Chesebro, J H

Mayo Clinic, Mayo Foundation, Rochester, MinnesotaPlatelets are believed to play an important role in the pathogenesis of atherosclerosis and thrombotic occlusive arterial disease. As part of a prospective study of peripheral occlusive arterial disease in diabetes mellitus, platelet survival half-life (PS) was determined in years 1 and 2 from the disappearance pattern of 51cr-labeled platelets obtained by measuring radioactivity in serial samples over 8 days in four groups of patients age 50-70. Using computer assisted least-square analysis, a single exponent is fitted to the data and half-life determined.Groups included (1) normal subjects (NC); (2) subjects with clinical and objective evidence (transcutaneous doppler ultrasound and treadmill exercise) of peripheral arterial occlusive disease (AS0); (3) subjects with diabetes mellitus without AS0 (DM); (A) subjects with both diabetes mellitus and AS0 (DM+AS0). 112 subjects were tested in year 1 and 75 of these were available for retesting in year 2.In year 1, there is a difference in the distribution of platelet survival (PS) for the four groups (p=.002). PS is significantly short in groups AS0 and DM+AS0 compared with controls (NC), Year 2 values for PS (75 subjects) were compared to year 1. Using the t test on mean differences PS for each group was not significantly different year 2 vs year 1; mean percent differences year 2 vs year 1 were 1.2% (NC), 0.2% (ASO), 3.2% (DM), and -9.3% (9-3% lower than year 1 for DM+ ASO).Platelet survival half-life (PS) does distinguish popula tion groups and is reproducible when repeated.

In right-sided extracardiac conduits inserted for surgical correction of certain congenital heart defects, obstruction is a significant late complication requiring conduit replacement in about 5% of the patients. Our histopathologic study indicates a significant role of platelets in the pathogenesis. This study was designed to evaluate the feasibility of imaging procedure with 111-Indium-labeled platelets to localize and later quantify platelet accumulation in the conduits. Four patients with pulmonary atresia and 1 with truncus arteriosus underwent conduit placement, 2 with and 3 without porcine valve. Autologous platelets collected.from 43 ml of blood drawn prior to surgery were labeled with 111-Indium-oxine in ACD-saline medium (labeling efficiency 50-60%). 400-500 μCi of autologous 111-Indium-labeled platelets were administered intravenously immediately after surgery in 4, and five days after surgery in 1 patient. Imaging was performed at 6 hours and daily for 1-4 days using a portable gamma camera interfaced with a computer and fitted with medium-energy parallel hole collimator. Platelet deposition was noted at the site of the conduit in all 5 patients. Maximum accumulation (0.1-0.3% of dose) of platelets was seen within the first 24 hours. Activity over blood pool and lungs declined and over liver and spleen increased in a predictable manner over the imaging period. This technique has potential use as a noninvasive quantitative tool to study the effect of platelet inhibitor drugs in preventing conduit obstruction.