How much does aortic and pulmonary artery area vary during the cardiac cycle?
Cardiac output (CO), as measured by Doppler, is computed by multiplying vessel area by mean velocity. One unresolved problem is the magnitude of vessel area change during the cardiac cycle. Prior estimates have ranged from 2% to 30% area change during the cardiac cycle. The purpose of this study was to measure cyclic dimensional changes in the aorta and pulmonary artery of dogs by a very sensitive technique, mercury strain gauge plethysmography. Gauges were fixed around the pulmonary artery and the aorta and changes in vessel circumference were recorded under the following conditions: increased preload, increased afterload, decreased preload, and during administration of dobutamine, 5 and 10 micrograms/kg/min. Percent change in circumference of the aorta at baseline was small (mean circumference change = 4%, SD = 1%, SEE = 0.5). Percent change in the pulmonary artery at baseline was slightly larger (mean circumference change = 6%, SD = 5%, SEE = 2%). Mean aortic area change was 9% (SD
