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PubMed1999

Development of velocity profiles and retrograde flow in the porcine abdominal aorta under different haemodynamic conditions.

Low and/or oscillating wall shear stresses are related to the development of atherosclerosis and this oscillation is influenced by changes in basic haemodynamics (exercise). The objective of this study was to provide in vivo data on the development of velocity profiles and oscillating blood velocities in the abdominal aorta under varying haemodynamic conditions. Six anaesthetized, 90-kg pigs were used in the study. Abdominal aortic velocity profiles across the anterior-posterior diameter were acquired at different axial positions using 10 MHz pulsed Doppler ultrasound. Measurements were obtained under normal conditions and during cardiac pacing up to 170 beats/min. Velocity profiles were obtained during heart rates ranging between 58 and 169 beats/min, and during flow rates ranging between 0.57 and 2.89 l/min. Main outcome measures included minimum velocities, frequency index, shape of velocity profiles (velocity distribution index), Reynolds' numbers, and Womersley's frequency parameter. Velocity profiles were blunted, with lowest velocities at the distal posterior vessel wall. Multiple regression analysis showed the development of velocity profiles to be inversely correlated with the pulsatility index, Womersley's frequency parameter and the mean Reynolds' number (r = 0.89, p < 0.0005). Minimum velocities were negatively correlated with the PI, Womersley's frequency parameter and positively with the mean Reynolds' number (r = 0.94, p < 10(-8)). Retrograde velocities (and hence oscillating wall shear stresses) were present at mean Reynolds' number < 1000. The oscillation of blood velocities at the wall in the porcine abdominal aorta was highly dependent on general haemodynamics (i.e. flow, heart rate and vessel diameter as expressed in the Reynolds' numbers and Womersley's frequency parameters). The velocity profiles in the abdominal aorta were found to be far from parabolic. These findings have important implications for the understanding and future modelling of the complex haemodynamics in the abdominal aorta and their relation to the development of atherosclerotic disease.

Animals↗
PubMed2001

Quantitative determination of age-related geometric changes in the normal abdominal aorta.

PURPOSE: We conducted a novel quantitative three-dimensional analysis of computed tomography (CT) angiograms to establish the relationship between aortic geometry and age, sex, and body surface area in healthy subjects. METHODS: Abdominal helical CT angiograms from 77 healthy potential renal donors (33 men/44 women; mean age, 44 years; age range, 19-67 years) were selected. In each dataset, orthonormal cross-sectional area and diameter measurements were obtained at 1-mm intervals along the automatically calculated central axis of the abdominal aorta. The aorta was subdivided into six consecutive anatomic segments (supraceliac, supramesenteric, suprarenal, inter-renal, proximal infrarenal, and distal infrarenal). The interrelated effects of anatomic segment, age, sex, and body surface area on cross-sectional dimensions were analyzed with linear mixed-effects and varying-coefficient statistical models. RESULTS: We found that significant effects of sex and of body surface area on aortic diameters were similar at all anatomic levels. The effect of age, however, was interrelated with anatomic position, and gradually decreasing slopes of significant diameter-versus-age relationships along the aorta, which ranged from 0.14 mm/y (P <.0001) proximally to 0.03 mm/y (P =.013) distally in the abdominal aorta, were shown. CONCLUSION: The abdominal aorta undergoes considerable geometric changes when a patient is between 19 and 67 years of age, leading to an increase of aortic taper with time. The hemodynamic consequences of this geometric evolution for the development of aortic disease still need to be established.

Adult↗
PubMed1993

Preliminary observations on the use of the Palmaz stent in the distal portion of the abdominal aorta.

