MEMBRANE-DIFFUSION AND CAPILLARY BLOOD-VOLUME IN CHRONIC THROMBOEMBOLIC PULMONARY-HYPERTENSION

A reduced diffusing capacity for carbon monoxide (DCO) is common among patients with chronic thromboembolic pulmonary hypertension (CTEPH) a nd often persists for more than a year following successful pulmonary thromboendarterectomy (PTE). To determine the relative contribution th e pulmonary membrane diffusing capacity (D-M) and pulmonary capillary blood volume (V-C) make to the reduction in DCO, we measured both in 2 9 patients with CTEPH before and approximately 3 weeks after PTE, Mean preoperative D-M was reduced in patients with CTEPH (28 mL, min(-1) m m Hg-1 vs 43 mL min(-1) mm Hg-1 in control subjects; p < 0.001) and dr opped significantly following PTE (21 mL min(-1) mm Hg-1 p < 0.001). M ean preoperative V-C was mildly reduced in the CTEPH group compared wi th healthy control subjects (57 vs 67 mL; p = 0.044) and did not rise following PTE (57 mL pre-PTE vs 54 mL post-PTE; p > 0.05) despite subs tantial reduction in mean pulmonary artery pressure and increase in ca rdiac output after surgery. We conclude that the low DCO observed in p atients with CTEPH before and after PTE is principally caused by a red uced D-M and to a lesser extent by a low V-C. The mechanisms responsib le remain speculative but may reflect pathophysiologic changes in the pulmonary microcirculation caused by chronic pulmonary hypertension th at did not improve in the postoperative period studied.