Gas Exchange in Chronic Thromboembolism after Pulmonary Thromboendarterectomy: Discussion (Part 4)
These vessels anastomose with precapillary pulmonary vessels and thereby have access to the obstructed pulmonary capillary bed. Because of the proliferation of anastomotic bronchial vessels, pulmonary capillaries distal to even completely obstructed pulmonary arteries will not be blood-free, and therefore, will be available for CO exchange. Since CO uptake is diffusion-limited rather than perfusion-limited, even a small bronchial flow could contribute significantly to the Deo. Following surgery, these areas are reperfused with pulmonary blood, but this change in perfusion origin will not increase CO exchange. asthma inhalers
In summary, pulmonary thromboendarterectomy significantly improves ventilation-perfusion relationships in chronic thromboembolic pulmonary hypertension. Overall gas exchange improves remarkably, and the resolution of hypoxemia is secondary to both improved Va/Q relationships and the restoration of cardiac output and normal Pv02 values. Those patients with high grades of vascular obstruction achieve the greatest improvement in Va/Q relationships, and the discrepancy between the prompt hemodynamic improvement and the more gradual gas exchange improvement suggests that mechanisms, in addition to relief of central mechanical obstruction, also contribute to the improvement Va/Q relationships following thromboendarterectomy.