The opportunities to avoid surgical treatment of distal abdominal aortic occlusive disease are expanding because of the proliferation in catheter-based techniques. Since January 1990, 24 symptomatic patients with distal abdominal disorders have been treated percutaneously with balloon angioplasty and intraluminal stenting. A total of 38 Palmaz stents were deployed at distal abdominal aortic sites; 21 additional iliac stents were implanted. After the procedure all patients improved clinically, and 83% (21/24) improved by objective measurement (average ABI 0.93 +/- 0.21). Three access-related complications occurred (two hematomas, one thrombus), but no complications were related to the stents. At up to 29 months of follow-up (average 10.3 +/- 6.7 months), clinical improvement persists in all patients (average ABI 0.93 +/- 0.22). In 11 patients eligible for follow-up aortography, all aortic stents are patent without evidence of restenosis. With the low likelihood for restenosis in the abdominal aorta, the long-term outcome of aortic stenting looks promising and may equal or surpass that found in the iliac region.

Aged↗
PubMed1989

Effects of nifedipine on the hemodynamic response to clamping and declamping of the abdominal aorta in dogs.

Clamping and declamping of the infrarenal abdominal aorta may adversely affect cardiovascular function, particularly in the presence of heart disease. This effect may be further altered by drugs used in the treatment of symptomatic coronary artery disease. The effect of nifedipine on the hemodynamic response to aortic clamping and declamping was determined in 12 dogs anesthetized with 50% nitrous oxide and 0.6% end-tidal isoflurane and monitored with aortic, left ventricular (LV), and thermodilution pulmonary artery catheters. Six dogs received a nifedipine bolus of 100 micrograms/kg followed by an infusion of 4 micrograms/kg/min. Six dogs did not receive any nifedipine and served as controls. Before clamping, nifedipine produced immediate decreases in arterial pressure, systemic vascular resistance (SVR), and LV dP/dt, and a modest increase in cardiac output (CO). During aortic clamping, nifedipine-treated dogs demonstrated marked increases in heart rate (HR), dP/dt, and CO while maintaining a low SVR. There were no significant changes upon declamping. The nifedipine-treated animals maintained a high CO and low SVR. Thus, nifedipine greatly altered the hemodynamic responses to aortic clamping and declamping. Awareness of these alterations is important when caring for patients being treated with nifedipine who are undergoing aortic surgery.

Analysis of Variance↗
PubMed2006

The effects of aneurysm on the biaxial mechanical behavior of human abdominal aorta.

The biomechanical response of normal and pathologic human abdominal aortic tissue to uniaxial loading conditions is insufficient for the characterization of its three-dimensional (3D) mechanical behavior. Planar biaxial mechanical evaluation allows for 3D constitutive modeling of nearly incompressible tissues, as well as the investigation of the nature of mechanical anisotropy. In the current study, 26 abdominal aortic aneurysm (AAA) tissue samples and 8 age-matched (> 60 years of age) nonaneurysmal abdominal aortic (AA) tissue samples were obtained and tested using a tension-controlled biaxial testing protocol. Graphical response functions (Sun et al., 2003. J. Biomech. Eng. 125, 372-380) were used as a guide to describe the pseudo-elastic response of AA and AAA. Based on the observed pseudo-elastic response, a four-parameter exponential strain energy function developed by Vito (1990. J. Biomech. Eng. 112, 153-159) was used from which both an individual specimen and group material parameter sets were determined for both AA and AAA. Peak Green strain values in the circumferential (Ethetatheta,max) and longitudinal (ELL,max) directions under an equibiaxial tension of 120 N/m were also compared. The strain energy function fit all of the individual specimens well with an average R2 of 0.95 +/- 0.02 and 0.90 +/- 0.02 (mean +/- SEM) for the AA and AAA groups, respectively. The average Ethetatheta,max at 200 N/m equibiaxial tension was found to be significantly smaller for AAAs as compared to AAs (0.07 +/- 0.01 versus 0.13 +/- 0.03, respectively; p < 0.01). There was also a pronounced increase in the circumferential stiffness for AAA tissue as compared to AA tissue, indicating a larger degree of anisotropy for this tissue as compared to age-matched AA tissue. We also observed that the four-parameter Fung-elastic model was not able to fit the AAA tissue mechanical response using physically realistic material parameter values. It was concluded that aneurysmal degeneration of the abdominal aorta is associated with an increase in mechanical anisotropy, with preferential stiffening in the circumferential direction.

