CANINE BONE BLOOD-FLOW MEASUREMENTS USING SERIAL MICROSPHERE INJECTIONS

The objective of this study was to determine the reproducibility of se rial bone blood flow (BBF) quantitation using multiple microsphere inj ections. Three consecutive estimates of BBF were obtained, using 15-mu radionuclide-labeled microspheres from 21 anesthetized adult dogs. A dose of 3 million spheres/ kg was used in seven dogs (Cohort 1); a dos e of 0.5 million spheres/kg was used in the remaining 1 1 dogs (Cohort s 2 and 3). Estimates of BBF were made at an average of 129, 153, and 175 minutes after the animals had been anesthetized in the first two c ohorts and 179, 203, and 225 minutes in Cohort 3. The dogs in Cohort 1 had no surgical intervention; the dogs in Cohorts 2 and 3 had increas ingly complex surgical interventions. Despite stabilization of cardiov ascular status, BBF was found to vary by 33.4% in Cohort 1, 25.7% in C ohort 2, and 42.5% in Cohort 3 over the three injections. Cortical BBF fell by 13.9%, 12.1%, and 12.4% between the first and second, and by 31.0%, 11.2%, and 29.9% between the second and third estimates for Coh orts 1, 2, and 3, respectively. Variation in right to left blood flow was used as an overall measure of error caused by technique and did no t consistently increase between the first, second, or third BBF estima tes in any cohort. Cortical BBF data were found to be significantly mo re reliable than cancellous data (p < 0.01); error caused by technique was least in the midshaft femoral or midshaft humeral cortical sample s. Increasing the spheres administered from 0.5 to 3 million/kg for th ree serial microsphere injections increased the number of reliable sam ples and did not lead to increased technical error or shunting. This s tudy demonstrates that there is a significant decrease in BBF over tim e in the anesthetized dog; therefore, serial estimates of BBF can only be interpreted if the results are normalized or if a control group of animals is included.