Visceral Flow Research Articles

Fluid–structure interaction simulation of visceral perfusion and impact of different cannulation methods on aortic dissection

Hemodynamics in aortic dissection (AD) is closely associated with the risk of aortic aneurysm, rupture, and malperfusion. Altered blood flow in patients with AD can lead to severe complications such as visceral malperfusion. In this study, we aimed to investigate the effect of cannulation flow on hemodynamics in AD using a fluid–structure interaction simulation. We developed a specific-idealized AD model that included an intimal tear in the descending thoracic aorta, a re-entry tear in the left iliac artery, and nine branches. Two different cannulation methods were tested: (1) axillary cannulation (AC) only through the brachiocephalic trunk and (2) combined axillary and femoral cannulation (AFC) through the brachiocephalic trunk and the right common iliac artery. AC was found to result in the development of a pressure difference between the true lumen and false lumen, owing to the difference in the flow rate through each lumen. This pressure difference collapsed the true lumen, disturbing blood flow to the celiac and superior mesenteric arteries. However, in AFC, the pressure levels between the two lumens were similar, and no collapse occurred. Moreover, the visceral flow was higher than that in AC. Lastly, the stiffness of the intimal flap affected the true lumen's collapse.

Quantification of visceral perfusion and impact of femoral cannulation: in vitro model of aortic dissection.

We aimed to simulate blood flow at an aortic dissection in an in vitro vascular model and assess the impact of the cannulation method on visceral perfusion. An aortic-dissection model with an acrylic aortic wall and silicone intimal flap was developed to study visceral perfusion under various cannulation conditions. The primary tear was placed in the proximal descending aorta and the re-entry site in the left common iliac artery. A cardiovascular pump was used to reproduce a normal pulsatile aortic flow and a steady cannulation flow. Axillary and axillary plus femoral cannulation were compared at flow rates of 3-7 l/min. Haemodynamics were analysed by using four-dimensional flow magnetic resonance imaging. Axillary cannulation (AC) was found to collapse the true lumen at the coeliac and superior mesentery arteries, while combined axillary and femoral cannulation did not change the size of the true lumen. Combined axillary and femoral cannulation resulted in a larger visceral flow than did AC alone. When axillary plus femoral cannulation was used, the visceral flow increased by 125% at 3 l/min, by 89% at 4 l/min, by 67% at 5 L/min, by 98% at 6 l/min and by 101% at 7 l/min, respectively, compared to those with the AC only. Our model was useful to understanding the haemodynamics in aortic dissection. In this specific condition, we confirmed that the intimal flap motion can partially block blood flow to the coeliac and superior mesenteric arteries and that additional femoral cannulation can increase visceral perfusion.

A retrievable, dual-chamber stent protects against warm ischemia of donor organs in a model of donation after circulatory death

BackgroundIschemic injury during the agonal period of donation after circulatory death donors remains a significant barrier to increasing abdominal transplants. A major obstacle has been the inability to improve visceral perfusion, while at the same time respecting the ethics of the organ donor. A retrievable dual-chamber stentgraft could potentially isolate the organ perfusion from systemic hypotension and hypoxia, without increasing cardiac work or committing the donor. MethodsRetrievable dumbbell-shaped stents were laser welded from nitinol wire and covered with polytetrafluoroethylene. Yorkshire pigs were assigned to either agonal control or dumbbell-shaped dual-chamber stentgraft. A central lumen maintained aortic flow, while an outer visceral chamber was perfused with oxygenated blood. A 1-hour agonal phase of hypoxia and hypotension was simulated. Stents were removed by simple sheath advancement. Cardiac monitoring, labs, and visceral flow were recorded followed by recovery of the animal to a goal of 48 hours. ResultsCardiac stress did not increase during stent deployment. Visceral pO2 and flow were dramatically improved in stented animal relative to control animals. Five of 7 control animals were killed after renal failure complications, whereas all stent animals survived. Histology confirmed increased ischemic changes among control kidneys compared to stented animals. ConclusionA dual-chamber stent improved outcomes after a simulated agonal phase. The stent did not increase cardiac work, thus respecting a key ethical consideration. The ability of a dual-chamber stent to prevent ischemia during organ recovery may become a powerful tool to address the critical donor organ shortage.

Aortic flow below and visceral circulation during aortic counterpulsation: Evaluation of an in vitro model.

