INTRAMURAL BLOOD-FLOW OF SKELETAL-MUSCLE VENTRICLES FUNCTIONING AS AORTIC COUNTERPULSATORS

Background. Skeletal muscle ventricles (SMVs) working as aortic counte rpulsators have provided long-term left ventricular assistance under e xperimental conditions. However, gradual deterioration of SMV pump fun ction and rupture have beers observed, and this may be related to comp romised intramural blood flow during synchronized counterpulsation und er systemic working conditions. Methods. Transformed, double-layered S MVs in 6 sheep were stimulated for 3-minute periods (5 V, 30 Hz, burst duration and delay from QRS both 40% of the cardiac cycle) to work as diastolic counterpulsators in the systemic circulation at a 1:2 (SMV: heart) and 1:1 ratio, and on a mock circulation with low-pressure load ing conditions at a 1:2 ratio. Thoracodorsal artery blood flow was mon itored by ultrasonic flow probe, and intramural blood flow distributio n was investigated by fluorescent microspheres. Thoracodorsal venous l actate concentrations were measured before and after each period of st imulation. Results. Thoracodorsal artery blood flow increased signific antly (p < 0.001) after stimulation. The magnitude of augmentation (89 %; 95% confidence interval, 36% to 163%) was similar for all working c onditions studied. Reactive hyperemia was observed after most 1:1 regi mens but was pare after 1:2 regimens. A significant (p < 0.05) 15% inc rease in serum lactate levels was present after 1:1 regimens only. All regimens of stimulation resulted in a significant increase (p < 0.01) in blood flow to sections in the outer wall of the SMV, but a signifi cant increase ((p < 0.05) in blood flow to sections in the inner wall was observed only under low loading conditions. Conclusions. Skeletal muscle ventricles subjected to 1:1 systemic counterpulsation regimens work under partly anaerobic conditions. High loading conditions may co mpromise SMV inner wall blood flow.