Central and peripheral pulmonary vascular resistance: Implications for who should undergo pulmonary thromboendarterectomy

Pulmonary thromboendarterectomy remains a technically challenging procedure with variable outcomes with regard to improvement in pulmonary function. Reducing the resistance to flow between the pulmonary valve and the pulmonary capillary bed is the key aim of surgery. The resistance to flow is due to the combination of resistance due to the central clot and distal capillary resistance. We hypothesise that the use of fluid mechanics in combination with modern radiology and electronic circuit theory can potentially predict who should or should not undergo a thromboendarterectomy. Electronic circuit theory of two resistors in series was utilised to demonstrate the concept of a model of a central clot and the peripheral pulmonary capillary bed. A simplified 2D model of the lungs utilising finite element analysis and Poiseuille's law was constructed for proof of principle. Modelling predicts that cardiac output and anatomical obstruction interplay and can have profound effects on the outcomes after thromboendarterectomy. Identical pulmonary artery pressures, due to differing cardiac outputs and identical anatomical obstructions due to thrombus can have very different physiological outcomes with regard to changes in pulmonary artery pressure. Modelling the pulmonary vasculature to determine central and peripheral pulmonary vascular resistance may help in predicting who should undergo pulmonary thromboendarterectomy. Mathematical modelling can potentially predict which patients have haemodynamically significant clots in their pulmonary arteries that thromboendarterectomy may potentially help in the setting of pulmonary capillary disease.