Haemodynamic changes due to clamping of the abdominal aorta.

Haemodynamic changes due to aortic cross-clamping were examined in 18 patients. It has been shown that the distal occlusion of the abdominal aorta induces an increased impedance to ejection. Because the mechanisms controlling the auto-regulation of cardiac output and the circulatory reflexes are damped by anaesthesia, the augmentation of resistance is not followed by any increase in contractility or vasomotor tone and thus the cardiac output falls. Patients with chronic obstructive disease (Leriche) did not differ significantly from subjects with more acute obstruction (aneurysm), though the latter have a tendency to show more important changes in their haemodynamic response.