Effect of Extracorporeal CO₂ Removal on Pulmonary Capillary Endothelium-Bound Angiotensin Converting Enzyme Activity in the Human

Abstract

The pulmonary vascular endothelium possesses major metabolic functions such as synthesis and degradation of vasoactive peptides. Enzymes that catalyze these reactions are located on the luminal surface of the capillaries and their activities may be measured in vivo by means of indicator-dilution techniques. Among these enzymes, angiotensin-converting enzyme (ACE) has been extensively studied in animals and more recently in humans. Pulmonary capillary endothelium-bound (PCEB) ACE activity is reduced in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), reflecting the underlying endothelial dysfunction (Orfanos et. al., 1996a). In this study we report preliminary results of PCEB ACE activity assessment in two subjects with severe ARDS (NIH ECMO study criteria), who were treated with Low Frequency Positive Pressure Ventilation with Extra-Corporeal CO ₂ Removal (LFPPV with ECCO₂R). Our purpose was 1) to investigate if ECCO₂R application, per se, affects PCEB ACE activity, and 2) to assess if the degree of endothelial dysfunction correlates with the clinical severity and the evolution of the syndrome.