Gas Exchange in Chronic Thromboembolism after Pulmonary Thromboendarterectomy: Discussion (Part 1)
The central conclusion of this study is that pulmonary thromboendarterectomy, on average, returns the Va/Q distribution to nearly normal in chronic large vessel thromboembolic pulmonary hypertension. Thus, the improvement in hypoxemia is not simply due to the improvement in cardiac output which follows relief of central obstruction. This conclusion is based on the postoperative reduction in Va/Q heterogeneity measured with the multiple inert gas elimination technique and by the postoperative reduction in regional perfusion heterogeneity observed with Tc perfusion scanning. The improvement is not uniform, however, in that four of nine subjects had only a modest reduction in Va/Q heterogeneity, and one subject was unchanged. buy flovent inhaler
Unfortunately, for obvious reasons, this study lacks a control group of matched patients who were not treated surgically. However, chronic thromboembolic pulmonary hypertension is characterized by progressive pulmonary and cardiac impairment without remission, and it is very unlikely that the observed improvement in gas exchange was not related to the surgical removal of thromboemboli and the resolution of pulmonary hypertension.
It is interesting that the improvement in Va/Q matching afforded by surgery correlates more strongly with the magnitude of the preoperative obstruction than it does with the magnitude of surgical reduction in obstruction. Thus, if two patients each receive a 30 percent reduction in vascular obstruction, the patient with the poorer gas exchange initially will achieve the greater gas exchange benefit. This suggests that when vascular obstruction is severe and the majority of bloodflow is diverted to only a small volume of lung, the normal compensatory mechanisms controlling Va/Q relationships may be overwhelmed. Under these conditions, even small reductions in vascular obstruction may result in significant gas exchange improvement.