INCREASED LEFT-VENTRICULAR CONTRACTILITY DURING CROSS-CLAMPING OF THEDESCENDING THORACIC AORTA

Objective: To evaluate how left ventricular (LV) dimensions and contra ctility and proximal systemic hemodynamics respond during and after 30 minutes of cross-clamping of the descending thoracic aorta. Design: T he study was prospective and controlled. Setting: The study was perfor med in a university animal laboratory. Participants: Ten pigs (bodywei ght: 22 to 30 kg). Interventions: The pigs were anesthetized with fent anyl and ketamine, and the heart and aorta were exposed through a left thoracotomy. The aortic root pressure and flow and LV dimensions were monitored with a high-fidelity pressure catheter, a precalibrated ult rasonic transit-time flow probe, and by two-dimensional ultrasound ima ging, respectively. Measurements and Main Results: After 1 minute of c ross-clamping, LV end-diastolic and end-systolic diameters were increa sed 17% and 32% above baseline (both p < 0.001), respectively, whereas LV fiber shortening was decreased by 35% (p < 0.05) corresponding to the 257% increase in wall stress (p < 0.001). After 5 minutes, LV dime nsions, fiber shortening, and wall stress had returned to baseline lev els. After 10 minutes, fiber shortening was increased 67% (p < 0.05), although wall stress was maintained at baseline levels. Simultaneously , the aortic mean blood pressure, heart rate, and cardiac output peake d 112% (p < 0.001), 81% (p < 0.001), and 125% (p < 0.01) above baselin e, respectively. Conclusions: Cross-clamping grossly increased systemi c afterload grossly and was followed by moderate LV dilation, which re solved after 5 minutes owing to the combined effects of proximal vasod ilation. increased myocardial con; tractility. and tachycardia. This h yperdynamic circulatory state was maintained during cross-clamping and decreased after declamping. (C) 1995 by W.B. Saunders Company