Continuous measurement of aortic radius changein vivo with an intra-aortic ultrasonic catheter

The radii of the inner and outer walls of the aorta and the intravascular blood pressure were recorded simultaneously in the descending thoracic aorta of intact, living dogs using 7·5 MHz ultrasound. Blood pressure and the A-mode signals containing wall echoes were also recorded on videotape which was later replayed for processing. Thein vivo data were compared with data obtained on the same vessels post mortem. The change in radius due to a pressure change from 80 to 125 mmHg was calculated from thein vivo andin vitro data. After normalising the radius changes with respect to the radius at 80 mm Hg, the ratio of thein vivo andin vitro values ranged from 0·66 to 1·36 with a mean of 0·94. The changes in radius were comparable with previously reported values obtained using various techniques.