DIMENSIONS AND MECHANICAL-PROPERTIES OF PORCINE AORTIC SEGMENTS DETERMINED BY COMBINED IMPEDANCE PLANIMETRY AND HIGH-FREQUENCY ULTRASOUND

The aim of the study is to devise a method for direct measurements of pressure, cross-sectional area (CSA) and wall thickness of a vessel wh en pressurised. Segments of porcine descending thoracic aorta from 22 and 35 kg pigs (in groups I and 2, respectively) and of abdominal aort a from 35 kg pigs are studied in vitro. Impedance planimetry provides measurements of the luminal pressure and CSA of the aorta. The wall th ickness is measured simultaneously by means of 201 MHz A-mode ultrasou nd. The pressure, CSA and wall thickness are registered at, different pressures at steady state. At maximum pressure, the CSAs are 107 +/- 1 0, 215 +/- 19 and 257 +/- 17 mm(2) in the abdominal, group 1 and 2 seg ments, respectively. There is a difference between the abdominal group and groups 1 and 2 (p < 0.05), but not between group I and 2 segments (p > 0.2). At maximum pressure, the wall thickness is 0.52 +/- 0.04, 0.79 +/- 0.07 and 1.07 +/- 0.02mm, in the abdominal group 1 and 2 segm ents, respectively (p < 0.05). The circum-ferential stress-strain rela tionship accorded well with stress=a x exp(b x strain). The stress-str ain curve of the abdominal aortas is shifted to the left, indicating a n increase (p < 0.05).