Bone blood flow measurement — 3: Arteriolar blockade

Abstract

Arteriolar blockade depends upon the fact that appropriately sized particles introduced into the circulation, usually the left ventricle of the heart or the aorta, will be distributed throughout the tissues in proportion to the cardiac output per-fusing that tissue. Assuming an appropriate size in relation to afferent arterioles of the capillary beds, it is assumed that total extraction occurs in the first passage. The concept was originally introduced by Saperstein (1958), who suggested 42K as a completely extractable tracer for clinical use. Kane & Grim (1969), however, later applying this technique to bone, found that 42K was not removed in a single passage. In the same study they introduced the use of glass microspheres labelled with 24Na as a quantitative vascular tracer. Glass microspheres are much heavier than erythrocytes, and hence subject to rapid sedimentation in the circulation. Brookes (1970) used 59Fe-labelled cationic exchange resin particles to measure blood flow in rat hind limb bones, using the term arteriolar blockade for this technique. In the same year Lunde & Michelson (1970) introduced the use of labelled Dextran microspheres for measurement of bone blood flow in bone, using a reference artery method (see below) to determine absolute flow rates. Arteriolar blockade allows flow rates to be measured in tissues which are otherwise inaccessible to direct measurement.