PO2 and PCO2 levels despite advanced disease. Examination of arterial blood gases invariably reveals an increase in the A-a PO2. With greater disease severity and further loss of capillary perfusion, the DLCO falls, leading to exercise-related and, ultimately, resting arterial hemoglobin desaturation. Hypercapnia, respiratory acidosis, and a compensatory metabolic alkalosis are common in severe disease.