Morphologic changes of the aortic wall due to reduced systemic pulse pressure in prolonged non pulsatile left heart bypass.

The morphologic changes of the aortic wall due to reduced systemic pulse pressure in prolonged non pulsatile left heart bypass (LHB) were investigated. Sixteen adult goats were divided into three groups: the non pulsatile group in which non pulsatile LHB was conducted for 137 days on average, the pulsatile group in which pulsatile LHB was conducted for 79 days on average, and the control group used as the normal control. The average aortic pulse pressures were 12, 48, and 37 mmHg, respectively. At the end of the experiments, the descending aorta was excised and subjected to morphologic examination. The wall thickness of the aorta in the non pulsatile group (1.4 mm) was significantly thinner than that in the pulsatile group (2.2 mm) and the control group (2.0 mm), and the volume ratio of smooth muscle cells (SMC) in the non pulsatile group (37%) was lower than that in the pulsatile group (48%) and the control group (49%). In SMC classification, the proportion of SMC with low activity and low contractility in the non pulsatile group (57%) was high as compared with that in the pulsatile (2%) and control (5%) groups. These results strongly indicate that prolonged non pulsatile LHB causes substantial morphologic changes in the aorta.