Anisotropy↗
PubMed1991

[Aneurysm of the abdominal aorta and preoperative disseminated intravascular coagulation].

A case of abdominal aortic aneurysm associated with preoperative signs of disseminated intravascular coagulation is reported. The 69-year-old female patient presented with spontaneously appearing petechiae and bruising. She had 0.95 g.l-1 fibrinogen, 105 G.l-1 platelets, and 100 micrograms.ml-1 fibrin and fibrinogen degradation products. Investigations revealed an 80 mm diameter aneurysm of the abdominal aorta, extending from the coeliac trunk to the iliac arteries. Heparin 7,000 IU.day-1 resulted in a biological improvement for a week only. At that time, levels of coagulation factors were: 92% factor II, 88% factor V, 100% factors VII and X, 100% antithrombin III. Surgical cure of the aneurysm was nevertheless carried out. Twenty standard units of platelets, 8 g fibrinogen, four units of fresh frozen plasma, five homologous and two autologous red cell units were transfused during the procedure. No coagulation factors were necessary during the postoperative course, which was uneventful. The management of coagulation factor infusions, before or after aortic cross-clamping, is discussed.

Aged↗
PubMed1991

[Conventional and cine-MRT in patients with aneurysms of the abdominal aorta].

We studied 40 patients with aneurysms of the abdominal aorta by MRI. These results were compared with those obtained by real-time sonography (n = 40), angiography (n = 32) and CT (n = 16). In 30 patients the imaging results were compared--as far as possible--with the operative findings. MRI proved more reliable, especially if compared with sonography, in evaluating renal or iliac artery involvement. Mural thrombi were detected more often (93%) by MRI than by CT (85%) or sonography (83%). Cine-MRI showed strong turbulences in 33%. Turbulences did not correlate with the size of the aneurysm.

Adult↗
PubMed1981

Flow visualization in a mold of an atherosclerotic human abdominal aorta.

Flow in a mold of an atherosclerotic human abdominal aorta and common iliac arteries was studied by flow visualization at a mean Reynolds number of 500 during both pulsatile and steady flow. Flow separation and transient flow reversals were found distal to atherosclerotic plaques during pulsatile flow; whereas flow separation resulting in regions of permanent eddies were observed distal to plaques only during steady flow.

Aorta, Abdominal↗
PubMed1985

The elastic properties of canine abdominal aorta at its branches.

The elastic properties of the abdominal aorta at regions of junctions were studied using strips from 17 dogs. Strips of tissue cut longitudinally and circumferentially at the celiac, mesenteric, and renal branches were used to compare the properties of the proximal and distal junctions, as well as the aorta and artery regions adjoining. The tissues were stored for at least 24 h to ensure that no active component of the smooth muscle remained. The elastic properties measured here are due to elastin and collagen, with a small contribution from dead smooth muscle cells. The tissue strips were tested at 20 degrees C while immersed in saline using an Instron tensile testing machine. Elongation of the three regions was measured from photographs taken as the tissue was stretched. Stress values went to 200 kN/m2 as the strain increased to approximately 0.8. (The physiological range for the dog was calculated as 40-85 kN/m2.) The distal junctional region was found to be the most extensible for both longitudinally and circumferentially oriented strips. These results have important implications for flow models as they imply that the shape of the junctional region probably changes between diastole and systole.

Animals↗
PubMed1997

[The establishment and evaluation of abdominal aorta thrombosis model in rat].

An animal model of abdominal aorta thrombosis based on Virchow's thrombosis principle was induced by endothelium denudation with a polyethylene catheter combining severe stenosis with an aortic constriction in rats. A total of 37 rats were involved in thrombosis induction. Among them thrombus developed in 27 rats. Mean length of thrombus was 8.53 +/- 1.42 mm. The contractibility of vascular wall in the thrombotic group significantly reduced.

