Acute and chronic flow-measurements in experimental arteriovenous fistulas.

Abstract

In 13 dogs a large sized iliac arteriovenous fistula is established following laparotomy. Measurements of local blood flow and of general hemodynamic changes are performed immediately after construction of the shunt as well as 3 (stage II) and 6–12 months (stage III) later. The following results are obtained: 1. Arterial pressure drops in the acute phase from 146 to 130 mm Hg (p<0.05) and increases at stages II and III to pre-shunt control pressure. 2. Cardiac output rises immediately after opening of the av-fistula from 127 to 162 ml/min/kg. In stage II a maximum of 288 ml/min/kg has been reached. No further increase is measured in stage III. 3. Heart rate accelerates instantly from 111 to 188 beats per minute. It slowly declines to preoperative control rate within one year post-shunt. 4. There is a 20-fold increase in proximal artery flow immediately after opening of av-shunt while flow in the distal fistula artery decreases to 1/3 of control flow. In the acute phase retrograde flow is not yet measurable in the distal artery. Compared to stage I flow in the proximal fistula artery does not significantly change in stages II and III. A retrograde flow in the distal fistula artery is measured in stage II in each animal increasing up to 1,2 l/min within one year post-shunt, thus constituting 40% of the shunt volume. 5. In the acute phase all shunted blood flows through the proximal vein. In stage II 41% and in stage III 47% of the shunt volume run off in retrograde direction through the distal vein and its collaterals. 6. Immediately after opening of the av-fistula shunt-flow averages 2,5 l/min (or 56% of cardiac output). In stage II shunt flow is 3,3 l/min (or 47% of cardiac output). In stage III fistula flow remains unchanged but constitutes a larger portion of cardiac output (58%) due to a decrease in cardiac output indicating myocardial insufficiency. 7. Total peripheral resistance decreases immediately after opening of the av-fistula and remains low during the following months. Systemic resistance however, increases in stage I by 52%. In stage II it approximates preoperative control, but is elevated again in stage III.