Flow estimation by DSA in bypasses with or without a distal arterio-venous fistula

Flow of contrast medium in bypasses with or without an arteriovenous fistula (AVF) has been measured using a densitometric technique. Modern digital subtraction angiography (DSA) equipment has the ability to produce images related to the density of the bolus of contrast passing down the vessel and to measure flow from them. Three studies were performed; (1) the method was tested in a model where it was compared with direct flow measurement; (2) A flow study was carried out in four groups of different below knee bypasses; (3) A study to examine the distribution of flow in adjunctive arteriovenous fistula was performed. The first study showed that the method was reliable and highly reproducible; the mean relative variance of DSA measured flow to the real flow being 3.05% and never more than 10%. The second study showed mean flow for various bypasses as shown below: (1) 10 fem.pop. bypasses (61-202 ml/min). 120 ml/min; (2) 10 fem.tib. bypasses (41-190 ml/min). 120 ml/min; (3) 10 fem.tib. bypasses with AVF(243-455 ml/min). 321 ml/min; (4) 10 pop.pedal. bypasses with AVF(112-382 ml/min). 261 ml/min. The differences between group 1 and 2 and group 3 and 4 are significant (P less than 0.005). The third study showed that relatively little of the blood entering an AVF passes distally into the arterial bed (Mean: 11%, 6-19%). In conclusion, DSA flow measurement is a reliable method of flow measurement. An AVF increases graft flow 2-3 times but only about 10% of the blood passes distally into the arterial system.