Validation studies for the use of the microsphere method in cats and young minipigs

Abstract

Radioactive microspheres are suitable for measuring cardiac output, its distribution and organ blood flow if certain criteria are met. Cardiac output may be determined with the reference flow method if microspheres do not recirculate. In case 10 micron microspheres were extracted completely by the lungs. The use of microspheres for the determination of cardiac output is therefore not limited by recirculation of microspheres down to this size. Under baseline conditions we found no preferential streaming with 50 micron spheres in young minipigs and with 25 and 15 micron spheres in cats At high cardiac output values induced by the administration of 0.4 mg/kg of Dihydralazine in cats, 25 micron but not 15 micron microspheres showed a small, non significant tendency to stream preferentially into the upper body. Thus, under rapid flow conditions 15 micron microspheres may be preferable to larger ones from the rheological point of view. Under baseline conditions the distribution of cardiac output to a wide range of organs was very similar when comparing 25 and 15 micron microspheres in cats and 50 and 15 micron microspheres in minipigs, whereas 10 micron microspheres were poorly extracted by most organ in cats. 15 micron microspheres were found to be suitable for the determination of cardiac output and its distribution in both species provided that bronchial and arteriovenous shunt flows can be neglected.

Calcium antagonist and the peripheral circulation: differences and similarities between PY 108–068, nicardipine, verapamil and diltiazem

“…Exceptions were the blood flow and conductance values of the adrenals (significant difference between the PY and N group in the Mann-Whitney test), and the lungs (significant difference between the PY and V group). In the latter case it should be remembered, that microsphere accumulation in the lungs represents bronchial flow plus a contribution, estimated at 90% or more from microspheres crossing through arterio-venous shunts in this cat model (Hof, Wyler & Stalder, 1980). Spontaneous changes occunring during the experiment in the control group were generally small.…”

“…The microsphere method as used in this laboratory has recently been described in considerable detail (Hof, Wyler & Stalder, 1980;Hof, Hof, Salzmann & Wyler, 1981). In short, about 1.5 x 105 15 pm spheres (3M Company), suspended in 10% dextran and labelled with 1251, 141Ce, 51Cr, 85Sr or 46Sc having a specific activity between 0.5 and 5 ct/min per sphere, were filled into mixing chambers.…”

PY 108-068, a dihydropyridine derivative, and verapamil interact differently with the ouabain effects on the heart and the peripheral circulation

“…The preparation of the experimental animals and the use of the microsphere method have been described previously in detail (14,15,17,21). The differences described below were kept as small as possible to facilitate the comparison of the "anti-vasoconstrictor" effects in the present experiments with the vasodilator effects reported previously (14,16).…”

Methods in Cardiovascular Safety Pharmacology

“…Using different radionuclides, repeated determinations are possible. The method is applicable not only for dogs, cats, and minipigs (Hof et al 1980) but also for rats (McDevitt and Nies 1976;Bonnacrossi et al 1978;Ishise et al 1980;Stanek et al 1985) using microspheres of appropriate size.…”