This study aimed to test a computer-driven cardiovascular model for the evaluation of the visceral flow during intra-aortic balloon pump (IABP) assistance. The model includes a systemic and pulmonary circulation as well as a heart contraction model. The straight polyurethane tube aorta had a single visceral while four windkessel components mimicked resistance compliance of the brachiocephalic, renal and sub-mesenteric, pulmonary, and systemic circulation. Twelve flow probes were placed in the circuit to measure pressures and flows with the IABP on and off. With the balloon off, the meantime to reach the steady state was 48 ± 16 s; with the balloon on, this figure was 178 ± 20 s. The stability of pressure and flow signals was obtained after 72 ± 11 min. The number of cycles of stability of the system was 93 [86-103]. Measurements were reliable either with samples of 10 or 20 beats. Bland Altman method demonstrated the reliability of measurements. Finally, all measurements were comparable to published in vivo data. The presented mock circulation was reliable and gave values with high accuracy both at baseline and during mechanical assistance. This system allows evaluation of the mesenteric flow during IABP, under different clinical/hemodynamic conditions. Nonetheless, its translational potential needs to be further evaluated.

Chimney Technique to Preserve Visceral Flow in a Coral Reef Aorta

The coral reef aorta (CRA) is a rare phenomenon of extreme calcification in the juxtarenal and suprarenal aorta. Open revascularization has an overall in-hospital mortality rate of 13%. We present a patient with a suprarenal CRA with colon ischemia. She has an extensive past medical history of percutaneous transluminal angioplasty and stenting of the celiac trunk (CT) and superior mesenteric artery (SMA). The computed tomography angiography showed a CRA of the suprarenal aorta with occlusion of the CT stent and near occlusion of the SMA stent. Our case illustrates that the CRA in the suprarenal part of the aorta can be treated well by chimney graft procedure, although owing to lack of long-term follow-up, it might be reserved for high-risk candidates for (thoraco)abdominal aortic surgery.

A three-tier Rescue stent improves outcomes over balloon occlusion in a porcine model of noncompressible hemorrhage.

Noncompressible hemorrhage remains a high-mortality injury, and aortic balloon occlusion poses limitations in terms of distal ischemic injury. Our hypothesis was that a retrievable Rescue stent would confer improved outcome over aortic balloon occlusion. A three-tier, retrievable stent graft was laser welded from nitinol and polytetrafluoroethylene to provide rapid thoracic and abdominal coverage with an interval bare metal segment to preserve visceral flow. Anesthetized swine had injury of the thoracic or abdominal aorta followed by balloon occlusion or a Rescue stent. A 1-hour long damage-control phase with blood repletion was used to simulate the prolonged interval between injury and repair, especially in the battlefield setting. Following the damage-control phase, the balloon or stent were retrieved followed by vascular repair and recovery to 48 hours. Animals were compared in terms of hemodynamics, blood loss, neurophysiologic spinal cord ischemia, ischemic organ injury, and survival. Despite antegrade hemorrhage control, balloon occlusion averaged 3.5 L of retrograde hemorrhage, loss of visceral perfusion, and permanent spinal cord ischemia by neurophysiology in six of seven animals. After permanent repair, all balloon occlusion animals died with only a single short term (5 hours) survivor. Conversely, Rescue stent animals revealed rapid hemorrhage control (in under 2 minutes) whether the injury was thoracic or abdominal with improved hemodynamics, preserved visceral flow, reduced spinal cord ischemia, negligible histologic organ injury and survival to end of study in all abdominal injured animals (n = 6) and four of six thoracic injured animals, with two deaths related to arrhythmia. Compared with aortic balloon occlusion, a Rescue stent offers superior hemorrhage control and survival by virtue of reduced ischemic injury and direct control of the hemorrhagic injury. The Rescue stent may become a useful tool for damage control, especially on the battlefield where definitive repair presents logistical challenges.

Is visceral flow during intra-aortic balloon pumping size or volume dependent?

We evaluated the influence of intra-aortic balloon size and volume on mesenteric and renal flows. Thirty healthy swine underwent 120-minute ligation of the left anterior descending coronary artery followed by 6 hours of reperfusion. Then, they were randomly assigned to the following five groups of animals, with six animals in each group: no intra-aortic balloon pump (IABP), a short 35-mL IABP, a short 40-mL IABP, a long 35-mL IABP and a long 40-mL IABP. Superior mesenteric artery (SMA) and renal flows were measured at baseline (t0), at 2-hour ischemia (t1) and every hour thereafter until 6 hours of reperfusion (from tR1 to tR6). SMA flows increased significantly at tR1 only in the two short IABP groups (p<0.001) and balloon volume did not appear to affect flows which, at any experimental time-point, were comparable using 35 mL or 40 mL balloons (p>0.05). Renal flows appeared to be influenced by balloon length, but not by volume. Indeed, flows in the renal arteries rose during IABP treatment; the increase was significantly higher in the short balloon groups and throughout the whole reperfusion (all, p<0.001). Changes in visceral perfusion during IABP assistance were significantly related to balloon length, but not to its volume. This could be relevant for the evolution of balloon engineering design in order to reduce the incidence of mesenteric ischemia following IABP. Further research is necessary to confirm these findings.

