Measurement of Renal Blood Flow with Radioactive Microspheres

Abstract

Various methods have been used to measure total renal blood flow. Of these the most commonly employed are the clearance of paraamino-hippurate (PAH) and techniques that make use of the electromagnetic flowmeter. PAH clearance (corrected for extraction ratio) is a cumbersome method requiring catheterization of the renal vein. It would be desirable to have a method which is simple and less traumatic but equally reliable. Neutze et al. (1) have shown that total renal blood flow can be determined using a radioactive microsphere (MS) technique, and that values so obtained correlate well with renal blood flow as determined by using the electromagnetic flowmeter. Neutze and co-workers measured renal blood flow by multiplying cardiac output by the ratio of counts in the kidney to total body counts. Thus, their technique involved determination of cardiac output and total body counting and is obviously no less cumbersome than any of the other commonly used techniques.

Using the Fick principle we reasoned that total renal blood flow could be obtained by the ratio of radioactivity in the kidney to that in arterial blood sampled immediately after the injection of microspheres. This report describes this technique and the results obtained using it as compared to PAH clearance.

Methods. Twelve female dogs were anesthetized with sodium pentobarbital and catheters were placed in the left ventricle (for microsphere injection), the femoral artery (for blood sampling), and the femoral vein (for PAH infusion). The left kidney was exposed through a flank incision and the renal vein catheterized via the ovarian vein. The ureters were cannulated by a suprapubic approach. Renal plasma flow was measured by the clearance of PAH using Wolf's equation (2): RPF = (U – R) × V/(A – R)(A, R and U represent PAH concentration in arterial, renal venous and urine samples, respectively; V is the urine flow expressed in ml/min).