The differential ratio. A method for describing blood flow in renal transplants.

The blood flow in renal transplants can be represented by (1) a K/A ratio, the ratio of the slopes of the ascending part of the renal perfusion curve and the arterial curve, (2) a perfusion index, the ratio of a part of the area under the first-pass arterial curve and renal curve, and (3) a height ratio, the ratio of the height of the renal curve and the arterial curve at the point of time upon which the arterial curve shows its very first maximum. Because it is sometimes rather difficult to find suitable parameters for these three methods, a differential ratio is proposed, the ratio of the maxima of the 1st derivative of the first-pass renal and arterial curve. Good correlation is found between the K/A ratio and the differential ratio as well as between the perfusion index and the height ratio. This implies that the differential ratio could be used instead of the K/A ratio and that the height ratio is a very good alternative for the perfusion index.