Gas Exchange in Chronic Thromboembolism after Pulmonary Thromboendarterectomy: Discussion (Part 3)
A more uniform perfusion distribution returns over the first postoperative year, and it is accompanied by resolution of hypoxemia. This time course suggests that either the nonobstructed vasculature undergoes remodeling which reduces its vascular resistance, or that the previously obstructed areas gradually recover vascular tone and gas exchange function. Shunt and high Va/Q regions were not present a year postoperatively. Buy Asthma Inhalers Online
The increased cardiac output following surgery and the corresponding increased mixed venous Po2 are important contributors to the resolution of hypoxemia. Theoretic considerations suggest that the lowered Po2 accounts for about one-third of the increased P(A-a)Oa present preoperatively. Although the present study does not provide a direct test of this estimate, it does provide circumstantial support. The average fall in P(A-a)Oz postoperatively was 59 percent, while the average reduction in log SDq was only 19 percent. The Po2 and cardiac output increased 22 percent and 41 percent, respectively.
The resolution of segmental perfusion defects on postoperative radionuclide scanning is evidence that the relief of central obstruction ultimately leads to reperfusion of previously unperfused pulmonary parenchyma, but surprisingly, the Deo was not increased. One possible explanation for this discrepancy relates to the remarkable hyperplasia of the bronchial circulation observed in these patients preoperatively.