Aorta Of Dogs Research Articles

Light and electron microscopy of polytetrafluoroethylene arterial grafts in dogs.

Reinforced expanded polytetrafluoroethylene grafts with fibril lengths of approximately 17 to 25 micrometers were inserted into the infrarenal aorta of dogs for periods ranging from 24 hours to eight months. The grafts were studied by light and electron microscopy, which showed that polytetrafluoroethylene consists of ridges or nodes connected by fibrils. Initially red blood cells passed down in the pores of the polytetrafluoroethylene, and then the surface was covered with fibrin. A new endothelium developed by the twelfth day. The new intimal lining became thicker owing to the appearance of smooth muscle cells deep to the endothelial cells, forming a neointima 120 micrometers thick by eight months. Fibroblasts and collagen penetrated the graft, but vasa vasorum did not, although they were present in the external connective tissue.

Position sensitivity of hot-film shear probes

The position sensitivity of hot-film shear probes was studied with the use of pulse-echo ultrasound. The ultrasonic probe was placed opposite the hot-film probe across a rigid tube. The accuracy of measuring hot-film probe position by ultrasonic methods was studied with the aid of a mechanical micrometer. A similar study was conducted in vivo on the thoracic aorta of dogs to maintain flush conditions between the hot-film probe and arterial wall. The sensitivity of hot-film probes to position with respect to a rigid wall was studied. Probe position was determined by ultrasonic methods. The results showed a 20% deviation in hot-film anemometer bridge voltage with a change in probe position of 0.3 mm from the wall. This could result in a 50% error in computed wall shear stress. Resolution of the method of ultrasonic positioning of the hot-film probe was determined to be 0.1 mm.

Glutaraldehyde-tanned ovine collagen conduits as vascular xenografts in dogs: a preliminary report.

Collagen tubes grown in sheep around Silastic mandrils were tanned in neutral, buffered glutaraldehyde and deployed as arterial xenografts in the aorta of dogs. The grafts maintained patency for up to three years and did not show any signs of aneurysmal dilation or luminal narrowing. The lumen became lined with a neointima, and host collagen was deposited around the periphery so that the thickness of the wall of the graft approximated that of the aorta.

The mechanical properties of soft tissues—II: The elastic response of arterial segments

The mechanical properties of dog aorta were examined using microprocessor based instrumentation described elsewhere. In seven in vitro experiments, specimens were continuously loaded and unloaded axially at a fixed stretch rate while the luminal pressure was continuously varied so as to maintain a constant diameter. Force, length and pressure were recorded digitally and subsequently analyzed using the theory of large elastic deformation. Assuming a circular cylindrical cross-section and homogeneous, incompressible and isotropic behavior, the pressure and force can, for a given load or unload cycle, be expressed in terms of a strain energy density function and initial specimen dimensions. A Taylor series expression for W containing up to four terms resulted in good agreement, in a least squared sense, with the data. Significant differences between loading and unloading cycles and large stress gradients in the walls were observed.

Electrical characteristics of flowing blood.

Erythrocyte orientation, deformation, and axial accumulation cause differences in resistance between flowing and resting blood. Through theoretical calculations and experimental measurements, we studied the effects of these factors and of sinusoidal and pulsatile flow on blood resistivity. The effect of axial accumulation is least significant. Frequency characteristics of blood resistance under sinusoidal and pulsatile flow showed that erythrocytes cannot orient in response to rapid flow changes of a few pulses per second. From dog aorta investigations, we conclude that the orientation effect on impedance plethysmography pulse waveforms nearly equals that of blood vessel diameter change, and that waveform analysis must consider both effects.

Positive feedback sympathetic reflexes and hypertension

A pressor reflex that can be elicited from the thoracic aorta in conscious dogs is described. Distension of the aorta excites sympathetic afferent fibers and results in an increase in arterial blood pressure because of increased sympathetic outflow to the heart and blood vessels. The reflex center for this positive feedback mechanism is located in the spinal cord and, when the reflex is activated, it can modulate other negative feedback control systems.

Morphologic variations and aging in the atrioventricular conduction system of large breed dogs

The microscopic anatomy of the atrioventricular node, bundle of His, both bundle branches and surrounding fibrous cardiac skeleton was studied in 40 large breed dogs of various ages. In the AV conduction system of all dogs over five years of age there was an increase of fibrous connective tissue, an infiltration of adipose tissue, loss of conduction fibers and focal fibrosis extending from the central fibrous body. Fibrosis was seen in the summit of the interventricular septum posterior to the AV node in dogs of all ages. Chondroid metaplasia was consistently observed in the central fibrous body and the root of the aorta in large breed dogs, including ten Doberman Pinschers of all ages. This metaplasia varied from a few chondroblasts and chondrocytes to mature chondrocytes with mineralization. Bone formation was seen in eight dogs. These changes appeared in close approximation to the cardiac conduction system above the bundle of His. No degenerative changes were seen in the AV bundle. Approximately one-half of the large breed dogs five years of age and older had thickened medial and intima proliferation in the small coronary arterioles supplying the AV node. The results of this study suggest that the presence of cartilage and bone in the central fibrous body is a normal occurrence in large breed dogs at all ages.

