Ultrasonic crystal measurement of blood volume changes in liver and spleen

Two methods of measurement of splenic and hepatic vascular capacitance responses were compared in cats anesthetized with pentobarbital. For the spleen, measurements using ultrasonic crystals were compared with recordings of splenic weight. The cube of the relative change in thickness at one point on the longitudinal axis of the spleen was closely correlated with the overall change in spleen weight. For the liver, measurements by ultrasonic crystals were compared with plethysmographic recordings of liver volume. Individual measurements of cubed relative thickness did not correlate well with plethysmographic volume, and two sets of crystals on the same liver lobe gave different estimates of relative liver volume. However, averaged measurements for a group of animals showed similar means by the two methods. We conclude that ultrasonic crystals, when appropriately attached, can reliably monitor changes in splenic volume, but that for the liver, the variability in thickness responses at different sites on different livers is high. Unless a large number of observations are made, the results will be unreliable.