A New 35-mm Short Intra-aortic Balloon Catheter: A Suitable Option Also for Non-Small-Sized Patients?

Visceral ischemia can be a potentially life-threatening complication of intra-aortic balloon pump (IABP) support. A shorter IABP catheter might lead to a reduction of visceral complications. In this animal study, we evaluate the effects of a 35-mL short catheter in comparison with a 40-mL standard-sized catheter. Eighteen healthy swine underwent 120-minute ligation of the left anterior descending coronary artery followed by 6 hours of reperfusion being supported by either a short IABP catheter (short group) (n = 6) or a long IABP catheter (long group) (n = 6) or with no assistance (controls) (n = 6). Hemodynamics, visceral and coronary flows, as well as biochemical markers were evaluated throughout the different phases of the protocol. Mesenteric flows increased significantly at reperfusion (P < 0.001 both) remaining constant afterward (all, P > 0.05) in the short group, while remaining significantly lower in the long group at the start of reperfusion, remaining constantly lower than the short group and controls (P < 0.001 vs short, P < 0.003 vs controls). In both long and short groups, catheters improved renal flows at reperfusion (P < 0.001 both) without any further variation (P > 0.05). In the short group, the flows were higher during the whole of reperfusion (all, P < 0.05). Intra-aortic balloon pump support improved hemodynamic indices and coronary blood flows during reperfusion to a similar extent in both the small and the long group (P > 0.05). The short IABP catheter proved to be as effective as the standard-sized catheter in supporting hemodynamics and coronary circulation. Furthermore, it even improves visceral flows in comparison with conventional IABP catheters.

The Optimal Weaning Strategy for Intraaortic Balloon Counterpulsation: Volume-Based Versus Rate-Based Approach in an Animal Model

Changes in hemodynamics, coronary circulation, visceral flow, and biochemical marker rate reduction or volume deflation for intraaortic balloon pump discontinuation were assessed. Twelve healthy pigs were randomly assigned to two groups, the rate-based (RB, n = 6) and volume-based weaning groups (VB, n = 6). Hemodynamics and visceral and coronary flows were measured at baseline after 2 hours of intraaortic balloon pump 1:1, during the first 5 hours of weaning (frequency rate reduced to 1:2 in the RB group and volume decreased by 10%/h in the VB group), after 1 hour of frequency rate 1:3 in the RB group or a volume decrease by 75% in the VB group, 2 hours after withdrawal, and 4 hours after withdrawal. The animals weaned by progressive VB deflation showed a greater degree of vasodilation, better cardiac output and stroke volume, fewer negative values of cardiac cycle efficiency, and higher dP/dTmax compared with those weaned by RB reduction (p < 0.05 for all). The VB group also exhibited increased coronary flow, lower oxygen consumption of the myocardium, and coronary resistance during VB weaning (p < 0.05 for all). The serum lactate level was lower in the VB group at each experimental point (p < 0.05 for all), but visceral flows were scarcely affected by the weaning method. Volume reduction was the most effective weaning method considering that frequency reduction weaning was responsible for significant negative effects on hemodynamics and coronary circulation.

Comparing short versus standard-length balloon for intra-aortic counterpulsation: results from a porcine model of myocardial ischaemia-reperfusion.