Role of vasa vasorum in nourishment of the aorta.

The media of arteries is virtually avascular. Thus, oxygen and nutrients must reach the cells of the media by diffusion from the lumen of the vessel and from adventitial vessels. The thickness of the thoracic aorta of man and dog exceeds the effective diffusion distance of oxygen, but nutrition is supplemented by vasa vasorum which enter into the outer layers of the media. Occlusion of vasa vasorum in dogs produces medial necrosis, which indicates that these vessels are essential for the nourishment of the aorta. Recently the microsphere method has been used to provide the first measurements of blood flow through vasa vasorum. There is substantial flow to the outer layers of media of the thoracic aorta in dogs, with virtually no blood flow in the inner layers. The vessels are very responsive to physiological stimuli: they dilate during infusion of adenosine and constrict during stimulation of sympathetic nerves. During acute increases in arterial pressure, blood flow to the media decreases probably from distortion of vasa vasorum. Vasa vasorum may play role in disease states. Insufficient blood flow through vasa vasorum may contribute to medial necrosis of the aorta and to aortic atherosclerosis. A role of vasa vasorum in aortic changes in hypertension and other vascular diseases merits further study.

Cathepsin D activity of venous and polyester vascular grafts implanted in the abdominal aorta of the dog

Autogenous veins and polyester prostheses were implanted in the abdominal aorta of dogs. The venous or polyester grafts were removed together with sections of the normal arteries and veins 1 month, 4 months, and 3 years after the operation. This material was then dissected into the intimal, medial, and adventitial layers, and homogenized after which their cathepsin D activity was determined. It was found that the cathepsin D activity was far higher in all the layers of the venous grafts, particularly in the polyester grafts, than in the corresponding layers of the normal arteries and veins.

Cardiovascular trauma from angiographic jets--validation of a theoretic concept in dogs.

The relationship of angiographic injections to cardiovascular trauma was determined. The aorta of dogs was studied by a mathematic model that (a) defines the kinetic energy of contrast-media jets emanating from the exit holes of catheters and (b) enables precise correlation of energy levels to potential trauma. A universal curve independent of the Reynolds number of the jet readily determines how far the jet penetrates intravascular blood. A traumatic histopathologic spectrum was found for those injections predicted by the model to be traumatic. The curve enables the angiographer to calculate the safe operating range of any catheter.

Blood inflow into intra-arterial catheters following injection of contrast medium.

Inflow of blood into intra-arterial catheters following injection of contrast medium into the common carotid artery in patients and into the aorta in dogs is investigated. Influence of form and orientation of the catheter in the vessel and the effect of constant flushing are determined as well.

Effects of anaesthesia and chronic catheterization on circulating levels of prostaglandins (PGE2 and PGF2alpha in dogs.

Chronic catheterization of aorta and inferior vena cava in dogs did not significantly affect circulating levels of prostaglandins (PGE2 and PGF2alpha). Pentobarbital (30 mg/kg i.v.) anaesthesia produced a significant decrease in PGF2alpha.

Mechanical properties of arteries

Mechanical properties of arteries

Morphometric observations of the effects of normothermic ischemic arrest on dog myocardial ultrastructure

The design of the experiment was to examine, using stereological techniques, ultrastructural changes in the left ventricular myocardium of dog hearts exposed to cardiopulmonary bypass with normothermic ischemic arrest. Normothermic ischemic arrest was induced in dogs by cross-clamping the aorta proximal to the brachiocephalic artery for 1 h, after which the hearts were perfused with fixative. For control purposes after achieving cardiopulmonary bypass, the aortas of dogs were cross-clamped proximal to the brachiocephalic artery, and the hearts were immediately perfused with fixative. Normothermic ischemic arrest was associated with a loss of glycogen stores, disrupted sarcoplasmic reticulum and T-tubules, and vacuolization and decrease in matrix density of mitochondria. Stereological measurements showed that the percent volume of myofibrils, mitochondria, T-system, and SR declined significantly following normothermic ischemic arrest. It was also found that although the membrane area of SR and T-system per unit myofibrillar volume remained constant in controls and ischemic hearts, that the membrane area of SR per unit SR volume and the membrane area of the T-system per unit volume of T-system significantly increased in ischemic hearts suggesting vesiculation of these organelles.