Animals↗
PubMed1991

[Early prognostic factors of the surgery of aneurysms of the abdominal aorta with renal artery clamping].

The aneurysms of the abdominal aorta requiring suprarenal clamping are rare. Suprarenal clamping was required for only 43 of 544 aneurysms operated electively from 1981 to 1989. Twenty-five patients had a juxtarenal aneurysm, without any normal aortic segment under the renal arteries, and suprarenal clamping was therefore necessary while the upper anastomosis was being established (group I). Eighteen patients had an aneurysm enclosing the root of at least one renal artery (group II). Several prognostic factors have been assessed: patient's age, presence of preoperative renal insufficiency, of arterial hypertension or of coronary insufficiency, and revascularization method. Five patients died. Four of them belonged to group II and were over 75 years old. All presented with a preoperative renal insufficiency. Two of these deaths were caused by mesenteric infarction. Four cases of regressive postoperative renal insufficiency were observed in patients for whom renal clamping had lasted longer than 45 minutes. This study allowed outlining three prognostic factors: the patient's age, preoperative renal insufficiency, a period of renal ischemia exceeding 40 minutes. On the other hand, the severity of hypertension had no predictive value. Coronary insufficiency requires a strict hemodynamic surveillance, but is not a contraindication for revascularization.

Age Factors↗
PubMed1991

[Chronic rupture of an aneurysm of the abdominal aorta].

The chronic rupture of an aneurysm in the abdominal aorta produces an atypical clinical picture. Computed tomography is the method of choice for diagnosis. This is a therapeutic emergency because of the risks involved by evolution.

Angiography↗
PubMed1988

[Ultrasonic diagnosis in aneurysm of the abdominal aorta].

The sonographic diagnostics of an aneurysm of the abdominal aorta has obtained a high value on account of the high reliability and the rapid availability of the investigation in connection with the absolute safety of the method. Form, extension, calcification, haemodynamics, thrombosis and dissection of an aneurysm of the aorta can sonographically be demonstrated and measured by longitudinal and transversal sections. As non-invasive approach the ultrasound tomography in the order of the graduated diagnostic method stands before the computed tomography which is not always at once available and before the angiography which have their qualification in the case of a planned operative approach above all for the purpose of the exact topographic differentiation between suprarenal and infrarenal extension.

Aorta, Abdominal↗
PubMed1985

[Aneurysms of the subrenal abdominal aorta. Apropos of 115 cases].

115 of infra renal abdominal aorta have been operated upon between 1969 and 1984. 107 male patients (93%) and 8 female (7%) were treated. Age was 65.5. Associated high blood pressure was found in 43%, smoking in 74% and coronary disease in 20.5%. Non ruptured aneurysms were 84 (73%) and diagnosis was made chiefly in ischemia of lower limbs, ruptured were 31 (27%). 4 fistulas between aorta and lower vena cava were found at surgery. Aortograms have not been done in every case, even for non ruptured aneurysms, as 19 patients have been operated without (22.6% of non ruptured aneurysms). Ultrasonography have been done in 37. Among 84 patients with non ruptured aneurysm, 6 were not operated, 2 got only palliative surgery for rest pain, and 76 (85.7%) underwent resection and grafting. 31 patients were operated when ruptured. Post operative mortality for non ruptured aneurysms was of 2 (2.63%) for resection and grafting. It was of 24 (77.4%) if ruptured. Follow-up study shows that at a five years range 62.7% of surviving operated patients are alive. Authors point out that lower limbs ischemia is still often a revealing symptom. Post operative colic ischemia is rare.

Aged↗
PubMed1978

Some ultrastructural characteristics of the renal artery and abdominal aorta in the rat.