We compare a short and a standard-size balloon with same filling volumes to verify the differences in terms of visceral flow, coronary circulation and haemodynamic performance during aortic counterpulsation in an animal model of myocardial ischaemia-reperfusion injury. Eighteen healthy pigs underwent 120-min ligation of the left anterior descending coronary artery followed by 6 h of reperfusion, and they were randomly assigned to have intra-aortic balloon counterpulsation (IABP) with a 40-ml short-balloon (n = 6) or a 40-ml standard-length balloon (n = 6), or to undergo no IABP implantation (controls, n = 6). Haemodynamics and visceral and coronary flows were measured at baseline (t0), at 2 h of ischaemia (t1) and every hour thereafter until 6 h of reperfusion (from tR1 to tR6), respectively. Mesenteric flows increased significantly at tR1 only in the short-balloon group (P < 0.001) and it was constantly higher than in the standard-balloon group regardless of mean arterial pressure, systemic vascular resistance and cardiac output (CO; all, P < 0.001). Renal blood flows were significantly increased during IABP treatment with values constantly and significantly higher in short balloons at any following experimental step (all, P < 0.05). IABP improved CO and coronary blood flow, and reduced afterload, myocardial resistances and myocardial oxygen consumption without differences between the short and the standard-length balloon (all, P > 0.05). The short balloon prevents visceral ischaemia and, compared with the standard-size balloon, it does not lose IABP beneficial cardiac and coronary-related effects. Further studies are warranted to confirm our findings.

Short intra-aortic balloon pump in a swine model of myocardial ischaemia: a proof-of-concept study.

This proof-of-concept study examined the haemodynamic performance as well as the coronary and visceral organ perfusion using a new short balloon for intra-aortic counterpulsation (IABP) in a swine model of myocardial ischaemia. Eighteen healthy pigs underwent 120-min ligation of the left anterior descending coronary artery followed by 6 h of reperfusion, and they were randomly assigned into 3 groups undergoing IABP implantation with a 35-ml short balloon (n = 6), a 40-ml short balloon (n = 6) or no IABP implantation (controls, n = 6). Haemodynamics, and visceral and coronary flows were measured at baseline (t0), at 2 h of ischaemia (t1) and every hour thereafter until 6 h of reperfusion (from tR1 to tR6), respectively. Mesenteric and renal flows increased significantly at tR1 only in the IABP groups (all, P < 0.001) and were significantly higher than controls throughout the reperfusion periods (P < 0.001). Coronary systolic and diastolic blood flows increased only at tR1 in the IABP groups (all, P < 0.001) but were higher than controls at tR1-tR6. The IABP was associated with enhanced haemodynamics compared with controls. No difference was detected using different balloon volumes (all, P > 0.05). The new short balloon significantly increased visceral flow, enhanced haemodynamics and improved coronary circulation during reperfusion following myocardial ischaemia in our experimental model.

CANULACIÓN DE LA ARTERIA INNOMINADA PARA CONEXIÓN A CIRCULACIÓN EXTRACORPÓREA EN CIRUGÍA DE LA AORTA

innominate artery cannulation for aortic artery surgery with extracorporeal circulation Surgery of the ascending aorta and its arc with extracorporeal circulation require an arterial cannulation that assures and adequate systemic circulation and reduces the risk of neurological complications. A peripheral cannulation such as the femoral artery, a central extra-thoracic approach such as axillary, subclavian or carotid arteries or a central intra-thoracic approach such as aorta and innominate arteries, are valid alternatives. Innominate artery cannulation can be carried out without the need of a second incision. It is an easily accessible and large bore vessel. It allows an anterograde brain and visceral flow. In cases of aortic arch surgery, the clamping of the artery in its origin, allows a selective anterograde brain perfusion. The surgical technique for innominate artery cannulation is herein described.

Everyday International Relations: Garbage, Grand Designs, and Mundane Matters

Garbage is stuff that matters: the generation, disposal, and management of waste represent some of the most visceral flows in our society. Yet most international scholars continue to regard it as trivial to focus on the mundane practices and menial materiality associated with managing rubbish. Contra this dissociation, and through an analytics of assemblages, I argue that international theory can (and nowadays must) encompass both the grand designs of diplomacy and the mundane cosmopolitics of everyday life. In the everyday, the “international” is embodied, performed, and domesticated. I chart these multi-scalar connections as they unfold in Sydney, Australia, demonstrating how a focus on a global challenge such as climate change has been redefining the mundane realities of waste management.

Chimney grafts preserve visceral flow and allow safe stenting of juxtarenal aortic occlusion

