The Lack of Effect of Hemodilution, Myocardial Water Content, and Increased Coronary Artery Blood Flow on Integrated Myocardial Ultrasonic Backscatter in the Beating Canine Heart

The effects of coronary blood flow, tissue water content and hematocrit variation on the Integrated Myocardial Backscatter Rayleigh 5 (IBR5) and Fourier coefficient of amplitude modulation (FAM, an index of cardiac cylce-dependent variation in IBR5) were measured in five open chest dogs. Data were obtained at baseline, during adenosine infusion and after two hours of crystalloid hemodilution (Hct 15%). IBR5 of −46.4 ± .94 dB at baseline did not change significantly during adenosine infusion (−45 ± .85 dB) and after hemodilution (−46.4 ± 2.0 dB). FAM at baseline was (4.0 ± 1.0 dB) (3.8 ± −1.0 dB) during adenosine infusion and after hemodilution (5.0 ± 1.8 dB). Myocardial water content increased significantly (p < .05) from 78 ± .20% at baseline to 80.7 ± .17% after hemodilution. Coronary blood flow demonstrated a three-fold increase with adenosine and two-fold increase with hemodilution. Electronmicroscopy demonstrated an increase in intracellular and extracellular water content. In conclusion, IBR5 and FAM did not change significantly despite significant increases in coronary blood flow and myocardial water content. Myocardial cellular derangements seen with nonischemic cell swelling, increased blood flow and a fall in hematocrit are insufficient to affect integrated backscatter.