The rat renal artery and abdominal aorta have been studied by light and electron microscopy. In rats of 200 g body weight the extracellular space in aortic media ranges between 50-60% and that of the distal renal artery between 15-25%. The surface to volume ratio of aortic smooth muscle cells is 2.7 micron2/micron3 compared to 1.6 micron2/micron3 in the distal renal artery. Dense bodies are rare in aortic smooth muscle cells but are abundant in those of the distal renal artery. Other ultrastructural details of the smooth muscle cells are similar in the two types of artery. Cell-to-cell contacts consist of simple apposition of plasm membranes and their number is proportional to the total length of cell membrane profile. Mitochondria represent 7-8% of the cell volume in both arteries. The proximal renal artery shows structural characteristics which are intermediate between those of the aorta and distal renal artery. In all renal arteries examined, bands of longitudinal smooth muscle are present in the adventitia, principally at branch points. In older rats, regions of discontinuity of the internal elastic lamina have been observed.

Animals↗
PubMed1984

[Management of anesthesia for surgery of the abdominal aorta].

Anesthesia and post operative care of patients requiring abdominal aorta surgery are frequently complicated because of associated ischemic cardiopathy or respiratory insufficiency. Pre operative evaluation indicates the optimal peri-operative strategy and the need to appropriate peri-operative monitoring. This applies to patients with a previous history of myocardial infarction or with a poorly or not controlled cardiac insufficiency. The use of Swan-Ganz catheters allows monitoring of the hemo-dynamic parameters during operation, especially at the moment of clamping or unclamping of the aorta. Vasodilators and optimal volume loading allow myocardial adaptation and reduce the incidence of myocardial infarction, the main cause of peri-operative death. To perform these operations in the best conditions requires a close medicosurgical cooperation in specialized teams.

Anesthesia, General↗
PubMed1984

Atherosclerosis and lipid composition of the abdominal aorta. Comparison of autopsied New Orleans and Guatemalan men.

Abdominal aortas from 78 Guatemalan men and 79 New Orleans white men were examined for lipid composition and for the extent of grossly visible atherosclerotic lesions. In the specimens examined, atherosclerotic lesions were more extensive in New Orleans than in Guatemala, confirming findings of studies performed 10 and 20 years earlier. Lipid accumulation differed greatly between the geographic locations with new Orleans specimens having more chemically determined lipids. Differences in lipid accumulation between New Orleans and Guatemala are more striking when expressed in terms of content (milligrams per 100 square centimeters than when expressed as concentration (milligrams per gram of dry defatted weight). Chemical analyses indicate that lipid accumulation in the aorta results principally from the atherosclerotic process rather than from aging. In the 15- to 24-year age group, the gross extent of fatty streaks was similar in both populations, but content and concentration of free cholesterol was significantly higher in New Orleans specimens than in Guatemalan specimens. This finding might be related to the more extensive development of raised lesions at later ages in New Orleans subjects.

Adolescent↗
PubMed1994

Modes of presentation and management of inflammatory aneurysms of the abdominal aorta.

The preoperative diagnosis of inflammatory aneurysms of the abdominal aorta (IAAA) is seldom made, yet knowledge of its presence would be an aid to the surgeon. A heightened awareness of the variety of clinical presentations of IAAA should prompt the clinician to consider this entity in the differential diagnosis of back pain, weight loss and obstructive uropathy. Hypovolemic shock, gastrointestinal bleeding and asymptomatic IAAA have also occurred, albeit much less frequently. Patients who are hemodynamically stable might benefit from a short period of diagnostic and therapeutic measures before operation. Patients undergoing aneurysm repair on an "urgent" rather than "emergent" basis have been shown to have lower mortality and morbidity rates with enhancement of their cardiopulmonary and renal status. Computed tomographic scanning preoperatively in stable patients using careful supervision can confirm the diagnosis and allow more time for patient and surgical team preparation. Knowledge and avoidance of technical pitfalls intraoperatively further lessens mortality and complications.

Aged↗