Chimney grafts have proven useful for urgent endovascular repair of juxtarenal aortic aneurysms. Stenting of juxtarenal aortic occlusive disease is not routinely advocated due to the risk of visceral artery obstruction. We report on the potential applicability of chimney grafts in 10 patients with juxtarenal aortic stenosis or occlusion. To our best knowledge, chimney grafts have not been applied previously in this challenging setting. Ten high-risk female patients (mean age, 68 years) with severe stenosis or occlusion of the aorta at the level of the visceral arteries were offered stenting. "Chimney" stents or stent grafts (20-40 mm long) were implanted from a brachial approach into visceral arteries that needed to be covered by the aortic stent. The chimney stents were then temporarily obstructed by balloon catheters to prevent visceral embolization until the aortic stent or stent graft was deployed. All procedures were technically successful, and patency was obtained in all visceral arteries and the aorta without distal embolization. One patient died after 9 days of acute heart failure. The nine surviving patients presented no complications, and all stented vessels remained patent at up to 6 years. Another patient died after 5.5 years due to lung cancer. All three patients with renal impairment have improved renal function, and a reduction in antihypertensive medication has been possible. Chimney grafts may allow stenting of juxtarenal aortic occlusive disease by protecting the patency of visceral arteries. Further evaluation with more patients and longer follow-up is required.

Endovascular treatment for a thoracic-abdominal aortic aneurysm without fenestrations or branches

We describe a case of a patient with a thoraco-abdominal aortic aneurysm, affecting the origin of the celiac trunk, with the particularity of the normal aortic diameter in the segment between superior mesenteric artery and both renal arteries. Endovascular treatment was performed with no fenestrated or branch endoprosthesis. The procedure was divided into two steps. In the first attempt, an aortic prosthesis was deployed at the infrarenal aorta. Then, a thoracic endoprosthesis was deployed in a second procedure. In this case, the celiac trunk was intentionally occluded in order to increase the distal landing zone. At the end, the segment between the superior mesenteric artery above and below the renal arteries was covered by the uncovered struts of both endoprosthesis, with no effects in visceral artery flow. Multislice computed tomographic angiography after six months revealed complete patency of the superior mesenteric artery, both renal arteries and good back-filling of the branches of the celiac axis, with no evidence of aortic endoleak.

Changes in Visceral Flow Induced by Laparoscopic and Open Living-Donor Nephrectomy: Experimental Model

Increased intra-abdominal pressure during laparoscopy changes visceral flow. The objective of the present study was to analyze the changes in peripheral and intra-abdominal flow induced by laparoscopic living-donor nephrectomy in an experimental model. Twenty pigs underwent left-sided nephrectomy, 10 at laparoscopy and 10 in an open approach. Renal blood flow (RBF), hepatic arterial flow (HAF), portal flow (PF), and carotid flow (CF) were measured using an electromagnetic probe placed around these vessels. Comparative analysis between the groups demonstrated increased CF (mean [SD], 125.73 [41.69] vs 291.70 [51.52] mL/min; P < .001) and decreased PF (973.67 [131.70] vs 546.83 [217.53] mL/min; P = .001) and HAF (278.00 [94.71] vs 133.33 [112.32] mL/min; P = .03) in pigs that underwent laparoscopy compared with those who underwent open surgery; no significant differences were observed in RBF. In conclusion, laparoscopic nephrectomy induces increased CF and decreased total hepatic flow, at the expense of PF and HAF. With adequate intravascular volume expansion, no differences were observed in RBF between the laparoscopic and open approaches.

ICU Controlled Delay for Acute Type A Aortic Dissection Repair after Intervention for Total Visceral Malperfusion: A Way Out of a Dilemma?

Despite immediate surgical repair of the entry site in acute thoracic aortic dissection with visceral malperfusion, the results are poor. Primary restitution of visceral flow by intervention might be one way to cope with this problem, but probably causes ischemia/reperfusion associated problems after prolonged complete visceral ischemia. In this report, we demonstrate a successful attempt of controlled delay of thoracic aortic surgical repair after visceral flow restitution with stable hemodynamics.