Analysis of disorder in pulsatile flows with application to poststenotic blood velocity measurement in dogs

Digital techniques for performing analyses of disorder in a pulsatile flow are presented. Examples are taken from in vivo, hot film anemometer measurements of blood velocity in the descending thoracic aorta of dogs with a controlled degree of stenosis imposed. It is found that flow disorder, as described by this analysis, is a sensitive indicator of the presence of mild constrictions in the vessel under study. Implications to the recognition of localized, occlusive vascular disease are discussed.

The effects of changes in inspired oxygen concentration on the experimental production of pulmonary edema in the dog with chronic left ventricular overload.

A twofold increase in left ventricular output was achieved by suturing a Telfon graft between the aorta and left atrium in dogs. Three weeks after surgery the animals were anesthetized and found to have left ventricular end-diastolic pressures averaging 36 mmHg with markedly elevated right ventricular systolic pressures (RVSP). Oxygen breathing resulted in a decrease in left ventricular pressures, RVSP, and arterial pressure in those animals which survived hypoxia. Fifty percent of the shunted dogs subsequently developed fatal pulmonary edema when allowed to breathe 10% oxygen in nitrogen. These animals showed no change in left ventricular function or pulmonary artery pressure (RVSP) in response to pure oxygen administration. It is suggested that there is a gradation of hemodynamic response to pure oxygen depending on the severity of left ventricular overload. In the severest case the 'fixing' of pulmonary hypertension may be due to neurohumoral mechanisms. The subsequent development of pulmonary edema in these animals with hypoxia either involves a change in permeability or a redistribution of hydrostatic pressure within the pulmonary vasculature.

Closure to “Discussions of ‘Measurements of Velocity Wave Form in the Dog Aorta’” (1977, ASME J. Fluids Eng., 99, pp. 606–607)

Closure to “Discussions of ‘Measurements of Velocity Wave Form in the Dog Aorta’” (1977, ASME J. Fluids Eng., 99, pp. 606–607)

Effects of acute myocardial ischaemia on platelet aggregation in the coronary sinus and aorta in dogs.

The effect of an acute myocardial ischaemia on circulating platelet aggregates (CPA) in the coronary sinus and aorta was studied in open chest dogs. Even before induction of myocardial ischaemia significantly more CPA were found in the coronary sinus than in the aorta. Acute myocardial ischaemia produced by a non-thrombotic coronary artery occlusion increased CPA in coronary sinus, but not in aorta. Administration of acetylsalicylic acid (ASA) reduced the extent of the myocardial ischaemia as evidenced by reduced ST-segment elevations in epicardial ECG. Before induction of myocardial ischaemia, ASA significantly reduced CPA in coronary sinus, but no significant effect was observed during myocardial ischaemia. In the aorta no effect of ASA on CPA was found.

Partial standing wave formation above an abdominal aortic stenosis.

Reflection from an arterial discontinuity, such as a stenosis, would be expected to produce partial standing waves of pressure and flow proximal to the stenosis. This phenomenon is demonstrated by determining the amplitude changes of the harmonic components of pressure and flow waves recorded at three sites at different distances from an experimental stenosis of the abdominal aorta in dogs. To minimise the effect of reflections from other arterial sites, such as the peripheral beds, the animals were vasodilated. Impedance and propagation velocity measurements were made to estimate the contribution of peripheral reflections in the harmonic components of the aortic pressure and flow pulses. In general, the peripheral contribution appeared to be small for harmonics greater than the first. The results indicate that, for the 'closed' type of reflection at the stenosis, a pressure antinode and a flow node occur immediately proximal to the stenosis. As the distance from the stenosis to the measurement site is increased, nodes and antinodes of pressure and flow occur at frequencies which correspond to integer multiples of lambda/4. Similar fluctuations take place in the impedance modulus proximal to the stenosis, such that close to the stenosis the modulus is a maximum, at the lambda/4 distance the modulus is a minimum and at the lambda/2 distance it is again a maximum. The extent of these impedance changes with distance indicates that the attenuation of the reflected, backwardgoing waves is greater than found for forwardgoing waves and that the diagnostic assessment of a vascular obstruction by means of a proximal measurement of pressure or flow may be subject to error if the measurement is not made close to the obstruction.

Closure to “Discussions of ‘Measurements of Velocity Wave Forms in the Dog Aorta’” (1977, ASME J. Fluids Eng., 99, pp. 262–263)

Closure to “Discussions of ‘Measurements of Velocity Wave Forms in the Dog Aorta’” (1977, ASME J. Fluids Eng., 99, pp. 262–263)