Control of Left Ventricular and Proximal Aortic Dimensional Decompensation During Clamping of Descending Thoracic Aorta

Abstract

The dimensional changes (mea sured by ultrasonic miniaturized transducers) of the left ventricle (LV), and proximal aorta (PAo) that accompanied hemodynamic changes during a forty-minute period of cross-clamping of the descending tho racic aorta without (Group A, 5 dogs) or with (Group B, 5 dogs) controlled vasodilation with sodium nitroprus side (SNP) infusion were evaluated in 10 open-chest anesthetized dogs. In both groups, measurements were re peated for another thirty-minute pe riod after declamping. In Group A, during clamping, systemic vascular resistance (SVR), PAo pressure (PAoP), LV systolic pressure (LVSP), and PAo midwall stress increased sig nificantly (p < 0.001). LV end-diasto lic pressure (LVEDP), stroke volume (SV), cardiac output (CO), and coro nary blood flow (CBF) did not show major variations, whereas systolic and diastolic LV wall thickness were significantly reduced (p < 0.02). A re duction in systolic shortening and thickening was observed also (p > 0.05). In Group B, during the same period, CO and CBF increased substantially (p < 0.02). SVR, PAoP, LVEDP, PAo midwall stess, and SV remained close to baseline values, while systolic and diastolic (p < 0.05) segmental length and systolic short ening and thickening increased (p > 0.05). Furthermore, the velocity of systolic shortening in Group B was significantly higher (p<0.005) than in Group A. In conclusion, the data indicate that significant changes, as detected continuously by sonomicro metry, in LV wall geometry and PAo midwall stress were observed during aortic cross-clamping. SNP infusion appeared to be an effective pharma cologic intervention to control these changes and to preserve cardiovascu lar performance.