BLOOD FlOW IN ABDOMINAL VISCERA AFTER THE CYCLING EXERCISE MEASURED BY DOPPLER ULTRASOUND

598 The blood flow (BF) in the abdominal viscera (VIS) after the graded cycling exercise was examined using Doppler ultrasound. Eleven healthy subjects performed three exercises at the goal of corresponding to 30%, 50%, and 80%(n=6) of maximum oxygen uptake (VO2max), respectively. After exercise in the supine position, BF was measured in the upper abdominal aorta (Ao) above the celiac artery bifurcation, and in the right common femoral artery (RCFA), repeatedly. Ten times of BF measurements was done during 15 min recovery. Heart rate was measured simultaneously. It was found in a preliminary study that BFRCFA was same range with BFLCFA at the resting level. Thus, it was decided that both common femoral arterial flow values were calculated as 2-folds BFRCFA (2BFRCFA). The changes in blood flow values relative to the pre-exercise levels were determined as ▵ BF. The ▵ BF in two vessels obtained after the exercise were plotted as a function of time. These plots were fitted to an exponential characteristics. ▵ BFVIS was determined by the subtracting calculated 2 ▵ BFRCFA from calculated ▵ BFAo obtained by the two curves at 90, 300 and 600 sec during recovery periods. At 80% VO2max, the 2 ▵ BFRCFA was greater than the ▵ BFAo between 90 and 600 sec. BFVIS at the resting level was 2463±253 ml/min(mean±SE). A significant decrease in BFVIS was demonstrated at 90 sec(1561 ± 229 ml/min; p<0.001) and 300 sec (1162± 234 ml/min; p<0.001) during 80% VO2max exercise, and at 90 sec (1399±323 ml/min; p<0.001) during 50% VO2max exercise. However, during 30% VO2max, BFVIS did not show a significant decrease. It was concluded that the continuous decrease in abdominal visceral flow after the high intensity exercise was confirmed using Doppler ultrasound, noninvasively.

Distribution of blood flow during exercise after blood volume expansion in swine

To study the distribution of blood flow after blood volume expansion, seven miniature swine ran at high speed (17.6-20 km/h, estimated to require 115% of maximal O2 uptake) on a motor-driven treadmill on two occasions: once during normovolemia and once after an acute 15% blood volume expansion (homologous whole blood). O2 uptake, cardiac output, heart rate, mean arterial pressure, and distribution of blood flow (with radiolabeled microspheres) were measured at the same time during each of the exercise bouts. Maximal heart rate was identical between conditions (mean 266); mean arterial pressure was elevated during the hypovolemic exercise (149 +/- 5 vs. 137 +/- 6 mmHg). Although cardiac output was higher and arterial O2 saturation was maintained during the hypervolemic condition (10.5 +/- 0.7 vs. 9.3 +/- 0.6 l/min), O2 uptake was not different (1.74 +/- 0.08 vs. 1.74 +/- 0.09 l/min). Mean blood flows to cardiac (+12.9%), locomotory (+9.8%), and respiratory (+7.5%) muscles were all elevated during hypervolemic exercise, while visceral and brain blood flows were unchanged. Calculated resistances to flow in skeletal and cardiac muscle were not different between conditions. Under the experimental conditions of this study, O2 uptake in the miniature swine was limited at the level of the muscles during hypervolemic exercise. The results also indicate that neither intrinsic contractile properties of the heart nor coronary blood flow limits myocardial performance during normovolemic exercise, because both the pumping capacity of the heart and the coronary blood flow were elevated in the hypervolemic condition.

Mesenteric flow velocity variations as a function of angle of insonation

This study was designed to quantitate variations in duplex ultrasound arterial flow velocities (cm/sec) in the common carotid artery and the superior mesenteric artery that were produced by changes in the angle of pulsed Doppler insonation. Duplex scanning was used to measure peak systolic flow velocity and mean velocity at angles from 30 degrees to 80 degrees; individual measurements were made at 10-degree increments in both the common carotid artery and the superior mesenteric artery in normal subjects. Peak systolic velocity in the common carotid artery varied from 86 cm/sec at 30 degrees to 168 m/sec at 80 degrees. Over the same transducer angle variation mean velocity ranged from 28 to 53 cm/sec. Similar changes in the superior mesenteric artery flow velocities were observed by varying the angle of insonation, where peak systolic velocity varied from 108 cm/sec (30 degrees) to 280 cm/sec (80 degrees), and mean velocity ranged from 29 cm/sec (30 degrees) to 71 cm/sec (80 degrees). Measurements taken from 70 to 80 degrees produced the most dramatic deviation from those taken at 60 degrees. In the common carotid artery the 70- and 80-degree angles produced 14% and 59% increases, respectively, in peak systolic velocity and 16% and 63% increases, respectively, in mean velocity. In the superior mesenteric artery 70-degree and 80-degree angles produced 16% and 120% increases, respectively, in peak systolic velocity and 17% and 111% increases, respectively, in mean velocity. At 80 degrees the percent increases in measured flow velocities for the superior mesenteric artery were significantly greater than those for the common carotid artery. The noninvasive investigation of normal mesenteric vessels may be dependent on accurate absolute flow velocity values, especially if these values are used to calculate volume flow. This study demonstrated that significant variations in resting flow velocities may be introduced by variations in the angle of pulsed Doppler insonation, particularly at angles above 70 degrees. Strict control of this variable will be essential in future studies, mainly those addressing normal visceral flow variations in response to physiologic stimuli.